97 TJ still sputters and stalls after replacing computer

Deepsouthgt

Deepsouthgt

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Jun 18, 2022
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Gulf Coast, Alabama
I have a 97 TJ 4.0 Auto transmission. 186k miles. After driving in Louisiana in a monsoon rain, I had a terrible sputter and thought it was water in gas. Long story short, it was not. I have emptied the fuel cell, replaced with 110 octane racing fuel, replaced the following items: thermostat with a 185 degree one because it started running on the hot side when sputtering, crank position sensor, both O2 sensors, Throttle position sensor, complete distributor assembly, all 6 plugs, cleaned idle air controller, replaced PCM with a rebuilt one from Flagship One, New Battery, cleaned battery connections very well.

After saying all that, as soon as the engine gets to temp, if you are driving or put it in Drive, it begins to sputter and will eventually stall out if you don't mat it to the floor from a stop. Now, it has gotten to the point where you cannot get over 20 mph from a stop when engine is warm. When it starts to sputter if you put it in Neutral or Reverse, it immediately smooths out. It only does it when in rolls even a foot or two in Drive. You can hold the brake in Drive and run it up to 3000 rpm with no problem, but as soon as it rolls, it sputters and tries to stall out.

Someone please tell me there is a transmission sensor or wheel speed sensor or something that I am missing that could cause this. Makes no sense. Not throwing any codes on a Snap On computer.

Thanks for any suggestions,

Greg T
 
I'm gonna go out on a limb and say you're the only one here running 110 octane.
 
Put the correct 190 thermostat in.

Is CKP sensor Mopar? Its been well documented that other brands wont work well with the TJ.

Same with O2 sensors. Did you use NGK or mopar? Any other brand is hit or miss.

Plugs--the early distributor TJs like Autolite or Champion plugs.

Flagship one blows. And your computer was likely never at fault. Its rare they fail.

What is your fuel pressure?
 
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tworley said:
Put the correct 190 thermostat in.

Is CKP sensor Mopar? Its been well documented that other brands wont work well with the TJ.

Same with O2 sensors. Did you use NGK or mopar? Any other brand is hit or miss.

Plugs--the early distributor TJs like Autolite or Champion plugs.

Flagship one blows. And your computer was likely never at fault. Its rare they fail.

What is your fuel pressure?
Click to expand...

Thanks, that is a lot to consider and look into. Is there any of this that would cause the issue only when moving forward? Thanks again.
 
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There is no sensor that would account for this that I can think of. That it seems to be fine in R but not D makes it sound like a transmission problem.

You could put the transfer case in neutral and give it gas to see if the trans acts weird there, but without an output load it might not act the same.

In R the front clutches & low/reverse band are in use, but they aren’t in use for D1 & D2, so maybe they aren’t disengaging? Does it do it in manual 1? Manual 1 doesn’t use the overrun clutch so if M1 works that could be it.

Also, check your trans fluid level with the engine warm & trans in neutral.

C8812F14-A881-4FF2-88A5-4050F392CBC6.png
 
All grounds are secure. It only does it in Drive when moving forward. Drove it until was sputtering and almost stalling, stopped quickly, put in reverse, matted to the floor, smooth as glass up to 30 mph. Back into drive, as soon as it rolls, it starts sputtering even without touching the pedal. Bump into neutral, smooth. Park, smooth. Drive, smooth. Rolling, sputtering until it stalls. I can put it in drive and hold the brake, flexing the suspension, smooth. As soon as it rolls, sputters until it stalls or I put it in neutral. This even works when going 40+ mph and it sputters, neutral is smooth. Cleaned all the connections on all 3 molex plugs on the transmission and transfer case, they were corrosion-free, but cleaned with CRC electric cleaner, and brushed them very lightly with dielectric grease.
 
hear said:
There is no sensor that would account for this that I can think of. That it seems to be fine in R but not D makes it sound like a transmission problem.

You could put the transfer case in neutral and give it gas to see if the trans acts weird there, but without an output load it might not act the same.

In R the front clutches & low/reverse band are in use, but they aren’t in use for D1 & D2, so maybe they aren’t disengaging? Does it do it in manual 1? Manual 1 doesn’t use the overrun clutch so if M1 works that could be it.

