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I need some help troubleshooting the possible causes for OBD code P1486 on my 2002 TJ.  The MIL has been on for weeks now with this code because I cannot figure out the problem, and three repair shops have not been able to figure it out either.

 

P1486 is a kinked hose in the evaporative emissions system.  I have checked the hoses between the charcoal canister and throttle body, etc, and do not find any kinked hoses or hoses with a blockage.  The first repair shop thought this was caused by a leak, and did a smoke test but found no leaks.  The third shop thought there was a problem with my gas cap, but it was replaced with no change.  All of the shops could not find anything conclusive and suggested I go to the Jeep dealer for diagnosis.

 

I have read up on the components of the system and the automatic tests it performs, and if I understand correctly the leak test is the first test run on this system followed by a blockage test.  I assume the leak test passed because I do not have a code for a leak, only the kinked hose.  Using this assumption I ruled out the leak detection pump needing replacement.  Since the hoses were all OK, I decided to forego the trip to the dealer because the charcoal canister and purge solenoid cost less than what the dealer would charge to diagnose for an hour.  I replaced the canister and solenoid.  When replacing the canister I found one of the hoses was cracked where it attached to the canister so I cut off enough length to get rid of the crack.  No other cracks or blockages were found in any of the hoses.  The MIL was reset by disconnecting the battery.  Three or four days later the MIL was back on with the P1486 code again.

 

I don't know where else to look and would rather not go to the dealer and risk them not finding anything but still paying their diagnostics and labor rates. Any suggestions?

 

The Jeep runs well most of the time, but since the MIL is lit all the time I don't know if there is another problem coming up.  This is even more annoying because I am getting an intermittent misfire code about once every two to four weeks which sends the computer into limp home mode and causes performance issues.  I can't tell right away that this has happened because the MIL was already on for the emissions fault, which means I can't be sure what driving conditions I was in when the misfire occurred.  The same shops were looking into the misfire and the engine would not misfire at all while they had it.  I'd really like to take care of the emissions issue so I might have another clue to add for solving the misfire.

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I have an update on my previous post.  I noticed some valve knocking yesterday climbing some steep hills on my drive home so I checked to see if any new codes popped up since I last checked a few days ago (the MIL has been on this whole time).  I still have the P1486 code, but I am now getting the P0455 (evaporative emissions gross leak) code as well.  Is this logical?  Can I have both a leak and a blockage and the OBD will catch them both at the same time?  I checked my gas cap which was tight, and hissed when I opened it...  I checked all the hoses around the charcoal canister and LDP again and still don't find any tears, cracks, etc...

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Marc, this sounds like a gross vacuum leak, not necessarily vacuum hose leaks.  The knocking could be lean fuel mixture at one or more cylinders, Marc. 

 

At the mileage, I would review our other case of #1 misfire, as this may foster an "Ah, ha!" moment.  Try this, we have quite a lengthy discussion and troubleshooting stream at:  http://forums.4wdmechanix.com/topic/73-40l-jeep-six-cylinder-1-misfire-trouble-code/.

 

I believe the symptoms could be one device that's causing overlapping symptoms and even throwing codes.  The TPS switch could be involved, but I'm not one for "parts replacement" trials.  Let's get a clear sense for what's not working.  Vacuum leaks, TPS, vacuum hoses (seeping or crossed), a MAP sensor and so forth—each could be possibilities.  We'll be systematic in our approach.

 

Moses

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Hi Moses,

 

In my first post, I meant to say great job on the magazine and forums.  I've been on other forums and none are as well organized or provide as much valuable information as your does.

 

I joined this forum because a few months ago I found and followed through the post on #1 misfire.  At the time I was having a #6 misfire and no luck troubleshooting or addressing it.  Last year my wife and I had out first child, and we live in the country about 45 minutes from where we work.  I had just enough time between working for a living, taking care of my responsibilities at home, but with the adjustments to life as a parent I decided to let the local mechanic do the troubleshooting and repair work on our vehicles.   By the time I had found the post on your forum I had replaced several parts.  The history goes a bit like this:

 

The P1486 DTC came and went intermittently for about 8 months.  Initially the local garage replaced some hoses and each time the code disappeared for several weeks, but then last fall it came on and they couldn't find anything wrong.  They checked all the hoses and components but couldn't find anything wrong.  They did a smoke test and couldn't find any leaks, so they recommended I take it to the dealer rather than going through the "parts repacement trials" you mention.  The Jeep ran OK and I didn't want to deal with the dealer (the local dealers don't have a very good reputation for honesty) so I put it off and tried to use the forums more heavily and find a solution.  I couldn't find anything.

