It’s a 1999 7.4l MPI in a boat. Seems to have an injector sticking open. Doing the key on pressure test, it sometimes holds pressure at the rail when the key is flipped off. Other times it goes right to zero.

Sometimes it runs smooth then a minute later it’s running rough and dumping raw fuel in the exhaust.

Anyone ever have any luck pouring in something like a few bottles of Techron or Seafoam and bringing an injector back to life?
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6-4 UPDATE - I’m not sure it’s an injector. It runs rough and weak. The entire passenger side plugs are fouled. I’m sure they were wet. The ceramics are black. The 4 on the other side are white. Each cylinder has its own injector in this MPI setup. Can one bad injector foul every single plug? Would this mean a bad ECM? It believe it is a MEFI2 system.

This message has been edited. Last edited by: Oz_Shadow,

Try Lucas injector cleaner. I’ve had some success with that.

Techron Injector Cleaner seems to work as well as any I have used

quote:

Originally posted by bettysnephew:
Techron Injector Cleaner seems to work as well as any I have used

This is the best I have used.

Gentlemen,

Fuel injector has a small electric solenoid that opens a passageway. This allows high pressure fuel to lift a small needle with a metal cone or ball away from a seat with small injector holes.

If the interior is compromised by large debris in the fuel the chemistry in the fuel injection cleaner will do nothing. The chemistry is to clean deposits from injector and intake valve that are caused by the fuel properties and the combustion heat.

When we find injectors stuck open we have to remove them and mechanically clean them using solvents and ultrasonic vibration.

Most of the time we have to replace the injector.

Agreed ^^^^^^^^^^^

I just went through this.
Tested with a fuel injector tester.
Had to remove manifold, fuel rail, replace 2 injectors, reinstall fuel rail, new manifold gasket, reinstall manifold.

Good to go!

quote:

It’s a 1999 7.4l MPI in a boat.

Big block Chevrolet? A marine engine may be different, but in a GM truck I'd look first at the fuel pressure regulator. Pull the vacuum line off and see if any gas drips from it.

My riding lawnmower had an rpm surging issue at low throttle. My dealer said there is probably an issue with the carb but he is concerned about taking it apart because if needs parts he may not be able to get them. He said he hates to do it but he used Mechanic in a Bottle in the fuel system. Guess what, the surging it gone.

It cant hurt to try a bottle fix. Double check the parts availability before getting into a tear down.

Sometimes fuel injector cleaner can help if it's not sealing well, either cleaning a deposit or the difference in viscosity vs gas can dislodge crud. It's a cheap & easy try and unlikely to cause any further issue/delay/misdiagnosis.
It sounds like your injector is beyond needing a little help, although 'goes right to zero (@ key off)' does sound like fuel pressure regulator issues at first thought.

I may attempt some Techron while I shop for a replacement set of injectors. Looks like it will be a remanufactured set if I can’t absolutely cross reference the injector. I suspect this is mostly due to sitting around unused for 6 months every year with a lot of green Stabil in the fuel. That stuff is kind of sticky. It has a fuel filter the size of a oil filter.

I’m going to pull the plugs today to see which cylinder is the problem child. I ran out of time and good weather yesterday.

The Merc/GM part # for the injector is 25180245


It’s basically a Chevrolet engine but the regulator is a little different. The rail mounted one does nothing. It has a second one at the fuel cooler. It seems to hold pressure when running.

If the can of stuff doesn't work, you'll only be out of $12.

If it does, you would have saved the cost of the repair (of which $12 may be a rounding error).

I don’t know how much new injectors cost, but a racing friend of mine runs an injector cleaning company - I’d trust him to get it right. https://www.injectorpulse.com/

Injector Pulse does good work. Before and after reports are sent.

If you all are curious if premium fuels can clean your injectors, they surely can. My employer supplies two international oil companies with fuel additive chemistry, and our tests show cleaning of both intake valves and injectors. We have been their chemistry supplier for decades.

If it is stuck open with the long term additive stabilizer, then a chemical solution could solve your problem. Overdosing stabilizers can create deposits that are quite sticky. The internal valve cannot open or shut, depending, and your problem is created. If you can run the boat engine long enough, a top treat cleaning might restore the injector.

If I needed a fuel injector cleaner, I’d get a can of BG 44K. It’s always been sold wholesale, not retail, but any auto shop or mechanic could get you a can of it.
.

If I were going to try cleaning the injectors with a fuel additive I would find a way to connect the engine to a small nurse tank and send a concentrated mixture through them as opposed to dumping 16 ounces of cleaner in twenty gallons of gas. For example add the cleaner to one gallon of gas and run that through. If that doesn't work it sure wouldn't work being added to a bunch of fuel already in a large tank. If that doesn't work pull all the injectors and send them in for repair.

Don’t think the Techron is going to work. It idled rough but got up to full speed for a couple minutes even with a miss then it fell on its face. I could only get it up to 2k rpm under load and not back upon plane. Very noticeable rich exhaust smell and if it was on land it would have had white smoke. Oil in the engine is still new and clean. No hint of gas.

I hope it’s only the injectors and not the ECM. It’s not easy to test this design since the entire intake plenum covers the injectors.

Looks like this. https://terminalmarine.com/inb...i-marine-engine.html

I still have to pull the spark plugs to see which are wet.

It's extremely doubtful that any snake oil is going to fix an injector that's sticking open. Probably a bad spring in the injector.

More info posted.

quote:

The entire passenger side plugs are fouled. I’m sure they were wet. The ceramics are black. The 4 on the other side are white. Each cylinder has its own injector in this MPI setup.

A bad oxygen sensor or wiring issue to the oxygen sensor on that bank could cause that condition.