99 XJ shuddering at speed and rough idle when warm - JeepForum.com
 
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post #1 of 9 Old 09-21-2017, 08:46 PM Thread Starter
dzywicki
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1999 XJ Cherokee 
 
Join Date: Nov 2013
Location: Aldie
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99 XJ shuddering at speed and rough idle when warm

Been chasing a problem for a few weeks now and I am stumped. This is a problem on TubThumper (http://www.jeepforum.com/forum/f177/...rokee-3777121/). Hs been running great up until it stalled on my wife a week ago. It's been difficult to diagnose since I can't figure out if it's completely temp related or not. Here are the symptoms and what I have done:

- Idles well until it gets up to temp and then feels like it is missing.
- When it misses, the RPMs drop to ~500 and then come right back. This repeats every couple of seconds.
- When driving, it will drive fine until it gets to operating temp and will then start shuddering a few times. It feels like the transmission is surging. I can't tell if it's right as the temp gets to operating temp or if it's speed related but it will do few minutes into a drive that coincides with a higher speed and hitting operating temp.
- It will continue to shudder intermittently. It feels like it is coming from the trans. I am not seeing the engine RPM surging.
- If I come to a stop and put my foot on the brake, it feels like the car wants to lurch forward.
- If I let it idle long enough it will stall. I can start it right back up.

I am not getting any DTC codes.

Things done so far:
This XJ has ~225k miles and I have replaced many sensor over the past 2-3 years. I also have been picking up spares to swap for testing when I got to the pickpart. Also have a '98 that runs perfectly and I swap parts to check things.

- IAC and TPS replaced with MOPAR sensors. Have also swapped with 98 to test. No change
- New MOPAR CPS (just changed this tonight. I had it in my inventory and the temp thing made me think it could be related).
- New A1 Cardone distributor.
- Mechlin Crank position sensor ( have also swapped the '98 one in with no change)
- Very recent NAPA/Mechlin cap and rotor
- New Champion copper plugs
- Very recent spark plug wires
- O2 sensors replaced with NTK 2 months ago
- Trans fluid changed 4k miles ago with DEXIII
- Engine compression is 150 in all cylinders and leak down test showed very little leakage.
- Original coolant temp sensor (temp readings look normal through OBD reader)
- Original IAT sensor (readings look normal through OBD reader)

I have put an OBD reader on while it's running and throttle position readings looks fine. O2 sensor readings look normal too.

Fuel pump is original.
Exhaust system is original
Fuel injectors original but have replaced the orings
Checked fuel pressure 2 years ago chasing an idle problem (checked fine then but am going to check again)

The shuddering at speed starts me thinking transmission or torque converter.
It kind of feels like the torque converter is going in/out of lockup mode.

I'm out of ideas on the engine side which is leading me to the transmission. Does this sound like it could be torque converter related? Is there any way to check the solenoids?

I will be renting a fuel pressure tester this weekend to verify fuel pressure. Assuming that comes back normal all I can think of are:
- something with fuel injectors
- something with fuel pump
- something with the torque converter

any other ides for what to check?

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post #2 of 9 Old 09-22-2017, 08:24 AM
S8NNG8
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Location: Helena
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Catalytic converter plugged, O2's will operate but send the wrong message to the motor, which in turn sends the wrong message to the trans. This causes the trans to be suspect when you may actually be looking at the chain reaction from the wrong end. With all the other things you've done, it's worth checking.

D3<!L!>3D
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post #3 of 9 Old 09-22-2017, 08:54 AM Thread Starter
dzywicki
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Join Date: Nov 2013
Location: Aldie
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I was thinking that as a possibility too. It is the original exhaust system. I don't know if there is an easy way to check it without replacing it. I just had to replace the cat on my '95 YJ because the insides separated from the shell. MAde a heck of a racket rattling around and I could feel it prevent proper acceleration etc. I know the front connection is pretty mused fused together after 18 years. The underside is in remarkably great condition. No rust anywhere, bolts come free without a problem etc. That's really the reason why I'm putting work into this (besides this being my wifes car from new).
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post #4 of 9 Old 09-22-2017, 09:09 AM
S8NNG8
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My muffler guy was able to tell just from listening to it run. I was also able to trust him, so I knew he wasn't just telling me that to get a sale.

