03 5.7 350 with Bravo 3 drive keeps stalling and racing

[Justin Snow]

I have an 03 5.7 mercruiser stern drive that we just did an engine rebuild on and now when I start it up on the trailer (after running smooth for almost 20 hours now) she runs smooth for a few minutes and then starts trying to stall out. At first it just sounds like a few misses but eventually she winds all the way down. When I start shifting forward and reverse the problem seems to get worse but every now and then she starts surging between shifts for about 5 seconds before coming back down to idle. Any suggestions are appreciated. I’m losing my mind and savings on this one!!

 

[Scott Danforth]

got a serial number?

carb or MPI?

what is your compression numbers?
what is your fuel pressure?

what diagnostics have you done?

 

[Justin Snow]

I hooked it up to a computer and am getting no relevant codes. It does however count the errors that happen a couple times a minute when it’s stalling. I tested the fuel pressure and it’s 40 something which is good. Don’t know the serial number at the moment but my service manual is for OM300000 and above it’s fuel injected

 

[Justin Snow]

I also replaced the crank shaft sensor and the plug that come into it from the harness. Put new Spark plugs in.. just did a bunch of out drive work too but that’s prob irrelevant

 

[Scott Danforth]

your fuel pressure is 40 something, or 43 psi?

going to assume its an MPI motor

it should hold 43psi thru the entire RPM range from no load to fully loaded.

what is your compression?

you probably wont see "codes" you have to look at each parameter and compare to what its supposed to be.
when plugged in, what is your injector duty cycle?
can you post a screen grab? there are a few forum members that live and breath MPI diagnostics.

 

[Justin Snow]

So I just noticed something when I went to pull the new crank position sensor.. it was scratched up pretty badly. When I first pulled the old one I noticed that it was scratched up pretty good so that’s when I first thought to replace it.. now the new one is scratched up.. I’ve seen old ones that look pristine.. would anyone know why the sensor is getting scrached and what to do to fix it?

 

[Scott Danforth]

got pics?

 

[tpenfield]

It's like the computer diagnostics should be sold with each EFI/MPI engine . . . If you have got the diagnostic software (or tool) post what ever info, screen shots you have.

The surging makes me think air/fuel mixture fluctuating, but the scratches on the CPS, are troubling . . . I assume it is coming in contact with the crank shaft (balancer ?) . . . so fix that first. Then see about the engine behavior and any changes.

 

[Justin Snow]

So after I bought 3 crank position sensors the last one came with two thin washers that said to install as spacers because thrust bearings wear out on old motors and you need to maintain a gap or the magnet will scrape it up. She running smooth now!