Logo
FULL SITE MENU

Mercruiser 57L engine backfires

S

smais

Guest
"Hello! We have a 23' Bayl

"Hello! We have a 23' Bayliner with a mercruiser engine which I think is 5.7L. 1998
We have a recurring, intermittent problem. After about 20 minutes running on plane at about 37000rpms the boat suddenly loses power, back fires and then there is a smell of gas. Temp is at 175 and oil gauge OK. If we wait a while we can get the boat to start again but as soon as we put any pressure on to get up on plane she backfires and loses power again. The mechanic serviced the engine - changed the impeller and thermostat, checked raw water flow, and checked the timing. When we complained it wasn't fixed he changed the fuel filters and found a small piece of loose silicone in the fuel line near the check valve. He figured taking this out would solve the problem - it hasn't! Any suggestions as to what he should do next - he doesn't know and we are non-mechanical so no help! Thanks"
 
"Back firing and losing power.

"Back firing and losing power.. check to see if the disrtibuter is loose, could be moving on you messing up the timing.. my piece of sh*t boat did it to me once..there is a bolt/bracket that holds down the distributer, may be a little loose.. just a suggestion, no guarentee thats it.. hope that helps."
 
New spark plugs? Plug wires m

New spark plugs? Plug wires may be crossed and miss firing. Does it idle smooth? Timing wrong?
 
I haven't been able to tal

I haven't been able to talk to the mechanic yet as he is out on a job. Thanks for these suggestions. The engine sounds smooth when we idle and most times goes for about 20 minutes on plane before suddenly losing power and doing its backfiring thing.
 
"yes,the mechanic said it was

"yes,the mechanic said it was a lean backfire -so he changed the fuel filters - see post above - but we still have the problem!!! any other ideas?
Thanks"
 
""After about 20 minutes r

""After about 20 minutes running on plane at about 37000rpms the boat suddenly loses power, back fires..."

Coil may be on its last leg; try a new coil. Borrow it from the mechanic."
 
"Sarah,
Coil would be a good

"Sarah,
Coil would be a good place to start, like Guy mentioned. Also the ignition module may be heating up, and failing. After it, or the coil cools down, it will run ok for a while."
 
"I have the same problem with

"I have the same problem with my 89 350, I ran it combined slowly and at 3500 for approx. 30 minutes under all circumstances and it bucked a couple of times and stopped. Elimated fuel problem, heat guage is good not overheating, going to try a coil. as suggested, baffels me"
 
Mechanic decided he was going

Mechanic decided he was going to cut a hole in the fuel tank to see if he could see a foreign body but when he pulled out some connection to begin looking for where the baffles were he found a sleeve had slipped off the end and dropped to the bottom. He found it was crushed so replaced it and said this was the problem - we took it out again but it still backfired. I reckon he must have caused it to fall off when he pulled the connection out and then crushed it when he pushed it back in. I have asked him not to cut a hole in the fuel tank as I think this is a very drastic measure. Now he is going to replace the fuel pump. Should he try emptying all the fuel by siphoning and then swish it round with some new fuel and siphon it out again?
 
You might want to bypass the b

You might want to bypass the boats fuel tank and temporarily hook up an auxilliary 6 gallon outboard motor type fuel tank to see if the problem is in fact fuel related.
 
Thanks guys! We`are going out

Thanks guys! We`are going out tomorrow to try out/check out your suggestions. Fingers crossed!!
 
"He put in a new fuel pump and

"He put in a new fuel pump and went out on sea trial and it conked out completely and he had to be towed home. Then, at last, he put in a new coil! She has run for 3 hours with no problems so i think it is finally solved. thanks for all your help. I wish he would have listened to your suggestions earlier!!! Thanks again!"
 
Back
Top