 

Before I did anything else, about 2 months later I noticed the Jeep was running rough and performance was down (low power).  I checked for additional DTC's using the method with the key in the ignition and found a P0301 code along with the P1486 code.  I took it to the garage rather than looking into it myself and they did a power cleaning of the fuel system (not just a bottle of fuel injector cleaner in the gas tank), and replaced two of the O2 sensors that were out of spec.

 

The Jeep was happy for a while after that, but then it came back with a P0306 code and another code for one of the two catalytic converters ( I forget if it was bank 1 or 2) in the down pipe between the exhaust manifold and the larger cat in front of the muffler being bad.  The pipe with the two cats was replaced.  Again it was happy for about a week or two, then came back with the P1486 and P0306 codes.

 

At this point there was 2 feet of snow on the ground and temps were in the single digits for the week.  I don't have access to a garage or a warm dry place to work, so I took it to another shop hoping to get out of the parts replacement trials.  They replaced the bar with the three coil packs in it for the ignition.  After this it was happy again for about a week or two, and then you guessed it.  I got a P1486 code followed by a P0306 code again.

 

It was still freezing so I asked around for recommendations on a better mechanic, and was pointed to one near work.    By this time I has seen the #1 mnisfire thread on this forum, and suggested the perform a cylinder leak down test because I wasn't sure how to do it and it was freezing cold.  They checked compression, inspected the injectors, checked fuel pressure, etc. They diagnosed it to be a clogged fuel filter because it had never been replaced (it's in the gas tank) and the Jeep would not show a misfire while they had it running either in the shop or on the road. I opted to have the filter replaced because I suspected that myself, but at the same time had them replace the entire fuel pump assembly because of the age and the fact that my fuel gauge would drop to empty sometimes when my tank got to around 1/3 of a tank and not come back until I filled the tank.  The new fuel pump assembly made a noticable difference in the performance of the Jeep until the P0306 code came back on a week later along with the P1486 code.  They checked it again and it would not misfire at all while they had it running in the shop or on the road.

 

About a week later my Jeep would not start after I got gas on the way to work.  I had it towed to the garage hoping whatever was causding the ghost misfire had finall failed and it would be obvious what was wrong.  It turned out to be a bad battery.  Having seen the voltage issues in the #1 misfire hread I was hopeful this was the problem.  A week later the P1486 and P0306 codes were both back and on top of it my steering box started leaking badly.

 

I took it to the garage again to have the steering box replaced.  They cleared the codes after checking again for the cause of the misfire, and finding nothing.  About a week later (this is getting old hugh) the 1486 code was back and I was driving home on the interstate when my cruise control stopped working.  I turned it back on and a few seconds later it shut off again and would not turn back on.  Before I got home I noticed the Jeep was lacking power on a steep hill so I checked for the P0306 code when I got home.  There was no misfire code, but I had a high voltage code on the TPS.  I also noticed my horn wasn't working.  Looking up these symptoms on the forums led me to believe my clockspring was bad, so I ordered a new clockspring from the dealer.  By the time the new clockspring came in my cruise started working again.  I replaced the clockspring anyway figuring the garage likely damaged it when they had the steering gear disconnected.  I didn't think it was a coincidence otherwise I wouldn't have bothered with the $300 clockspring.  The TPS code didn't go away so I replaced it.  I didn't have time to go to the dealer and the sensor I got was a duralast from Autozone, but so far I have not gotten a new code for the TPS.

 

The battery was disconnected when replacing the clockspring so the MIL was out for about a week again before it came back on with the P1486 code and about a week later I noticed low power and found the P0306 code.  I called the garage to let them know what had gone on since they had it and see if it shed any light.  The tech that had worked on my Jeep each time said he had been looking on forums after the last time I was there and was convinced I had an exhaust valve or two that was sticking enough to give me an intermittent misfire and throw the DTC.  I ran seafoam through the engine, then a bottle of Chevron Techron in the gas tank.  The P1486 code came back in the usual weeks worth of time, and this is when I replaced the charcoal canister and purge solenoid.  When the 0306 code came back three weeks later I ran another can of seafoam through the engine, added the proper amount to the engine oil, and half a bottle in the gas tank, then changed the oil a few days later.

