185/195 degree thermostats: Reduce Pings - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 07-19-2003, 12:36 AM
mindbender
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185/195 degree thermostats: Reduce Pings

I have read and been part of the discussion on the merits of the high temp thermostats on CJ7 that have had the 4.0 head and MPI conversion. However, I have checked fuel (lean - rich); changed plugs; run higher octane gas - but still get a pinging whenever I step down on the accelerator. I have been reading other material that indicates using a lower temp thermostat is supposed to help reduce pinging. Is that a real option and if it did help would the performance consequences be equally a problem? Just trying to avoid the purchase of a spendy adjustable pressure regulator - which I understand only helps on occasion; or having the computer reprogrammed; or shimming the CPS and distributor. Thanks, WES
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post #2 of (permalink) Old 07-19-2003, 09:07 PM
 
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Re: 185/195 degree thermostats: Reduce Pings

Wes, the thermostate will not help the ping. Temperature will affect the ping but only if it is unusually hot.
First off check the heat range of the plugs you installed, normally one or two ranges hotter will not lead to ping unless you have combusion chamber deposits, but it appears from your bio that the heads are clean "no carbon build up".
Did you (or previous owner) change the distributor or even play with it (-: ? Also you can change timing, retarding it a few degrees may solve the problem.
Many vechicles will ping under full throttle from a standing start and this is not unusual. The ping is dangerous when it is extended. (a second or two)
So to save money in the long run, take it to a good electronics shop and have the spark curve checked also the mixture under actual driving conditions. It may be a little costly but it is a lot better that putting holes in the pistons. [img]images/graemlins/thud.gif[/img]
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post #3 of (permalink) Old 07-19-2003, 11:56 PM
 
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Re: 185/195 degree thermostats: Reduce Pings

I doubt that the lower temp thermostat will do anything for you. At best, it will just mask the real problem. The first thing I would check is the timing adjustment. A timing too far advanced will cause pinging. When I set my timing on my older (carburated and non-computer) cars, I initially set it to what the manual specifies, then I take the car out on an open road, advance the timing slightly, step on the gas from a dead stop and repeat the process until I get a ping. Then I back off the timing about 1 degree and I am at the optimum timing for my engine. Also, check your vacuum advance connections to the distributor to make sure that everything is hooked up correctly. You can check the vacuum advance with a timing light while pulling a vacuum on the distributor diaphragm and check it against specifications (usually around 10 degrees or so). If that still doesn't work, then remove the distributor, take it to a performance shop and have them check the mechanical advance curve on a special machine.
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post #4 of (permalink) Old 07-21-2003, 12:35 AM
bmwfirearms
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Re: 185/195 degree thermostats: Reduce Pings

I just installed the MPI and have the same problem,some what. mine only pings above 2,000 rpm.......

After talking to hesco they recomended the fuel regulator also.......(i have not installed this yet)

I just filled up with 92 octane gas and the pinging seemed to slow a bit.

The bad thing about the MPI, is not being able to adjust the timing without the OBD II computer
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