502MPI - Odd IAC and spark readings
07-26-2011, 11:43 PM
#1
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Thread Starter
502MPI - Odd IAC and spark readings
Motor ran great up until a couple weeks ago when I got water in the tank. Motor is procharged but other than fuel pressure issues I think its more in the base engine. Has been basically inoperable and finally had a couple minutes to look at it.
At idle:
Eng rpm fluctuated non stop between 510-720rpm with no noticeable change in engine.
IAC Follower: 0#
Basic IAC Pos: 255#
IAC Position: 150#
Spark Adance: fluctuated nonstop between 11 - 24. Would not sstay constant. (Off idle it jumped and locked in to 39.5)
Even with rpm fluctuation, it seemed odd spark would jump 15deg.
Fuel Pressure: fluctuating between 32 and 45. Does have the stock Procharger regulator which is known to be junk. All I have at the moment. Added a return from regulator, now holds steady but drops to zero within 10 seconds of turning motor off. Doesn't seem quite right yet.
Got too late to do much else, plan for tomorrow is to run the sacanner again with fuel pressure stable.
Next up is cap, rotor, wires, plugs. From there it will be test injectorss, sensors, etc
Figured I throw it out there and get some feedback. Thoughts?
At idle:
Eng rpm fluctuated non stop between 510-720rpm with no noticeable change in engine.
IAC Follower: 0#
Basic IAC Pos: 255#
IAC Position: 150#
Spark Adance: fluctuated nonstop between 11 - 24. Would not sstay constant. (Off idle it jumped and locked in to 39.5)
Even with rpm fluctuation, it seemed odd spark would jump 15deg.
Fuel Pressure: fluctuating between 32 and 45. Does have the stock Procharger regulator which is known to be junk. All I have at the moment. Added a return from regulator, now holds steady but drops to zero within 10 seconds of turning motor off. Doesn't seem quite right yet.
Got too late to do much else, plan for tomorrow is to run the sacanner again with fuel pressure stable.
Next up is cap, rotor, wires, plugs. From there it will be test injectorss, sensors, etc
Figured I throw it out there and get some feedback. Thoughts?
Last edited by fantastixvoyage; 07-26-2011 at 11:48 PM.
07-26-2011, 11:52 PM
#2
Registered
The spark will constantly change at idle due to the idle spark stabilization. It is trying to maintain a consistent idle.
The IAC postion should be at or near 0 at idle in neutral. If it is really open, then it is obviously trying to keep the engine running due to something else. However, the ecm has no idea where the IAC actually is. It only tells it to open or close, but doesn't know if it actually does it or not.
I would start with the IAC. Pull it out and clean it up. Make sure it and the hole it sits in are free of carbon build up.
Eddie
The IAC postion should be at or near 0 at idle in neutral. If it is really open, then it is obviously trying to keep the engine running due to something else. However, the ecm has no idea where the IAC actually is. It only tells it to open or close, but doesn't know if it actually does it or not.
I would start with the IAC. Pull it out and clean it up. Make sure it and the hole it sits in are free of carbon build up.
Eddie