 

That was about a month ago, and the 0306 code has not yet returned, but the 1486 code has always come back within a week of the MIL being turned out, and now last week I also have the 0455 code.

 

I don't know whether the misfire "ghost" and the 1486 code are related.  Reading the #1 misfire post as well as other posts on this forum, there were times when things seemed to match up but I'm lost.  I have a mechanical engineering background working mainly with very large grinding mills in the mining industry.  What I know about cars I have learned from working on my Jeep and the cars my wife has had over the past 12 years, and I was lucky that most issues were minor and I was able to easily diagnose the issues.  I am not confident at all when it comes to the electrical system or the sensors involved with the OBD2 system because until now I have not had to deal with them.  I am willing to learn, and when joining this forum hoped to be pointed in the right direction.  It isn't 9 deg F outside right now, so I don't plan to rely on the local garage either.

 

Sorry for the very long post, but I wasn't sure which information was useful and which wasn't even though I realise some more specific information may have been more useful but I don't have it because I left the diagnostics to the local garage until now.

 

Since the TPS was recently replaced and from what I have seen the Duralast is often acceptable, I'm going to rule out a malfunctioning TPS for now.  I'll check the threads to see how to check the MAP sensor as soon as I have time (probably during the weekend) and will let you know what I find.  I'll also check for a diagram that shows how the vaccum hoses should be routed for the evap system since two different shops worked on it before I touched it and I can't be certain they didn't cross a hose.

 

If anything else jumps out for me to check based on the additional info I provided in this novel let me know, and thanks for the help so far!

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The PCV on this TJ engine is just an orifice that meters air flow from the crankcase.  Moses might have a good strategy for checking the function of this.  I think if you could get it out of the valve cover, you could feel with your thumb (or a gauge) if it's pulling vacuum through it.  If no vacuum, it's plugged and not ventilating your crankcase.  Cleaning it is probably easier than getting it out.  I tried this once years ago and broke the thing off.  Had to have the mechanic fix it because at that time I was too chicken to pull the valve cover off.  I remember kind of an oily film on the valve cover near where the hose connects to this and I think that was why I was trying to pull it out and clean the orifice.  Haynes also mentions that fuel vapor smell under the hood is a common indicator of an evap system problem.  Not sure if you notice this in your case?  Haynes also mentions that manifold vacuum is used to actuate the purge valve when it's time to purge the vapors stored in the canister.  Is it worth putting a vacuum gauge on the vac line that opens the purge valve and see if you're getting full vacuum?  

 

Your post peaked my curiosity enough to crack open the repair manual.  Just thought I'd pass along what I saw...  Good luck.  I'm sure Moses can help you fix this.  

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JJ_Jeep refers to a traditional Positive Crankcase Ventilation valve or PCV, which the later 4.0L engine does not use.  Instead, it has an orifice elbow on the valve cover, similar to what JJ_Jeep describes.  JJ_Jeep offers some good strategies for the purge valve and vapor or EVAP system.  Vacuum hoses can cause issues as we have discussed.  Thanks, JJ_Jeep.

 

Thanks for adding information and history, Marc.  I'm actually starting to think you have a PCM problem or at least poor connectivity at the PCM plug connections.  Another possibility is faulty grounds, we're working with a DC system where weak or high resistance grounds can create a voltage drop.

 

Have the PCM plugs ever been disconnected and re-plugged?  Try this and examine the contacts for "black" oxidation that can raise resistance.  The PCM itself can be defective, but let's not leap to more "parts replacement".  Try the plug connections first.  Trace down underhood battery connections, grounds to the body from the engine, the grounds to the PCM, and frame to engine grounding.  Corrosion, paint, oxidation and any other resistance can cause troubles.

 

You are experiencing random fault codes, some asymptomatic troubles, some symptomatic troubles.  Either the Jeep has high parts duty cycling or there is a universal source for the faulty behavior.  At the very least, rule out the PCM.  I've seen cases where the PCM has a short or intermittent open that is very hard to trace.  Solid state circuitry and electronics can be difficult to address.  The PCM may be incapable of identifying its own defects—despite a manufacturer's insistence that the PCM/ECU/ECM can "self-interrogate" or troubleshoot.  This is not always true. 

