2000 Jeep Cherokee Rough running afer warm, popping in airb

CSH82

MEMBER
2000 JEEP CHEROKEE
4 CYL
4WD
AUTOMATIC
135,000 MILES

Ok, so I bought this vehicle from a person who was told they had valve issues. Sure enough no compression, and one valve was stuck on the cylinder that was missing, cyl. #5. Had head checked and it was cracked between cyl. #3&4, common issue I guess. After alot of research, decided to buy an aftermarket cast head that is supposedly sturdier in the problem areas. Shipped from a machine shop in Florida. Put head on and still have same issues with bogging down, dying out, popping in intake on hard accel, valve clatter, only once nice and warmed up. Have compression back on all cylinders within spec. One rocker bridge was bent, off the same #5 cylinder, so replaced that. Replaced spark plugs, has coil on plug system. Reset all adaptives and afraid to drive to get fuel adapt relearn back, so not picking up misfires. Scoped crank and cam sensor today with Modis, nothing out of ordinary while acting up. Everything seems to be where it should on Datastream. Vacuum will start to flutter, 1-2 in, when acting up and once the valve clatter starts will actually drop 10 in or so sparatically, then back to same flutter spot. Checked at 3000rpm to see if drop below 10 in for clogged cat and it didint. Seeming to be a valve issue again but brand new head and compression is back, checked cold and after acting up. On first start up of the day vehicle will idle fine, none of the issues as before. Did not think to check vacuum while running fine. Maybe I should do that. Let run for awhile and the valves will start to tick slowly and if you give gas it will start the bog down on decel then starts with all the problems. Oil pressure will drop from about 50 on the dash gauge to around 20, still within spec on Alldata. Had it die a few times while driving at a stop and it will also do it occasionally while sitting at idle, usually pulls out of it before it bogs so far down to actually die. I work at a repair shop and eveybody is stumped. Saying take it to the dealer, but I would rather not have to go that route. Some have mentioned a lower end going out, but wouldnt the issues be there somewhat on the first start up of the day then just get worse, instead of just arrising after warmed up? Anybody who has any ideas or have dealt with same problem any help would be greatly appreciated. Thanks.

6 Replies

SERVICE WRITER

MECHANIC
9,123 POSTS

Have you monitored the fuel pressure when the problem happens? I'd suspect a weak fuel pump or a pressure leak down thats allowing fuel to boil or vapor lock in the rail.

Are any other codes present yet?

4 cyl with a miss on #5 lol.
I assume 4.0?

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Friday, October 16th, 2009 AT 6:18 AM

CSH82

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Not sure why it says 4cyl in the vehicle description. Anyways, yes 4.0l. And yes, fuel pressure was monitored durring problem and is all within spec. Cannot drive enough for fuel adapt relearn to run so I dont pick up misfires. All adaptives were reset once new head was put on and still running rough. Did check vacuum cold and still fluttering 1in. This was all checked at at shop and nothing out of the ordinary could be found accept it was running like crap. So I took to the dealer. They verified all sensors and timing and fuel was all good. Told me it is either in the head (which is brand new) or in the rocker setup, or lifters sticking once oil warms up. Possibly build up in the lifter journals from the antifreeze coming down through the cracked head. Kinda suprised that a sticky/collapsed lifter could be causing it to run this bad. It feels like the timing just goes to hell and it runs rich, you can smell it. Have been told the lifters can be pulled through the head, so no head removal needed. Guess I will try pulling a few and see what is there. Some suggested running motor flush thorugh before I do that to see if it clears up. Anymore suggestions would be GREAT!

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Saturday, October 17th, 2009 AT 10:05 AM

SERVICE WRITER

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Damn. Wish we nailed it before the dealer stepped in.

Gotta give this more thought.
I would definitley call the head supplier and ask them for possible insight. I would think they would want to exhaust other sources that may be there. You know how remans are. Compression test probably verifies it good, but they may have something helpful anyways.

IMHO. The sticky valve is out. If this was a 4.0 with some miles on it I'd agree, because of they way they are designed. Carbon build up was a prob on them.

Fuel injectors were also a problem with the 4.0 motors I found. Sometimes cleaning helped and sometimes it didn't. I think the fifth or 6th cyls were the problem childs.

Disconnect the upstream o2 sensor and see if that changes it. May still be rough, but better. Cheap enough to try and have seen it solve one I can think of.

There were crank sensor issues but scoping should have caught that.

Update when you can.

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Saturday, October 17th, 2009 AT 1:51 PM

CSH82

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I drove the jeep back home across town from the dealer and still no MIL. Thing ran just as bad as ever. Never really drove while cold, noticed it still had the issues once getting up in the rpms past idle. Got horribly worse as it warmed up. Called supplier of cylinder head and their response was "cant be the head its brand new with all brand new parts, check the lifters". This was an aftermarket brand new casting head, different from factory. Supposedly stronger/thicker in the problem areas. Bought some gunk brand motor flush today and oil change supplies. Got stuck diagnosing a constantly running blower motor with key removed from ignition today, so couldnt get to the jeep (short in remote start heater option circuit in controller). Going to ohm the injectors tomorrow cold then run the motor flush through. Then let it sit and run with new oil and see what happens. If still getting issues gonna disconnect front O2 and see what happens. I remember now noticng that the catalyst efficiency monitor had not run since reseting all adaptives also. Probably ohm injectors warm also. If still having issues gonna pull valve cover and take a look, yet again. Im almost to the point of just trying to find a reman short block. If lifters are bad, am I gonna have cam/crank bearing issues next. Strong top half going to just start exposing all the weak lower half areas? Anything comes to mind for anybody dont hesitate to post on here. Thanks for all the help so far. I will post more tomorrow evening.

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Sunday, October 18th, 2009 AT 10:09 PM

CSH82

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Got to ohm injectors while cold. 13.2 +/- 1 ohm across board (alldata spec 12 +/- 1.3 ohm at 68 degrees F). Ran motor flush through and then changed oil and let run for awhile, still had the problems. Unhooked front O2 sensor and still had the issues (MIL caught that one). Injector ohm test warm produced 15 +/- 1 ohm across board. Ate dinner then pulled valve cover. Couple lifters seem squishy, assume those are bad. Pulled rocker arms and plugs and turned motor over by hand. Do not feel any sticking while holding top of pushrod. Did not get a puller and my magnet does not fit through the hole. It does not appear they will fit through the pushrod hole in the cylinder head going by looks. Possibly smaller hole since aftermarket casting. Might buy enough new ones to replace the squishy ones and a removal/install tool. See if one will fit from the top. One of the rocker arm pivots was out of alignment on the oiling groove marks to the rocker arm. Put that back the way it should be sitting. Not sure how important that really is. Surely not enough to be causing my problem. Reman short block looks like around $800. Might be better off saving for a month or so and doing a full swap. Not sure yet, going to ask around some more. (It doesnt require a core so could in turn rebuild/stroke my old block possbily)