Jeep YJ Wrangler 2.5L TBI Troubleshooting


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Moses, your website has been extremely useful for me while working on my 1989 Jeep YJ Wrangler 2.5L TBI engine. I have used it for testing just about everything on my jeep. I have replaced several items because of extremely high emissions. Today was the 4th pass through the test, and I finally passed my emissions test.

 

I have replaced the ignition coil, ignition control module, spark plugs, cap and rotor and set the base timing, map sensor (because it did not hold vacuum), coolant temp sensor and my fuel injector. With all of that, my emissions finally were within spec.

 

I am still having a loss of power issue with my jeep, and the only thing that helps is when I run Seafoam through the vacuum lines. It helps for about 2 days and then the same issue. Any ideas would be extremely helpful. One possible clue: The wide open throttle switch is in-op (cannot locate the part), and my throttle position sensor does not put out a signal if this helps any.

 

Stinger87 (Josh)

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Thanks for the compliment, Josh.  The TBI signal could be a factor, although the Seafoam has me looking at the oxygen sensor, EGR valve or an exhaust obstruction...The '89 YJ Wrangler is early OBD and awkward for testing the onboard diagnostics.  If you do have access to a scan tool that will work with Chrysler's early OBD hookup, try getting a DTC trouble code from the ECU.  You do have a diagnostic test plug on the Jeep engine bay wiring.

 

Make sure that the exhaust is unrestricted, and consider the EGR valve and oxygen sensor.  Test parts before replacing them.  Even though the oxygen sensor is a higher mileage "perishable", you should still make sure that it is defective before buying a new O2 sensor.  Same with the EGR valve. 

 

As the issue goes away when you sweep Seafoam through the vacuum hoses, this may be a clue.  Seafoam flows through the combustion chambers and exhaust, which may be cleaning a sticky EGR valve or dirty O2 sensor.  Unseated and stuck open, the EGR will generally cause a rough idle or low speed performance quirks.  An EGR valve stuck shut will create upper cylinder heat and possibly erratic fuel mixtures.  The EGR controls NOx and can affect other exhaust gases. 

 

Considering your troubles to this point, the EGR valve would be worth testing.  If you have a hand vacuum pump, you can quickly test the EGR with the engine idling.  Attach the pump hose to the EGR.  Pump down vacuum with the engine idling, enough to open the EGR valve.  You should hear a change in engine speed and smoothness as you open the EGR valve at an idle.  No changes would indicate that the EGR valve is either stuck or defective.  The valve has a diaphragm that can be weak or leak with age.

 

Be cautious when working around the EGR valve, it gets very hot!  Handle with care...If you attempt to remove and clean the EGR valve, do not soak the diaphragm in solvent or carburetor cleaner.  Try to submerge the base of the EGR valve (metal parts only) in carburetor cleaner, and make sure you get the valve plunger to open and shut freely—and seat completely.  Rinse away any solvent or carburetor cleaner before reinstalling the EGR valve and running the engine.

 

Moses

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Good afternoon Moses...Thanks for the quick reply, and I forgot to add that I did replace the egr valve even though my old one was good. I replaced because I got a good deal on it and it looked ancient. I had the jeep running really well but I did notice that a few days after I changed the fuel pressure regulator that is when I had the idling issue.

 

The regulator removed my issue of the loss of power but now it just feels as if it were about to stall during stop lights and when in neutral idling. I installed the old fuel pressure regulator and the hard idle and loss of power issue are there. Tomorrow I will throw the new regulator in and now I just have to sort out the idling issue.

 

I had a local exhaust shop test my o2 sensor and inspect my exhaust for back pressure and to see if my cat was plugged but they both passed. The only things I can think would be my idle speed control which does work. When I start the jeep up my rpms go to about 2000 and then idle around 1000 but then seems the engine starts to sputter like it's not getting enough fuel. As soon as I give it some throttle the engine wakes up and runs smooth. Thanks again with the quick reply.