 

When new, our '05 Dodge Ram Cummins engine acted up with cylinder misfires that roamed from cylinder to cylinder when the truck had 800 actual miles on it.  The warranty tech insisted that the ECU was defective, Chrysler made him change and swap injectors, load test ground circuits, lamp load test the injector grounds and spend days of pointless work on a brand new truck.  Eventually, Chrysler conceded that 25 late trucks with similar trouble in the zone must mean there was a universal problem.  The dealership was "permitted" to install a Cummins Recon replacement ECU (a quick job on these engines).  End of problem, the first solved in the zone, this truck has run over 130,000 miles since without a problem.  Chrysler recently notified owners of a "lifetime warranty" extension on the ECU.  I received a notice along with many thousands of others.  Moral of story:  PCMs do not always self-interrogate properly, kind of like "HAL" in 2001: A Space Odyssey

 

I had conversations over the last few days with John Herrick (CRAWL Magazine publisher).  We both attended the BFG new tire launch of the All-Terrain KO2 at Baja, Mexico and flew out of and back to Reno, Nevada together.  John has an LJ Wrangler with a 4.0L that had similar symptoms to your Jeep.  Turned out to be the PCM, which had taken a hard jolt on the previous owner's watch.  John replaced a laundry list of parts, trying to cancel MIL signals.  Coil on plug bar, many of the items you've done.  Of course, at high mileage, there are often trouble spots like the TPS, the fuel pump module and sock, the injectors and so forth.  But all at one time?  That can point to a global problem.

 

Follow up on plug connections to the PCM (use care on these connectors, they are plastic and fragile!) and the ground system...Do you have any aftermarket software upgrades (a "chip") in the PCM?  Wiggle the PCM bodies while you're getting a code.  Cancel the code, and see if it stays off.

 

Do the vacuum checks at the MAP, which can be tested with a vacuum hand pump...We'll move on from there.

 

Moses

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Moses, I see you suspect a PCM issue now that I've posted the history on my Jeep for the last several months.  I will check the connections to the PCM because I have never checked these yet, and I don't think the mechanic I had been taking it to did either.  I also want to check the vacuum at the MAP.

 

I also plan to check the grounds.  I know there is a big one at the firewall, but can you let me know where the other(s) are?

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Marc, your 4.0L does not have an EGR valve system, or I would suggest checking that area, too.  For older model Jeep engines, EGR can create issues and symptoms like you describe. 

 

For anyone interested in how Mopar got around the need for EGR on the MPI 4.0L engines, here are the parts schematics for an '02 Jeep TJ Wrangler 4.0L exhaust system, very busy by any standard.  These parts cost a pretty penny when they exceed their duty cycle.  Older EGR systems were cheaper by comparison:

 

2002 TJ Wrangler Exhaust and Manifold.pdf

 

Back to 2002.  Do check the PCM connectors and contacts.  Any resistance or opens in these circuits can wreak havoc.  We'll go from there, Marc.  Let's solve this riddle and get your Jeep running reliably and without the MIL displays.  You have considerable time and parts expenditures, the aim is to get some ROI!

 

Please update on the vacuum circuit checks, MAP test and PCM connector findings...

 

Moses

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Hi Moses,

 

I got home too late last night to be able to check anything we discussed, but this morning on my way to work I noticed a noise that I haven't heard before now.  It sounds like something is rubbing/vibrating at high speed and it seems to start when engine revs get to about 1500 rpm.  Around 1700 rpm it goes away and the slower rattle can sound starts.  If I get off the throttle while it's happening, it goes away.  I'm not sure it is happens above 1700 rpm because there is too much noise from the exhaust, road, and loose interior door panels to hear it at that point.  I'm not sure if this is called pinging (because I don't think I've experienced it before) or if it's something else.  I know pinging is bad, so how can I tell for sure if that's what's happening?

 

I plan to check the electrical connections and ground, and reset the PCM tonight.  If it goes away for my drive to work tomorrow I'll let you know.  I'll check the vacuum pressure tonight if I can as well.  I'm not sure I know how to check the function of the MAP sensor, but I plan to look it up.  Unless you have a quick procedure you can give me...

 

BTW...  No change in the DTC's.  Still P0455 and P1486. And to answer one of your earlier questions, I don't have any performance chips, programmers, or other software upgrades.

