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post #1 of (permalink) Old 09-05-2002, 12:37 PM Thread Starter
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Detonation, open air filters & high air temps

Background info:
1982 CJ-7, manual trans, 4.56 gears
1990 XJ 4.0L (pre-HO) engine, original manifolds, fuel rail, injectors
Mopar MPI harness, sensors (everything other than the intake manifold and fuel rail/injectors)

Will an open element air filter (Rock-It tube/K&N filter) drawing superheated under hood air aggravate detonation? I have been fighting a pining/detonation problem for some time now and I have read a lot of posts on the subject but most seem related to the MPI conversion on 258 not a 4.0L conversion. One post recommended an adjustable pressure regulator but at $200+ I want to eliminate other problems first.
Fuel pressure is within specs according to the FSM (34 to 40 #.) I even road tested with a pressure gauge attached and the pressure was 38-40 # at 1/2 to full throttle, ping or no ping. Engine temp runs 200 Ė 210 depending on load (195* stat). For curiosity I checked for trouble codes, there was a 23 (low/high inlet air temp) and a 54 (no cam signal) I donít know why the 54 as I havenít had any starting problems. A DVM shows the temp sensor to be within specs although I havenít checked it at operating temp yet (FSM says it should be < 4k ohms). Finally, can I clear the codes by pulling the fuse for the MPI system and for how long? Any thoughts or suggestions?

Thanks in advance,

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post #2 of (permalink) Old 09-05-2002, 01:48 PM
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Re: Detonation, open air filters & high air temps

One thing you could try is to move the Intake Air Temperature (IAT) sensor onto the air tube just behind the stock box. This fools the computer into thinking that cooler, and therefore more dense air is being fed into the engine. The computer will compensate by supplying more fuel, which may help with the detonation problem. The best part is that this mod is free!
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