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post #5 of 9 Old 09-22-2017, 09:39 AM Thread Starter
dzywicki
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Would a faulty transmission speed sensor cause problems like this at speed? I'm just walking through sensors that are original. I have not changed out the transmission speed sensors. Seems easy enough to swap and test with the '98.
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post #6 of 9 Old 09-22-2017, 10:53 AM
S8NNG8
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Not sure how that'd relate to the warming up to reach the trouble area. However warming up the cat could bring on issues when plugged.
I dont have an auto trans in my rig. And I dont know alot about them in general. I experienced the issue With the cat in my wifes '98 4.0 ZJ. New cat and precat O2 fixed the whole problem. Stalling, stumbling, no acceleration, couldnt get it past 35mph, no rhyme or reason to shift patterns.

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post #7 of 9 Old 09-24-2017, 07:14 PM Thread Starter
dzywicki
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Made quite a bit of progress today. First thing I did was backtracked to the last thing I did which was replace the distributor. I think I was a degree or two off from TDC last time. It will definitely change a bit depending on the angle you look at the timing marks. When I reset the distributor, I made 100% sure that the circular piece did not move when I twisted it in. Depending on how you do both things (TDC and twist the distributor in while making sure the ring doesn't move at all) I think you can definitely get the distributor off by a degree or 2 or 3. I think I was off before TDC and not after. That fixed my shuddering at speed problem.
I was able to rent a fuel pressure gauge and it is rock steady t 49 regardless of what else is going on. Next I did another vacuum check. Vacuum is steady at ~15 psi. I pulled a connector from the intake and the gauge went all over the place si I think I'm good there too.
Now I am back to rough/blip of idle when hot. I swapped a complete throttle body in from the pickaaprt. Had original equipment IAC, TPS and MAP sensor. No change...still terrible idle. I did notice it is not as bad and pretty much a steady idle with the AC off. I had injectors from the pickapart and decided to swap those out too just to eliminate that. At first I thought tht was it, but the longer it idled, it was back to it's old tricks.
I did notice one oddity. When the compressor kicks on, the voltage would drop under 13. At good idle it was just above 13.
For comparison, I checked the 98 XJ I have. I was seeing 14 volts at all times, compressor on or off. I am going to check voltage a little closer tomorrow, but thinking tht might be a big clue. I changed the alternator 7-8 years ago so may try swapping that out next.
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post #8 of 9 Old 09-24-2017, 09:12 PM Thread Starter
dzywicki
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Did some comparisons between the 98 and. Of course it looks like the alternator changed between the 98 snd 99 so I can't swap to test. On the 99, I get 13.8 volt reading at idle with the headlights on and 13.2 max with the headlights and AC on. The idle is definitely a lot better with he AC off.
On the 98, I get 14.2 at idle with headlights on. 13.8 at idle with headlights and AC on. Will do some more checking on current output tomorrow.
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post #9 of 9 Old 10-03-2017, 06:52 PM Thread Starter
dzywicki
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Join Date: Nov 2013
Location: Aldie
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Wanted to close the loop on this thread (I hate when threads are left dangling with no resolution). I triple checked several things with no change and then finally decided to try swapping the coil. I had replaced the original coil a few years ago with an Echlin from NAPA so I really didn't think that would be the problem. I had the very original one and one from a replacement motor on the 98 sitting around. I swapped in the one from the replacement motor and no more hot idle problem. I had moved the fuel injector connectors to make sure they were tight so it could have been that but I doubt it.
I always thought that coil location was terrible since it's right up against the block and takes an excessive amount of heat that it doesn't seem to have to. I checked the resistance on the two I had out and they were the same. If I think about it I may heat up the echlin one and see what happens. Runs and idles great now.
Now I am just left with completing the OBD emissions monitors for the emissions test for annual registration. Those bastards reset every time the battery is disconnected. t least I now know how to check them and get them to complete. I got caught off guard last week when my wife took it to get emissions and the technician said that 3 of the monitors were not complete. Did some reading and was able to get them to complete pretty quickly.
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