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Marc, I want you to review the information at the engine-codes.com site.  Pay close attention to the overview/generic diagram on the P0455 system.  The problem can be as simple as a poor sealing gas cap or as complex as an LDP Pump or even the PCM.  I'd certainly try for the gas cap fix first:

 

P0455 Jeep Code

 

- Missing or loose fuel cap
- Incorrect fuel filler cap used
- Fuel filler cap remains open or fails to close
- Foreign matter caught in fuel filler cap
- EVAP canister or fuel tank leaks
- EVAP system hose leaking
- Fuel tank leaking

 

http://engine-codes.com/p0455.html
 

P1486 Jeep Code

 

- Leak Detection Pump (LDP) pressure hose obstructed
- Faulty Leak Detection Pump (LDP)
- Obstructed hose
- EVAP canister obstructed

http://engine-codes.com/p1486_jeep.html

 

As for the noise you describe, it could be ping or lean fuel mix.  There could be a vacuum or intake manifold leak that's causing a lean mixture.  With the engine at an idle, try misting a lower-volatility spray (WD-40 or similar penetrant) along the intake manifold to cylinder head seam.  To prevent a fire, avoid spraying directly on the header/exhaust.  If engine speed changes, you've got a leak.  Cool the engine down and try tightening the manifold bolts.  Test again.  If still leaking, considering a gasket change.  (This could be the on and off #6 misfire code, too.)

 

I'd resolve the code throwing issues before plunging deeper.  We can ride this through to a solution!  How many miles does the Jeep have on it?

 

Moses 

 

 

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Moses, I checked the pcm connections tonight. There are three plugs that plug into it and the two outside plugs and the corresponding pins were clean. The middle plug was filled with what looked like engine oil and the electrical tape wrapped around the wire bundle going into the plug was worn through in one spot.  The insulation on the wires inside was intact.  I cleaned all the plugs and the pins with electrical cleaner, and applied dielectic grease before plugging them back in.  I found the ground strap from the block to the firewall was dangling, but the other grounds were ok.  I pulled the ground screew out and for a temporary fix fished the loose ground ribbon through the hole in the other ground so the screw would capture it and make a connection.  I'll replace the ribbon altogether after I get to the parts store.

 

 I ran out of light before I had a chance to check the vacuum, but I went out for a quick drive.  The knocking/pinging was still there at the same RPM, but the engine was running and idling much more smoothly.

 

Thanks for the engine code info.  I did not see that much info for each of the codes before now.  I guess I'll get a new gas cap while I'm picking up the ground ribbon, and I'll let you know the vacuum after I check it.

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Moses, forgot to tell you the Jeep has 202,000 miles on it. Its been highly reliable and mostly free of major repairs.

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Marc...Could be time for a cylinder leak down test.  You shared earlier that the shop did a compression test, and this is not the same thing.  Do you have an air compressor at home?  A wonderful tool for pinpoint diagnostics of engine seal is the leakdown tester.  I share details on leakdown testing and vacuum tests at these forum discussions, including tips on DIY work:

 

http://forums.4wdmechanix.com/topic/164-how-to-make-an-inexpensive-engine-cylinder-leak-tester/

 

http://forums.4wdmechanix.com/topic/165-vacuum-tests-for-quickly-pinpointing-engine-trouble/

 

http://forums.4wdmechanix.com/topic/174-quick-test-for-engine-timing-chain-wear/

 

The first two tests are definitely useful.  The third as well, though I doubt you have an issue with timing chain wear yet.  Your engine has a camshaft position sensor and crankshaft position sensor.  If the PCM is doing its job, you will get a MIL if these two measurements are out of spec.  Out of sync camshaft and crankshaft positions indicate severe timing chain wear.

 

A manifold vacuum gauge test is quick and can reveal valves not seating properly...Let's hold to the immediate codes and issues.  We can advance from there if necessary.

 

Moses

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OK.  So I finally had the time to make these quick checks.  I took the vaccum readings at the MAP at idle and the needle holds steady at 17.  It drops initially as I apply throttle, and then smoothly climbs to about 22 at nearly full throttle in neutral.  I tested the MAP sensor itself and it's working correctly.

 

While I was testing the MAP sensor I found the end of one of the vacuum lines going to the LDP is split and probably causing the P1486 code.  I checked all of the other vacuum lines and connectors again and didn't find anything else wrong.   I'm going to go to the parts store tomorrow and get a new connector and hopefully that takes care of the P1486 code.

