Pinging under load

hi guys,

As the title states, I experience a pinging type noise along with a loss of some power and often a cylinder 8 misfire. The issue is periodic but predictable under certain conditions.

This problem occurs when the engine is under load or accelerating up a hill. The haynes manual suggests ignition, fuel delivery, or vaccuum leak issues.

A tune up this summer has not fixed this problem, this rules out ignition. I have not tested the fuel pressure yet. I spoke with Eric in person and these symptoms are evidence of the plenum gasket failure. I have looked into the intake and the plenum pan looks moist but i can not tell if it is showing oil.

I took it to Paul Baileys (this explains/relates to my RI inspection post in General) and the first mechanic could not duplicate my problem in order to diagnose it. This is crap I think, because this ping happens very often. He did a vaccuum test on the plenum and said he believed it was fine.

I was dissatisfied with this and had someone else look at it. Mark, at paul bailey’s, drove it as well and yet was unable to duplicate this issue. I can not understand why cars don’t have problems when the doc is looking at them?!? yet, this issue happened all the way to paul baileys.

After Mark looked into the intake and talking at lenght about the problems, he believes it to be the plenum gasket as well. he also believes the other mechanic may have done the vaccuum test incorrectly.

Any suggestions for a diagnosis? Any other areas i should check? maybe cylinder pressure test?

Right now, i do not have the time to tear into this engine on my own. Paul Bailey’s will do it but at a nice price. Anyone with a garage, good tools, and time willing to help and make some good cash? ( i would do it with someone) I need this done by next week before i drive to upstate NY with it. Anyone have experience with this procedure?

Thanks for your thoughts.

Its a 98, 5.2L.

Does the ping go away if you run 93 octane? That’s what I do in my Ram until I get around to fixing the plenum gasket which will probably be next spring.

BTW, what is a “nice price”? I think the book says its a 6 hour job times about $100 per hour equals $600 for labor.

Well the price is $610 for parts, labor, and tax. I believe that includes a new plenum/intake pan just like the Hughes kit as well as the other necessary seals.

Its seems like an ok price, but like everyone i try to keep the cost down. I wish attempted to fix this problem during the summer months when I had time and good weather.

My other concern is that no one knows for sure if this is the fix, since i nor the mechanics have been able to properly diagnose the true cause. its only a guess right now.

I would be willing to pay someone some decent money to help.

had a similar prob this past summer on my silverado…turned out to be the coil packs. fortunately i got fairly new but used ones for free…otherwise an expensive fix. does the engine have coil packs. if so, swap cylinder 8 with another and see if you are still getting the misfire. also, pull the #8 plug and compare to that of another cylinder. as far as the pinging, like eric said a higher octane gas, and you may also want to check you EGR to see if its all carboned up

pinging under a load is usually common if the motor is out of time. I would check there as its pretty easy to check

also you can try a higher octane as mentioned or add an octane booster and see if that makes any difference

I did ask the jeep dealership about the timing being off, but they said it was unlikely since it uses a chain for the system. if it were out of time, would it misfire only periodically under load? or would it misfire constantly?

I will try higher octane, but that would only be a bandaid.

the 5.2 has only one coil which feeds the distributor. This condition existed before i did a full tune-up this summer. I have swapped plugs and wires to double check my assumption that the ignition system is all good.

I’ll check the egr valve.

96+ does not have EGR.

Thank you

Buy the parts yourself and ill help you or do it myself lol.

Pm sent

replacing MAP sensor (mine is faulty) and PVC valve tomorrow.

Next I will test the fuel system and tripple check my ignition system to ensure proper operation.

I also plan to conduct a leak down test on all the cylinders especially cylinder 8 to rule out excessive blow by.

After that, i only have the plenum gasket to test via vacuum or smoke test. If i am replacing the plenum, i will do it next week with the hughes kit.

if Bigred helps, i’ll post pics of the process.

I may have fixed it! i’ll share how soon.

I tested the plenum gasket to find it in working order. My PCV valve was stuck open so that was allowing oil into the intake. This was replaced along with its fitting. while i was at it, i replaced the breather elbow and fitting on the driverside valve cover.

I determined the primary problem to be electrical induction between spark plug wires. the solution was to buy proper wiring clips/spacers and plastic wiring wrap for insulation. I installed these items and rerouted the coil wire away from all the other wires to avoid any induction.

There is a TSB out on this for the 5.2s. Problem solved. Thanks for the advice guys.