seamate

I have recently rebuilt from the crank up a 95 502 EFI. In the process I added a hotter cam, roller rockers, stainless valves, and stainless marine exhaust in preparation to add a Procharger after I have some additional time on it. Still has stock circulating pump and stock EFI system. This weekend I finally got it on the water for first shake down. It ran fine for about 15 minutes then stopped dead in the water. After about 2 minutes it would restart but then die again in under 30 seconds. It has new filters and am running 89 octane gas but am a little concerned that fuel is now 10% ethanol. Any possibilty of filter clogging because of this? It also runs stone cold even though I have a new 160 degree thermostat in it. My scan tool shows only a persistant MAP sensor failure even though that is also new.

Any thoughts? I am starting to get tired of all the electronics and am considering going back to a carb except I already have my Procharger which is set up for EFI. So I really want to make this work.

Any input is greatly appreciated.

Dave

kennyo

If your tool says Map sensor that is what i'd check. Don't change to a carb or you will be sorry.

RichardCranium572

When you change things in the engine, the computer has to be re-mapped to match the new components.

stevesxm

if it REALLY runs dead cold then the water temp sensor will get "out of range" and has the potential to shut the thing off when that status doesn't agree with other values... not to mention that it will eventually wash all the plugs etc...

my suggestion would be to make sure the tsat is working and and start it and let it idle to temp in the water. it should reach 150 in a matter of just a few minutes... and with an EFI motor it HAS to do this... all the time doing a real time read on the sensor array with your scanner. compare THOSE values w/ what the factory manual says they should be at various temps and you will have your answer.

also... your post doesn't really say how it shuts off... as in " like you turned the ignition off" or it stumbles, coughs and dies... or what the fuel pressure gage says when it does it...

your answer lay in all the basic diagnostic stuff... no magic

seamate

The engine shuts off "like you turned off the ignition". I now believe that the themostat is installed incorrectly with the spacer above the thermostat instead of below, now that I study the diagrams more closely. I bought this engine completely disassembled and am feeling my way along via the service manual and OSO. So now I think I'm close to the reason for the cold temp. Can the ECM actually shut it off if it doesn't warm up correctly?

Thanx for the feedback
Dave

stevesxm

the ecm compares all the sensor values to each other looking for a place on the map where they make sense. if all the sensors "agree" and one is something else entirely then it makes a choice about what to believe and what to do about it.

it can go into guardian mode or in some cases try to wildly compensate with some other setting that will make the thing run very weird.

if yours is shutting off like the key was off, it doesn't sound like that... but having said that, if it is full cold, it will be so rich that it might just seem that way.

my suggestions from my first post remain the same. hook up the scanner, get the answers and the problem will be self evident if it is systemic. if it ISN'T then that tells you something as well.