 

Josh

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Good evening...Another thing i was curious about is the thermostat on my jeep. From my understanding it should have a 195 in it. My gauge at times tells me different because it seems like it is running around 165-175 on an average sometimes the temp will spike to where it looks close 200 and that is when it runs the best . I am guessing this would cause an issue with the computer and not allowing the engine to go into a closed loop to properly function properly. I was actually looking to swap that out to make sure that it is running correctly at 195. i was wondering if anyone had anything to add to this?

 

Another thing is for my previous comment about my rough idle. I did a ohms test on my intake air temp sensor and cold it was close to 2000 ohms. I do not know the specs for this but to me it sounds out of range. While the engine was at operating temp or to what the gauge says about 165-175 the ohms rating was around 1500. If anyone had any insight of this or any more knowledge about the IAT that would be great. Thanks again for any help and hopefully this all can help someone later on.

 

Josh 

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Josh...Glad to see your follow-up, I'm focused on your second post as possible ties to your problem.  For openers, you're absolutely right, the engine will not come out of cold start mode if the IAT is out of sync or the engine coolant temperature is off.

 

Jeep constantly emphasized a 195-degree F thermostat to assure adequate temp for the closed loop mode as you comment...Definitely replace the thermostat unless you suspect that the gauge is inaccurate—I like to use a surface temp IR tester to check the actual temperature.  You can temperature probe around the engine block, at the radiator, hoses and, importantly, at the thermostat housing.

 

As for testing the IAT (actually called the manifold air/fuel temp sensor or MAT), here are the specs for your '89 TBI system:

 

Degrees F   Ohms

212              185

160              450

100            1600

  70            3400

  40            7500

  20          13500

    0          25000

 

The two adjustable features on your TBI are 1) the TPS (throttle position sensor) and 2) the idle speed actuator motor or ISA.  Have you adjusted either of these devices?

 

Moses

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Good morning sir,
 
I will double check the MAT sensor tonight and log my readings. The TPS sensor when i losen it and rotate it i still get zero signal out of it so i am assuming that is part of my issue. The idle speed actuator i do not know how to adjust unless it is just turning the threaded part of it. Today i drove the jeep to work with the bad fuel pressure regulator in it and it drives decent. Enough power through all gears but sputters a little bit around 1500-2000 rpms. At red lights and stop signs the motor will idle down to 1000 rpms and sounds good but then drops to about 500, it does not stall but it does sound rough. Even sometimes at 1000 rpms the tac and engine jump around and this idling issue just started happening once i put the new fuel pressure reg in it. I ensured the TBI was clean made sure that the 4 vacuum lines were in good shape no cuts or anything. I also replaced the TBI gasket to make a good seal. Last thing i noticed was unplugging any of my sensors did not effect the way the vehicle ran anymore such as MAP sensor MAT. The MAP sensor used to shut the vehicle down but it doesnt effect it anymore.

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Alright so i did some troubleshooting. In my previous post i said that this all happened after i installed the new fuel pressure regulator. I left out one key detail. I ordered this regulator from Rockauto and the spring that they gave me did not have enough resistance on it but i used it anyway thinking it should work since it's new and they sent it to me. Wrong.... it actually flooded the engine with so much fuel and back fired out of the intake with this happening i'm almost certain that damaged the MAT sensor causing the rough idle. My issue now is actually locating the MAT for a 1989 and Chrysler is saying that it has been discontinued. I have found a similar sensor for a 91 the only difference is the way it is wired up but it still is a two wire. Right now i am looking at getting the sensor for the 91 and buying a few snap together connectors and making my own harness for it.

