Rough idle after exhaust manifold replacement

PeterN · Nov 24, 2009

1996 XJ 4.0

My exhaust manifold cracked a while back and I procrastinated on replacing it until recently. A few days before I put the new manifold in my jeep started running real rough and the check engine light came on. I thought it was just from an O2 censor because of the exhaust leak. Once I had replaced the old with the new I noticed the rough idle was still present, only now I could hear a very distinct clicking. I ran some throttle body cleaner through it and put in some injector cleaner and nothing changed. Scanned the computer and the only thing it was saying was too much voltage from engine temp censor, I got the new one about to be installed but I have to remove the valve cover because of the location of the bolt. I don’t even see how this could cause rough idle, when I did my transmission I accidentally unplugged this censor and drove it to get it scanned to see why the check engine light was on and it ran just fine.

As for troubleshooting the rough idle and clicking noise from my motor (injectors?) I thought it was just because of the cracked exhaust manifold, but im not too sure of that. I tried unplugging the fuel injectors while the motor was running and the only one that made a noticeable difference was from cylinder #3.

Does this sound like a bad injector? The spark plugs seemed a little lean but nothing to obvious.

I would really appreciate any info thanks in advance.

Mr. mud · Nov 24, 2009

First of all you should not have to remove the valve cover to get your temp sensor out, you need an 11mm deep socket. As for the clicking noise, it is more than likely a tapping lifter. 4.0s are famous for that, try some seafoam.

PeterN · Nov 24, 2009

What is seafoam and where can i get it? I was afraid somebody was going to say lifter.

As for the censor the bolt for it is right up against the valve cover which is leaking oil so i should remove it and put a new gasket on anywho.

Also is it safe to drive? or hard to replace?

joe_peters · Nov 25, 2009

I'm a little curious, and you will have to be patient with me, as I am old and I drive a Renix XJ. What "bolt" are you trying to remove to replace the coolant temperature sensor? I'm actually using a late model thermostat housing with a radiator drain petcock in the sensor spot for "burping" my closed radiator system. There is no bolt I would have to remove to access the petcock, and by extension, a sensor located in that thermostat housing. Explain please?

ehall · Nov 25, 2009

temp sensor can cause the computer to enter open loop, where it will dump fuel to try and warm up the exhaust. the clicking could be the injectors, I don't know anything that makes a distinctive click

sjx40250 · Nov 25, 2009

If you scanned the computer, then if there was an injector problem, the code would come on.

+1 to ehall comment.

Clearly, with the connector disconnected, it ran fine. What more evidence do you need?

Harbor Freight has a cheep scanning tool for OBDII, which a 96 has (I think). You can pull the codes and clear them for under $40.

PeterN · Nov 25, 2009

Thanks for the input guys, i really appreciate it ill try clearing the codes. My friend keeps on telling me bad injectors because of my exhaust leak the motor ran full rich and ruined the injectors. This sound plausible?

Mr. mud · Nov 25, 2009

Possible, yes. Not plausible though. A distinct clicking in a 4.0 is usually a dirty and/ or sticking lifter. Having a lot of carbon build up around the valves and lifters will cause a clicking sound, and if a lifter is sticking it can cause a miss/ rough idle. Just try the cheapest route first. Spend 8- 10 bucks on a can of seafoam motor treatment and follow the instructions on the back of the can for inducing it into the vaccum/ air induction system. I'm 90% sure that will fix your clicking, and fairly confident that it will help your rough idle. And if it doesn't your only out ten bucks or so. I think its just carbon buildup from running rich thats causing your problem, or your new manifold gasket didn't seal correctly and you have a massive vaccum leak at the intake, which can also cause a miss. let us know what you find man. Oh, and do you know how to test for a vac leak around the manifold?

PeterN · Nov 25, 2009

Mr. mud said:
Possible, yes. Not plausible though. A distinct clicking in a 4.0 is usually a dirty and/ or sticking lifter. Having a lot of carbon build up around the valves and lifters will cause a clicking sound, and if a lifter is sticking it can cause a miss/ rough idle. Just try the cheapest route first. Spend 8- 10 bucks on a can of seafoam motor treatment and follow the instructions on the back of the can for inducing it into the vaccum/ air induction system. I'm 90% sure that will fix your clicking, and fairly confident that it will help your rough idle. And if it doesn't your only out ten bucks or so. I think its just carbon buildup from running rich thats causing your problem, or your new manifold gasket didn't seal correctly and you have a massive vaccum leak at the intake, which can also cause a miss. let us know what you find man. Oh, and do you know how to test for a vac leak around the manifold?

A friend of mine has acess to a smoke machine, not too sure how it works but it worked bitchin for my friends ford. He just has to sneak it out of his work. Ill try the sea foam tonight.

Rough idle after exhaust manifold replacement

PeterN

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Mr. mud

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PeterN

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joe_peters

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ehall

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sjx40250

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PeterN

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Mr. mud

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PeterN

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