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Fuel in water

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kimosammy

Contributing Member
"New to the board...looks very

"New to the board...looks very active, good to see.

I have a 98 Caver Mariner 350 with twin 454xli's. They run excellent, seems there is only one problem.

Both engines while at idle, there is a light slip of unburned fuel coming from the exhaust. It has a heavy gas smell and the exhaust smoke is dark. More black in color and also has a heavy fuel smell. Engine temp all seems fine. It's runnning rich, I was wondering what might cause such a problem?"
 
"I would start by renewing all

"I would start by renewing all filters and inspecting all fuel lines and connections. This is most likely no your problem, but it's good to start with good fresh filters. Also, dump out the filters into a clear glass container and look for signs of water. It is also a good idea to do a spark and compression test and read the plugs. You will want to determine if this condition is being caused by all or just one cylinder.

It is possible that the throttle body is "dumping" fuel. Remove the flame arrestor and, with the engine at idle, look at the fuel flow into the venturi. Compare it to the other engine.

If you find this engine dumping or flowing noticeably more fuel than the other engine, you have to look closer at the FI system. You could have a faulty sensor telling the ECM that the engine is too lean and needs more fuel, you could have a faulty injector nozzle.

It would be a good investment to have a code reader. This inexpensive tool will read any DTC codes stored in the computer. Most ofter, conditions like this are not FI related but without this tool you can not tell. In fact, your engine should have one built in. Look at the blank cap on the engine harness up on the intake manifold, you might already have it.

Check these items and let us know what you find. This will lead to your answer.

Good luck,
Rick"
 
""I would start by renewin

""I would start by renewing all filters and inspecting all fuel lines and connections. This is most likely no your problem, but it's good to start with good fresh filters. Also, dump out the filters into a clear glass container and look for signs of water." = Done

"It is also a good idea to do a spark and compression test and read the plugs. You will want to determine if this condition is being caused by all or just one cylinder." = In this case, the engines run perfectly so I haven’t considered this approach.

"It is possible that the throttle body is "dumping" fuel. Remove the flame arrestor and, with the engine at idle, look at the fuel flow into the venturi. Compare it to the other engine." = Even for EFI? And both do the same thing.

"If you find this engine dumping or flowing noticeably more fuel than the other engine, you have to look closer at the FI system." = Both engines are doing the same.

"You could have a faulty sensor telling the ECM that the engine is too lean and needs more fuel, you could have a faulty injector nozzle." = I think it’s a faulty sensor, specifically the MAP sensor.

"It would be a good investment to have a code reader. This inexpensive tool will read any DTC codes stored in the computer. Most ofter, conditions like this are not FI related but without this tool you can not tell. In fact, your engine should have one built in. Look at the blank cap on the engine harness up on the intake manifold, you might already have it." = Now this would be cool, I'll look for it."
 
"A MAP sensor is easy to swap

"A MAP sensor is easy to swap from the other engine so it's worth a try. Also, don't overlook the spark and compression test. That is the starting point for all undertermined promlems. If you page through the posts on this forum you will find plenty of cases where guys just started replacing parts, expensive parts, because they had a cracked distributor cap or a bad spark plug. Don't take anything for granted.

Keep us posted."
 
Update - while I'm at it...
Had injectors rebuilt, no change.
I'm leaning towards valve stems are a bit worn, oil passing through them out the exhaust.
When its warm outside and the motors are warm, it is unnoticeable, cold is another story.
Needs a head job…
 
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