build thread for 2.8 carb to chevy tbi.

[cammeddrz]

my mechanic friend keeps saying that i need a 9-13psi fuel pump instead of the 90 psi fuel pump

he is wrong,

am i wrong in thinking that if the fuel regulator is working properly it doesnt matter what pump you have as long as it supplies enough flow and pressure at wot

you are right.

just because someone is a "mechanic" it doesn't mean that they are even capable of thinking outside-the-box, in fact I have found that "mechanics" have the hardest time thinking outside the box

the 90 psi pump is fine, I have used them with gm tbi several times......you wasted $113.00

Im starting to understand what my mechanic friend was saying about having to high off a pressure pump, in that the tbi wasnt designed for that, then again it isnt designed for a 84 bronco 2 but thats besides the point. even with the flaws as stated, she runs 3 times better and smoother than she did with the old carb.

i am quite serious when i say that both the trucks that Rico, and i drove to work today (he works 100 yards from me) have GM tbi units with 90psi+ pumps. not only that, mine has been that way since 2009! if your pump was the problem, it wasn't due to the max psi capability of it, it was for another reason

i can't say this enough:

IT WORKS F-ING FINE.........PERIOD!

 

[Lil-Pony]

Ok ok, i can return the pump, im going to have to figure this out then.

 

[dangerranger83]

Updates?

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[Lil-Pony]

Been having fuel starvation issues, rebuilt the tbi and it became much more reliable. But now after driving for more than 20 my fuel pressure begins to drop and once she is warmed up under heavy acceleration the pressure drops to 5psi im thinking the ign module is getting to hot again...
Other than that she runs beautiful, so much more get up and go!!!


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[cammeddrz]

if it has fuel pressure issues, I sincerely doubt it is because of the ignition module. it has no way of affecting fuel pressure, even if it was failed.

are we 100% certain that the electric pump has an adequate supply of fuel to it?

btw, I just barely looked at this thread after like a month. You didn't need to return that pump, it would have worked just as well too.

you are having a fuel supply issue, or a pumping issue. it is not electronic

what is the current setup your fuel system is running? so the fuel tank has an outlet on the top of it, where does it go from there? piece-by-piece tell me how your fuel system is constructed so we can figure out the issue

 

[Lil-Pony]

From the fuel tank i have a sending pump with a pre filter that i need to check. This pump also has a one way valve. From this pump it travels to a 17psi pressure pump in the engine bay. This pump i believe has no check valve since the pressure in the fuel line drops to 5psi "pressure rating of sending pump" when the motor is off. From here it enters the tbi and the return line runs to the modified explorer filler neck, reason i say ign module is b/c i have developed a rough starting idle and the pressure pump is turned on as the engine rotates via the ign modules signal to the ecm? Am i wrong?


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[cammeddrz]

there is a "crank" signal wire that should be attached to the starter relay, this is how the ecm knows you are cranking, and to send fuel into the engine, after it starts running the ecm senses it is at idle rpm and takes over. I just run my pump to a switch, that is attached to switched ignition, this way I can control when it is on, and off

next, so you aren't using the mechanical diaphragm pump to "suck" the fuel upward out of the tank? electric pumps aren't designed to do that, and after they get hot their already small ability to "suck" gets lessened, therefore less fuel even gets to that pump than is needed. also they wear out quickly when used this way. these are the reasons the tech article says to use the mechanical pump as the primary. being that it is a diaphragm pump, it does have the ability to "suck"

before we go jumping to that, you need to find a way to temporarily gravity-feed the high pressure pump, if you do that, and it runs fine, then you know the problem is up-stream of the high-pressure pump. if it still runs the same way, you know it is down-stream of the high pressure pump, maybe the regulator in the TBI, or the filter after the pump etc.

 

[Lil-Pony]

I under stand what your saying but i was fiddling with the distributor while the key was in run and when i rotated the distributor the pressure fuel pump kicked on. This is why im saying the ign mod has something to do with fuel delivery while the motor is running, im going to check my filter and swap in a know good pump, see if any thing changes then rig a gravity feed fuel system... Would a water bottle work?


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[dangerranger83]

When I changed my filter on my pump, the mr. Gasket 12s, the fuel coming out of the tank has a suction on it from the electric pump meaning it isn't having to suck the fuel since out has a siphon effect going on.

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[cammeddrz]

like i said, the ecm does take sparking as and indicator that it is running, since spark signal is often weak at cranking speeds, it also uses the crank input wire

a water bottle would work, but not for long, since it is a return style regulator, it will send whatever isn't used back to the tank, so it will drain it quickly.

in the past I have taken a long length of fuel hose, stuck one end into a fuel can (above the level of the pump, usually just set it in the back), got the hose siphon-started with fuel, and hooked it onto the pump. it will siphon-feed the pump from then on.

I drove my truck like 20miles home that way when the pickup hole in my tank got clogged

 

[Lil-Pony]

like i said, the ecm does take sparking as and indicator that it is running, since spark signal is often weak at cranking speeds, it also uses the crank input wire

Ok, would it be safe to hot wire the pump, whil doing this gravity feed thing? Ill use my gallon fuel tank, im guessing to also loosen the gas cap so pressure doesn't build up in the tank...


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[cammeddrz]

Ok, would it be safe to hot wire the pump, whil doing this gravity feed thing? Ill use my gallon fuel tank, im guessing to also loosen the gas cap so pressure doesn't build up in the tank...


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just make sure the pump can be switched off somehow. your fuel tank has a ventilation system, no need to loosen the cap.

 

[cammeddrz]

any update???????

 

[Lil-Pony]

Havent had time to jack with anything been busy rebuild this shed for my grandma



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[Lil-Pony]

----update----
VIDEO
the video shows, if you cant hear me say it, that ive hot wired the fuel pump and its still doing this which either point to a bad fpr which was just rebuilt. a defective fuel pump, or fuel delivery issues... im going to try to set up a gravity feed system today or tomorrow, and check my filters