Jamesp
Member
have 1991 corvette won't hold fuel pressure, could use some help.
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1991 Corvette Won't Hold Fuel Pressure
- Thread starter Jamesp
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Welcome to the Corvette Action Center!
I've moved your thread into the C4 Tech forum for greater exposure.
I've moved your thread into the C4 Tech forum for greater exposure.
Hib Halverson
Technical Writer for Internet & Print Media
have 1991 corvette won't hold fuel pressure, could use some help.
Well, there are a number of reasons why your '91 won't hold fuel pressure. There also is a specific way you need to test fuel pressure.
Lots of information is available in a factory Service Manual. CAC sponsor Zip Products sells them. Once you have the manual, look in Section 6A for information on fuel pressure testing and fuel system diagnosis.
DonB
Well-known member
I agree with Hib. The FSM is the best resourse. The fuel system is complicated and there can be numerous reasons to NOT hold pressure. First is to determine where the cause is.
You could pull the spark plugs and if any are wet. That could indicate a drippy(non-sealing) injector, bleeding down in that cylinder, a bad connection or a multitude of things. Also try taking the vacuum hose off of the fuel regulator. If there is gas in it, the regulator diaphragm is probably ruptured. These are both serious issues and need to be fixed NOW!
These are only scratching the surface. There are many reasons. Get the FSM and follow the diagnostic flow chart. Guessing will only cost you money and aggravation.
Corvette Central, another of our sponsors I believe, also sells the FSM on CD.
You could pull the spark plugs and if any are wet. That could indicate a drippy(non-sealing) injector, bleeding down in that cylinder, a bad connection or a multitude of things. Also try taking the vacuum hose off of the fuel regulator. If there is gas in it, the regulator diaphragm is probably ruptured. These are both serious issues and need to be fixed NOW!
These are only scratching the surface. There are many reasons. Get the FSM and follow the diagnostic flow chart. Guessing will only cost you money and aggravation.
Corvette Central, another of our sponsors I believe, also sells the FSM on CD.
- Thread starter
- #5
Jamesp
Member
I will check vacumm hose , did I mention when pressure falls off it goes fast 1 second or less
DonB
Well-known member
NOTE that if there IS gas in the regulator vacuum hose, you need to replace the regulator diaphragm IMMEDIATELY! This means you are sucking gas into a "DRY" intake system that is NOT designed to be wet. All you vacuum lines will eventually have gas in then and need to be flushed. This COULD be a dangerous condition!!!
At that bleed down rate something is leaking fast. Try also pulling the engine oil dipstick and smell it. Does it smell like gas in the oil? If so, you probably have a drippy injector and it is best to replace them all, while you are "in there." The Accel #150824 are a 24lb. injector that works nice in the stock L98. They sell for $279 a set. I would avoid rebuilt ones.
While you are there replace the regulator diaphragm(per instructions...which means do NOT use the diaphragm screws to pull down the regulator cap against the spring. You will rupture the diaphragm. C-Clamp it down or use a vice), reseal the fuel rail and use new injector clips too(the original ones usually break off when removing them from the injectors.) You will also need a"tamper-proof" #10 torx screw wrench to remove the regulator screws(Home Depot).
If it isn't the things I mentioned, and you can't see/smell a physical leak, at this point I'd have to lean towards the fuel pump. Even if it is pumping OK, there is a check valve to keep the fuel from bleeding back and all it takes is a minute piece of dirt to get in the check valve to cause that issue. It's been known to happen. The best recourse is to change the pump then. It isn't too bad job. The sender unit is under the rear gas door rubber neck insulator.
Keep me posted. Good Luck.
At that bleed down rate something is leaking fast. Try also pulling the engine oil dipstick and smell it. Does it smell like gas in the oil? If so, you probably have a drippy injector and it is best to replace them all, while you are "in there." The Accel #150824 are a 24lb. injector that works nice in the stock L98. They sell for $279 a set. I would avoid rebuilt ones.
While you are there replace the regulator diaphragm(per instructions...which means do NOT use the diaphragm screws to pull down the regulator cap against the spring. You will rupture the diaphragm. C-Clamp it down or use a vice), reseal the fuel rail and use new injector clips too(the original ones usually break off when removing them from the injectors.) You will also need a"tamper-proof" #10 torx screw wrench to remove the regulator screws(Home Depot).
If it isn't the things I mentioned, and you can't see/smell a physical leak, at this point I'd have to lean towards the fuel pump. Even if it is pumping OK, there is a check valve to keep the fuel from bleeding back and all it takes is a minute piece of dirt to get in the check valve to cause that issue. It's been known to happen. The best recourse is to change the pump then. It isn't too bad job. The sender unit is under the rear gas door rubber neck insulator.
Keep me posted. Good Luck.
- Thread starter
- #7
Jamesp
Member
jamesp
had this problem the other day didn't have no fuel pressure then found to have split short hose on fuel pump changed it ,then I had good fuel pressure for a while ,but then it started acting up again ,so maybe its a bad pump ,is the check valve in the pump
had this problem the other day didn't have no fuel pressure then found to have split short hose on fuel pump changed it ,then I had good fuel pressure for a while ,but then it started acting up again ,so maybe its a bad pump ,is the check valve in the pump
aklim
Well-known member
What hose did you use? There is a fuel rated hose that you should be using and not simply any old hose that fits. Get a kit from Racetronix that has the right screws, gasket, hose, etc.
DonB
Well-known member
Yes James, the check valve is in the pump. Use the at least the OEM A/C Delco pump with a new sock. Don't use cheap knock-offs. While the tank unit is out, check for dirt in the bottom of the tank and remove it.
The hose to use has to be "fuel injection" 3/8 I.D. hose. Ask for it specifically at the parts store and double clamp it with the clamps 180* offset. DO NOT use regular fuel hose or anything else! It isn't rated for this kind of pressure and won't last. Could very well burst and cause a fire. Fuel dripping on the hot exhaust is NOT a good thing.
The hose to use has to be "fuel injection" 3/8 I.D. hose. Ask for it specifically at the parts store and double clamp it with the clamps 180* offset. DO NOT use regular fuel hose or anything else! It isn't rated for this kind of pressure and won't last. Could very well burst and cause a fire. Fuel dripping on the hot exhaust is NOT a good thing.
aklim
Well-known member
- Thread starter
- #12
Jamesp
Member
went to racetronix site found good deal on pump set great price , will have to order it thanks for info on racetronix
- Thread starter
- #13
Jamesp
Member
fuel pressure problem
went and checked fuel regulator took vaccum hose off found to be wet with ,so I will replace regulator,hope it will fix it
went and checked fuel regulator took vaccum hose off found to be wet with ,so I will replace regulator,hope it will fix it
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