Re L29 454 7.4 fuel fill low pressure!! Help!!
 

So I wasn’t able to get over 3500 RPM so when I came back in I tested the fuel pressure after I diagnosed everything else and I’m coming up with 29/30 pounds at idle and 35 at key on.

I removed the fuel, cool system, checked everything replaced the fuel pressure regulator, because the one I had was rusted out at the vacuum connection. replace the fuel pump check the wiring and then I put everything back and I’m getting the same. I also replace the filter on the fuel water separator. Hold pressure pretty well, so I’m not worried about the injectors leaking and I just had them all flow tested.

There was an intermittent issue at the relay, but I fix that.

Any help would be appreciated I’m buying beers.

Also, if anyone has a scan tool for this military, they’re willing to lend me or live in San Diego. Let me know.

Your injectors all passed and held pressure well? Ive almost given up on flowing/cleaning the l29 injectors and just started stocking new quality replacements because I almost NEVER see 8 of them even after cleaning, testing, etc that dont have a couple that dont leak or flow erratically. Have you tested the fuel pressure on the water, at wot under full load when it doesnt get past 3500?

pressure holds with engine off and drops but very slowly overtime. The injectors were flow, tested and cleaned and they flowed 1% better after cleaning so they were fine. The fuel pump is louder than the previous one because I thought the previous one was bad but I might just swap it back to the old pump. The original owner said he just replaced it last year. However, a lot of the things told me didn’t turn out to be true.

I’m getting 30 pounds right after the pump and I tested that by hooking up a fuel line to the outlet of the fuel pump and connecting the pressure gauge directly to that line bypassing the rail and got the same pressure.

It’s struggling to get fuel so my next step is to take that siphon out of the fuel tank and make sure that’s clean, but I have to put some PB blaster on there let it soak for a while and then blowback the line from the fuel water separator.

I removed all the fuel lines and blew them all out. They seem fine, and I replaced the fuel water separator filter.

I almost feel like pulling out the whole fuel system and mounting a fuel filter, adjustable, regulator, and fuel pump right on the firewall there.

Yes, I also check for air leaks, and once I bled off the original key from the gauge, there was no more air bubbles if I bled more fuel off.

what I’m hoping is there is something in between the fuel tank and the fuel water separator that I’m missing hopefully once I check that out and I can eliminate it but it’s just extremely frustrating.

The motor has two hours on it. I just put back the original equipment for the fuel system since the owner said he replaced the pump once I took it off I replaced the pump again and a fuel pressure regulator but again Still same issue.

Did it ever run right ? or did you buy it without a water test, is the fuel vent to the tank clear, have you tried taking off the fuel fill cap and retest fuel pressure.

I bought the boat knowing it had engine and outdrive issues so I rebuilt the engine and outdrive. Prior to removing the engine it had 42 pounds of pressure but only 110 pounds of compression per cylinder and that’s why they’re decided to pull the whole motor and rebuild it.

I did not take off the fuel cap or test to see if the vent is clear. Great ideas… I’m also thinking that the low pressure fuel lines from the fuel water separator to the pump and regulator should be replaced but I can’t find anybody that makes them and I’m not spending $500 a line. If anybody knows someone that makes fuel lines, let me know.

I replaced almost everything in the complete and all the surrounding parts.

One thing I did notice is that when I went from 1000 RPMs to 2000 RPMs, the fuel pressure dropped I don’t know if that means anything or not but I think it’s starving for fuel.

In neutral, it means little/nothing.
In the water under load, it does mean something.

got it.. makes me feel a bit better. I will check the vent line and the pickup tomorrow or early next week. The boy was sitting for a long time prior to me purchasing it last year and only ran a bit. Took out old gas put in new but could be something before the pump.

i wish they just had the pump etc on the firewall.

Hook up a remote tank to bypass tank and lines.

I planned on doing that pulling it off the tank and then throw it in a 5 gallon and see if I can run it that way. This way it bypasses the tank and pickup