Also, check your trans fluid level with the engine warm & trans in neutral.

View attachment 368106
Click to expand...

Would this make the engine sputter and backfire? It shifts nice and smooth, no jerking or slipping. Thanks.
 
hear said:
There is no sensor that would account for this that I can think of. That it seems to be fine in R but not D makes it sound like a transmission problem.

You could put the transfer case in neutral and give it gas to see if the trans acts weird there, but without an output load it might not act the same.

In R the front clutches & low/reverse band are in use, but they aren’t in use for D1 & D2, so maybe they aren’t disengaging? Does it do it in manual 1? Manual 1 doesn’t use the overrun clutch so if M1 works that could be it.

Also, check your trans fluid level with the engine warm & trans in neutral.

View attachment 368106
Click to expand...

Transfer case in 4 Hi, or 4 Lo, same sputter when it moves. Neutral, smooth. Put in M1 or M2, sputters as soon as in engages.
 
Update as of 10/27/22; Dropped the skid plate and checked every wire I could see. Replaced the speed sensor on the transfer case tailstock. Found two sets of wires that were melted, touching together and touching the transmission housing. the ones for the Neutral safety switch, and the ones for the torque converter lockup solenoid. Cleaned them up, repaired with new wiring and used dielectric grease, shrink wrap butt connectors and wire loom. Made a ground from the PCM housing directly to the negative battery terminal, so grounds are bypassed as far as the computer knows. Checked the TPS with an Ohm meter, 272-2000 on one side, 2000-272 on the other side. Still has a terrible stumble when barely pressing the accelerator pedal, feels like a plug wire off, it stumbles and sputters so hard. Then, will not accelerate past 15-20 mph unless you mat it to the floor from a stop. Any further suggestions? Please read the beginning to see what all I have already done.
 
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When you Ohmed the TPS did the needle move smoothly as you rotated its input shaft? It's for applications like this that I'll always use an analog VOM so I can see if the resistance or voltage move up and down smoothly via its moving indicator needle when turning their controls. As a guy who grew up working on electronic circuits there were very few times I would not select my trusty analog VOM.

And what brand of upstream O2 sensor did you install? Hopefully it was NTK, NGK, or Mopar... all of which are made by NTK. Bosch O2 sensors are well known to not work properly in Wranglers due to them requiring a different bias voltage than what our Wranglers provide.
 
Yes, it moved very smoothly, I could even get it to move 4-10 ohms at a time when rotating slowly. The brand of sensors from the local parts store is NTK brand. I called and he said their first choice is OEM replacement due to issues with others. Is it ok that the TPS started/ended at 272 ohms, not 0?
 
Have you put a good scan tool on this and watched live data ? You need to record data while hot and in park and shift to drive and compare data. If you don't have a scan tool take it to someone who does.
 
Yes, used a Snap-On scan tool. It still shows an intermittent CPS signal interrupt code present in the memory. No active codes when running. No codes coming up when running or driving. The active data just shows the O2 sensors going from lean-normal-rich, while idling. Like I have written previously, it only does it when it rolls, even a few feet. If you mat it to the floor from a stop, it will run smoothly and tach up to 4000 rpm and shift 1-2 fine, but when it shifts from 2-3 at 42-45mph, it immediately stumbles and sputters and will not gain any more speed. Bump it into neutral and fine. I even put the factory 195 thermostat back in it, no change. With all the things I have repaired that were wrong and replaced that were throwing codes, it has stayed consistent with what it is doing. It is like the crankshaft sensor and cam shaft sensor are not communicating.
 
Your 97 can spit codes on the dash. Turn the key on/off/on/off/on and wait. See what #s the dash reads. I

To me, it sounds like the ignition pickup coil (also known as CAM sensor) at the distributor is bad. On the 97, that code can mean CPS and/or CAM sensor. Its possible your timing is whack which is sending the interupted signal to the CPS sensor, which you replaced. If its stock, it will have brass contacts. See if there is anything damaged/dirty. There is a magnet that spins over the contacts, if its separated, loose, dirty etc.. it could lead to faulty and intermittent readings.
 
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