could engine cutting out at high rpm's be shift assist module?

[taxijim]

Help! i am pretty frustrated right now. I have an older '79 omc sterndrive i/o with a gm 350 small block engine in it and this season I have had intermittent trouble with the engine suddenly cutting out at higher rpms. At first I was convinced it was the carb not functioning properly so I replaced it (not cheap!), then it started doing it again, and so I decided after checking what was going on while it was underway and viewing the fuel input into the carb that perhaps it was the fuel pump, so I replaced it. I have also replaced the points, plugs, condenser, and plug wires, and coil, and am still having intermittent trouble with this problem. I was pretty convinced that it must be a vapor lock, and so after replacing the fuel line and insulating it to insure it wasn't touching the coolant hoses in any manner and making some small adjustments to the carb linkage going to the secondary it started running great again today. Then whenever i tried to bring it out of gear and put it into neutral, it got stuck and I was unable to shift into neutral or reverse. So I checked back at the cables and pushed them around a little and had my friend try to shift into neutral and then it went into neutral and I could shift into reverse and forward again, however the engine sounded like it was missing out at times and almost like it was going to die. So my friend got out to get the trailer and I decided to see if it was still running great while waiting for him so when I gave it full throttle - it cut out and lost almost all power again just as it has been doing intermittedly all season thus far,however now I had no problem with it sticking in gear. I must mention however,that when it does lose power and I have to pull the throttle back to get it to start running well again, that the engine never completely dies, but rather kind of "diesels" like a car that won't shut off when the key is turned off does sometimes, until I pukll the throttle back and then it regains all it's power (at the reduced throttle and rpm's). I am very frustrated because it does not do this EVERY time, in fact as I stated earlier it was running GREAT at full throttle for a good 10 -15 minutes before we reached the boat ramp and I found it was stuck in forward. Could the shift assist module be the culprit here? Since I have replaced almost every other thing I can think of, I am beginning to believe it MUST be what's wrong. And also My shift assist module bears the number 982-749 T9 8 cyl. and in the iboats catalog for engine parts doesn't have a listing for that exact replacement part. Any one know if the replacement parts listed would be compatible with the part number I mentioned?

 

[shdw2001h]

Re: could engine cutting out at high rpm's be shift assist module?

if it was me I would start looking for water in the gas tank and change the fuel filter, dump the old filter to see what is in it also get some gas from the lowest point in the tank and see if it has water in it. try running the motor from a gas can and see if it clears up. if it does clear up you might have a fuel problem. I am not sure if you have one, but you may also have a antisiphon valve on the gas tank were the fuel line is connected, if that is bad it might case the same problems. I hope this helps.

 

[taxijim]

Re: could engine cutting out at high rpm's be shift assist module?

Thanks, yeah I neglected to mention in my post because it was already so long winded, that I have done those things, even installed a new water separating fuel filter AND siphoned out about 20 - 25 gallons of gas into 5 gallon clear glass water bottles to observe the condition of the fuel. Did this at the onset of the problem and I got the fuel from the lowest point by attaching a hose to the fuel line output nipple on the fuel tank itself. The 1st 5 gallons DID have about an inch of water in it, but this was before I replaced the rest of the fuel system including carburetor, in fact the fact that there was water in the fuel played an important role in my decision to replace it. however, subsequent checks have found nothing but good slightly amber colored fuel without water. Also checked the filter right after installing the new filter and there was no water or other contaminates that I observed. Replaced the filter anyway. Not sur about anti- siphon valve that's a new one to me. I do know that my tank has a vent coming out of the side of the boat with 2 large holes in it that when filling the tank up will begin to spew fuel out when I get close to full, and it is working properly as far as I can tell so that leads me to believe that it couldn't be getting a true "vapor lock" as in not being able to "breathe" because those holes in the vent are each about the size of a dime. Just to be cautious though, I put fuel stabilizer/ water remover in amounts enough to cover the amount of fuel in my tank just in case.

 

[shdw2001h]

Re: could engine cutting out at high rpm's be shift assist module?

the antisiphon is connected to the tank, it is a barbed fitting that the fuel line goes on. but I am not sure if your boat would have it. is there a fuel filter built in to the carb? did you check the screen on the end of the tube that goes in the tank? could be very dirty.
check you grounds, could be loose or corroded. and for any loose or broken wires. have your battery(s) and alternator tested, the battery(s) might not hold up under use or the alternator might not be charging.

check with crowley marine in colorado he deals with omc. he might have the part you want. I when through the same thing with my volvo, the things I am suggesting is what I did to fix the same problem.