 

I replaced the gas cap a week ago and the P0455 code has gone away since then.  I didn't suspect it was the cap at first because it was a brand new cap.  The parts store must have given me the wrong part.

 

I also changed out the half torn-ground wires and replaced with new ones.

 

I pulled the center PCM plug out again to see if it looked better than it did before I cleaned it two weeks ago, and it looks almost as bad.  I would post the two pics I took, but I'm not sure how to do that on this forum...  The pins and plug are filled with some kind of oily black liquid.  Do you think this could be causing the knocking or pinging that I mentioned just started about two weeks ago?

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Marc, this is very good news.  You've narrowed down strong possibilities for these two codes!  Good job...Imagine how many consumers spend good money on bad repair bills when the problem is as simple as a bad seal at the gas cap or a leaky vacuum hose...Always best to pursue these simple solutions first.

 

The black oxidation is troubling.  You do need to eliminate oxidation.  Chrysler emphasizes not scrapping the contacts.  I would use chemical cleaning (electrical contact cleaner) again and be optimistic that there was still corrosive/oxidant in the connections.  Use Scotch Brite (Fine grade) if you must clean any contact surfaces.  Avoid use of scrapers, screwdrivers or razor blades.

 

As for whether that was the knock cause, I see bad grounds and poor connections as an obvious possibility.  Let's get that TJ reliable and predictable, then see if the ping occurs again...As for posting photos, here's a recent post I did...

 

Note: Some members are having difficulty adding photos or illustrations to posts.  Simply click on "More Reply Options" next to the "Post" button.  Drop to the bottom of the full editor box, and you'll find the "Attach Files" button at the left.  That will open up your computer file browser, where you can pick the photo file or any other file (several at one time if you like), then add it/them to the attachments.  You'll see the photo(s) or file load.  Now place the curser at the point in the edit box where you want the photo to appear.  Click on the "Add" button next to the loaded file.  The bracketed file description will appear in the edit box.  When you "Post", the photo (thumb) or file (like the PDFs I like to toss out for folks) will appear in position at your post!

 

Moses

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Good photos, Marc...You describe using dielectric grease.  There's a lot of chatter about the use of dielectric grease.  Permatex suggests that Dielectric Tune-Up Grease is a good barrier to oxidation at plugs, connectors and terminals.  There are some online comments at forums that say not to place dielectric grease on connector pins. 

 

I've gone to the Permatex site, and the information is vague: 

 

"Protects electrical connections and wiring from salt, dirt and corrosion. Extends the life of bulb sockets. Prevents voltage leakage around any electrical connection. Also prevents spark plugs from fusing to boots. Required for modern high energy ignition systems."

 

Another quote from the Permatex site:

 

Directions for Connectors: 1. Make sure ignition system is off. 2. Clean surface with Permatex® Contact Cleaner. 3. Coat both parts of terminal contact with Dielectric Grease. 4. Reassemble, maintaining metal-to-metal contact. - See more at: http://www.permatex.com/products-2/product-categories/specialized-maintenance-repair/electrical-system-maintenance/permatex-dielectric-tune-up-grease-detail#sthash.mSLOFJcy.dpuf

 

Also, here's the PDF product information download from Permatex:  Permatex Dielectric Tune-Up Grease PDF.pdf

 

In the PDF, Permatex cites uses for the Permatex Dielectric Tune-Up Grease:

 

TYPICAL APPLICATIONS

• Spark plug boots

• Distributor cap nipples

• Battery terminals

• Ignition coil connectors

• Headlamp connectors

• Trailer electrical connectors

 

The "metal-to-metal contact" reference may create suspicion for some about "Dielectric Tune-Up Grease".  I've used this product for years around tune-up work without reservation.  I searched around and found an engineer's assessment of dielectric grease that suggests Permatex Dielectric Tune-Up Grease should work well on a variety of pin connector materials without creating any kind of resistance or barrier to current flow.  This commentary is worth reading: http://www.w8ji.com/dielectric_grease_vs_conductive_grease.htm, the author seems well informed, experienced, and he uses a scientific approach.  According to the engineer, metal-to-metal pin contact should result if pins are clean and not tarnished, with or without dielectric grease on the pins. 

