502 mpi won't idle down
09-22-2009 | 07:30 PM
#31
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Joined: Jun 2004
Posts: 1,144
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From: Sun Prairie, WI
A quick update:
The distributor was set at 8 degrees of base timing before i picked up. Boat ran great. Idled perfect, top rpm and power was perfect. Ran 30 gallons of gas through it, stopped the engine multiple times, idled multiple times. Everything was good.
Two days after this initial run, there was one occassion that the idle would remain high, but it did come back down in the same day within minutes, and I wrote it off as a fluke.
One week from that run, it idled high the whole day long. No one moved the distributor, but it is apparent that the base timing went to 14 degrees ( or just never took all the advance back off when coming to idle after a run) My question is: What component of the MEFI 1 system would be the most obvious to raise this base timing? It seems to me that it could be multiple things (TPS, MAP, MAT, WT, ECU, or the distributor module) but I do not have a lot of experience with this. Maybe someone else has been there done that and knows of a particular component that more often than not is the culprit..............
As of now, the shop's answer that is working on it is to move the distributor, and set base timing at 9 degrees and run it. I don't think they feel that whatever component is messing with the base timing is worth chasing down. I'm more worried about that the component that is goofy, is messing with the fuel curve as well or something different.........
Thanks
The distributor was set at 8 degrees of base timing before i picked up. Boat ran great. Idled perfect, top rpm and power was perfect. Ran 30 gallons of gas through it, stopped the engine multiple times, idled multiple times. Everything was good.
Two days after this initial run, there was one occassion that the idle would remain high, but it did come back down in the same day within minutes, and I wrote it off as a fluke.
One week from that run, it idled high the whole day long. No one moved the distributor, but it is apparent that the base timing went to 14 degrees ( or just never took all the advance back off when coming to idle after a run) My question is: What component of the MEFI 1 system would be the most obvious to raise this base timing? It seems to me that it could be multiple things (TPS, MAP, MAT, WT, ECU, or the distributor module) but I do not have a lot of experience with this. Maybe someone else has been there done that and knows of a particular component that more often than not is the culprit..............
As of now, the shop's answer that is working on it is to move the distributor, and set base timing at 9 degrees and run it. I don't think they feel that whatever component is messing with the base timing is worth chasing down. I'm more worried about that the component that is goofy, is messing with the fuel curve as well or something different.........
Thanks
Last edited by cloudmaster_321; 09-22-2009 at 07:51 PM.
10-09-2009 | 03:43 AM
#32
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Joined: Jan 2005
Posts: 185
Likes: 1
If I'm understanding you correctly, it sounds like the timing was set and it moved again????... if this is true and the distributor did not move, the reluctor inside the distributor is moving. This is not uncommon in aged distributors. If you are a diy kinda guy, take the distributor apart and check the 4 post "trigger" and see if you can move it on the shaft, it should NOT move. If it does, replace the distributor.
Be careful about what you buy, MSD as well as most replacement distributors(napa included) do not have the correct reluctor/pickup interface and will cause a loss of higher rpm horsepower. Make sure to replace with an 8 pickup 4 pulse reluctor like GM used.
Be careful about what you buy, MSD as well as most replacement distributors(napa included) do not have the correct reluctor/pickup interface and will cause a loss of higher rpm horsepower. Make sure to replace with an 8 pickup 4 pulse reluctor like GM used.
