Engine light on for ever!

[bobng]

Hi gents,
Please help & advise as my 2000 Grand Cherokee engine light was on earlier and I turned to a mechanic for help. It indicated #3 cylinder miss-fire. Ok, I had the sparkplugs changed and the ignition bar changed & injectors all flushed. Have the computer reset and a couple days later the light is up again, "same #3 cylinder miss-fire". The same mechanic checked it and said the care is perfectly ok, nothing wrong and running good. He can't help! Can you experts?
Thanks first.

[Bob D.]

Find another mechanic.
Seriously, if a cylinder is misfiring bad enough to set a fault code it has to be severely missing.
How does it run? If the missfire is intermittent it may set a code then run fine. Trouble shooting an intermittent problem is difficult.

[hardisk_c]

Plugs and wiring didn't fix it, so its time to delve deeper (and probably find a different mechanic, sorry). It may be worth your time to find a local auto store (We have Advance Auto up here) that may be able to help you pull the codes yourself, see, just on the off-chance, that there isn't a code hiding in the computer somewhere.

As Bob asked, does the Jeep run rough and the MIL light flash a little bit before going solid, or does it seem to be running well? Could be as simple as a bad batch of gas. Up here in the Dakotas we put a fuel additive containing Isopropyl alcohol (fuel drier, sometimes branded as 'Heet') in the tank along with every other tank or so. Helps clear out water contamination. Might try a different gas station for a tank or two. It could be that simple, but I doubt it.

Did you get a chance to look at the old plugs? If so, were there any unusual deposits on any? Properly operating engine spark plugs have a light grey to white powdery coating. Anything else can mean trouble. Also, a compression test may be in order if not already done. Don't know how much of a DIY'er you are, but this test can be done with a Haynes or Chilton manual and a compression tester rented/bought from a local auto store.

If you don't feel comfortable with any of this, do what people do in the medical realm. Get a second opinion. Another mechanic's unique viewpoint may bring some knowledge to the table that the previous mech may not have been familiar with.

Just my

[rocksteel]

Originally Posted by bobng

Hi gents,
Please help & advise as my 2000 Grand Cherokee engine light was on earlier and I turned to a mechanic for help. It indicated #3 cylinder miss-fire. Ok, I had the sparkplugs changed and the ignition bar changed & injectors all flushed. Have the computer reset and a couple days later the light is up again, "same #3 cylinder miss-fire". The same mechanic checked it and said the care is perfectly ok, nothing wrong and running good. He can't help! Can you experts?
Thanks first.

Harddisc C is on the right track on this. If the plug had, or if it is still missing, if it has deposits on it in #3 cylinder, you might have a problem getting oil into the cylinder. If the compression checks out ok, go to a reputable shop with a diagnostic tester that can overlay one cylinder over another and have them put #3 cylinder over another or several other cylinders. This firing curve will give a good detail on whether you have an ignition issue or something else wrong. Since you said it keeps pointing to the #3 cylinder, I would just do a comparison check between this cylinder and several of the others. Your readings may be a little lower than what the book calls for, but as long as all the cylinders are close on compression readings, you should be ok. Good luck.