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1994 YJ 2.5L Long Crank Time and Hesitation Upon Quick Acceleration


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Hello there, I've been having some problems with my 94 YJ 2.5L Jeep Wrangler. I bought it broke. It was a crank all day, no start. then one day over the previous winter I decided to try it again. To my surprise it started. Ive been testing things & replacing things.

So far I swapped out my gas tank with a good known to work fuel pump. I took the original tank and put it on the side. I put a new fuel filter in it.

I also replaced some fuses under the dash & PDC as they were blown when I bought it from the previous owner. I know there was one 10 amp in the PDC that needed replacing

This week I have replaced the spark plugs as I pulled them and found they were pure black with the smell of gas. It didnt take the new plugs long to look the same and smell the same with gas. They also look wet from gas. That was just a few quick starts and letting it idle. 

The ECU seems to be okay as the check engine light does come on.

One problem I have found amongst my search over these months of fiddling with it was the power to the coil is 0.04. I checked the battery and i have 12.7 volts on that. I go directly to the coil wire (Key on) and I get 0.04 on the multimeter. I believe I have the multimeter set up correctly as I get a correct reading on the battery. I have tried to get some tests on some sensors, i.e. map, crankshaft position sensor, O2 sensor but I havent been successful at it as I think I using the wrong settings for ohms. 

I have cleaned the throttle body on it. I have also cleaned the IAC sensor. 

The jeep does have a wire mishap somewhere around the PDC/battery area. I know it cut out all power to the computer and everything was completely dead. I notice when I shake the wire loom that those wires lead to the front axle diaphragm is when it cuts power to everything. I havent been able to locate that yet and it hasnt happened lately. But then again I havent been using this thing as I work on it as funds & time allow. 

I test the fuel pressure with this known fuel pump to be good and pressure held after shutdown and it also held over night. I did swap the fuel pressure regulator with a good used one I had laying around. I also pulled the vacuum line on the fuel pressure regulator while I had the testor on the rail. It jumped to around 39lbs off. And then returned to 31 or 32 when placed back on. 

I have posted a recent video of when I try to start it for the first time of the day. Once it starts it seems to start much easier. No so many cranks to take it to fire up. But after it sits for a long period its back to usual with long crank times. I also noticed it is hesitation on a quick rev of the gas pedal. But if you ease it, it acts normal. 

I put a new alternator on it as over time the original froze up on me. I also put a new serpentine belt on it. I just recently cleaned the screens on the valve cover along with a nee valve cover. The 4 bolts on the back of the valve cover were loose. When I bought it the motor and underneath was covered in oil. So over the months I have been cleaning everything up. Its looking much better than it once did now if I can only fix the problem to get it running better. lol! 

I have enclosed a couple photos as well. One is how I have everything set up for testing the voltage to the coil plug. One is of the old plugs that came out.  One is from after shut down showing the pressure held. One of is a blue wire that has been spliced with connectors on it by a previous owner. 

A few things when funds allow in the future would be to replace the spark plug wires, cap, & rotor. I also want to buy a timing light to check the timing. Otherwise Im not really sure what else to do here and was seeking some advice on where to look next. 

I did notice the front axle diaphragm is leaking. It looks like the whole housing is compromise some way. I see a gasket there but also see blue rtv added along with two large radiator clamps tied together to hold the thing on. I do see the housing has all 4 bolts on it as well. I have yet to dig into that. lol !

 

Here is the video link of how its acting. 

 

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  • Moses Ludel changed the title to 94 YJ Long Crank Time & Hesitation Upon Quick Acceleration
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See my take below, Gorilla:

 

23 hours ago, Gorilla said:

Hello there, I've been having some problems with my 94 YJ 2.5L Jeep Wrangler. I bought it broke. It was a crank all day, no start. then one day over the previous winter I decided to try it again. To my surprise it started. Ive been testing things & replacing things.

So far I swapped out my gas tank with a good known to work fuel pump. I took the original tank and put it on the side. I put a new fuel filter in it.

Presume that you changed or at least checked the pump sock/pickup screen while the pump module was removed?

I also replaced some fuses under the dash & PDC as they were blown when I bought it from the previous owner. I know there was one 10 amp in the PDC that needed replacing

This week I have replaced the spark plugs as I pulled them and found they were pure black with the smell of gas. It didnt take the new plugs long to look the same and smell the same with gas. They also look wet from gas. That was just a few quick starts and letting it idle. 

The ECU seems to be okay as the check engine light does come on.

Make sure the check light is hooked up...You should have codes stored with the engine running this poorly.

