Help Getting gasoline in the engine oil?

I have a 99 Malibu with the 325 Monsoon. I've had the injectors reconditioned , new spark plugs, the compression test was good , I even tried letting the pressure off of the fuel system when I was done. It starts and runs great, but after about 4 or 5 hours of running it gains about a quart on the dip stick. I thought I was a decent mechanic , but this one has me stumped. Thanks in advance for any help out there!

Does it have a mechanical fuel pump? I know cars have electric pumps in the tank for injection but not sure about boats. Chevy mechanical pumps had a problem leaking into the crankcase when the diaphram would get old and leak.

You need somebody very squared away on the tuned port engines. That isn't me but if I was going to guess...
There are a limited number of ways fuel can get into the oil...if it is really running fine but is dumping that much fuel into the oil, I would suspect an injector(s) is bleeding fuel pressure off into a cylinder(s) after engine shut down, like when picking up a skier, boarder, etc. Not necessarily when you are done for the day. I don't think you even have a provision for a mechanical pump on that engine. A vaccuum leak sucking fuel into the lifter valley via the intake tract would show a loss of performance, which you don't indicate you have.

Obviously, ya don't want to run this machine until the problem is solved, you are washing all the wearing surfaces with contaminated lubricant, and you will see some increased wear on the bearings, valvetrain, bore, etc.

If you know a good chevy tech, you might run this problem by one of them, there may be a service bulletin out on the engine, or one close to it via GM. I am reasonably certain the marinizers don't fiddle with the internals of the injection when they set the engines up.

The fuel delivery pressure is from a external electric pump. I took samples of the bypass water when I run it on land and didn't notice any raw gas in the exaust water. Then when I had it in the lake I would watch the water around the exaust, nothing noticeable. Now the puter is out of my leauge, maybe theres a sensor making it dump more gas in it at times? The fuel rail only has injectors on it, no diaphrams or vacuum lines. Thanks Sparky Jay and Army Dad for your input :-)

If something was causing the system to put too much fuel into the engine when it was running, I think you would notice it in a loss of performance, and maybe even a miss, because at some point the fuel mixture would become too rich for the O2 sensor to compensate for.

That is why I think maybe the injectors are bleeding off the fuel left in the rails when the ignition is off. No spark to burn it, the fuel runs by the rings and into the crankcase.
When you bleed the pressure off of the system at the end of the day, you are taking the fuel source away, but think of how many times you start and stop the engine during the course of a day, and how much fuel is in the system under pressure while the engine is off.

I think you have injector problems, or perhaps an electrical problem that is opening the injectors and allowing them to dump fuel with the key off. But I would bet on the injectors.

I am no EFI expert tho, so carry on! Please post the solution when you find it, I am interested in what the problem is.

Army Dad, what you are saying all makes sense.I did send the injectors to a service that reconditions and puts them on a flow bench tester. They said some of the spray patterns were off a bit, but they responded well to the cleaning. I have a GM guy with a puter analyzer coming over Saturday morning. He mentioned if the coolent sensors aren't working right it can throw other things out. So its worth a shot. I'll be sure and let ya know when I find the problem. Thanks again.

ArmyDad,

There are no O2 sensors on boats. O2 sensors can't handle wet exhaust. They have to heat up to a certain temp to work. The water in the exhaust would keep them too cool read properly. Other than that I think your on the right track with your diagnosis.

It sounds like you have an injector that is sticking open and dumping fuel into the cylinder when the engine is off. It may even be stuck open all the time so one cylinder would be running excessively rich.

You may be able to tell if a cylinder is running excessively rich by looking at the plugs or if the exhaust has black smoke coming out.

If it is an injector flooding a cylinder it will ruin that cylinder pretty quickly because fuel washing the oil film off the rings causes excessive wear on the bore.

Get it looked at right away and don't run your boat again until it's fixed. At least take the injectors back out and have the place that serviced them test them again.

Since I have all the oil out of the crank case , I thought I would try to keep pressure on the fuel line , by turning the key on here and there and let it sit over night , then in the morning see if theres gas in the bottom of the oil pan? I checked voltage at the fuel pump, when the key is off , there is no power. I'm getting ready to check the new spark plugs I put in , to see what color they are, I'll let ya know on that. Thanks Everyone! :-)

Army dad is right on. The injectors must maintain fuel pressure when the system is de-energized. My guess would be that you have an injector bleeding dowing into the motor when the boat is shut down. There are 2 ways to dx this. Start the boat with a fuel pressure guage on the rail, then shut down and watch the pressure. It shouldn't bleed down. If it does, then you need to pull the injector rail with the injectors attached and see which one is bleeding down. This is a fairly common problem and may not affect the spray pattern of the injector, or the performance of the boat.

On a side note... Stop running the boat like that. Having fuel in the oil is not only dangerous, but will cause excessive engine wear. Get it fixed ASAP.

Hey C.I.E that sounds like a great way to diagnose the injectors and fuel line. I wasn't sure if the injectors would stay in place with only the top attacted to the fuel rail. But I'll go for it, I did notice that after the power is turned off for a while, and I push on the fuel line pressure valve , it kind of just varley runs out slow. So I'll put a gauge on it. I did notice all the spark plugs look like there burning very rich, I can wipe black off of them and they smell like gas, I didn't taste them though lol Thanks everybody for the great advise !

Hey everyone, I put on a fuel line pressure tester today.... it jumped up to 40 psi and then within a couple of minutes it was down to 30 and then it slowed down but it finally went down all the way. Soo I have one or more injectors bleeding down. What really through me a curve was I sent them into Accurate injector service from Arizona and they checked them and said they were fine! Well I'm getting ready to get all new ones, soo I'm sure it will be fine now. Thanks again for all the input and help in the right direction ! :-)

Accurate Injector Service owes you a refund, and needs to add a step to their evaluation process.