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Josh, if you do get the later MAT, you need to compare the ohms settings and make sure they're right.  1991 is definitely an MPI engine, not TBI, Chrysler discontinued TBI after 1990.  Here is the OEM Mopar part number for your MAT sensor:

 

33002382 SENSOR, Intake Air Temperature

 

This part also fits a 1991 3.0L Dodge Monaco V-6.  It has been discontinued by Mopar.  However, I found this remarkably lengthy cross-reference chart courtesy of a Google Search.  Verify the cross-reference.  The Chrysler number above is from my set of Mopar Catalogs and is reliable.   If the part numbers below do cross over (verify before buying), we can thank "Hornbrod" at the Comanche forum http://comancheclub.com/topic/30054-where-to-get-a-mat-sensor/ for this effort: 

 

AIRTEX 5S1004
AUTO-TUNE PT9599
BIG A 53-1009
BORG WARNER WT5502
CHRYSLER 33002382
ECHLIN TS5016
FILKO CS-62
GP/SORENSEN 779-19015
KEM 139-411
NAPA TS5016
NIEHOFF TS81351
NIEHOFF WA629EL
STANDARD/HYGRADE AX9
TOMCO 12120

WELLS SU330          

 

Let me know what works here.  If you decide to set the ISA, I have the OEM specs, let me know...

 

Moses

 

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I currently have a MAT for a 91 on order which will be in tomorrow morning so i will compare the ohms readings and post them on here tomorrow. In addition if the ohms readings are the same.Here is the current part number that i will be trying tomorrow that is the closes match to what i am currently running MPE TS5014TB this here is a Napa prolink number and i am not 100% sure that it will work but i will verify tomorrow and keep you updated. All of the crossover number that you posted Moses i could not find anywhere. I am not sure if it is because its not the full part number but i even tried to interchange those part number through several other sites and i couldn't find anything. Anyway tomorrow i will have an update. Thanks again for the help its much appreciated.

           

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These are all national brands and available product lines, whether the specific part numbers are still active is another story.  Try the NAPA number at your local NAPA store.  See if Rock Auto carries any of the other lines, and if so, whether they can furnish the part from their Warehouse Distributor sources.  There are way too many numbers here to strike out...eBay might be another source, Josh.

 

Also, check the individual product lines, as most should have an online catalog at their official website.  Search by part numbers and manufacturer at Google.  See if that yields anything...As for the part you ordered, the oddball 1991 Dodge Monaco 3.0 V-6 listing suggests that some Chrysler engines were still using this MAT after 1990.

 

Moses

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Regarding the rough idle, have you tried finding a vacuum leak?  Have you changed the PCV valve?  Back to the Seafoam temporary fix, the PCV valve could be involved...The valve is a routine replacement service part.

 

Moses

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Yes sir, i changed the PCV valve on my oil change which was about 200 miles ago. As for vacuum leaks i havnt not found any. While the motor was cool i used carb cleaner and sprayed the hoses to see if the rpm would fluctuate but i didnt get any findings. When i reinstall my fuel pressure reg i will replace the 4 vacuum lines on the TBI. I didnt get to do any more troubleshooting lastnight but i will pick up my sensor and see what i can do tonight

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Let's see what that MAT does...You'll check ohms range first...The carb cleaner usually turns up leaks.  We'll stay after this, there's always a reason for the hunt-and-peck idle!

 

Moses

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So I have the new mat sensor and the ohms readings are very low 10.5 ohms but the jeep is idling good. I am going to use this since it is running better then with a broken sensor in it. I will post a better part number once I cross ref another. I tried to add some picks of the new sensor wires up just have to see if they load. Tomorrow I will put the new pressure reg in it, I had to order another since my wife tossed the other one on accident haha. Also on my drive to work tomorrow I will get the engine nice and warm and see if the sensor keeps the engine running good or it if goes way out of spec. More updates tomorrow!

 

post-93-0-33339100-1384906365_thumb.jpg post-93-0-48974500-1384906379_thumb.jpg

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Gotcha, Josh...Can see the plug and wiring differences.  Suggestion for your use and others: When working with an EFI system, I use solder for splices and cover with multi-layers of heat shrink tubing, enough tubing to emulate the insulation strength at the wires.

 

EFI circuits are hypersensitive to ohms resistance, and with a sensor like the MAT, Josh, ohms resistance accuracy is critical.  When we use a butt connector and crimp approach, there's a lot of room for ohms mismatch.  The crimp, by design, simply cannot lock all strands of the two wires together.  Also, vibration is clearly an issue with any automotive application, more so with a Jeep 4x4.

