mfp189

I've been in the process of ironing out some of the problems that have occurred after completing an engine swap with an Edelbrock pro flo 3503 system on it. My problem now is that the engine seems to get starved of fuel when it is driving after it gets warmed up. It will cut out and sputter until I let off the gas to a really light load, and the problem will go away entirely for a few minutes when I shut the car off briefly. I have considered various causes from the ignition/spark system and the fuel system, but these very specific symptoms seem to be stumping my ideas. My best idea is that the pump is going out but I would like some support before I buy a pump and realize It won't fix the problem and can't get my money back.

Today, I started the car up in the cold and let it run for about 45 minutes. I ran it so long because the fuel pump did not produce any whining and the engine would not cut out when held at a higher rpm range for a couple seconds, much like it would when the whining pump symptom comes around. Then after I let it run for so long I thought I'd move it back a few feet (I can't drive it because of snow, but it can be backed out of the shed some). Only a few feet out and I could hear the pump start to whine. I moved back and forth a few times and the whining became slightly louder each time until it reached kind of a peak. This is when the engine would cut out if I tried to get it above 2000 rpm at all. I shut the car off for about 10 seconds, started it up, and the whining was gone and it didn't cut out! This only lasted, however, for about a minute or two. So, what could possibly be the culprit here? It might actually be something with the fuel tank but would anyone have any more of a professional idea?
Now I'm fairly sure that nothing is plugged in the fuel system, however the injectors COULD be dirty. I don't believe that is the case because the car runs great until it was moved. Then I don't think much with the ignition system could be faulty because it sat there and ran just fine for almost an hour until it was moved. ALSO: the floor is kind of slanted, but now extreme so the tank would be dipping at a different degree of incline as I back out and move into the shed from outdoors.

The possibilities I'm not ruling out are: Fuel pump going bad, gas tank pickup bad or something with the tank or line from the tank, ooorrr something I haven't thought of.

Also I have moved fuel lines away from any hot spots like headers, and replaced the fuel filter. I have also driven it without the gas cap on, and the charcoal canister vapor line is unplugged so I'm ruling out the inability for the tank to breath.
Sorry for the long post! I'm just a guy with lots of time and plenty of thinking to do now that snow has come!

I have yet to perform a pressure test, but I will be able to soon. I'm just trying to figure out this problem in the case that it actually IS losing pressure. I'll be able to confirm that later.

Damon

You already tried the gas cap, which I was going to suggest.

Assuming your fuel gague isn't lying to you and telling you you've got half a tank when you're actually near empty, a bad pump sounds like a likely culprit. If they're noisy, they're almost always bad. If they're quiet, they could still be bad.

Do the fuel pressure test as a confirm. If the fuel pressure is dropping as the "cutting out" happens, it's almost certainly the pump. Don't know what pressure the (TBI-style??) ProFlow system runs at normally- might want to check the specs, but it should be well within spec under all conditions.

The only other thing I can think of would be a pretty massive voltage drop at the pump, greatly decreasing it's pumping capacity. (wiring issue) Just remember that a pump on it's way out can also load up the electrical draw and cause a voltage drop, so don't be too quick to assign blame to the wiring system if you see this happen. It could still be the pump causing it.

Tibo

iTrader: (15)

Fuel pressure test is where you need to begin. Check to ensure that you have a stable fuel pressure at idle, then rev it a few times and ensure that the fuel pressure is increasing when the engine is revved. If you could you would want to put a gauge on it and drive it under acceleration and watch the gauge to make sure it is not losing fuel pressure. If you have proper fuel psi and maintain it you automatically rule out everything behind the injectors. You can test the resistance of the injectors across the terminals and that will give you an indication of their electronics. Past that it is unlikely that most of them are dirty enough to give you this problem unless they are really old with a lot of miles on them.

Are you also making sure that the engine is receiving enough fuel from the injectors? Like you have the correct engine size entered in? You have the correct injector size programmed? MegaSquirt uses those and a few other variables as one of it's basic calculations, get that wrong and everything else will be wrong.

mfp189

Damon - My fuel gauge has lied to me all its life. Sending unit either needs replaced or the float is stuck. Anyways I put 7 gallons in it when I first got the engine fired up and that was on top of the maybe 2-4 gallons already in the tank. Definitely over half when it started having problems after first start up.

I know a guy who knows his stuff and can really help me with this probably on Sunday, he'll be doing the pressure test. The Edelbrock system runs 45-50 psi I believe, if memory of the manual serves well.

The voltage dump could be a possibility, thanks for that note! I'll check on it when I run it next.

Tibo - Like I mentioned before, the guy I know can help me out a lot with the pressure testing, so I can at least get that far. Thanks for the note on the injector testing. As far as them being proper for the engine, I got the whole engine with the system on it from a gm truck. It's a GM Goodwrench 350 crate motor, and I know the Edelbrock system is properly setup for that engine, tuning and everything. The whole thing has something like 40,000 miles on it. I'm still hoping to rule out the injectors as a problem after the pressure test, given the symptoms I'm getting.

Thanks guys!

Tibo

iTrader: (15)

So the engine and the EFI system were originally paired together and you are just transplanting them into your vehicle? If not I would really urge you to check the main parameters that your ecm is using.

mfp189

Yep, it was just a direct swap. Didn't disrupt anything with the original setup, and the tune is that which was originally used for it while it was in the previous vehicle. I don't have the best knowledge of the system yet as far as tuning it and changing spark/fuel modifiers properly, but I am getting a basic understanding of it. Luckily their are still presets saved for it that were used while it was in the other vehicle. So that's why I'm thinking it is definitely not a problem, other than any damage that may have occurred to the system during the swap, which I'm doubtful of.

Damon

What fuel pump do you have in it now? No 83 F-body came with a high pressure EFI-style fuel pump from the factory. In tank? Frame mount?

The factory installed a low pressure in-tank electrical pump on all F-bodies originally equipped with the L69 HO 305 carb motor. By now, almost all of them are dead as a door nail. If you leave a non-functional in-tank factory electric pump in there and then try to suck fuel through it with another pump up-stream of it, things never work out very well. It's just too much of a restriction. Still, even this "gotcha" shouldn't cause the problems you are seeing at such light throttle openings- barely off idle. This issues usually pops up when you dig deeper in the throttle than that.

Something's definitely amiss. Definitely do a fuel pressure test- you'll know real quick if your fuel delivery system is the problem.

mfp189

It's the pump that came with the system edelbrock 3594 and the car was mechanical pump previously so there's no intank pump. And the intake/return lines are proper sizes.

Damon

Like I said, IF the car was an original L69 305 HO carb engine car, there IS an in-tank pump IN ADDITION TO the block-mounted mechanical pump. Chevy did this to help eliminate hot-start vapor lock problems. If it's still in the tank and it's dead, it'll be a problem trying to suck fuel through it. Not likely to cause a problem like what you're describing, but once you get it running good it will be a severe restriction under heavy load/high RPM conditions (WOT).