One problem I have found amongst my search over these months of fiddling with it was the power to the coil is 0.04. I checked the battery and i have 12.7 volts on that. I go directly to the coil wire (Key on) and I get 0.04 on the multimeter. I believe I have the multimeter set up correctly as I get a correct reading on the battery. I have tried to get some tests on some sensors, i.e. map, crankshaft position sensor, O2 sensor but I havent been successful at it as I think I using the wrong settings for ohms.

You won't get coil voltage readings unless the PCM is sending firing signals to the coil, engine cranking.  5 volts would be a normal square wave signal for triggering the PCM ignition and injector pulse signals.  The coil has a constant 12V primary voltage source lead;  the PCM furnishes a ground signal to fire...It doesn't sound like a coil issue, anyway. 

Hook up an induction timing light to #1 spark lead and see how strong the spark is.  Or get an inexpensive inline spark tester and watch the spark intensity.  I don't believe you'll find a problem here, once the engine is running, it sounds like it is firing.

I have cleaned the throttle body on it. I have also cleaned the IAC sensor. 

The jeep does have a wire mishap somewhere around the PDC/battery area. I know it cut out all power to the computer and everything was completely dead. I notice when I shake the wire loom that those wires lead to the front axle diaphragm is when it cuts power to everything. I havent been able to locate that yet and it hasnt happened lately. But then again I havent been using this thing as I work on it as funds & time allow.

Absolutely...Eliminate any voltage drops in the wiring, including poor grounds.  The PCM needs strong, consistent voltage, at least 12.6 volts.  Check the battery with a load test (AutoZone, O'Reilly's, etc., will test the battery for free.)  There could be a dead cell, rule this out.

I test the fuel pressure with this known fuel pump to be good and pressure held after shutdown and it also held over night. I did swap the fuel pressure regulator with a good used one I had laying around. I also pulled the vacuum line on the fuel pressure regulator while I had the tester on the rail. It jumped to around 39lbs off. And then returned to 31 or 32 when placed back on. 

Should show a change, that's the cranking pressure.  As a test, hook your vacuum pump/gauge to the regulator and manually change pressures.  See whether the engine roughens up.  Make sure that you're not flowing too much fuel.  This is one possibility.  Check the fuel return flow to the tank and make sure there are no restrictions.  Check the EVAP hoses for misrouting.

I have posted a recent video of when I try to start it for the first time of the day. Once it starts it seems to start much easier. Not so many cranks to take it to fire up. But after it sits for a long period its back to usual with long crank times. I also noticed it is hesitation on a quick rev of the gas pedal. But if you ease it, it acts normal.

CHECK THE THROTTLE POSITION SWITCH (TPS) VOLTAGES...These switches wear out and send erratic voltage signals that can cause roughness and over-fueling! 

I put a new alternator on it as over time the original froze up on me. I also put a new serpentine belt on it. I just recently cleaned the screens on the valve cover along with a nee valve cover. The 4 bolts on the back of the valve cover were loose. When I bought it the motor and underneath was covered in oil. So over the months I have been cleaning everything up. Its looking much better than it once did now if I can only fix the problem to get it running better. lol! 

I have enclosed a couple photos as well. One is how I have everything set up for testing the voltage to the coil plug. One is of the old plugs that came out.  One is from after shut down showing the pressure held. One of is a blue wire that has been spliced with connectors on it by a previous owner.

Verify the spliced wire from a color code FSM diagram.  Determine the function and voltage requirement for that lead. 

A few things when funds allow in the future would be to replace the spark plug wires, cap, & rotor. I also want to buy a timing light to check the timing. Otherwise Im not really sure what else to do here and was seeking some advice on where to look next.

A timing light with built-in advance would be nice... 

I did notice the front axle diaphragm is leaking. It looks like the whole housing is compromise some way. I see a gasket there but also see blue rtv added along with two large radiator clamps tied together to hold the thing on. I do see the housing has all 4 bolts on it as well. I have yet to dig into that. lol !

Worth pursing the front disconnect housing issue.  Check to see whether the vacuum leak is part of your engine issue.  See my final comments below.

Here is the video link of how its acting. 

 

20200814_163532-0.jpg

20200814_142523-0.jpg

20200814_163751.jpg

20200814_163751-0.jpg

20200811_223816.jpg

Reading your spark plug photo, it's difficult to tell whether this is ignition misfiring or oil consumption (not fuel) that is fouling the spark plugs.  Yes, it could be ignition fouling, but do check for oil burning to rule that out...Have you run a compression check, or better yet, a cylinder leak down test?  This is not typical sooty plugs from a rich mix and could be oil fouling.  With a catalytic converter, you sometimes get very little blue tailpipe smoke (from oil burning), which can be deceptive.  How many miles are on this engine?  Does it smoke on startup then clear?  That would be worn valve guides and/or guide seals.  

