Warp Factor

Several of us are having the same problem. We have the same systems others are using successfully at about the same horsepower, but fuel pressure will drop as low as 30 psi after driving for a couple of hours when the pump and fuel get warm.
Pumps have been replaced multiple times with no improvement. Same with fuel filter/regulators.
I realize I could go to a bigger pump (Bosch) or run multiple pumps and probably get around the problem, but I'd like to figure out what's going on.

Things as I understand them:

(1) It's normal for pump output to drop when hot, but others have adequate performance in spite of this.

(2) Fuel comes from the pump to a "Y", which diverts some to the jet pump in the passenger side tank, which keeps the driver's side tank full until there is no fuel in the passenger side tank.

(3) Fuel next goes through a check valve which maintains pressure in the fuel rails when the engine is off (for a while anyway).

(4) Next, it goes through the filter/regulator, which feeds a hard metal line running up the torque tube tunnel to the fuel rails (non fuel rail return style). Whatever the engine can't use is returned to the driver's side tank when pressure exceeds about 60 psi.

Question: What might be causing this problem that would be present on some cars and not others?

Could the "Y" supplying the "jet pump" have too large an opening and be bleeding off too much fuel? And how would I know? (manual has no specs)

Could the the jet pump not be working properly, allowing driver's side tank level to be low, allowing the pump to run hotter than normal?

Could either the "Y" or the check valve have a manufacturing defect, such as molding flash protruding and restricting flow?

Could some of the hard metal fuel lines have been "tweaked" a little on the assembly line, causing a partial kink and reducing flow?

Anything else I haven't thought of?

Or better yet, does anybody know what's causing our problems, or has anyone fixed a similar problem, staying with a Racetronix or LPE pump with Racetronix harness and maybe a BAP?

Thanks.

0EG@EnglandGreen

Has anyone looked at the in-tank sock (the filter on the pump itself) for possible blockage? The Racetronix kit does not come with a new sock, I do not know if the LPE pump does or not.

I am one of the "lucky" ones that sees steady 62psi dropping to 58psi under heavy boost even in very hot conditions. This is with just a Racetronix - KB BAB is not hooked up yet.

Like you, I am puzzled by this seemingly random pressure drop in only some cars.

Warp Factor

Already tried the LPE which included a new sock.

0EG@EnglandGreen

Now I am really stumped....

Z_Rocks

I guess this is one thread that I'll keep my eyes on.

IM QUIKR

Ditto here. I have 65 cold pressure and 58 hot. Has anyone tried to use a 97-98 filter and then use an aftermarket regulator just off the filter returning the fuel back to the tank. This would allow you to adjust the pressure up a little to 70# to compensate. Then there would be no need to run a return line all the way back from the rail. It would take a little customizing but surely it can be done. If I had this problem that's what I would look at doing. The filter with the built in regulator is produced by the lowest competing bidder. I would think the quality is questionable.

Tony @ MPH

Cheers for trying to tackle this one and figure it out. I could never make sense out of it myself. My input is below...

The orifice is tiny, tiny, tiny. I would almost just say "replace it and see", it can't be an expensive part... it's just a little plastic piece.


Possible, however... AT LEAST as of FFS and likely before, there are two level senders, one in each tank. The PCM will throw a code if the driver tank drains before the passenger, and the gauge will go to zero.

Again, possible... and I've seen on various cars from year to year GM will use more than one manufacturer for some pieces. I wonder if there is a way to trace back the manufacturer of the plastic fuel pieces, jet pump, etc. and see if the cars that fail have something in common?

Good thought -- I would note that after I added braided stainless in place of the factory hard lines my 2002 still had fuel delivery trouble.

Let's keep this thread going, if someone can figure out why some cars can see 600rwhp on factory components + a BAP and others can barely hold 500rwhp, that will save a bunch of guys on unneeded significant upgrades. In my case I want to take my Z06 to around 700rwhp so I love my ECS system, but for those that don't want to go that far it would be nice to drop a BAP in and forget it!

xtream1

Maybe it's not that some componants (like the pumps) are substandard but rather that the majority are above spec with some having exceptional output.

As for the venturi, orafice, hard lines, factory rails, and 'Y', I had fuel issues for a long time which I eventually solved. But, for the record, I am using all of these stock componants. So I'd have to say that the problem lies elsewhere.

From what I found the pump is the issue as it's expected to push the volume required along with the distance to the front compounded by heated fuel and bends in the line.

leojnknsC5

Could the pressure drop be the result of voltage variations to the pump? If you could hook up a voltage tester to the pump and drive teh car around until the pressure drops, you could find out if it's teh result of voltage dropping. Then at least you'd know it's not the pump.

Racetronix harness and KB BAP cured pressure drops

QuickSilver2002

I think the root of the problem is some type of pump cavitation, but I don't know what the solution is.

Do you notice a difference in the sound of the pump when this condition starts to occur?

