454 mag mpi chuggles/stalls

[alldodge]

Your thread at Marine Engines list you swapped the ECM's and harnesses and there was no change. Swapped complete intake with all sensors and no change

Everything on the new motor works fine on the old motor, and everything on the old motor has no effect on the block motor. Prior to new long block, that motor was doing same thing as this one.

You say long block, so the new motor comes with new heads?
Are you using new intake gaskets for each swap or reusing old one?

 

[vroom ZOOM]

BTW - I had to Google "chuggles" . . .

"Chuggle" can refer to two main things: a type of dog breed or the act of drinking something quickly. As a dog breed, a "chuggle" is a cross between a Chihuahua and a Puggle (itself a Pug and Beagle mix)

Perhaps your engine is 'drinking too quickly' . . .

I dunno... this is what mercruiser calls it... straight from the manual!

 

[vroom ZOOM]

Have you checked ALL / each sparkplug to see if some are different ? Like the start of a head gasket starting to leak ? Been there and hated the random problem.

took them out, looked a little sooty but all the same.

 

[vroom ZOOM]

Your thread at Marine Engines list you swapped the ECM's and harnesses and there was no change. Swapped complete intake with all sensors and no change

Everything on the new motor works fine on the old motor, and everything on the old motor has no effect on the block motor. Prior to new long block, that motor was doing same thing as this one.

You say long block, so the new motor comes with new heads?
Are you using new intake gaskets for each swap or reusing old one?

I only swapped the upper part of the intake with the sensors and throttle body. And yes new gaskets if any were torn.

No parts swapped had any effect, except for the injectors. Today I decided to try swap injectors again. What do you know, the engine fired up and ran perfectly for about 2 minutes, then it slowly got worse and worse until it quit. At this point I am thinking maybe I have a defective fuel filter or something. It ran good for a while before, but that was off the remote tank, and I must have not run it for very long after connecting the boat tank, thinking it was fixed. I will try put the injectors back in the other motor and I hope the other one wont run which would indicate i have found the problem.

 

[alldodge]

ok, your swapping the intake plenum not the intake

Still don't think it's fuel, more intake leak or temp sensor

Place voltmeter on intake sensor wire feeding ECM. Note voltage with key on motor off. Start motor and note changes if any

 

[tpenfield]

I only swapped the upper part of the intake with the sensors and throttle body. And yes new gaskets if any were torn.

No parts swapped had any effect, except for the injectors. Today I decided to try swap injectors again. What do you know, the engine fired up and ran perfectly for about 2 minutes, then it slowly got worse and worse until it quit. At this point I am thinking maybe I have a defective fuel filter or something. It ran good for a while before, but that was off the remote tank, and I must have not run it for very long after connecting the boat tank, thinking it was fixed. I will try put the injectors back in the other motor and I hope the other one wont run which would indicate i have found the problem.

It would be good to have the Diacom connected and recording when you do these tests. Lots of folks go through endless frustration swapping and throwing parts at MPI engines.

 

[vroom ZOOM]

It would be good to have the Diacom connected and recording when you do these tests. Lots of folks go through endless frustration swapping and throwing parts at MPI engines.

I have a rec file. Will send it to you via pm

 

[vroom ZOOM]

ok, your swapping the intake plenum not the intake

Still don't think it's fuel, more intake leak or temp sensor

Place voltmeter on intake sensor wire feeding ECM. Note voltage with key on motor off. Start motor and note changes if any

Put the voltmeter on the tan wire from the ECM with the IAT unplugged. Started the engine and the reading stayed around 5.2 volts. Also wasn't able to get the meter on the wire with the sensor plugged in but here are the diacom readings from the sensor with the engine running. ECT sensor paints a similar picture, just a little warmer obviously.

 

[alldodge]

Was looking for water temp and forgot about your diacom. Motor started, air temp went from 119* to 118*, and then motor died, correct?

 

[vroom ZOOM]

Was looking for water temp and forgot about your diacom. Motor started, air temp went from 119* to 118*, and then motor died, correct?

Yes, I guess the temp went down a little as it started pulling air through the plenum.