Use the search box to find "leakdown" or "leak down" testing information.  If the engine is consuming oil, the Oxygen Sensor could be messy.  Pull the O2 sensor and look for signs of oil coating on the probe.  You may be experiencing an O2 sensor, TPS, coolant temp sensor or MAP sensor issue.  This could also be nothing more than an oil soaked Crankshaft Position Sensor (CPS) at the back of the engine where you had the oil leak...Rule out an oil leak or oil consumption troubles before any other work.

Let us know what you find.

Moses

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7 hours ago, Moses Ludel said:

Presume that you changed or at least checked the pump sock/pickup screen while the pump module was removed?

What I did was took the 94  gas tank out and put my 95 gas tank in as I knew there were no problems with the 95 gas tank. I didn't take anything apart as I figured I had it so why run to the parts store for something it may not need. I still have the 95 gas tank in and hooked up. I do plan on rechecking the 94 gas tank but since it is running I figured leave the 95 hooked up for now. 

 

7 hours ago, Moses Ludel said:

Make sure the check light is hooked up...You should have codes stored with the engine running this poorly.

The check engine light does come on. I have checked for codes but only getting 12- battery disconnected, 33 A/C which is not equipped with the Jeep, and 55- End.I was surprised to see no other codes show up with it running this way. I am unaware if any showed up for the previous owner and when I asked he said he didn't know and just couldnt get it started. 

7 hours ago, Moses Ludel said:

You won't get coil voltage readings unless the PCM is sending firing signals to the coil, engine cranking.  5 volts (square wave) would be normal trigger signals for PCM ignition and injector firing pulses.  The coil has a constant 12V primary voltage source lead; the PCM furnishes a ground signal to fire...It doesn't sound like a coil issue, anyway. 

Hook up an induction timing light to #1 spark lead and see how strong the spark is.  Or get an inexpensive inline spark tester and watch the spark intensity.  I don't believe you'll find a problem here, once the engine is running, it sounds like it is firing.

Ahh! Okay I have a lil bit better understanding on the coil after reading your comment. I was following this guys tutorial video  Im not sure how he got the 12v constant reading without it running. I do have an inline tester I shall have to try this out. I tired it a few weeks ago and it did have spark. Im not sure how strong the spark was though. 

 

 

7 hours ago, Moses Ludel said:

Absolutely...Eliminate any voltage drops in the wiring, including poor grounds.  The PCM needs strong, consistent voltage, at least 12.6 volts.  Check the battery with a load test (AutoZone, O'Reilly's, etc., will test the battery for free.)  There could be a dead cell, rule this out.

Okay thanks I will have the battery tested and see what the read out says on it.  I have cleaned up the grounds as I read that is usually the first problem on these vehciles is corrosive grounds. 

 

7 hours ago, Moses Ludel said:

Should show a change, that's the cranking pressure.  As a test, hook your vacuum pump/gauge to the regulator and manually change pressures.  See whether the engine roughens up.  Make sure that you're not flowing too much fuel.  This is one possibility.  Check the fuel return flow to the tank and make sure there are no restrictions.  Check the EVAP hoses for misrouting.

 

I have not done any of this and will have to research how to . Thank you.

7 hours ago, Moses Ludel said:

CHECK THE THROTTLE POSITION SWITCH (TPS) VOLTAGES...These switches wear out and send erratic voltage signals that can cause roughness and over-fueling! 

Beauty!!! Something else I wasnt aware of and didnt check. I will have to search on how to test that. 

 

7 hours ago, Moses Ludel said:

Verify the spliced wire from a color code FSM diagram.  Determine the function and voltage requirement for that lead. 

Gotcha!! I will check the wire diagrams. 

7 hours ago, Moses Ludel said:

A timing light with built-in advance would be nice... 

I will have to see what and where I can get one. 

7 hours ago, Moses Ludel said:

Worth pursing the front disconnect housing issue.  Check to see whether the vacuum leak is part of your engine issue.  See my final comments below.

 

Thanks for mentioning that. I never gave that a thought. I would like to remove the wire loom and have a better look at all the wires as well. When I bought it, it was just so dirty with oil and grime that it took me some time to get it this far where you can actually see what youre working on. It shaped up pretty nice but wondering if it will continue to stay that clean as Im wondering if it has a rear main seal leak or was it from the 4 loose valve cover screws? 

