jjmoos

Okay, I have a 1997 27' Fountain with the 502MPI. Went to start it Sunday and it just cranks. The VST fuel pump does not kick on for 2 sec when you turn the key on nor does it come on when you crank. I checked the fuel pump fuse-good. I changed the relay-didnt help. when you turn the key you can feel the ECM relay kick but the fuel pump relay does nothing. I got the service manual out and followed the fuel pump trouble shooting guide. When i jump from positive on bat to pos on pump it runs. The ECM ground is good. The last thing in the book was check continuity on green/white wire from relay to ECM plug if ok ECM is bad. Thats where I am but I am not convinced enough to spend $832.00 on a reman ECM yet. Am I missing something? Am suggestion would be great. Thanks guys.

Justin

Boat Tech

Have you checked for 12v at the fuel pump where you are able to by by pass it, If no power is there Then trace that wire back in the manual and on the engine to see where it gets all it power. This is going to sound dumb but make "sure" the kill switch at the helm is on [run] Also make sure the tack is moving while cranking you need to see at least 300 - 450 rpms at crank. Also turn the key on a do a wiggle test to the main wire harness at the engine and see if the fuel pump turns on. If all that checks out ok, then do a wiggle and push in test to the too "wires" harness plugs at the ECM with the key on and see if it turns on. Then pull the too wire plugs off the ECM and look at all the wire pins to see if any has pull out or away from the pins in side the ECM. Also ohms check the wire the book said to do. Also the ECM tells the fuel pump to turn on for 2 sec at key up. Good luck.

stevesxm

if in your position , the next step i would try is doing just what you did w/ the jumpeer wire to make the pump run and then try to start the boat. if it starts, then disconnect the wire and see if it continues to run. that pump signal comes from two places... the ecm that tells it that that the motor is running and that the pump needs to continue to run, and the circuit that tells it that the the boat is NOT running but needs to start. if the boat starts and runs w/ the pump hot wired and CONTINUES to run when the jumper is off, that suggeststhat the ecu is ok but is , instead, the timer relay ( not certain where that is on the vst motors) . if this is a two motor boat, you might just swap the ecus and see if it fixes it. or in the end, just hotwire the pump to the ignition circuit and bypass that safety if you are so inclined.

Thunderstruck

I had a friend whose 502 Mag had the same problem. We could jump the pump straight from the battery and it would run OK. The problem was the wiring harness wire that powered the fuel pump was chaffed due to rubbing on the corner of the block and was shorting out. Try tracing the wire for the fuel pump back to the source and checking to see if the wire has shorted.

jjmoos

Thanks for all of the suggestions guys. I ethered the engine cranking and it has spark. I tried to jump the pump and crank and it won't run off of that pump. I tried to hok a scan tool to it form the marina here in town and it says that it is not able to communicate. I will try some more of these suggestions

thanks,

Justin

stevesxm

when the scanner says that it can't communicate, that means it doesn't think the ignition is on. what that means , in your case is that if you have spark and the ignition IS on but still no communication then you have a bad wire/relay somewhere. thats hard to understand tho, since to run, the ecu has to get signal so it is very hard to understand how the whole system can be live except the fuel pump circuit and the communications link... ohhhhh wait a minute... it DOESN'T run except on the start signal so the ecu ISN'T seeing the power... that should be easy... that harness has its own descrete 12 gage ground wire that breaks all the time and its fed by a big 2 position power plug in the back of the motor that might have fallen apart.

do you have the factory workshop manual ? the diagnostic process there will id this problem quickly. and mi mean the real factory manual... not the aftermarket ones.

jjmoos

i have the Clhymes (sp?) manual on it. I keep thinking something like that (a ground) made more sense than the ECM all the sudden being bad after the winter. i pulled various wires around the block one at a time and cleaned them last night. I tried to take the wires loose at the starter solenoid and broke the little nylon block fuse dealeo so I have to replace that tonight cause I have no power to anything now.

stevesxm

you really need the factory manual. they are expensive from merc but all over e bay cheap. the factory diagnostic procedure is so clear and easy that it makes these problems a snap to fix. my 502's are later than yours but on mine, at the rear of the right bank as you face the motor, on the rear, there is a heavy two wire harness , red and black, that powers and drives the electronics. there is also a 12 gage black ground wire thereabouts that grounds all the elctronics and has a ring terminal for a 3/8 bolt. i see those break all the time and cause weird things to happen. barring not having the factory book ( which if you are going to keep this boat you absolutely have to have ) thats where i would look first.

people talk about the injection being so hard to fix... carbs are so much easier ... and in instances like this where an individual tries to apply an analog diagnostic approach to a digital system then yes... they are hard to fix... but an average smart individual with a the factory manual, a scanner and a vo meter would have this problem fixed in an hour. its all in knowing where to look for the problem and the book does a fabulous job of telling you that.

jjmoos

I will look into getting a factory manual. Last night I unplugged one injector and probed to ground. Both terminals lit up as they should. I plugged a noid light in and cranked and it did not blink. I plugged the injector back in and pulled the ECM back plug "J2" and probed sockets 5 and 21 which are injector drivers. Both lit up. the book that I have for now says that if that happens either the ECM is faulty or the injector wire harness is shorting to a power source somewhere. What is the best way to isolate the injector wiring harness to test for a short?

Thanks guys

Boat Tech

[QUOTE=jjmoos;2860906]I will look into getting a factory manual. Last night I unplugged one injector and probed to ground. Both terminals lit up as they should. I plugged a noid light in and cranked and it did not blink. I plugged the injector back in and pulled the ECM back plug "J2" and probed sockets 5 and 21 which are injector drivers. Both lit up. the book that I have for now says that if that happens either the ECM is faulty or the injector wire harness is shorting to a power source somewhere. What is the best way to isolate the injector wiring harness to test for a short?

Thanks guys[/QUOT] You will need a VOLT/ OHMS meter, unplug the wires at the injector and "J2" plug and ohm check the wire between the too it should be low reading that will tell you the wire is not broken. Now to test for a short to ground in the wire harness leave it unpluged at each end and use A test light, Or you could use a meter in the same way as a test light. The following procedures test for a short to ground in a circuit.
1. Remove the power feed [i.e fuse, control module] from the suspect circuit in your case just unhook the J2 plug. 2. Diconnect the load [Injector]. 3. Connect one lead of the test light to battery positive voltage. 4. Connect the other lead of the test light to one end of the circuit to be tested [Injector plug]. 5. If the test light illuminates, There is a short to ground in the wire harness circuit. Now to test for short to voltage in the wire harness just move the test light to a good ground and re test it should not light up.