 

I always use rosin-core solder on electrical splices like this.  Flux helps, easier in the core so you can solder steadily.  Consider soldering, it's really quick in the long run, and you'll take the guesswork out of ohms resistance.  (Crimping can often work okay for trailer lights and such, I still prefer solder.) 

 

Another very good feature of heat shrink, when done properly, is to prevent corrosion wicking up the wires.  A 4x4 Jeep gets wet, let's face it, that's what a Jeep does!  So, preventing water from wicking up wires will go a long way toward eliminating corrosion over time.  Again, a good reason to use rosin-core solder and heat shrink tubing! 

 

As a footnote, when I bring the two wires together for soldering, I face the stripped wire ends toward each other and try to lap and interlace the strands evenly.  Solder can fill tiny gaps and secure the wire joint together.  Keep strips of heat shrink well up the wires, away from heat, while soldering.  Then slide the heat shrink into place and shrink it.  Wooden matches (move quickly or hold away from the tubing) work well for me when shrinking the tubing.  Use care not to melt through plastic!  I know the joint is laced and soldered properly when the finished "bulge" is minimal.

 

Moses

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I am having all of those sensors crossed and i cannot find a single one because they are discontinued.

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Josh, I read the post at the Jeep Forum/link.  The Jeep owner used a Wells unit that also fits a later application.  It sounds like your approach has its match.  If your ohms readings are correct for the '89 specs I furnished, you bought the right sensor and simply needed to modify the wiring...See my comments about soldering, your best assurance of ohms integrity.

 

We should have reverse engineered the switch by ohms rating in the first place then sought out a two-wire replacement sensor with the right thread pitch and ohms readings.  Apparently, Chrysler and Renix MAT sensors have reasonably close ohms tolerances, maybe other applications, too...Good job, Josh!

 

Moses

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Alright so i just picked up my new fuel pressure regulator from advanced auto because they had the fastest delivery rate. I took the tbi off to get to the regulator and installed the new FPR. Reassembled everything but i look the tbi cover off so i could see the spray pattern and check for excess or not enough fuel. Crack the motor over and the engine spikes to 3k rpms so i get out to look at it and fuel was spraying out of the bowl. I shut the engine down cleaned up the fuel and figured i would try again. Cracked the engine over but it didn't start. Assuming the engine was flooded i figured it was a bad regulator so i took it all apart again and installed the old one. Once i re installed everything i cracked the engine over again and it fires up and runs perfect......I am drawing a blank because the idling issue is gone and it doesn't sputter. I did check the ohms for my new IAT/MAT sensor and at operating temp my sensor was at 1780 ohms which doesn't seem in spec but as of right now its running with no issues. That may change in the morning when i drive it to work and put a load on the engine. as of right now i am running out of ideas

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All interesting, sounds like the first regulator had a plugged passage or flow.  The trip up to 3000 rpm should have cleaned things up, and you did do a removal and replacement of that first regulator (now in place again)...You'll know in the morning, also whether the MAT ohms rating will work...Moses

 

P.S.:  If this does work out, great...Otherwise, you're back to the drawing board...Clogged or blocked passage would be the only explanation for a "cure".

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As of right now i have not had any issues with the jeep (knock on wood). It is idling at 1000rpms and drives good and doesnt bog down when stopping at red lights or stop signs.

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Really good news, Josh!  When you have time, post some pics of your '89 Jeep YJ Wrangler at the 'Tech and Travel' Forums...Looking forward to your posts...Welcome!

 

Moses

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Haha so the jeep drove good this morning and then this afternoon it was running like hell. Attempted to drive it home since I only live about 5 miles away and got outside of work and it died. Cranked it over a couple times and still no start. Called a tow truck and waited for it to come but every 5 minutes I would crank it to test my luck. After about 40 minutes it did finally start and I hauled ass home it was bucking and jerking like crazy. I figured it is the fuel pump since it is pretty much the only thing in the fuel system that hasn't been changed. Should get the pump tomorrow and I'll drop the tank and go from there.

