1997 TJ stalling sputtering and backfiring when warm

T

theonetruetom

New member
Hey everyone, I'm Tom, and I'm new here. I've been combing every forum online and every possible place I can think of, but I've got a doozy of a problem and it's stumping me.

I have a '97 TJ 2.5L 4 cyl 5 speed. A couple of weeks ago, I was in the mountains on some windy roads and the truck started acting like it was running out of gas in the middle of the road. It would just stall, and if it had enough momentum, it would pick back up again, the engine would start, it'd backfire, and we'd be moving back down the road again. For a little while. Then it would happen again. It acted fine when we got up to 55-60 on the way back home. We got back into town, and it wouldn't stay idling, it'd act like it was bogging down when you'd try to start from a light, but once it got moving all was good. So, I replaced the fuel pump. The tank strainer was nasty disgusting, and the truck ran better after I did this (it'd been hard to start when cold and would kinda fall on its face if you went past 3/4 throttle, it still doesn't do that anymore, so one problem is down! :D). It was a little difficult to take off from stops, sometimes it'd bog down and try to die but if you feathered the throttle it'd move and have no further issues. For about a week. Then my current problem reared its ugly head:

While driving, when the truck was cold, it would be fine. Then the engine warmed up, and it would start bucking and sputtering and backfiring a lot, and the tachometer would suddenly drop to 0rpm and then flutter around /below/ where the RPMs actually are. It still idles well. I should add that it always starts right up after this. Except for the other day, when it didn't. And wouldn't. And I had to get it pushed by a Ford over an overpass on a surface street so I could pull off. :x I checked the codes at a friend's shop that I was close to, and got 5 results: P0123, P0132, P0551 (which has been there since I bought it), P1294, and P1391. Then began a weekend of parts ordering and cursing, and as of today I've replaced:

  • the distributor
  • the crank position sensor (since replacing this, the tach is still fluttering when the issue occurs but it flutters towards the higher end of the RPM spectrum instead of the lower end)
  • the cap/rotor/wires (after replacing the wires today the idle kinda surged a little for a couple of drive cycles, but that went away)
  • the upstream oxygen sensor (under warranty, I replaced the original in October when I had a bad cat because it was masking the symptoms)
  • the coil
  • and I've tried removing the plug from the TPS and driving it, and it still happens.

I'm all out of ideas. I checked the resistance on the coolant temp sensor as it was warming up to where it'll do this, but didn't get any flat spots or shorts. I also didn't have a helper to check engine temperature while I was watching the meter. I'd think that if it was TPS related the issue would've gone away in limp mode, and it didn't. If it was spark plugs, why does it only happen when the car's hot? If it was a battery/alternator issue, why does it only happen when it's hot AND why does it start right back up again afterwards? And what's with the tach? That started on Saturday when the seriously undriveable condition happened. Before then it was difficult to take off from lights, but with no visible symptoms inside the cab.

Sorry for writing a novel, I just wanted to be as clear as possible so I can get this fixed with the internet brain trust's help. Thanks in advance for any suggestions!
 

P1294. Target RPM not reached.
What rpm do you idle at?

P1391 - Intermittent Loss of CMP or CKP Loss of the Cam Position Sensor or Crank Position sensor has occurred.
Where did you buy the CKP?

After the pump replacement did you reset the PCM?


P0551-power steering pressures sensor. Have you changed the sensor?

p0122 & P0123 TPS sensor- use OEM TPS.

Only buy OEM sensors for jeeps. Aftermarket sometimes fail right out of the box.
 
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JPNinPA said:
P1294. Target RPM not reached.
What rpm do you idle at?

P1391 - Intermittent Loss of CMP or CKP Loss of the Cam Position Sensor or Crank Position sensor has occurred.
Where did you buy the CKP?

After the pump replacement did you reset the PCM?


P0551-power steering pressures sensor. Have you changed the sensor?

p0122 & P0123 TPS sensor- use OEM TPS.

Only buy OEM sensors for jeeps. Aftermarket sometimes fail right out of the box.
Click to expand...

It idles pretty steadily around 5-600 RPMs. I bought the CKP from RockAuto (don't judge me, $100 for 3 sensors and a set of plug wires vs. 100 for a sensor in town). How does one reset the PCM on these things? I'm not getting any light flicker, just the tach sweep towards the top of the spectrum, and the radio doesn't lose presets. The 0551 has been present since I bought the Jeep and doesn't seem to have caused any driveability concerns, is there any reason it would start now? Also, when I tried disconnecting the original CKP, it wouldn't even start. I'm also pretty sure that disconnecting the TPS and the issue recurring would indicate that the issue isn't TPS-related, but maybe I'm wrong. I've replaced the PS Pressure switch (because, as I said $100 for 3 sensors and plug wires..), but the code's still there.

At this point I'm operating under 1 or 2 possible scenarios: 1, the issue is occurring when the engine gets warm because that's when it switches to a closed loop, in which case the O2 sensor should have resolved it. Or 2, the issue is occurring when the engine gets warm because I've got an open or a short that isn't showing itself until it's hot enough. Tomorrow I'm going to try clearing the codes completely and driving it with the CT sensor disconnected to see if that improves matters.
 
*cough* I think I figured it out. this morning I disconnected the battery for 5 minutes to clear the codes and tightened the ground screws underneath the coil and then drove it for about 20 mins and it drove like a brand new Jeep.

Now I feel like an idiot.
 
