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Timing problems on 7,4 MPI

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Old 06-16-2005, 03:32 PM
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Question Timing problems on 7,4 MPI

I was earlier asking for advice on this forum due to the lack of power in my engine and now I´ve found something what could be the explanation. I was able to use a Mercruiser tester for checking up error codes etc. No error codes found but timing advance seems working really strange to me.
The initial timing is set to 8 deg as far as I know.
At 1000 rpm advance is 5 deg, 1400rpm 16 deg, 2000rpm 25deg. But after that the advance is dropping, 2400rpm 20deg, 3000rpm 16deg and will stay at that to max 4200rpm 16deg advance. The tester does not indicate that the knock sensor is retarding the advance.
Shouldn´t the advance stay at this 25deg or increase all the way to max rpm? Is the problem in the MEFI3 box or? Are there any solutions to this problem at reasonable price?
Thanks for replies.

Last edited by sorrento454; 06-20-2005 at 07:23 AM.
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Old 06-19-2005, 05:50 AM
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Default Re: Timing problems on 7,4 MPI

Somebody...
Must have some information?
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Old 06-19-2005, 09:58 AM
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Default Re: Timing problems on 7,4 MPI

Is this a Thunderbolt IV or V? I believe you have to ground the purple/white wire on the V to be able to check it. It's got a lil rubber plug in it. The V is always varying the timing to match the load, at no load just revving it up, it might be doing something strange...
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Old 06-26-2005, 01:30 AM
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Default Re: Timing problems on 7,4 MPI

I have made some more testings and found out that with shift in neutral position the timing advance will increase to 31 degrees at 4000 rpm. We went then again out driving and found out that the timing was very late again ( 16 degrees at 4000 rpm).
What does make this MEFI3 box to retard the timing under load? The tester does not indicate knock retardant.
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Old 06-26-2005, 01:09 PM
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Default Re: Timing problems on 7,4 MPI

You may want to try running in Distributor Module Mode to see what happens. This would cause the engine to run on the ignition modules internal advance curve, thus eliminating the ability of the ECM to change/retard the timing. You don't want to run that way all the time, it's just a test to help diagnose the real cause of the problem.

To force the engine to run in Distributor Module Mode you need to disconnect the Ignition Control circuit (white wire) at terminal "D" of the four pin connector at the distributor. Remvoing the pin temporarily from the connector would be the preferred way to do it, but you need a Metri-Pack pin tool to do it. But you could just cut the wire and reconnect it after the test if needed.

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Old 06-30-2005, 02:34 AM
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Default Re: Timing problems on 7,4 MPI

Thank you very much Dave.
I´m going to test this asap and I will let you know the result. They say that one problem doesn´t come alone and yesterday I found out that the engine is taking in water in 7:th sylinder!!! I haven´t yet found out what is causing this problem but it is quite strange because the motor has been running for only 116 hours! This water caused probably a bearing problem because it has started to make some noise.
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