 

It's realistic to presume that the degree of conductivity is governed by the tension of the pin and socket fit, not whether we use dielectric grease.  Whether or not you use the dielectric grease, I would use a quality electrical contact cleaner to get rid of the oozing material at your PCM plug and terminals.  Make sure you flush out all residue and allow complete evaporation to prevent dilution of remaining grease or any issues with spark arc hazards.  I would at least place dielectric grease on connector lips to act as an effective moisture and oxidation barrier.  

 

Personally, I'm good with the use of dielectric grease, others should use their own judgment.  For me, the engineer at the www.w8ji.com site confirms and clarifies its intended uses.

 

Moses

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Hi Moses,

 

After posting the photos last night I was searching the web for anything about an oily residue in PCM contacts.  I found several posts for several different vehicle manufacturers related to engine oil leaking from a sensor and wicking up the wiring harness into the PCM.  The descriptions and photos I found are exactly what I am seeing.

 

When I originally posted about it two weeks ago, I can tell you that the oil was there before I cleaned the connections with electrical contact cleaner (allowing proper drying time afterword) and used the dielectric grease.  I don't think the residue is from the grease since it was there before I put it on.

 

I found information related to the 4.0 in a Cherokee with engine oil seeping into the PCM.  One of the forum users who responded was a mechanic and had seen this issue before.  He said to check the crank sensor or the oil pressure sensor for an oil leak.  The original poster did not confirm this was the case and solved the problem, so I don't know for sure it was correct.  On a Dodge Neon forum there was a very similar post and it was suggested to check the crank sensor, oil pressure sensor, and cam position sensor for leaking oil.

 

When trying to diagnose the Cylinder 6 misfire I was having my crank sensor was ruled out because if it was not working the Jeep just wouldn't run.  Do you agree with this assessment, and if you do is it still possible there is a leak around the sensor even though it is working?  What about the cam position sensor?  If it was damaged and leaking oil would it function correctly?  I am not getting and DTC's other than the P1486 (pinched evap hose), and I would expect to get a code for either the crank sensor or the cam sensor, however I can see possibly causing the knocking/pinging issue that just started.  Coincidence?

 

I replaced the oil pressure sensor about 3 years ago, but that doesn't mean it isn't leaking.  I'm just wondering if it's more likely one of the other two sensors due to the engine issue...

 

Regardless, I am planning to pick up those vaccum hose connectors to replace them tonight, and I also have to replace the drivers door handle assembly (which sticks open sometimes).  Hopefully I can get underneath and assess these sensors before I lose daylight after work.

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I do agree that the CPS would likely cause more than a #6 cylinder misfire.  A more likely cause would be PCM connectivity issues.  The CPS can be tested for ohms resistance if you're suspect that the sensor is acting up.

 

This oil wicking is intriguing.  The PCM is way up in the bay on your TJ model.  I could see the issue with a low mounted PCM, which was the case with earlier Mopar EFI systems.  For a TJ Wrangler, this is a long way to wick!  If there really is that prospect, a test might be to unwrap electrical covering from the oil sensor lead and look for evidence of oil weep.  To suggest that oil wicks this far through actual wiring inside insulation is asking a lot.  If true, however, any oil leak and wire to the PCM would be susceptible. 

 

I'm very curious what you find with the oil wicking prospect.  It's hard to imagine oil wicking from the CPS or oil pressure sensor to the PCM in the volume that's visible here.  I do agree, though, that the substance does look like oil.  This is a whole new possibility for PCM malfunctions if engine oil wicking is prevalent and able to wick all the way to the PCM!  Could there be a substance inside the PCM that behaves like oil and leaks outward?  This would point to a PCM issue.

 

A footnote on gas caps.  It's helpful to press downward slightly when securing the cap to assure a good fit.  The ratchet override is a preset for tension and does not always produce enough torque for a quality seal.  Also, the tank filler tube lip needs to be clean and smooth for a good seal.  This all sounds obvious, but a simple gas cap leak can lead to expensive and unnecessary troubleshooting and erroneous parts replacement. 

 

Aftermarket caps are not always the greatest quality, either.  I've had issues with key mechanisms, and it's reasonable to assume that the ratchet or sealing elements could fail early—which it did in your case.  Same applies to Brand-X sensors, oil and temp in particular.  I've had TPS switches and oxygen sensors fail, too.  My suggestion is to cross the OEM part number over and use of the OEM parts supplier as a source for the correct part.  As an example for Jeep applications, I use either genuine Mopar or strictly NTK (division of NGK) replacement oxygen sensors under the OE part number's direct crossover.  This number is usually stamped on the original Jeep sensor.

