5.7L - Lack of Power / Surging / Ocassional Backfire

[Sman0624]

I wanted to get your opinions on this issue, it's driving me nuts.
Boat is a 1997 215 Express Cruiser Alpha1 Gen 2
Engine is a 5.7 L EFI with Delco HEI ignition.

Here's the issue. When I take the boat out it runs fine, strong starts and lots of power. Then after about 45 minutes of operation I would notice that when I give it anything over half throttle the engine surges, ocassional backfire through the throttle body (carb, the engine is fuel injected), just a total lack of power. When this happens the tach will jump all over the 4,000 to 5,000 range even though I know I'm only doing about 3,300 to 3,500 RPM. Note: When "cold" the engine runs fine and the tach does not jump.

After a pressure check of the electric fuel pump I found it was losing pressure and I was running lean (fuel starved which explains the backfire). After replacing the fuel pump the problem came back. I did the basics also, fuel seperator (fine, no contamination), anti-siphone valve, new plugs, cap, rotor, wires, electronic control module in the distributor yet the problem still occurs. All wire connections are clean and good.

I'm thinking a bad coil?? In the process of doing a compression check but I doubt that is the issue otherwise the engine would run bad all the time and not just after the first hour..correct? It's not bad fuel either otherwise the problem would be there all the time. I'm thinking electrical since the problem is worse after things heat-up.

What are your thoughts? Has anyone ever had this problem and if so then what did you do.
Thanks for your input.

 

[northern]

I had a bad coil on an engine. It worked well at RPM under 2000 or so, but when you put a load on the engine it would not provide normal power. No back fire just loss of power. Changed coil and allwas well.

 

[Alex D]

I had exactly the same thing last fall on my star board 8.1s engine. Started with rpm hunting, then after a while massive backfires at over 3000 rpm under full load.

My SR dealer/shop checked everything including compression check (@180 psi on all cylinders, so great).
The only thing wrong was the spark plugs. They even looked fine when the shop took them out but they had a row of similar spark plug problems lately and recommended replacement (OEM SR @ $10 each ... Ughhh!) .

Before you do anything else change them with new OEM plugs!

 

[fc3]

It's not clear if you fixed the fuel pressure problem. Have you checked the pressure at the rail when the problem occurs?

 

[bartlett]

I had a similar problem. I replaced everything. Coils can begin to malfunction when they get hot. This might explain your problem. But what fuel are you using? 10% Ethanol? If so you need to get a Starbrite or similar additive. Once I replaced the fuel/water separator and used the additive EVERY TIME my problem went away.

 

[Sman0624]

Plugs are NGK and have about 4 hours on them. This problem occurred in the past prior to replacing the plugs, actually new plugs made no difference but will look into.

Fuel pressure was check at the rail. Holding steady at around 29psi. I will check again.

Fuel is 10% Ethanol and both Starbrite and SeaFoam were added prior to storage. Fuel/water separator has about 2 hours on it. I emptied it to a glass jar, no water present.

I'm still thinking it could be a bad coil or maybe a bad shift switch. Will keep you informed when I have time to work on this.

Thank you all for your replies!

 

[brains06]

did you fix your problem? If so, what was it?

 

[Sman0624]

Haven't had the time to get into this yet, I hope to by this weekend but a new baby in the family tends to take away a lot of my free time. I will post back when I learn more.

 

[ultratiger89]

Check the rotor cap, mine became corroded and did the same thing. Definitely sounds like an ignition problem.

 

[Sman0624]

Just wanted to provide an update.
It appears the problem to be the shift interrupter switch. I connected an Ohm meter to the switch and monitored the switch state during boat operation. The Ohm meter was reading all over the map.
Ended up by-passing the switch with a paper clip and test drove the boat. The jumping tach and backfire disappeared. After installation of a new shift switch I drove the boat for about 1 1/2 hours with no issues.
Hope this kills the problem once and for all.

 

[Tail Chaser 661]

Thanks for the update :thumbsup:

 

[Sman0624]

Seems like a lot of people are fighting a common problem - "Boat lacks Power" so I thought I'd bring this topic back up for review.

It's now 2 weeks plus since I replaced my shift interrupter switch and the boat runs perfectly! No lack of power, no engine surge and no backfire. I've already gone through two 50 gal fill-ups and the boat couldn't be running better. Good luck to all of you who are experiencing similar issues. Hope this thread helps!