I was getting a 302 error code and made the mistake of resetting the error codes. My mechanic told me 1) not to reset the codes as it takes three consecutive errors to trigger the Check Engine light and a 302 code (or any specific cylinder misfire code) is too general to track down the problem. He spent over an hour checking everything that we did to my '97 Grand Cherokee 4.0L 6-Cyl 4x4 that included a head gasket repair ( heads were warped and not cracked and I invested in the repairs), replaced the fuel pump (hard starting and only on second attempt), changed pulleys and A/C Compressor, serpentine belt, bad sensors etc - over $4k in work but I've owned it since it was new almost 18 years with 153,000 original miles and in excellent condition (all service records kept and garage kept in Southern California Desert area). Hardly a scratch, no rust - I'm just in love with this model because of the beautiful Red finish and the plastic side panels that kept it from being Dinged.
Back to the the problem, it's been occasionally stalling and misfire ingredients, but I can't find the problem and neither can my mechanic. I started keeping it more than half full, changed hoses that were wearing out and put on a new gas cap.
Mechanic told me to stop using the fuel injector cleaner as that engine uses the engine heat to remove carbon buildup. He also said that the engine computer board requires three errors before it throws a code and since he couldn't find anything wrong he told me to run it until it those another 302 code but not to reset the error code. If I continue to run it it may throw another code to help narrow down the problem. So far it's been 3 months and it hasn't town another 302 code. I haven't been driving much as the temp in the desert here is around 115 degrees in the summer so it might start acting up again in winter when the temp drops to the 70's in the daytime.
One thing I did notice is while keeping the tank close to full I'm not having as much trouble but when I was misfire get I was typically below half a tank. I'm also retired and my mechanic knows that Zi can't keep trying to change out plus, wire or injectors while my wide and I have disabilities so he is doing the diagnostics step by step until we find out just what it is. Almost everything under the hood is new or grinder and flattened so there are no leaks. It turns over first time since replacing the fuel pump but it is only the second fuel pump I've had in 153,000 miles. That and hose replacements after getting emission error leaks and I couldn't find another 97 in as good a shape. I love the early Wisconsin built in-line six engines. Mostly mechanics and very little computer technology to deal with.
I'm sure you know the attachment you get after owning a new car for almost 20 years.
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