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Pinging Jeep 4.0L, need advice

C

CherokeeDad

NAXJA Forum User
Location
Colorado
Looking for advice/experience on eliminating Pinging in my '91 Cherokee’s 4.0L with auto when going up hills under moderate throttle pressure. I've replaced plugs, cap & rotor awhile back and have no other symptoms that might point to a bad Throttle Position Sensor.

My son has the same pinging problem with his '87 Comanche with 4.0L and 5 speed. He has replaced TPS, OX sensor, plugs, cap & rotor.

Could both of our Pinging problems be the EGR valve? Or perhaps MAP sensor? We both use regular gas.

If both our similar Jeeps are experiencing the same problems, there must be other folks out there who have had the same problems with Pinging. Any advice?

Thanks
 
AZ Jeff said:
How many miles on the engine? Carbon buildup on the head can contribute to pinging, and that's common on high mileage engines.
Click to expand...

Indeed it is. Try running some Seafoam or some Mopar Combustion Chamber Cleaner through the throttle body, watch large plumes of gray smoke come out of the exhaust, and hopefully the pinging will diminish or stop altogether.
 
We use whatever gas is cheapest usualy from name brand stations and our engines both have close to 200k on them. Running higher octane gas might be a temporary fix but I am hopeful that there are other options for our engines than dumping horribly priced gas in them.
 
CherokeeDad said:
We use whatever gas is cheapest usualy from name brand stations and our engines both have close to 200k on them. Running higher octane gas might be a temporary fix but I am hopeful that there are other options for our engines than dumping horribly priced gas in them.
Click to expand...
I don't know where you live but try and see if is just plain bad fuel. Name Brand what? You could have a dealer that's watering fuel in your town.
Of course you could both need new knock sensors.
 
I hate to bring this up, but did you replace the ping sensor? If not, and it is bad, you are guaranteed to get ping.
 
Just for the record. The computer controls the timing in a Renix system. It keeps advancing the timing until is senses a ping from the ping sensor and then retards it just enough to keep it from pinging. If the sensor is unplugged or not working, it will advance the timing to the point where it pings and not pull it back, because it doesn't "hear" the ping.

Start the engine, get it warm, let it idle. Crawl under and rap the block with a small ball peen hammer next to the sensor. If it is working, the rpm's will drop for a few seconds.

You should never get ping on a Renix based system for more than a few seconds unless you are running very lean. If you do, then the sensor is not working. Check how lean it is running by pulling the plugs and doing a visual reading, or look at the tail pipe.
 
Last edited:
NO, all you will end up doing is moving the distributor to where the spark has to jump the open space between the cap and rotor.
 
By the way, the 91 doesn't have a knock sensor or egr. Probably carbon buildup.

K
 
corbinafly said:
By the way, the 91 doesn't have a knock sensor or egr. Probably carbon buildup.

K
Click to expand...
Agreed. A 1991 model has an OBD-I control system, not Renix. With OBD-I, they eliminated the knock sensor.

Thus, the probably cause of your spark knock is carbon buildup.

Try an upper cylinder/combustion chamber cleaner, and see if that gets rid of the carbon. Otherwise, it's either premium (higher octane rated) gas, or remove the cylinder head to decarbonize............
 
old_man said:
Just for the record. The computer controls the timing in a Renix system. It keeps advancing the timing until is senses a ping from the ping sensor and then retards it just enough to keep it from pinging. If the sensor is unplugged or not working, it will advance the timing to the point where it pings and not pull it back, because it doesn't "hear" the ping.

Start the engine, get it warm, let it idle. Crawl under and rap the block with a small ball peen hammer next to the sensor. If it is working, the rpm's will drop for a few seconds.

You should never get ping on a Renix based system for more than a few seconds unless you are running very lean. If you do, then the sensor is not working. Check how lean it is running by pulling the plugs and doing a visual reading, or look at the tail pipe.
Click to expand...

Thanks Tom and others for the good advice. We replaced the platinum plugs in my son's '87 with regular Autolite plugs last night and it made a small difference. Since he has a knock sensor in his '87 that is probably the next part to try.

My '91 has 160k miles and no knock sensor so I'll have to keep looking for answers there. As for the gas we use, we buy from a variety of Phillips 66, Amoco-type national name brand stations (no Mom and Pops). So, unless they are all in cahoots nationaly, I doubt we are getting "watered down" gas.

Anybody have any luck with products from auto manufacturers that are supposed to get rid of carbon build-up? I'm talking about potions I've read about from GM and Chrysler that you dump in the throttle body and watch smoke billow out the tail pipe. Kinda seems too easy to be true but I could try it rather than doing major engine surgery.
 
Techron... (made by Chevron) place it in the gas tank at fill up. The Porsche people on the Pelican Parts board swear by it. Is available at lots of places.
regards,
jlex.
 
CherokeeDad said:
Anybody have any luck with products from auto manufacturers that are supposed to get rid of carbon build-up? I'm talking about potions I've read about from GM and Chrysler that you dump in the throttle body and watch smoke billow out the tail pipe. Kinda seems too easy to be true but I could try it rather than doing major engine surgery.
Click to expand...

Read my first post again and you'll find the answer. :)
 
I've got a 91 XJ 4.0L HO if it does not have a ping sensor what does it use to set the timing right, for sure something gets adjusted in there as this is the car than can go from sea level highway to 16,000+ ft heights and does not need any adjustment to the timing.

I've read in another answer that the 91 has an OBD-I sensor, can any body explain what is that?

Thanks

SACEM1
 
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