Superclyde

I have a 99 cherokee 4.0. Its throwing a multiple misfire code. What it is doing is hard to explain. I believe it is misfiring infrequently, but getting worse. This misfire, or bucking, as I call it can happen at any time while driving or idling. However, it is almost guaranteed to happen when shifting into reverse or turning right, to the point that the jeep will die. The bucking will also be aggravated by our bumpy county roads, but wont die. Only dies when turning right or shifting into reverse. Its crazy, this bucking has happened in all driving conditions, but seems to happen more on bumpy roads. It has also done it on start-ups but give it a little throttle and it will revert back to a smooth idle. Sometimes you can drive it 70miles and it will buck only a couple of times, other times you can go 5 miles and it wont stop bucking. Getting pissed because my mechanic and I can't figure it out, and I'm not ready to call it quits on my jeep. It does have 186K on it but has been well taken care of and been extremely reliable, no major issues.

So far I have replaced plugs, wires, cap, rotor.....the usual stuff, no luck. Mechanic thought it was a fuel issue, so checked the fuel pressure but it was good at 40psi. I changed all 6 injectors as he recommended, still have same problem, same multiple misfire code. I questioned the CPS and TPS, but mechanic said doubtful as the code does not indicate either. Last night checked for a wire shorting out, didn't see anything in the dark. Another mechanic said possibly the ignition control module? I'm stumped, ready to take its misfiring *** out to the pasture and put her down! Help, I'm dusting off the 12 guage now

wjnfirearms

I'd look at the coil pack as a possible culprit. I recently had a serious issue with the '97 sputtering and not running at all with no codes and that was the problem. It ate the coil wire in the process. The damage to the wire was covered up by the boot at the coil end.

Superclyde

When you say coil pack, do you mean the ignition coil?

Turbo X_J

1999 4.0 with a distributor?

Zack92MJ

I pulled my stock injectors (98) cleaned them and put them back in today with out any problems..even used the old rings.. knock on wood no problems with them so far

But anyhoo it got rid of my random miss...so far at least

CattyXJ

How did you clean your injectors?

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ryan_kelly

Crank sensors don't always throw codes. They are only 60 dollars and are stupid easy to change. If it is loose that would cause that problem. I can't think of anything else. Did you kick it yet?!

Superclyde

Yes it's a 99 4.0 with a distributor. Also I put new injectors in it as a possible solution to the problem, same problem with new injectors. I thought about the crankshaft sensor also, but the misfire when turning right??? I seen it was only two bolts, but a bear to get too.


Would the throttle position sensor, if malfunctioning, cause the misfire at shift points, engine strain or under vibration?

No kicking yet. However, a considerable amount of cussing and scratching my head.

Zack92MJ

pulled the rail and cleaned them with throttle body body cleaner and a rag, took like all of 10 mins once I realized the JY didnt give me the parts I needed to do my neon swap

CattyXJ

So you did the outside of them or will the throttle body cleaner spray through? I want to clean them without paying a mechanic $75!

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ryan_kelly

Would the throttle position sensor, if malfunctioning, cause the misfire at shift points, engine strain or under vibration?

This would cause the engine to stall or run really fat. Does the 99 have a mass air flow sensor? I don't think it does but if so then... I have seen many time the intake boot torn and she you put the car in rev the engine cuts out, or when you turn it would cut out. But like I said I don't think it has one. Gosh I wish I could see it in person. You in md?

Zack92MJ

I cleaned the actual injector tip its self out side of the rail

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Superclyde

Ryan, sorry not in MD, Indiana. Not sure if it has a Mass Airflow sensor, but tend to think that it doesn't? The problem is getting worse, the misfire is a lot more frequent. When its running, it runs good. but when it starts to misfire it misfires until it dies. It doesn't die when it misfires at driving speed but you can feel it misfire. However, when it starts to misfire closer to idle RPM's it continues to misfire until it dies.

Examples,
Shifting from park or neutral to reverse or drive, will cause it to go from a smooth idle to misfiring until it dies. Today, it was misfiring the minute I started it and when I shifted to drive it went to a smooth idle, which is the exact opposite?

When I am slowing to make a right hand turn, the minute I turn the wheel right it misfires and dies. If I accelerate through a right hand turn, it misfires bad and you have a 50/50 chance of it staying running. Stopping and proceeding straight, no problem. Left hand turns, no problem.

When I'm driving on our crappy county roads that are bumpy, almost every bump causes it to misfire, just for a split second. bump-misfire bump-misfire.

Don't misunderstand me though, it will misfire at anytime, however these three things aggravate or will almost always cause it to misfire.

Talked to a mechanic last night and he thought it could be the pick-up coil in the distributor, basically burning itself up. Not sure that I agree, but not sure that I disagree because I'm stumped.

Going tonight, to see if it is throwing any different codes as the problem is worse and the check engine light is on again.

I could really use anyone's help or experience, I need help. Thanks.

94JeepCherokeeMan

I would replace the ignition coil first. If that doesn't help, take it back and get a new crank sensor. If that doesn't work, the I really don't know wtf is going on...

94JeepCherokeeMan

*Snaps fingers* IDEA! Check your ground connections, man! Battery terminals, connections, engine ground, etc., etc. Takes thirty minutes to disconnect all grounds and clean them up!