 

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Gorilla...See my comments on your comments below:

2 hours ago, Gorilla said:

What I did was took the 94  gas tank out and put my 95 gas tank in as I knew there were no problems with the 95 gas tank. I didn't take anything apart as I figured I had it so why run to the parts store for something it may not need. I still have the 95 gas tank in and hooked up. I do plan on rechecking the 94 gas tank but since it is running I figured leave the 95 hooked up for now.

You've checked for pressure and it is smack on for both running pressure (31 PSI +/-) and cranking pressure (39 PSI).  I would also check for fuel volume flow at the rail.  The 4-cylinder MPI system's fuel pump should displace "at least 1 liter of fuel per minute".  Fuel can be bled off the rail and gauge with a safe "T", hose and steel fuel canister to catch the fuel safely away from any engine heat.  This test requires that the fuel pump is running the entire time, which is not a problem when fuel is bled off this way.  Your pressure gauge appears to have a bleed-off test tube for this purpose.  Correct?

The check engine light does come on. I have checked for codes but only getting 12- battery disconnected, 33 A/C which is not equipped with the Jeep, and 55- End.I was surprised to see no other codes show up with it running this way. I am unaware if any showed up for the previous owner and when I asked he said he didn't know and just couldnt get it started.

This makes me even more suspect about the burning oil factor.  All other parameters can be okay (no check light or codes), but burning oil will still cause roughness and misfire.  I would also add the timing chain and tensioner to my list of suspected troubles.  You may have a loose chain and sprockets, which delays valve timing and could create firing and performance issues...I would check and rule out these factors before plunging any further into "tune" troubleshooting:

1)  Sufficient compression or better yet a leak down test for piston ring, valve and head gasket seal.

2)  Correct valve timing (no loose chain, worn sprockets or defective tensioner).  If severe enough wear, the camshaft position sensor should throw a code.

3) Valve lift  to rule out camshaft lobe wear and lifter issues.

3)  Proper oil pressure and good oil flow.

 

 

Quote

Ahh! Okay I have a lil bit better understanding on the coil after reading your comment. I was following this guys tutorial video  Im not sure how he got the 12v constant reading without it running. I do have an inline tester I shall have to try this out. I tired it a few weeks ago and it did have spark. Im not sure how strong the spark was though.

This tech is verifying the KEY ON 12V source lead that is always power to the coil when the key is in the "ON" position.  When cranking or running, the PCM provides a ground signal to fire each spark plug at the correct time. The PCM provides the ground for the primary circuit of the coil.  These are high speed, square wave, lower voltage signals that your meter may or may not recognize or be able to pick up.  Testing the coil is actually a simpler ohms-resistance test as described in the FSM for your model and engine. 

I HIGHLY RECOMMEND THAT YOU GET A COPY OF THE FSM (FACTORY SERVICE MANUAL) FOR YOUR YJ WRANGLER.  Personally, I do not work on any engine, ignition, fuel system, transmission, transfer case, axles, steering, chassis or vehicle electrical system without an FSM within reach as a reference.  A used FSM print copy may be available through an automotive used book outlet or at eBay.  There may be a PDF/CD available at eBay.  Troubleshooting and diagnostics recommendations are available within the FSM.  My 1994 XJ/YJ Mopar Service Manual was purchased as a reference book for my work.  It holds a prominent place in the office bookcases.  I buy these books for each vehicle we own and model years that I address in the books that I have written.  I work with FSMs constantly and have done so professionally for over fifty years now.  A sound investment in your case...Please get your hands on an FSM if you do not have one yet.

There is one more item you need to check, based upon your comments about a major oil leak down the back of the engine.  This is where the Crankshaft Position Sensor resides and could be affected.  The sensor is at the back of the engine, approximately 11 o'clock when looking at the bellhousing.  It is very possible that the CPS is oil saturated, possibly the flywheel as well.  This could interfere with a normal pulse signal originating at the CPS and sent to the PCM.  The result would be erratic starting, faltering, misfiring, poor idle and bad acceleration.  Sound familiar?  Check for oil on the CPS and flywheel, clean it off thoroughly and check the engine performance again.  If this is the source of trouble, check for a continuing leak like the rear main seal, which could throw more oil at the CPS...Also distinguish between oil fouling at the spark plugs and ignition misfire fouling.

Okay thanks I will have the battery tested and see what the read out says on it.  I have cleaned up the grounds as I read that is usually the first problem on these vehciles is corrosive grounds. 

 

I have not done any of this and will have to research how to . Thank you.

Beauty!!! Something else I wasnt aware of and didnt check. I will have to search on how to test that. 

 

Gotcha!! I will check the wire diagrams. 

I will have to see what and where I can get one. 

