Ping

Who else's 4.0 pings on 87 octane fuel? Mine likes to do it. Or maybe my ping sensor took a crap and my ignition is advancing to much. Thoughts?

Mine always has since new. I always run at least 89 in it and it is happy...

I've NEVER had any of my 4.0Ls ping on 87 octane.

not the 89XJ w/ 320K miles

not the 87MJ w/ 2000mi on the rebuild

and my dad's 2001WJ with 90K on its 4.0L never pinged on 87.

One of mine pings and the other two don't. Not sure if the previous owner of the pinger did some hot rodding overhaul or not.

My '89 only pinged when the knock sensor was bad (I actually broke it in half ), when I replaced it all was well again.

I think I will try the knock sensor, I dammaged it when I pulled the motor last summer, but It seemed to work then so I didnt do anything about it. I was told that if the knock sensor went bad the ECU would default to a preset bas timing, and it would judt run doggy, I'll fill it up with some 89 and see what happens first. Thanks

All my driving is between 6500' to 9500' elevation, so I'm able to use 85 octane with no pinging. I'd go back to 87 at lower elevations. Think it has to do with thinner air causing the mixture to be richer. Just my two cents

an upper engine cleaning might help too....possible carbon build up on the piston/heads?

Yes, I agree with the bad knock sensor. The Renix XJs (87-90) have a knock sensor, the later XJs do not have a knock sensor.

If you are getting knock then the knock sensor is not working. I damaged my knock sensor like 3 years ago and about 18 months ago I installed a new one. Back then it was a dealer only item, now i hear you can get them at parts stores.

The knock sensor will retard your timing if it detects pinging. If you have ping then the sensor is not telling the computer.

I'd change the knock sensor and install a high alt CPS. The high alt CPS this will give you more advance and with the knock sensor working you will have no knock. You should notice an improvement in power. The final thing to do is install a new/rebuilt distributor. Worn bushings can also retard your timing. Once I had all those new parts installed my XJ had power I had never remembered having.

Pinging can be an indication of carbon build up in the engine and a good top cleaning may be in order. Hook up a vacuum gauge to a port in the intake, if you get 16 in Hg or more you have a clean top end so save your $ on top end cleaning.

Running higher grade fuel will prevent knock but that a band-aide on a Renix XJ since there is a knock sensor.