Does the problem totally go away when you put in a fresh tank of cool gas?

Have you attempted to measure the temp/pressure/vacuum of the fuel tank?

I may still have the same problem with mine, but it has been a while since I have ran my car for more than 1hr on a hot day.

peter pan

I had my car out yesterday for well over an hour temps 100 and at the end I did some WOT upto 4th and my fuel pressure was a steady 58 under WOT. I did convert my system to the 97-98 return style with a LPE (new sock, filter) and KB BAP during my build up and we set my system up for boost reference and I have had no issues and I pay more attention to my FP than boost becuase of all the problems I have been hearing about. I have the factory lines and rails, this is always a concern for me

IM QUIKR

Whatever happened to the Racetronix return system? It looked like it had a lot of promise. Did it just die or is it still in developement?

Warp Factor

If the problem was pump cavitation, wouldn't it get worse for those running a boost a pump?

Haven't noticed a change in sound, but the low pressure condition only occurs close to WOT, so I'm not sure I'd hear a change. Haven't noticed a change at cruise.

Problem is significantly improved with fresh cool gas.

No. What, you're going to make me work?
I was hoping you and diynoob would solve this for me!
Interesting thought about vacuum in the fuel tank. A malfunction of the evap system, perhaps? Might mess up calibration of regulator, or cause cavitation, or at least make the fuel pump work harder.

0EG@EnglandGreen

That's a valid thought. I have disabled my Evap system (don't ask) but that still would not account for my rock solid 58psi pressure with just a Racetronix at 10psi of boost.

Z_Rocks, for example, has both a Racetronix and a MSD BAP, and his pressure drops like a rock at WOT. And he is only pulling 5lb of boost. (stock Evap system, stock fuel system otherwise)

While CajunDude with just a Racetronix and KB BAP, holds 58psi solid at 14.5psi of boost. (stock Evap system, stock fuel system otherwise)

This is a great thread. I'm hoping the CF Tuners will chime in - along with RoadRebel and others

QuickSilver2002

I forgot you guys were talking about the return at the filter setups. I found that system to simply not work at all. I swapped mine over to a return system and with no other changes to the pump... the fp issues went away completely (for about 2 years).

LPE also found the same issue with all of their TT packages and installed the return at the rail style system as standard equipment.

I'm not saying that a return at the rail will solve everyone’s problems, but I think it is the most logical place to start.

Warp Factor

I can see how the rail return would eliminate any pressure drop between the rear-mounted regulator and the rail, but I don't know if it would cure the "drop like a rock" (to use EG's words) syndrome that a few of us are experiencing.
The drop isn't progressive with fuel demand. If it was consistant and not temperature related, we could just incorporate it into the tune. It's progressive up to a point, and then it just tanks! I can have 50 psi at 6500 WOT when cold, 50 psi @ 4500 rpm when hot, but see 20 psi with quick stabs at 6500 when hot. It's as if fuel pump capacity has been exceeded. But plenty of people run 500 plus horsepower with the same (non rail return) fuel setup without running into this problem.
What's different about the cars where this doesn't work?

0EG@EnglandGreen

It's not model years or RPOs, I know that much

My car - 2001 Coupe - works
Z_Rocks - 2002 Z06 - doesn't work
CajunDude - 2002 Coupe - works
Stangkiller - 1999 Coupe - works
StuzVette - 2001 Coupe - works

Skunkworks

Depending on year the “Y” connector can be slightly different ranging from external to internal (late model system). The opening is small say 0.030-0.040 as a guess, although I never measured.

Bad fuel can but this is very remote mess up pump for a while.

A vacuum can and certainly will mess up pump performance, NPSH (net positive suction head) is critical to all pumps and as this falls off so will peak flow. Also keep in mind pump is likely wearing out faster if cavitation is occurring. It will chew up even stainless steel (seen it numerous times) a pitting can be observed very easily.

Maybe check voltages and BAP operation.

Good luck,
Mike

Tony @ MPH

My symptoms mirrored yours exactly Warp Factor. I can verify however that the problem was not vacuum in the tank -- I disconnected my evap so that the tank could suck fresh air whenever it wanted as a trial and the problem persisted.

As you noted it's not just a small drop, it would drop like a rock to about 40psi, consistently, and stay there.

exploder

does anyone have an exploded diagram of the ffs system??? I think it would be helpful. Also, if you remove the hoses to the evap system do you need to cap off the old fittings. Is there any reason to try this? I have the ECS system and I still have a slight pressure drop and I am trying to figure out where it could be coming from. I fixed most of the problem by ditching the factory feed and replacing it with -6 stainless. I now drop from 60psi ro around 52psi at WOT and 6500rpm. Air fuel stays constant due to tuning, but fp still drops more than I would like. I am making 660whp. FP drops like you guys were saying after about an hour of driving to 58psi and holds until i get on it again. My life sucks...I cannot figure this out.