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Still running Rich

  • HFXJACK
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5 years 6 months ago #1468 by HFXJACK
HFXJACK created the topic: Still running Rich
As many of you know I replaced my engine last spring and since then have had nothing but grief. However we are getting close.
Long story short my fuel consumption at trawler speed is the same as running at 3800 rpm. As measured by fuel flow sensor.

When engine is cold I can start easily with no throttle. Same when engine is hot. Engine idles normally. However when the engine is warm say 140F I have to give it 3/4 throttle to get it to start and then I have to keep it around 1000 rpm to keep it running until it is warm > 170F on the gauge.

Now my theory. If the engine temperature sensor ( the one connected to the ECM ) is out of calibration and reads low then the ECM thinks the engine is running colder than it really is and therefore gives it more gas. On my dash gauge running at 3800 temp indicates 185F when at trawler it reads around 170F. A out of calibration sensor will not give a fault because it is not failed but simply not reading accurately.
When plugged into the computer there are no error codes However at idle on the muffs the engine never really gets to normal operating temperature as indicated on the computer and the pulse width on the injectors is longer than normal ( as if the ECM is giving a little choke )

SOOOO I am thinking I change that sensor. Opinions please

7.4L MPI

Thanks

HFXJACK

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  • k-townguy
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5 years 6 months ago #1469 by k-townguy
k-townguy replied the topic: Re: Still running Rich
I would swap out the ECT sensor, but i would also check the harness side of the connector for any abnormal resistance. Do you have an IR temp gun, or can get a hold of one? I would run it on the muffs at home, check what your gauge says for temp, then point the temp gun at your thermostat housing and see what it reads there and compare the two. If ect sensor indicates lower reading than the gun, then ect sensor is faulty. But if both are close, then there is another underlying issue.

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Why is there never enough time to do it right the first time, but always enough to do it right the second time.

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5 years 6 months ago #1470 by HFXJACK
HFXJACK replied the topic: Re: Still running Rich

k-townguy wrote: I would swap out the ECT sensor, but i would also check the harness side of the connector for any abnormal resistance. Do you have an IR temp gun, or can get a hold of one? I would run it on the muffs at home, check what your gauge says for temp, then point the temp gun at your thermostat housing and see what it reads there and compare the two. If ect sensor indicates lower reading than the gun, then ect sensor is faulty. But if both are close, then there is another underlying issue.


Thanks I agree. They did shoot it with an IR and compared readings to the computer. It does not agree but seemed reasonable. An IR is not that accurate because of the range of the sensor. I even changed the ECM and they have checked all connections. I was there when on the computer and everything behaves as it should for the temperature indicated that is why I suspected the sensor. A friend of mine who is into high performance cars "Bonneville" told me how they would put a 160 stat in a car to boost HP by tricking the ECM that was in the old days. I think a 1999 MPI qualifies as old as it was mercruiser 1st generation system.

Cheers

HFXJACK

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