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Heyoh!! 12-13-2012 04:51 PM

1999 Grand Cherokee misfire
First would like to say hello to the forum. As stated in the title I am having a misfire on my 4.7 GC. My " misfire " happens around 60-70 miles an hour on highways. I give it a certain position on the pedal and it gives me a lean pop through the airbox. If I am starting out and have the same pressure on the pedal no problems or pops. It seems to be only in higher gears. I have had computers hooked up while on test drives and results are pretty much lean 75% of time. I have replaced the following parts

All plugs, coils, TPS, IAC, fuel filter, checked fuel pressure when problem happens, nothing changes when it does. I have also NO codes at all. Light does work if codes are present. Replaced the O2 sensors as well. I have read about the Exhaust valves going bad...Possible? Runs smooth as can be otherwise. Even when it pops just have to get off of the throttle so problem stops. All help would be thankful.

Frango100 12-13-2012 06:13 PM

Re: 1999 Grand Cherokee misfire
If you really have a misfire, you should have a DTC set. Did you verify this, eventhough the check engine light is off?
Did you see the fuel trims of both banks, to see if there is a difference between the 2 banks?

Heyoh!! 12-13-2012 08:11 PM

Re: 1999 Grand Cherokee misfire
thanks for the response Frango... Answers are yes and yes. I also would like to add I did a smoke test to look for vacuum leaks as well as a top throttle cleaning with seafoam. My O2 sensors were not Chrysler but the more I am reading the more I am wanting to sway towards a valve spring or something? But who am I to say. Any tests to check valve springs or can they be checked without removing the heads? Thanks again

Frango100 12-14-2012 05:01 AM

Re: 1999 Grand Cherokee misfire
The only test i know of for the valve springs is with a special spring force tester. You donīt have to remove the head for that, but only the springs you want to test.
But about the fuel trims, where they equal on both banks?

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