Juuust kidding. :x it's back. The symptom went away for about a week, and now it's back. But with a P0108 claiming a MAP sensor high voltage. I've made sure both the grounds I tightened the first time are still tight (they are) and that the frame ground is tight... It idles perfectly fine, but I was climbing the hill out of the parking lot at work today and it sounded like popcorn and was extremely jerky and didn't want to rev above 3000. Got out on the main street and it did it a few times, but not enough to cause a safety issue. I've checked the charging voltage (13.7v at idle) and the MAP voltages by backprobing the sensor. I got well within normal ranges for MAP signal voltage, nowhere near 4.5V though which I'd expect to be considered high. I didn't pull it off and test it with the vacuum pump, though. That's tomorrow's project after I get some brake cleaner (the P0551 was due to a leaky sensor and because I'm lazy, and the fact that I'm a firm believer in "if it ain't broke don't fix it", I didn't replace it for a year. Control arm bushings got me black in places I didn't know I had...) or some degreaser and just pressure wash that side of the engine bay in the street.

It's very intermittent while driving, and at its worst it makes popcorn when you try to go up hills, but does this sound like a faulty MAP to you guys?
 

please post ALL the codes, you will need a scanner key trick will not display all codes.

any issues ie cruise control, ABS, fuel gauge.....
 
... All of the codes currently are P0108.

Issues with cruise control and ABS are that they aren't equipped on the truck, and the fuel gauge is fine. The tach keeps jumping up the range from where it is when this issue starts.
 
Lets try KOEO the map plugged in - probe the DK/RD (center) wire - what is voltage?
thn engine at idle what is voltage?
Chec the rubber vacuum connector.

FYI a skewed MAP reading will affect ign timing.
 

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oops wrong picture above the tests are the same
 
What brand O2 sensor?
Check the temp sensor cold, hot and when running funny.
Check for vac leaks by slowly spraying WD40 or carb cleaner...around the intake and vac lines. A change in rpm denotes the location of a leak.


Not going past 3000rpm is limp mode meaning the PCM is restricting RPM to avoid engine damage.

Have you cleaned the TB and IAC?


JPNinPA
Using Jeepz.com app
 
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I haven't had a chance to check the voltages on the MAP or run any other tests, because the problem seems to have gone away and taken the CEL with it. I did unplug the MAP briefly yesterday and that may have moved some wires around that were possibly shorting together, however.
 
It's back again and it brought a friend! :x Was driving for a bit yesterday and the stuttering came back, then went away and was replaced by a misfiring and really crappy-running Jeep. As of this afternoon I have a P0320 (engine speed input circuit) P0301 *and* p0300, and my P0108 is back. It rained yesterday, and this seems to be related to rainy days (or high barometric pressure?) more than anything. The weird thing is that it sometimes comes and goes, which makes me think this is a short somewhere in the electrics that's not playing up until there's just enough moisture somewhere to cause problems.

Edit: The misfire is definitely not a spark problem. I have as much spark (with a tester) on 1 as I do on 3. My noid lights and compression tester are down the street, I'll see what those tell me as soon as I can have them brought here. I don't want to foul another cat with unburned fuel from this misfire.

Edit 2: The reason for the misfire is low compression on cylinder 1. The oil doesn't look like a milkshake, but there does appear to be some coolant coming out from under the water pump. I removed the valve cover and the valves appear to be opening and closing normally on cylinder 1. When that spark plug came out it was damp, like it'd been soaked in fuel or oil. It looks like heads-off is my next step here, since I either have leaky piston rings that aren't holding compression and are allowing oil past (which I'd think you'd see out the tailpipe), burnt or bent valves, or a cracked head. None of which are nice options to look at having to repair on my budget.
 
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removing head - replacing engine sounds like a leap without testing....

Compression test, wet an dry, do you have shop air for a leak down test?

A leaking inj will cause low compression, wet plug, misfire. TEST FIRST!

GTG
 
So I pulled off the fuel rail (I'm right there anyway, what harm can it do?)

This is what I saw. The one on the left of the first image is #1, and the other 3 look the same. They're also different on the outside.
20170724_175250.jpg

20170724_175253.jpg

Something seems off about that #1 injector.

Edit: But it's totally not causing the lack of compression. I'm talking like 40psi in cyl #1 and 110 everywhere else. I don't have air to do a leakdown. But I swapped that injector over to #2, and #1 still had crappy compression, and #2 still had great compression.
 
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Are there o-ring gaskets on injector 1?
It can be a stuck open or struck closed injector. Swap injectors in the rail and see if the problem follows the injector. If it does clean or replace the injector. I had one stuck on a Honda and it would load the cylinder making it impossible to start. Hold the pedal to the floor when starting and it would shut off the fuel pump allowing the fuel to clear the cylinder. Then run lots of injector cleaner.
Do a wet compression test. That is run it dry and record the number. Then pour in some transmission fluid into the cylinder with low compression. Retest. If the compression comes up near normal the rings are leaking. If not it may be the gasket or a valve. But be sure the injector has the or both o-rings.


PS From the factory good compression is 120-150 in each. Delta of 30 is bad. I've seen readings as high as 190 after 8 good revolutions.

PPS the leak under the water pump is the water pump. With it leaking you must be adding water. If

Regards,
JPNinPA

Sent using TapTalk
 
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Either way it looks like I'm taking the head off this weekend. On top of trying to find a secondary daily driver because this thing keeps letting me down this way and I have a 2000 mi trip coming up that I need 100% reliability for.
 
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