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Mercruiser 7,4L MPI surging , please help :-)

F

Finn

New member
Hi , it start and runs okay , except that put on 1000 rpm it surges betwen 1000 and 1200 rpm , cold or warm. I have att. some ScanerPro screensots. New sparkplugs , fuel pressure tested and okay , IACvalve cleaned. With engine running it makes no difference if I disconnect the IAC valve . I am not that used to use ScannerPro that I am able to figure out what the problem is. I have no trouble codes shown from the MEFI 3 ECM. I suspect the IAC valve to be the problem, but I am not shure.

Does anyone have a guess ?

Engine :
OL 691258 , model no. 4542077N1 , 7,4 MPI Gen. VI L29. Bravo III. 1998.


Thanks

Finn.
 

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  • ScannerPro Cold idle.jpg
    ScannerPro Cold idle.jpg
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  • ScannerPro Cold with ignition..jpg
    ScannerPro Cold with ignition..jpg
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  • ScannerPro running temp IAC disconnected.jpg
    ScannerPro running temp IAC disconnected.jpg
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  • ScannerPro running temp idle.jpg
    ScannerPro running temp idle.jpg
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I am having the same issue; I can recreate by taking RPMs up to 1300 and backing off to 600 RMPs using throttle only. Immediately the engine will surge to 1200 or so then settle back to 600. No issue under load and on plane. 99% of the time it happens when backing off the throttle. Any ideas I would greatly appreciate.
 
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