454 XL TBI rpm issue

[390Express]

I'm at a loss, and leaning toward replacing the fuel pump. Replaced the MAP sensor in the starboard motor, and it instantly ran excellent- perfect idle, perfect RPM, perfect acceleration. Let it come up to temp, no issues. I couldn't have been happier, thought I had the issue licked, and a perfect running motor. Shut it off, cleaned up, started the port motor, (which is now running great), let it warm up a bit, and started stowing things to get ready for it's end of the year journey to winter storage.

Started the starboard motor that had perviously been running great, and it ran great again, for about 4-5 minutes... then the check engine light came on, and it instantly started doing everything it was doing before replacing the MAP sensor - ran like hell, popped through the carb, wouldn't RPM up past 3k, ran like hell after 2k, and struggled to stay running at any RPM. Shut it off, let it sit, started it again, ran like hell. Let the motor sit for a couple minutes, turned the key on and off 4-5 times, ran perfect again for 4-5 minutes, then started running like hell. Shut it off cycled the key on and off 4-5 times, ran better, but had the check engine light. Usually when I start it no check engine light, then 2-3 min. later it comes on. I did take a couple videos of what it's doing, but you can only hear a bit and see the tach. Any thoughts?

I'm thinking that it's starving for fuel. I plan on putting a real fuel pump gauge on it (mine is a crappy Pittsburg gauge from Harbor Freight), and seeing what it does. I need to see what the fuel pressure is doing when it's acting up. Does anyone know a fuel pump replacement that is not the peirburg pump? I'm considering the Carter P5001. It's the same pump that Volvo uses on this style of their version of the same motor. The Carter pump is not a discontinued pump (the pierburg of this model is, to the best of my knowledge), and it costs about 1/3 the price. Open to other suggestions.

[bud37]

By your explanation, it sounds very much like electrical, ignition related ( popping back thru the intake can be a firing/ timing issue)....I had some new digital controllers do just that kind of nonsense ........a check of the fuel pressure would be a good start though , before you buy any more parts.....hard to diagnose this type of thing remotely.....good luck man...

[390Express]

Fuel pressure would read fine, but the pump was bad. I too took it off yesterday and a bunch of rust and gunk came out of it when I took it off. I think the water and alcohol sitting in the pump caused it to decay from the inside out.

Ditching the pierburg and going with the Carter pump that Volvo uses on their engine with similar efi... regretting making the switch. I thought the Carter pump would have npt fittings, but it doesn’t. It has a weird 3/8 - 24 thread on the outlet, and nothing fits the damn thing. Went to a specialty fitting store today, nothing. I may be machining a piece to thread and tap. What a hassle.

[jcoll]

"Fuel pressure would read fine, but the pump was bad"
Just curious about this statement. Was it a volume problem? When I've had bad pumps and low volume the pressure would gradually drop off. More load less pressure. I know those TBI units have had some issues with the spring and diaphragm inside the injector.

[390Express]

Source of the post "Fuel pressure would read fine, but the pump was bad"
Just curious about this statement. Was it a volume problem? When I've had bad pumps and low volume the pressure would gradually drop off. More load less pressure. I know those TBI units have had some issues with the spring and diaphragm inside the injector.

Mechanic explained that when a fuel pump gets rusted and corroded inside, it can coagulate and add bubbles to the fuel pressure. The fuel pressure will read fine, but the pressure in the line is gas and air bubbles, so the end result is that the injector spits out the air/gas mix, and the motor starves for fuel.

New pump has been a bitch to put in. The Pierberg pump is made in Germany, and the thread on the pump is 10MM x 1.0. The replacement pump has a head with a 3/8 - 24 thread count, and nothing seems to fit it. 3/8 - 24 is approximately the same size, but I can’t re-tap the pump. So now tomorrow I have to try to find a male 3/8 - 24 coupler... pain in the ass... should be back together by hook or by crook tomorrow. I’m tempted to put a 1/2 fuel line over top of the fuel pump nipple and hose clamp it... patience is running thin with it.

[bud37]

If it turns out your pump has been cavitating, make sure there are no restrictions on the suction side and good connections ( no air leaks ) , so you don't take a chance and damage your new pump.

[390Express]

Source of the post If it turns out your pump has been cavitating, make sure there are no restrictions on the suction side and good connections ( no air leaks ) , so you don't take a chance and damage your new pump.

I definitely went through and re-did all of the connections on the supply side, but always appreciate suggestions. It already had a new mainline from the tank to the Oberg, but the lines from the Oberg to the pump, and the pump supply and feed to the fuel water separator were old. I took them all apart, cleaned them out with mineral spirits, and reusable nylon pipe cleaners, and buttoned it back up tight.

Runs mildly better, but still having an issue. Mechanic says next step is to change plugs and re-set timing.

[bud37]

Source of the post

Source of the post If it turns out your pump has been cavitating, make sure there are no restrictions on the suction side and good connections ( no air leaks ) , so you don't take a chance and damage your new pump.

I definitely went through and re-did all of the connections on the supply side, but always appreciate suggestions. It already had a new mainline from the tank to the Oberg, but the lines from the Oberg to the pump, and the pump supply and feed to the fuel water separator were old. I took them all apart, cleaned them out with mineral spirits, and reusable nylon pipe cleaners, and buttoned it back up tight.

Runs mildly better, but still having an issue. Mechanic says next step is to change plugs and re-set timing.

Its a process, It will be interesting to see what the mechanic finds with the timing, keep us informed.

[Bentone23]

I am going through similar issues with my port Crusader 454 TBI. 10 psi at the fuel rail. I am suspecting crud in the fuel system. I am starting at the oberg and supply lines. Then onto return lines and fuel tank pickup and check valve in the tank. It is a process. I hope to get this worked out after the battery and charger system is resolved.

[390Express]

Source of the post I am going through similar issues with my port Crusader 454 TBI. 10 psi at the fuel rail. I am suspecting crud in the fuel system. I am starting at the oberg and supply lines. Then onto return lines and fuel tank pickup and check valve in the tank. It is a process. I hope to get this worked out after the battery and charger system is resolved.

Good luck, let us know where you get stuck. It may be a good idea to pull your fuel pump off. It only takes about 20 minutes. Harbor Freight sells some nice, reusable nylon pipe cleaners for around $6. Pulling the pump assembly off and cleaning those lines out with some mineral spirits made a big difference. The line that goes from the pump to the water/fuel separator had gunk it in for sure. Cleaned it out in 5 minutes, more than glad that I did.

Also, the fuel filter at the top of the block (the steel filter) is definitely worth looking into, as is a rebuild of the TBI. The TBI rebuild is easier than a carb. You can do it yourself in under an hour, and it costs around $50. It's pretty self explanatory, let me know if you need any help. I have a spare that I could pull apart and walk you through it, if need be.