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Installed the new fuel pump this morning and fired the jeep up. It ran but barely. I don't have a fuel pressure tester but the i took the tbi cap off and looked in the bowl and the injector was spraying so much fuel. Also black soot was coming out the back kind of looked like a diesel truck. It sounded like it was missing really bad too so i shut it down. inspected the butterfly valve and opened it up and the intake had a puddle of fuel in there. I am not sure if it is in limp mode because none of the sensors determine how it runs. If it is running and i unplug the map sensor it used to shut the jeep down now it no longer does this. I took the spark plugs out and they were black and wet so i let them dry and cleaned them off. Now the jeep doesn't run at all unless i wait about 45 minutes after it running. This little guy is turning into a nightmare. Probably taking it to a garage this week...... 

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Josh, before you throw in the towel, let's look at this objectively.  You had no spillage or flooding issues before you changed the pump.  You have severe flooding issues now—and are likely in limp home mode as a result.
 
The 2.5L fuel pump for a 1989 Wrangler is a Walbro 550 or Chrysler 83502995.  Here are the 2.5L TBI pump specs: 

1989-1990 Jeep Wrangler Fuel Pump 4 Cyl. 2.5L (E) E.F.I.
 

OE spec Walbro electric fuel pump and installation kit fits directly into any 1989-1990 Jeep Wrangler 4 Cyl. 2.5L (E) E.F.I.. Detailed fuel pump installation instructions included. Made in the USA.

Fuel Pump Specifications
Walbro Part Number: 550
Minimum Current: 12 Volts
Operating Pressure: 17 PSI
Minimum Flow @ Outlet: 28 GPH Low Pressure
Fuel Pump Location: In-Tank

 
Now, let's look at a 1991 2.5L MPI fuel pump for a Wrangler.  It will fit your tank fine, as '87-95 tanks are similar.  This is a Mopar pump #04637193.  Here are the specs for the Walbro common equivalent: 

1991-1993 Jeep Wrangler Fuel Pump 4 Cyl. 2.5L (P) E.F.I. (Chrysler #'s 4637192 & 4637193)
 
OE spec Walbro electric fuel pump and installation kit fits directly into any 1991-1993 Jeep Wrangler 4 Cyl. 2.5L (P) E.F.I. (Chrysler #'s 4637192 & 4637193). Detailed fuel pump installation instructions included. Made in the USA.
 
Fuel Pump Specifications
Walbro Part Number: 5CA234
Minimum Current: 12 Volts
Operating Pressure: 65 PSI
Minimum Flow @ Outlet: 24 GPH High Pressure
Fuel Pump Location: In-Tank

 
Note the obvious pressure output differences for these two pumps that look similar.  The '91-up engine is MPI and operates at 31 PSI (regulated) injector pressure.  Your '89 TBI operates at a 14-15 PSI (pressure regulated) setting.  If you put the later pump into your tank, you will be pushing 65 PSI against a TBI pressure regulator designed to operate with a 17 PSI tank pump pressure.
 

This is likely your newly developed flooding problem.  My hunch: The new pump supplied is for a '91-'93 MPI engine, not your TBI application.  If you run a pressure check on the pump-only, you will likely turn up a 65 PSI output pump.  This would over-pressurize the TBI pressure regulator and cause flooding.
 
Check the new fuel pump part number and run the number at www.fuelpumps.com.  This is where I came up with pump output ratings for TBI versus MPI engines:
 
http://www.fuelpumps.com/-c-0/19891990-jeep-wrangler-fuel-pump-4-cyl-25l-e-efi-p-2212.html
 
http://www.fuelpumps.com/-c-0/19911993-jeep-wrangler-fuel-pump-4-cyl-25l-p-efi-chrysler-s-4637192-4637193-p-2210.html

 

Before dropping the tank again, I would run a pressure check of the fuel pump (before the regulator, pump-only pressure).  If you are confident this is the wrong pump, either by the part number or actual pressure tests, drop the tank and replace it with the correct, 17 PSI output pump.

 

Let us know what you find here...TBI and MPI requirements are dramatically different...
 
Moses

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