Running rich after about an hour

[rexinsea]

Intermittent problems can be the worst. Here’s my scenario – Mercuiser 350 Engine (315 Horse) Electric fuel injection, electric start. Just north of 600 hours on a 1995 engine. Last Saturday I took a ton of water over the bow with a huge wake. We ended up with about 2-3 inches of water in the bilge. Was close to the dock and got in no problem. Don’t know if that is significant but thought I’d mention it since water seemed to make some other engines run rough on other strings her. Re-launched and skied the next morning. We got 5-6 skis in (about 75 minutes of run time I’d guess) and all of a sudden we started running very rich. The engine was surging and we could hear a hissing sound at idle. Oil presser is 20 at idle 40 under load. Temp is around 170. Volts at 14-15. Otherwise, all normal in the gauges. Went to the mechanic, he suggested checking if there was water build up in the distributer cap. There wasn’t but it was loose. We tightened the distributer cap back down and went for a 30-45 minute test run on Monday. No problem. We skied today and after about 60-75 minutes the same thing happened. Intermittent rich gas. Whitish smoke, gassy smell. Surging engine but all gauge vitals read normal. The symptoms would come and go.

Swung by the mechanic. He thinks it might be a sensor of some kind but does not know which one. I’ve read here other rich running Mercuriser 350 engines it was bad sparks.

We had all new fuel injectors, new fuel filter, new sparks etc last August. I’m guessing we are 15 hours or so into running after the refreshed fuel system
Do you all have an opinion on what we should try next.

[River Runner]

Check fuel pressure. Possible vapor lock due to low fuel pressure????

[rexinsea]

Check fuel pressure. Possible vapor lock due to low fuel pressure????

How do I check fuel pressure?

[River Runner]

Im assuming its TBI??? There should be a schrader valve there to measure fuel pressure. For MPI its usually on the fuel rail. (You need a fuel pressure gauge.)

[lakebum]

My 97 tige was running rich and acting lije yours, it was the temp switch, my boat has two of them, one to the dash gauge and one to the computor. the one to the computor was bad, so the computor thought that the eng. wasn't up to temp.

[rexinsea]

Temp switch huh? OK - I'll check that out. I've also heard from people around the lake it could be O2 sensor. It's like chasing ghosts. Anybody else have an idea. thanks to both Lakebum and River Runner for some answers.

[River Runner]

Since you had most of the fuel system components replaced do me a favor and check the fuel line routing. My guess is it may have been mis routed(by accident) and getting too hot. If so re-route the fuel line.

Reason being your symptoms only seem to occur when hot from what you have stated. This leads me to think vapor lock. You could run the boat hard with the engine cover up for 60-75min and if it didnt act up you would have your answer. My

[rexinsea]

it turns out we had one fuel njector go bad. So now one whole side of injectors has been replaced. We also put in new sparks, fuel filter and a MAP sensor. Near as I can tell the fuel lines are running straight but I'm no expert. It does appear to run smooth now in test runs. If the winds die down here this weekend we'll bring it out for some skis. Anybody else have just some fuel injectors go bad? What could be causing this? Northlake Marina here in Seattle says they are not sure why we just had one go bad.

Thanks for the replies above. I really do appreciate it.