dzywicki

Been chasing a problem for a few weeks now and I am stumped. This is a problem on TubThumper (https://www.cherokeeforum.com/f2/reb...-apron-226647/). Hs been running great up until it stalled on my wife. 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?

Motojunky

For the symptoms above, does the behavior change between in-gear or neutral/park?

dzywicki

Great question. In Park/Neutral, it feels like it's an idle problem with the looping idle. I don't think I have let it idle in P/N long enough to see if it will eventually die (will try that). In D, it feels like it wants to lurch forward and will eventually die from the looping idle/lurching.

I'm confused because of what I get at idle and what I get at road speed. They must be related and would indicate more of an engine problem. But...the shuddering at speed makes it seem like a transmission problem.

Motojunky

Interesting. If it cleared right up out of gear, I'd be more inclined to guess transmission.

The fact that it drives well until operating temp has me thinking it may be a lean condition caused by who knows what. Could that lean condition then be causing the computer to react in a way that feels like a transmission problem?

Random anecdote: My daily is a chevy malibu. It started shifting horribly and I was sure the transmission had taken a header. Long story short, it was wiring to the MAF sensor that confused the computer. A quick solder and I was back in business. I'd have never found it if not for Google turning it up as a fairly common occurrence.

dzywicki

I am not convinced that there aren't two problems. One being rough hot idle and the other being something with the trans.

the part making it hard is trying to diagnose while it is cold. I really only get one shot per evening for about 10 minutes. After that's it hot and doing weird things. I'm really trying to determine if it's temperature related or not.

Turbo X_J

Vacuum leak.

dzywicki

I am going to double check for a vacuum leak too. I put my mity vac on the vacuum line t on the passenger side fender well and I wasn't seeing anything that looked like a vacuum leak. Was going to go through that exercise again too and make sure a deliberately caused vacuum leak will register on the mity vac so I' know what I'm looking for.

Brian Day

This seems like the same issue I'm having with my 99... driving me crazy! Hopefully someone can figure this out it seems to be a pretty common problem. I've read tons of threads with people having the same symptoms but nobody ever confirmed the cause... I truly hope for your sake, mine and many others that someone will confirm the problem here for now and future reference.

fb97xj1

The next time it starts to shudder at speed, take your foot off the gas. If the shuddering stops, it could be the torque convertor. Maybe. Ford had issues with that a while back with the AOD-E (its a computer controlled AOD). The entire vehicle would shake. Let off the gas and it would stop shuddering. The AOD-E takes a different fluid than the AW4 but one of the issues was the friction properties of the fluid would break down, even tho the fluid wasnt burnt. Replacing the fluid worked for some, but for others the torque convertor needed replaced because the clutch was too far gone. The shift solenoids were fine, however.

Just throwing that out there.

FePower

How many miles? Has the head been replaced? 99-01 crack between the 3-4 intake ports and egr. Pull the intame, if the middle ports are clean, it's cracked.

dzywicki

It has 225k miles. I did a partial rebuild a few years go due to cracked pistons. Compression is good oin all cylinders (150 psi) and leak down test shows very little leakage.

BillyBoy

Fuel pump is 225000.miles old... I'm changing mine now. Same.symptoms. seem random.

dzywicki

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.

Kymasabe

One Ford trans that had weird shuddering problems was the E4OD (like the one in my 92 F150) Replaced the fluid with new Mercon V and a bottle of Dr. Tranny Shudder Fixx and the shudder was completely gone and now shifts GREAT !

dzywicki

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.