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Category: Chevy
Satisfied Customers: 26417
Experience:  ASE certified tech ADVANCED LEVEL SPECIALIST. Wisconsin certified emissions state inspector
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98 Corvette: instantly..crank..Fuel pressure check indicates..loses

Resolved Question:

My 98 Corvette has always started instantly. It now intermittantly takes 7-10 seconds to crank. A Fuel pressure check indicates that the system sometimes holds pressure indefinitely, but sometimes loses pressure which then takes the 7-10 seconds to run fuel up to the engine. Have replaced fuel pump and seals, charcoal canister, gas cap, checked crank and cam sensors. Seems to have a pinhole leak somewhere to lose pressure. Currently trying die but no signs of a leak yet under the light. Sometimes will take the 7-10 seconds when hot, but by morning starts instantly. Other times the delay occurs hot or cold. Tried different fuel rails and injectors, no sign of leaks from that end. Zero problems with car, except this one. No codes when scanned. Have heard 98 system was different than later C-5's.
Submitted: 5 years ago.
Category: Chevy
Expert:  AMEDEE replied 5 years ago.

You did not mention anything about the fuel pressure regulator. The regulator could be leaking fuel causing the fuel pressure to drop down causing your long cranking condition.
Customer: replied 5 years ago.

I'm sorry, I don't know where the regulator is located, car is at the shop. Would the leak from the regulator be an external, visable leak? We're not detecting a leak of any kind or with dye.. I assume it has a fuel regulator, correct? I ask that because i thought i heard my mechanic say he was thinking about adding a fuel regulator, but he may have said he was thinking about adding a fuel pressure guage in the line because he's had gauges on it so often. Was thinking about trying to temporarily block off the return line to the tank. Idea being if fuel did not flow back to the tank it may indicate the problem was in the return line. Been chasing this problem for awhile, been to several LS/Corvette shops in Orlando. Was smelling gas toward the rear while cranking, changed the charcoal canister and smell is gone, but still loses pressure after sitting around awhile.

Expert:  AMEDEE replied 5 years ago.

The fuel pressure regulator is located on the fuel rail. If it leaks fuel, it will leak fuel into the line going to it.. you wont see fuel leaking out externally.

I would agree.. it might be a good idea to pinch off the return line at (rubber part) to see if the fuel pressure continues to drop down. I think you are very close to the problem especially if the fuel pressure is dropping down like you are describing.
Customer: replied 5 years ago.

If we pinch off the fuel return line and the problem stops, the next question would be what's wrong with the return line? Is there a valve in the return line which is supposed to close so the fuel won't return to the tank? I believe the return line is just one line most of the way back to the tank(s), there are two plastic tanks, but then the line branches out into 6 lines. If pinching off return line doesn't stop the backflow, is there a valve on the line back to the pump?

Regarding the regulator in the fuel rail I now recall that, and remember someone saying the 'diaphram' can go bad. That has been changed if not the entire regulator. Been chasing this a year.

Expert:  AMEDEE replied 5 years ago.

Sorry for the delay!

That is correct! Two plastic tanks on this vehicle. However, the fuel pressure regulator should be checked and verified that it is not leaking before we go any further. If this checks out ok, then we need to determine if the leak is back through the Check Valve in the rear fuel feed pipe or through the FPR back to the tank. My experience has been this problem is caused by the check valve in the fuel feed line inside the primary fuel tank (driver's side).
Customer: replied 5 years ago.

Regulator checks ok. Check valve from the feed line was my first thought too, but we have changed the fuel pump twice. Does the fuel return line also have a check valve so fuel can't drain back via return line?

You may be onto something big... I thought the check valve was part of the fuel pump assembly. You referred to it above as in the 'fuel feed line', as if it was separate from the pump, and more of an inline check valve. If that is the case, we probably haven't changed it. If it isn't part of the fuel pump how do we locate it, and does the return line have a valve too? Seems to be draining back to fuel tank in one direction or the other, and there is only so much it could be, feel like about to hit it.

Expert:  AMEDEE replied 5 years ago.
YES.. there is a separate check valve. Chances are this has not been replaced. You just need to get in there and check the fuel system and parts and see what has been replaced and what has not been replaced. Hands on repair will be your best bet. Once you see it you will understand what is going on.
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