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engine ping

lsc910

NAXJA Forum User
Location
New Jersey
I know I posted something about this before but I really need to fix this problem. Its an 88, 4.0L with 233000 miles and I just replaced just about everything you can. I did a complete tune up, meaning plugs, cap, rotor, wires, fuel filter, air filter, and oil change along with map sensor, IAC ,factory EGR valve, TPS, and O2 sensor. While doing the tune up I also did the valve cvr gskt and cleaned the crap out of it and the pots. I tried adding an octane additive and the higher drade gas but its still there on occassion. Is there anyone that can make a suggestion. Please help and thanks in advance.
 
...or you can use Mopar Combustion Chamber Cleaner instead of Seafoam. Grab a can or two from the dealership and follow the directions. It's the closest thing to a tune-up in a can that I've ever used...works great!
 
Pull the vacuum line from brakes (booster). Stick end of line in can. Start motor. Stop motor when can is 1/3 empty(or pour 1/3 can into another container and proceed). Regulate flow manually; the motor should bog but not stall. Let sit for a few minutes to 1/2 hour. Re-start motor and watch the smoke fly and the neighbors freak out.
 
It is most likely a carbon problem. Unless you want to dig in mechanically to remove the carbon, I'd try decarbonizing as mentioned above using a top end cleaner (Mopar/GM is about the same stuff and both work well) or Seafoam.

Don't these vintage (Renix) XJ's have knock sensors? I'd say carbon is more likely than the knock sensor but it may be worth checking out.....
 
it is on the side. about halfway iirc. I would do the combustion chamber cleaning first. Then start looking into the knock sensor. They are pretty finicky and have to be installed and torqued just right.
 
the MCCC is best put directly into the spark plug holes and allowed to soak, says this on the bottle. Pull the sparks plugs, and allow an overnight soak. Feeding it into the booster line reaches the cylinders uneven.

I've had 4 or 5 bottles over the years and none of them said to spray it in the plug holes, but that sounds like a good idea. Do you crank the engine over with the plugs out to blow out all the carbon?


The knock sensor would be one of the last things to check. I ran my 90 without a knock sensor for 6 months before I realized it was cracked in half..didn't seem to make a difference.
 
The MCCC says to get the engine to running temp and spray contents into throttle body, make sure it doesn't stall once done turn off engine let stand for 5 to 10 min then restart and run at low speeds for about 5 minutes to expel everything. I'm going to try it and see what happens in a few minutes when its at running temp.
 
The knock sensor is on the drivers side of the block, quite near the backside of the motor mount, just above the oil pan. Its the sensor with a connector resembling that of a fuel injector.

I don't know if you can test it without the DRBII tester.

Its simple to replace. Unscrew the sucker and torque the new one to 89 inch pounds.
 
Well I used the can of MCCC and it helped out a lot. I only had 1 can but hopefully I can pick up another and do it one more time. I drove the jeep all day yesterday and only heard it once or twice, which is great being I used to hear it every time it would downshift or just try to accelerate to fast. Thank you for all of your help. I'll keep everyone posted.
 
Well after driving the jeep for the day it still had a slight ping so I picked up a can of seafoam and ran that through and it is still there. I'm going to pick up a new temp sensor for the computer tomorrow at the dealer. I hope that fixes it.
 
The knock sensor retards the timing it wont help I was told by 2 Jeep A techs. I went to see what the temp gauge was reading today but someone has taken the wiring harness that is needed to hook up the DRB scan tool to my jeep.If they find it they were going to call me so I can bring it back up to them. Does anyone know where to locate the temp sensor on the block?
 
The knock sensor retards the timing it wont help I was told by 2 Jeep A techs.

But if the timing is retarded, it will cut down on the ping. When you could power tune a car (in the good old days), we would advance the distributor until we got a little ping, and then back it off.

Ping is pre-ignition which is caused by combustion too soon before Top Dead Center. Too lean a mixture or too early timing cause this. Some other factors such as higher compression or quench characteristics of the head can aggravate the problem. Ping is preignition is knock.
 
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