99 Jeep Grand Cherokee Laredo Issues

[Emtfire10]

I have a 99 Jeep Grand Cherokee Laredo 4.0 LTR 6 w/auto trans.
While driving down the road & attempt to give it more throttle (ie: to pass another vehicle) it will "buck" once it tacs at 3k. This will do this each time.
That problem became more erratic yesterday afternoon coming home. Acting as it was losing power & would buck more.

We replaced the motor last year around time, because of blowing the skirting off of #3 piston.
Have had no issues with this motor until approx 7 months ago when it would buck at 3k on the tach.

Codes that were pulled yesterday
P0 152
141
132
161
138
158
1494. P1494 is a leak detection pump, SW or mechanical fault. Leak detection pump switch does not respond to input.
All others were upstream/downstream O2 sensors high/low circuit or temp.

I have checked all vac lines & came across 1 that goes from the intake manifold to a small electric pump located underneath the air cleaner housing & right directly behind left headlight. The 90* elbows are brittle & started to fall apart in my hands while trying to remove them.
The motor may run good for a bit, however shut it off & turn it back on, it will run extremely rough as if it is missing.

Checked the fuel pressure which was around 52 psi, well in range.

I am at a complete loss with this, any ideas, input or help would be greatly appreciated

 

[spasm3]

Was the engine you swapped the same year ?

 

[Donald]

Ok, my 2001 Jeep GC had catastrophic engine failure due to piston skirts breaking off. So I know where you are coming from.

I installed a reman engine not a used engine.

I also had issues with vacuum lines and elbows cracked and leaking.

In my Jeep there were lots of vacuum lines including some running up near the headlights for the cruise control.

If you find and fix all the vacuum lines then maybe an injector problem.

Your Jeep has single port injectors. I swapped in 4 port rebuilt injectors. Much more reliable injectors.

 

[i_hate_autofraud]

Wow! What manufacturing or design defect is there to have piston skirts that crack off?

Anybody street racing a Jeep? lol

 

[HoosierJeeper]

I have a leak detection pump code on my LR3...wouldn't cause the issues you're having.

It's odd that all the O2 sensors are "failing" at the same time. The bucking could be from bad spark plugs or coils (if 99 was coil on plug) I'm at a loss, I'd check some Jeep forums out, almost any of them are great with 4.0 info.

I used to have 99 Grand Cherokee...got it new. Loved that thing! Miss it everyday.

 

[Emtfire10]

Yes same year motor

 

[Emtfire10]

I will have to check the injectors then. I had just mentioned that to my wife & then came in here and seen your response.

 

[toneydoc]

Mine had some missing/misfires and it turned out to be corrosion and a small crack of distributor cap.
I replaced plug wires at same time. It has been fine since.

 

[Donald]

Originally Posted By: i_hate_autofraud


Wow! What manufacturing or design defect is there to have piston skirts that crack off?

Anybody street racing a Jeep? lol



At some point Jeep move the rings closer together and you get wobble after 90k, the cracking of the skirt. Sometimes a piece breaks off and drops into the oil pan. Other times it falls off and jams things and you get catastrophic failure.

This is on top of the #331 head that cracks.

Jeep ruined a good engine.

 

[Donald]

Originally Posted By: Emtfire10
I will have to check the injectors then. I had just mentioned that to my wife & then came in here and seen your response.


I got rebuilt injectors from Paul on this forum.

 

[NStuart]

My wife's was doing the same thing and it needed a TPS, could be coil packs tune up, these things are also notorious for crank sensors deteriorating and random cut off from that and fuel pump relays failing

 

[jeepman3071]

That's extremely odd to have all 4 O2 sensors pop up at the same time.


Definitely check for vacuum leaks, possible crank position sensor. I've seen the crank position sensor cut power only at specific RPMs in its early stages of failing. TPS is another possibility. I really doubt it would be injectors on this engine. You would likely have problems at all throttle positions. Also the '99 WJ 4.0 engines were coil on plug, no distributor or plug wires.

 

[Emtfire10]

Originally Posted By: jeepman3071
That's extremely odd to have all 4 O2 sensors pop up at the same time.


Definitely check for vacuum leaks, possible crank position sensor. I've seen the crank position sensor cut power only at specific RPMs in its early stages of failing. TPS is another possibility. I really doubt it would be injectors on this engine. You would likely have problems at all throttle positions. Also the '99 WJ 4.0 engines were coil on plug, no distributor or plug wires.


Will check into those tomorrow. However no codes were thrown for the TPS or the CPS, but it doesn't mean those maybe tweaked. The coil rail idea I like < moving parts

 

[Kuato]

How long has it been since it had new spark plugs? That would contribute as well.

 

[spasm3]

Is this your ecm or the ecm that came with the engine? I'm wondering if there is a problem there.

 

[Alex_V]

Originally Posted By: Donald

Jeep ruined a good engine.


Jeep = AMC when the 4.0 was designed.

Jeep = Chrysler when it got screwed up.

 

[SwampSurvivor]

Check for a short on one of the oxygen sensor wires and for a blown fuse on one of the O2 heater circuits. I had a O2 sensor harness get caught up in the driveshaft and it caused a multitude of issues - including about 12 oxygen sensor codes (all 4 were acting real screwy), very poor running and a few other things that were on the same circuit stopped working.