Thanks for mentioning that. I never gave that a thought. I would like to remove the wire loom and have a better look at all the wires as well. When I bought it, it was just so dirty with oil and grime that it took me some time to get it this far where you can actually see what youre working on. It shaped up pretty nice but wondering if it will continue to stay that clean as Im wondering if it has a rear main seal leak or was it from the 4 loose valve cover screws? 

 

 

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  • Moses Ludel changed the title to 1994 YJ 2.5L Long Crank Time and Hesitation Upon Quick Acceleration

Much thanks Moses. Just to update a bit. I had some time to go over some small things the past few days. I cleaned the ECU contacts & used some die electric grease on them. Neither the connector or the ECU pins looked corroded. All looked well. I used a flashlight to see inside the holes on the plug connector side.  The firewall area around the ecu was rusty, Just some surface rust so I removed the surface rust and quickly spot painted that area. Used the air hose to blow out the dust too. I swapped out the cap rotor & plug wires. I had to fix up some of the bolts that hold the coolant reservoir & washer fluid reservoir. Its in alot better shape than what it was. 

I checked the Throttle postiion sensor tonight. DMM on DCV 20, Key on but not started. Stand still or Idle 0.81, Throttle wide open 3.78. 

I managed to find a source for a FSM on this year model jeep. I downloaded it but have yet to read it as my pc is having problems with abode reader. Some type of error is occurring. Ill need to fix my pc or find another to read the manual. 

I plan on getting a timing light and a compression test kit. I just havent gotten to the store just yet. I did read about doing a leak down test as well but need to research more on how to go about doing that. I did read all of your notes and will follow thru with them. Just wanted to give a small update on what I got to so far. 

 

I was in fact thinking along the lines of the CPS sensor being possibly saturated with oil from the oil leak. Im not 100% sure if the rear main seal is out as I did find the 4 rear valve cover bolts loose when I replaced the seal and cleaned the PCV/CCV screen on the cover. I am thinking all that oil was coming from the valve cover instead. Again not 100% sure but when it runs I do not see any blue smoke or smell of the oil burning. The muffler and tail pipe is off the jeep from the previous owner. It does have a catylitic on it. 

I was unsure if I could removed that CPS sensor or not. I wanted to check that a few months ago but I read somewhere online that you shouldnt remove it due to the sensor being in a certain position. I wanted to seek more information on someone more knowledgeable than I about removing it to check that? It sounds to me like it is okay to remove and inspect then correct? 

Another thing I wanted to mention was after getting everything back on the jeep and ready to test fire it to see if the cap rotor plug wires made any changes. I could not get it to start. A few coughs shakes etc but 12 to 13 times and it wouldnt fire up. So I sprayed some starter fluid into the throttle body. Just a couple squirts. Place the hose back on the air cleaner box and turned the key. Upon first crank it started VAROOOM!!!!! Sounding strong. It ran well. I am wondering if I have a clogged injector? I was thinking about taking the rail off and cleaning the injectors with some carb cleaner. I found a tutorial online on how to do it. Let me know your thoughts. Again I appreciate all your input and will follow thru with the other information you have listed. 

P.s. What are your thoughts on the TPS readings? 

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Gorilla...The starter fluid test is a definite clue.  If the plugs are fouled, the starter fluid success could be a simple case of overcoming poor combustion.  If lack of fuel, however, you might be onto a fuel supply problem.  The fuel volume flow test would be helpful here.

I am still focused on the CPS.  You can note the bolt and CPS tab alignment before removing the sensor if there is a concern here.  By all means, clean the CPS.  If oily, clean the flywheel and clutch through the open sensor hole or the lower dust shield.  This is not easy.  The flywheel hall effect points might actually be better exposed through the starter motor opening with the starter removed.

As for a compression gauge, that's useful for quick checks but not definitive like a leak down test.  OTC makes an affordable leak down tester, Amazon lists an off-shore (what isn't?) combination leak down and compression gauge kit for a mere $35, surely worth a try at that price:  Amazon listings for leak down testers.  I recommend a leak down test for pinpointing actual wear points. 

Years ago, I compared a compression check to a leak down test on a Toyota 4-cylinder engine.  The compression gauge read adequate cranking compression in each cylinder.  Leak down readings were 50%-80%!  How/why?  Because a cranking compression test can sweep air volume, enough to capture it and give an erroneous conclusion;  by contrast, a leak down test is with a stationary piston at TDC with the rings positioned at their maximum cylinder taper or wear point in the cylinder.  At this ring position, air rushed past the taper and expanded rings.  Although that engine ran okay and did not burn oil yet, I knew it was well worn without tearing it down.

Moses

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