91 cherokee with junkyard 89? motor, using 91 injection/ignition/flex plate...started detonating on light/low rpm load. Sheetz just changed to 10% ethanol...all local gas is now 10% ethanol...tried seafoam, Lucas etc.

I need this 240,000+ miler to run a long time...any suggestions?

 

pinging can be caused by a carbon buildup on the top end of the engine.

I usually try to "decarbonize" by either using one of the products from the major auto manufacturers (Chrysler, Ford, GM all have basically the same stuff) or SeaFoam works pretty well too.

SEARCH for the how-to. Adding it to the gas is not enough. Need to introduce it into a vacuum line. Then let the engine sit and the solvent to work.

 

You can also pull your plugs and spray "deep creep" into the plug holes. Let it sit over night and install cleaned or new plugs. When it starts it's gonna smoke like a house on fire for a few mins.
Deep Creep is just Seafoam in an arasol can. It will loosen up carbon deposits on everything in the cylinders and blow them out the exhaust.

 

switching to 10% ethanol dosent hurt octane. e85 is over 100 octane.

your ping is probabaly coming from weak spark, its time for a tune up.

 

This will not help carbon on the valve's, it will only clean the top of your piston.Valve's is where the carbon builds up and cause's problems , not the piston top's or walls.Deep creep is a lube, based on kroial, used to penetrate rust and seized up bolts etc etc.I guess you can use it where ever you think though.

 

Ever heard of BG44K? I bought a can and ran it through my XJ at about 210k miles, and the difference was very noticable. Its a bit expensive, but I recommend it if carbon build up is a concern here.

 

do the tune up as was previously suggested. if you have the '91 model 4.0 I6, then the gap on plugs should be .035. checkem, see what your current gap is.

what is the grade of oil you are using?

I use valvoline 10w-40. works just fine. and yes West Texas has higher concentration of the ethanol now, and I have no pinging

I get quite a bit o' valve clatter in the mornin when i fire her up, but hey she's gettin old (280K mile on ol red)., but once she is warm she is still smooth as silk!

cheers!

cpnwrench

 

Try this simple test. Next time you fuel up, use a mid-grade octane. So if regular is 87, try 89 or 90.

If this increase in octane helps or eliminates the pinging, the problem is almost always a carbon issue, where de-carbonizing can help.

Having fresh tuneup hardware is never a bad idea, but try the above as well.