Indmar Assault - cutting out

[LloydP]

I apologize in advance, this might be a little long...

My 21V has an Indmar Assault 325 engine. Never had any problems with it before this year. First time out this yer: when the engine has been running for at least 20 minutes, it will start to bog down - won't run over 2k rpm. It even backfires some. We thought it might be bad fuel, so changed the fuel filter, and replaced the gas. Still the same problem. Took it to my Indmar guy, who said he couldn't replicate the problem in the shop, and there are no error codes stored in the system. He suspects an electrical problem, and checked and tightened all the connections.

Ran it this weekend - same issue. Interesting twist...this only happens under load. If I push the transmission lockout button, it will run up to 4k rpm with no problem, but as soon as I engage the transmission, it will bog down at close to 2k rpm.

The Indmar mechanic has suggested that he hook up the computer to it while we are running it at the lake, and then see if he can figure out what might be happening.

Anybody else ever run across something like this?

Thanks.

[zalamander]

I had that problem with my old MC. I doubt if it is the same thing, but my distributor was frozen up (mechanical advance). It would idle like crap after running short time, and no power/intermitent power when towing, along with loud backfiring. I had the dist. rebuilt and upgraded to HEI and it solved the problem. You have an newer engine so may not be the same at all, but worth looking into. Make sure the springs aren't rusted up or broken.

p.s. I also did the fuel system flush, and even bought a new carb. before I figured out it was dist. related.

[LloydP]

Thanks. I talked to the mechanic this morning, and he still thinks it is electrical. He said he may try to replace the throttle position sensor, or the manifold pressure sensor (at least that is what I think he called it). He is meeting me on the lake on Sat. to try to figure it out. Can't ask for more than that!!

[zalamander]

Good luck! I wish I could be more help... I know how frustrating this kind of problem can be.

[Engine Nut]

Thanks. I talked to the mechanic this morning, and he still thinks it is electrical. He said he may try to replace the throttle position sensor, or the manifold pressure sensor (at least that is what I think he called it). He is meeting me on the lake on Sat. to try to figure it out. Can't ask for more than that!!

Tellhimto bring his fuel pressure tester along. FP should be 60 PSI.

[beast 496]

Ya, I suggest you check the fuel pressure also. More than likely a fuel pump problem. Al

[LloydP]

Thanks guys. He checked fuel pressure at the shop, and said it was right on.

[matts0246]

did you find out what the problem was, mine is cutting out and backfiring when i fill all my ballast and get it under aload.

[beast 496]

The fuel pump pressure needs to be checked at WOT. Especially at the time when engine is bogging. Fuel pressure at idle or not under load is easy for the pump to accomplish but at WOT the pump needs to flow much more fuel. Al

[LloydP]

The mechanic checked the fuel pressure on the water last weekend, and could see where it was cutting out. He replaced the fuel pump. Really happy to have such a great mechanic!!

He did go on a rant about gas with ethanol in it, and how bad it was for these engines. Said he never used to have to replace fuel pumps on 4 year old boats, but now it is routine. He suggested running marine Sta-Bil in every tank to avoid the problem.

Lloyd