jrwpmw

VEHICLE:
1999 Jeep Grand Cherokee Laredo, 193K, 4.0, auto/42RE, 4x4.

HISTORY:
Two problems.
#1 trans (42re) late shifting to 3rd usually when cold. Adjusted TV cable & replaced TCM and no change.
#2 rear axel bearings going out (Dana 3.73).

WHAT I DID THIS WEEKEND:
#1 replaced the tranny filter/fulid & adjusted the rear band only (inside tranny) to specs (72 inch pounds - then back off 3 turns). I didn't adjust the outer band because I didn't want too many variables if there was a problem (which is what happened)!
# 2 swapped the rear axel out with another from a junk yard.

WHAT IS HAPPENING NOW:
GOOD - Rear end/axel is very quiet/fixed!
BAD - I still have the late shift to 3rd when cold. But now the engine?/trans? is sputtering. Low speed/1st gear seems OK. But at higher speeds & even when cruising it will sputter/slip/surge, a few times it did a small backfire (pop/backfire from throttle body). NO CODES. This is all new, never done it before.

WHAT I HAVE DONE SINCE (to try & fix this new problem):
Dropped the trans pan & readjusted the rear band, this time backing it off 4.5 turns (was 3), specs say 3-4. I went a litte over 4 thinking I would see some type of difference (better/worse). Fluid full/ATF+4. Test drove, but no change in this new problem.

WHAT I CANT FIGURE OUT:
Logically I think this new problem is related to something I did. Obviously, my first thought is the trans band adjustment since I don't know how the rear end could cause this problem. But I'm stumped, what could I have done to cause this (given the work I did)?

Bit I also can't rule out the (small) chance this is an unrelated new problem.

ANY thoughts or suggestions would be appreciated.

dave1123

First of all, welcome to CF!

You seem like a guy who knows something about your jeep or you wouldn't have changed the rear axle or gotten into the tranny, SO, I think you have an unrelated problem. I would check the fuel pressure and spark plug insulators. They are under the coil pack. Judging from the mileage, there's a good chance they are fired. Why they acting up now is anybody's guess.

Also, check the output from the CPS. There is a chance it's starting to fail.

The late shift to 3rd may be caused by the thermistor in the tranny. It's there to sense fluid temp and not allow a shift into O/D if the fluid isn't at least 31*F or over 260*F. It also influences the governor pressure curves and may not allow a 2-3 upshift. An open circuit test of the thermistor is 1000 ohms at 70*F.

tlang

Oh man, Im not a tranny guy but I do diag for a living so hay lets all put our heads together.

My first thought is we need to pinpoint the symptom. You say "sputter/slip/surge." I would like to narrow that down and see if we cant figure out what portion of the vehicle we are dealing with.

Does it do it if you, say power brake it or put it under a load while at a stop? This can help determine if the tranny is involved.

I agree ignition components should be checked. I would just like to narrow it down before parts are thrown at it.

Let us know and Im sure with all the experience on here we can at least get ya going in the right direction.

Welcome to CF

jrwpmw

I will check those insulators tonight. What do I need to check the fuel pressure?

The motor seems fine, reving at idle or under a little load (foot on brake), driving at low speeds, etc.

The more I think about it the less I think it's the tranny. But they were the last things touched. So I can help keep thinking about that!

I will see if I can attach a 15 second video of the problem tonight.

But here is a slighty better recap of the problem. I will double check and better document this tonight.

Seems fine at idle and low speeds (1st gear). As you get into 2nd you may notice a hesitation/stutter/slip. Thus I think back to the tranny band adjustment.

After into 2nd or 3rd gear or simply cruising at say 50mph it will seem to the hesistation/stutter/slip. You might even get a single short backfire (sounded like a little pop probably from throttle body).

Similar to a car acting when the timing is off a bit.

PS just fyi.. I did the following over the last few months.

I replaced the CPS twice, the 1st was non-MOPAR and it didn't work. Second was MOPAR and has been fine since I replaced it last month. Lesson learned...

New plugs, all new fluids. Replaced TPS / adjusted TV cable. New battery. New brake booster. Brakes/rotors & shocks.

Thanks for the help!

tlang

hesitation/stutter/slip <--- This

To me a slip is the RPM's going higher then they should and the vehicle not getting power to the wheels.

A stutter or hesitation to me is the engine cutting out or the rpms dropping.

So is it doing both at separate times? Not trying to come off rude just trying to grasp whats going on.

jrwpmw

I started it this morning and got a P0306. So I thought I would try a coil pack. Autozone was the only parts store close with one in stock, so I figured.... I knew better but I figured it could not hurt. Put it on & could not get the Jeep to stay running. Took off reinstalled, same thing. Put the old one back on and it was OK. Does Duralast make anything that works?

Anyway, went for a drive and still the same problem, but worse today. Jeep died several times. Finally got it started and got it home. It's now idling real rough.

Have not got any more codes. But I'm starting to think it's the fuel pump now because of the dieing & not wanting to restart. That could also explain the cutting out/sputtering at higher speeds too.

But would a fuel pump cause the rough idle? That's a new symptom along with the dieing & not wanting to restart.

Thoughts? Thanks again.

dave1123

Go to Autozone or Advance Auto and rent/borrow a fuel pressure gauge. It screws into the schrader valve on the fuel rail. You should have around 50 psi. Rev it up and see if it changes.

With a relatively new Mopar CPS, I doubt it's bad already. When was the fuel filter changed last?

Low fuel pressure will cause a misfire code as well as the ignition. A single cylinder misfire may be the injector if it's constantly that one.