 

Moses

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Moses, I thought the same thing when I first read about the capillary action and wicking oil up inside the insulation on the wires all the way from the oil sensor or the CPS.  I need to take another look with this in mind tonight, but when I cleaned the connector two weeks ago I noticed a damaged section of insulation and there was oil on the wires.  I had already sprayed the contact cleaner on the plug at that point and I assumed it had run down out of the plug.

 

That being said, I sprayed more contact cleaner on the plug as many times as I needed until it stopped seeping oil, then let it dry.  When I pulled the plug out yesterday I half expected to see a little bit of residual oil that was stubborn and didn't want to come out from my cleaning, but  didn't expect to see the entire plug covered in almost as much oil as before I cleaned it.

 

I still don't know if I believe this is the cause, because there was no evidence of oil anywhere else around that area of the engine compartment, and I would think that air movement from driving would have made an adjacent area at least a little damp...

 

I'll let you know what I find.

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Last night I got home later than I would have liked but still had some time to work on these issues.  I was able to replace the cracked fitting on the end of one of the vaccum lines going from the LDP to the intake, and while I was at it, I replaced a few more that looked like they might crack in short order.

 

I also replaced the drives side door handle.  This is what took most of my time.  The door handle I received from Quadratec did not have threaded holes for fastening to the door, and I couldn't find M5-16 screws or a tap at either the auto part store or the nearby Lowes.  The closest Jeep dealer was too far and closed for the day so I opted to buy an M6 tap and the corresponding screws instead.  This worked out just fine, except I had to put a few extra washers under the head of the bolts to take up the extra length on the bolts.  I couldn't get screws any shorter at Lowes.  You can't see them because they're inside the door, they don't interfere with the mechanism, and they hold the handle in place securely so I don't plan to source shorter screws from another supplier.  I don't expect an issue with the door handle coming loose, but I did save the factory handle just in case.  Overall including the drilling and tapping it took about an hour to install.

 

This morning when I left for work the door wouldn't release.  I checked it last night after installation and it worked fine...  I ended up taking the interior door trim back off and found the clip that holds the connector rod to the latch had slipped off or it was never attached properly last night (it was dark, I could barely see, and I was going by feel inside the door at that point).  A little aggravating but a quick, easy, 10 minute fix.

 

Since it was dark I didn't have time to check the CPS or oil pressure sensor for leaks, but...  After I left the house this morning my check gauges light came on, and a warning tone sounded, then both went away.  As first I didn't notice what for but a few miles later I noticed my oil pressure gauge dropped to zero at a stop sign.  So...  I think that more than likely answers the question on faulty sensors...  I will have a look tonight and see if the CPS is leaking or anything out of the ordinary, but I will be picking up an oil sensor and installing it tonight.  I'll keep an eye out for signs of oil that would be wicking up the wires to the PCM.

 

I'll also be cleaning the PCM out again, hopefully for the last time, and hopefully the odd knocking goes away with a clean oil free PCM.  I'll keep you posted how I make out.

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Marc, this is really fascinating.  If the cause of the PCM touchiness turns out to be engine oil wicking from the sender to the PCM plug, please let us know.  This is a new one, but engine oil is easy to distinguish from other liquids, and your thoroughness may ultimately yield a valuable insight...We need to look at a factory wiring schematic to see whether the wire from the oil pressure sender goes directly to the PCM.

 

Keep us posted!

 

Moses

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Hi Moses,

 

I changed out the oil pressure sensor, and cleaned up the center connection in the PCM.  It's only been a few days but it seems that the oil is not building up in the connector anymore. If the oil starts to build up again in the connector over the next week or two I'll let you know, but for now it seems like that was the problem.   The "noise" is still there, but I'm attributing this to a symptom of old age.

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Marc...We'll see.  This is insightful, keep us posted...The noise might just go away if it's old age.  There are days when I just toss my leg right over the 37" high saddle of the Honda XR650R—then there are others.  Like your engine's ping, there's creaking faintly heard by ears not quite as sensitive as they once were, though my wife insists this is just "selective hearing"...

 

Moses

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