fuel pressure problems

I drive a 97 vortech supercharged z28. about a month ago the vortech inline t-rex pump died, my fuel pressure at idle used to read 40 psi and would go up on acceleration. When that pump died i just drove the car as is but making sure I didnt go into boost, and the fuel pressure stayed at 30 psi and would go up to 40 when i accelerated. About a week ago, the fuel pressure started dropping below 30 as i hit the gas and would go all the way to 20 psi and at one point went to about 10 psi and the car died. then it started and drove fine until last night when it dropped to 10 psi and then died and wouldnt start. the gauge reads about 0-5 psi of fuel when i turned the key, but the stock pump is definitely pumping as i could hear it. I got the car to a mechanic and he put in a new vortech t-rex in there, but the fuel pressure is still at 0 even though both stock and vortech pumps are pumping. He said that something is wrong with the primary (stock) pump in the tank and needs to replace it and to do that needs to cut my exhaust... I've very upset about this as i have a nice slp catback on there that i dont really want cut up :-( I just wanted to get a second opinion from all of you, do you think its the stock pump causing this? or could it be something down the line? like the FMU or something else?

Thanks everyone!

How reliable is the fuel pressure gauge? You need to verify the readings you're getting. If the stock pump really only primes to 5psi, and you have the FMU installed correctly, the in-tank is probably deceased.

Good chance you killed the in-tank pump forcing it to pump through the dead inline pump. Running the car with 20psi fuel pressure made no sense at all. You were only flowing 2/3 of the required fuel and could have seriously damaged the engine. Lucky its only the pump that died.

I've very upset about this as i have a nice slp catback on there that i dont really want cut up :-( Thanks everyone!

On a sidenote, if you do the "trapdoor method" and cut an access hole through the top, you won't have to worry about cutting your exhaust and dropping the tank from the bottom.http://www.taekwondoplus.org/z28/fuelpump.html

:confused:

The guy replaced both pumps and my pressure is still low and still dipping when i accelerate to almost 20, what else could it be? I spent $900 yesterday on replacing those pumps :-/ only have $200 left in my account..... :-/

quick followup... i disconnected the vacuum line from the fuel pressure regulator and the pressure jumps to 42 psi at idle, when i press gas at that point in neutral it dips down with each blip of the throttle. could it be the fuel pressure regulator?

The fuel pressure should not vary with the vacuum line disconnected.

Again... are you sure you have your FMU installed correctly?

We just had an endless series of posts over a 2 month period, from an individual who's blower motor ran like crap. After 2 months, he found he had the FMU in the supply line, rather than in the return line. The third response he got way back in November was "is the FMU installed correctly", and it took 2 months for him to realize it was installed wrong.

Just a thought.

yes, absolutely sure the FMU is installed properly, it has been untouched for about 20k miles, and has always worked perfectly in the past, unless something is wrong within that unit, the connection is definitely correct...

The fuel pressure should not vary with the vacuum line disconnected.

Again... are you sure you have your FMU installed correctly?

We just had an endless series of posts over a 2 month period, from an individual who's blower motor ran like crap. After 2 months, he found he had the FMU in the supply line, rather than in the return line. The third response he got way back in November was "is the FMU installed correctly", and it took 2 months for him to realize it was installed wrong.

Just a thought.

Im the 2 month guy. I tired everything before i found my problem. I was able to run the car with the sc belt off and it ran fine. I then disconnected the inline pump and all worked fine except for a slight fuel pressure drop. The car never made the boost necessary for the fmu to work so it is easy to check. Since you say the problem came about with nothing being changed something went bad. I would disconnect the sc belt and run it. I assume this is ok but maybe the vortech is different. I would also run it with the inline pump removed from the line. Mine takes a minute to disconnect it and plug the old lines back up. It almost sounds like a block somewhere. Maybe the filter. These are all free to test and a fuel filter is around 10 bucks. There is a way to check the fpr. Maybe someone else has that info to pass along.

mrmint69: my fuel pressure drops before I even hit boost... it drops on any load :-/ with the inline pump in the priming jumps to 43 psi, wihtout it, the stock pump would prime at around 20 psi and slowly climb to 30 psi after start. It definitely feels as though something is blocking the volume of fuel needed. The pumps are both pumping well and the frp is doing its job since with vacuum line removed i get around 42 psi on the gauge. the inline pump seems to be working very loudly, not sure why... but the old one did the same before it died. Now i have 2 brand new pumps on there and something is still causing this. I also did change the filter to be sure that wasnt clogging it, but same effect :-/ where else can there be a 'clogging' condition happening?

For what it's worth, if your inline pump is loud, it's restricted at least if not already shot. That would indicate to me that your in tank pump is creating the problem to the inline pump. My opinion would be to do away with the intank pump and only rely on the inline pump.

Just for laughs, to test if the noise in the inline pump is caused by a restriction of sorts. Split the connection to the in tank pump and feed the inline pump from a seperate source of fuel like a container held up high next to the vehicle. See if the noise diminishes. See also what the pressure does.

Just a thought

I had a similar problem on a mustang i was working on, took a long time to finnally figure it out It was the pressure regulator and vortec fmu