out of no where the other when i stomped on the car the fuel pressure dropped off to about 45 pnds.. i immediatly came out of it and it shot right back to about 58 pnds. ever since that ive been monitoring it more closey and have found that at idle its at about 57 pnds, when it used to be 60pnds or better, even on a smooth acceleration i find it dropping to about 52 pnds now. for about a year now ive been running around on 7psi and 650rwhp and have had no problems. so i dont suppose that all of the sudden i would need a fuel system upgrade?? is it the guage? is it a bad injector? im stumped.. help me out guys thanks!!

 

First
Do you have a BAP installed? Make sure it is functioning and turned on high.

...What $ucks about the fuel systems in C6's is the fact that you cannot replace the fuel filter. You could have a restriction in the filter. If so you would have to change out your complete sending unit. That's what it sounds like your problem is if you have been driving for a year and it never dropped out before.

.....Chevy designed these fuel systems to last about 100k on a unmodified vehicle. So if the filter starts to get restricted there is enough pressure by the fuel pump to compensate for the loss of volume from the restricted filter. Even if the fuel pressure was down your O2 sensors will compensate even further ( up to 50%) adding pulse width to your injectors.

Now if your car is modified (which yours is)and needs much more fuel, which you do, the restriction/loss of volume will hurt you because your engine needs it, while a stock one would be OK. It will slowly get worse .

....That is the first thing I took care of when I made my custom fuel sending unit with the bigger Bosch fuel pump. Now I have a replaceable filter and 2 Bosch pumps to meet fuel demands. I also have a provision for a third pump if I ever need it.
They get clogged more frequent than you think. I use to change my fuel filter in my 92 vette every 5000 miles. I would always blow through them and they always had restriction.

Now, I don't know how many miles you have on your car, but I'm sure with the gas we get today your filter is slightly restricted. Around 25k is my guess is what you have...

I drained my tank when I changed my motor and you should see the black dirt/crud that was in there, I was quite shocked. My car has 8900 miles.

What you can do to compensate for your loss of volume is to add an external Fuel pump to make up the difference and then some. I'm making a system for a member in New York at the moment for his C6 Z06.
Andy at A and A Corvettes also has a nice add on system that would work for you .


Good luck
Perry
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i have 8,500k on my car, your absolutlycorrect it has been slowly getting worse every week. last week at idle was 60 now its about 57. so you recommend if its clogged dont even bother replacing it with stock, just upgrade the fuel system becuase there is a strong chance this will happen again?

 

also,about 3 months ago i added a meth injection kit, would this possibly have anything to do with it or no?

 

No, the meth would not drop your fuel pressure.
You cannot check your regulator either because it's on the sending unit in the tank.

If you are dropping off ,your problem is definitely in the tank.
You can leave it be and get what I told you above, a second pump.
That will give you the extra fuel you need and more to spare. Plus you don't have to worry about the factory filter any more.

 

thanks allot bro. ill be looking into this option.

 

As ambient air temps increase the fuel pressure drops. You will see higher fuel pressure readings in the cooler weather.

 

i see under 60 most of the time 57-59 . What is the correct amount 60

 

58 to 60 psi at idle is what we normally see. Bob

 

58-60psi is fine as long as it doesn't drop off at high RPM's to 45psi like above. If it drops to 45psi at WOT when you need it the most, it means your are running out of fuel and running on Fuel pump head pressure which is not enough to keep your pressure at 60.
That's where the second fuel pump is needed to help sustain your regulated fuel pressure
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What is the lowest it could drop off to under WOT and still not be dangerous ? 50 , I'm thinking ?

 

before i had the problem with the pump at WOT it never dropped below 57-58 pnds that i ever seen.. 50 is very low if thats what your seeing..

 

No - Thank God I'm not seeing anything below 57 as well - I just want to know what the trouble point is , so I know at when I need to attend to it if I see a pressure drop off

 

So you had a bad fuel pumo ?

 

Finally got it looked at. It was indeed the Fuel Pump. The car now runs 64psi at idle and drops to about 61 under WOT. Much better then before.

 

Did you have the FP replaced or go with a secondary unit?

 

new fuel pump . there isnt really any room to add a pump. so ive been told anyway.

 

Thanks for the reply.

 

Your fuel pressure will be OK for a bit with your new pump assembly, but the same thing will happen after a while ( about a year again ). Your fuel pressure will drop slightly when your fuel filter gets restricted again. As you accumulate mileage on your car you will slowly lose fuel volume due to fuel filter debris accumulation.(OK for a stock Vette) because it doesn't need the all that volume. Your actual fuel pump was fine.

When you have any kind of FI you are relying on static fuel pump pressure at high RPM's (none is being bled back in the tank through the regulator). That is why almost everybody with FI and a stock fuel system are seeing lower FP pressures at 6000rpm or above, the pump does not have the volume.

By the way, your sending unit installer was correct, the second pump will not fit in a stock sending unit. You have to mount it externally with it's own feed line, return line and regulator then integrate it into your OEM fuel system.

You could play around with your tune and increase pulse width where you see a drop off in fuel pressure and it will be fine for a while. That is the band-aid most people use. The correct way is to increase the fuel supply via 2nd pump.
At 650rwhp your OEM fuel pump is barely enough to keep your FPP at 60 psi, even with a BAP.
Do you have a FP gauge mounted in the car to verify you are not still dropping off at high RPM's? I would be willing to bet you still are...
If you have a gauge mounted on your rail, and are a little brave, look at it on the dyno as he approaches redline.

Keep a close eye on it ,it can be costly if you don't.
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