5.7 Mercruiser MPI won't stay running

[jdubslopro]

Just swapped over from a v6. Has new IACV and TPS. Fresh rebuild.
Starts and idles great for a few seconds, then dies. Unplug TPS, runs at a high idle (1100 rpm or so) for as long as its unplugged.
If I shift into gear immediately after starting it runs great makes good power all the way through the rpm range, no hesitation or stalling. Drop the rpms back down, shift into neutral, stalls.
What do I look for?

 

[jdubslopro]

Re: 5.7 Mercruiser MPI won't stay running

Also doesn't matter whether shift interrupt switch is plugged in or not

 

[Don S]

Re: 5.7 Mercruiser MPI won't stay running

We need to know exactly what engine you have now to even come close to helping you. Is it a Mercruiser? If so, what is the serial number. If not, what is it, what ecm, impossible to say what the wiring is. What drive do you have?

 

[jdubslopro]

Re: 5.7 Mercruiser MPI won't stay running

Mercruiser 5.7, came with a horizon engine (plastic) cover serial is 0M3011xxxx I can't remember exactly what the serial is but I know it starts with those alpha numerals. It might be 0m011. It is completely stock as it would have come in a new boat.
I dropped it off to have some work done after I rebuilt and installed it. The place I dropped it off to said it was running like a champ, idled perfectly (at 800rpms, in my opinion a perfect idle would have been at the factory recommended 600). When I put it in the water it immediately died. Got it running, then noticed when I tried to give it throttle it was extremely doggish and wouldn't plane out. Advanced the timing and voila it has power. This was done on the water with no timing light, but I've done this plenty of times (albeit with carbureted engines) and been able to get the timing pretty spot on.

 

[jdubslopro]

Re: 5.7 Mercruiser MPI won't stay running

And it's a merc alpha gen 2

 

[jdubslopro]

Re: 5.7 Mercruiser MPI won't stay running

I'm thinking its either the tps or the IACV but without the merc scan tool it's hard to say for sure. The boat is back at the place I had working on it so hopefully they'll figure it out so I can get it back and clean it up for the weekend.

 

[Fun Times]

Re: 5.7 Mercruiser MPI won't stay running

Advanced the timing and voila it has power. This was done on the water with no timing light, but I've done this plenty of times (albeit with carbureted engines) and been able to get the timing pretty spot on.

In this particular case the correct serial number for your engine model is so important to be able to help guide you through the process between setting the correct engine timing on one engine model or properly setting the distributor assembly in due to engine timing on the newer MPI engine models are no longer designed to be adjusted. The two guessing numbers of 0M3011xxxx or 0m011 is two completely different engine models as mercruiser was going through big changes right between those numerals letters & numbers.

Setting the timing by ear and feel with an MPI engine is honestly a lot different then the carbed engines. Do you have access to a timing light if needed?

 

[jdubslopro]

Re: 5.7 Mercruiser MPI won't stay running

I called the shop it's at today, and they said that they believe they received a defective TPS, which is one of the causes I suspected. They also mentioned that the MAP sensor was reading 5 volts where it should be reading between 2 and 3 volts, so they ordered one of those. I'll update as soon as I hear back.

 

[Tail_Gunner]

Re: 5.7 Mercruiser MPI won't stay running

IF your have replaced a 4.3 with a 5.7 you will need to retune your ecm period. The intial timing is much different and the fuel metering will be different. If that's been done proceed if it has not been done you ned to find a shop that has some ideal of what they are doing.

Read the post futher you cannot set the timing on the fly with mpi..you need to post what you have going on there.

 

[jdubslopro]

Re: 5.7 Mercruiser MPI won't stay running

The 4.3 was 2BBL carbed...this 5.7 is a complete new rebuild with all the original components that it came with from Mercruiser minus the aforementioned TPS and IACV. Well, that and the internals, gaskets, etc.

 

[Don S]

Re: 5.7 Mercruiser MPI won't stay running

If you can't post the full serial number of the engine, then you are just wasting everyone's time. It's a VERY important number.

 

[jdubslopro]

Re: 5.7 Mercruiser MPI won't stay running

0M011557
I found it in my other thread from last year when I was figuring out where everything went.

 

[Don S]

Re: 5.7 Mercruiser MPI won't stay running

Now, we are getting some where. Yeah you have a weird engine to find info on.
You should put the following information in your signature or something so it doesn't take days to find the next time.

Horizon 350 Mag MPI (Gen +)
Thunderbolt Ign. Bravo
0M011557-444206HN1
Pts Catalog 809488 99

Since you have it at a shop, not much sense in giving you things to check for us.

 

[muc]

Re: 5.7 Mercruiser MPI won't stay running

“Also doesn't matter whether shift interrupt switch is plugged in or not”
Because this engine came out of a boat with a Bravo outdrive the ECM might not work with the shift interrupt.

Might have your shop run the serial number through MercNet/Product history. Looks like this engine might have been a “problem child”

 

[jdubslopro]

Re: 5.7 Mercruiser MPI won't stay running

When I got the motor it had a jumper wire harness where the shift interrupt would be, so I wired my shift interrupt into that. Any insightful info you might have as well as troubleshooting would be appreciated as I can tell the shop what to look for. I have a pretty good idea what I'm doing I just don't have the time for this project, hence why I dropped it off there. The guy was nice enough to let me supply my own parts and whatever parts he gets he charges me cost on them. Aside from the possibility of a defective tps we are both kind of stumped at the moment.

 

[Don S]

Re: 5.7 Mercruiser MPI won't stay running

Disconnect the shift interrupt switch from the system, and jumper between the two engine harness connectors and see if it will run.

 

[jdubslopro]

Re: 5.7 Mercruiser MPI won't stay running

Already tried jumpering the interrupt switch, no dice there. Shop called mercruiser tech and if the new tps doesn't do it it might have to get sent in for reflash. Any idea how much that runs, and whether there is someone on the forum capable of this procedure?

 

[jdubslopro]

Re: 5.7 Mercruiser MPI won't stay running

I can't imagine that the ECM is bad or even needs to be reflashed...as previously stated it has power and will stay running without skipping a beat as long as the throttle is held partway open. As soon as its allowed to idle, it will do so for 3-4 seconds and shut off.

 

[Tail_Gunner]

Re: 5.7 Mercruiser MPI won't stay running

Mercruiser 5.7, came with a horizon engine (plastic) cover serial is 0M3011xxxx I can't remember exactly what the serial is but I know it starts with those alpha numerals. It might be 0m011. It is completely stock as it would have come in a new boat.
I dropped it off to have some work done after I rebuilt and installed it. The place I dropped it off to said it was running like a champ, idled perfectly (at 800rpms, in my opinion a perfect idle would have been at the factory recommended 600). When I put it in the water it immediately died. Got it running, then noticed when I tried to give it throttle it was extremely doggish and wouldn't plane out. Advanced the timing and voila it has power. This was done on the water with no timing light, but I've done this plenty of times (albeit with carbureted engines) and been able to get the timing pretty spot on.

Well have you set the timing to its proper setting..........Mercruiser Marine Engine Timing Procedures | Performance Product Technologies

Was the main body computer part of the engine's oringal equipment?

 

[jdubslopro]

Re: 5.7 Mercruiser MPI won't stay running

Tech said he set the timing according to merc spec. When I got it running it would not get on plane (even with a 4blade 19p on a v6 drive-1.62:1- that would shoot right out with my 4.3). At that point I advanced the timing and got instant throttle response. But once the new TPS is in they will reset the timing and go from there.