fuel pressure problems

[Bruce Huey]

Could use help trying to figure out why my 86 can't deliver 35-40# pressure to pressure check valve. Have changed pump twice after replacing rail fuel filter. The car will run but surges badly, understandably. Have tried to plug return line which should put a lot of pressure to check valve but the best that pressure reads is 20#. The pressure regulator was changed after car showed same symptoms and ran fine for about 2500 miles before having the same problems. Could it be possible that the regulator has failed or is the regulator after the fact and shouldn't be the problem? Many thanks for any kind of suggestions. Bruce

 

[Ken]

Welcome To The Corvette Action Center Bruce Huey!

Did you change the fuel filters out at the same time the pumps were changed? The pump has a "sock" (filter/strainer) attached that should be changed when changing pumps, and there is a filter in-line below the passenger side, at the frame rail. You may even have two filters there because of a noise problem some C4s had with rattling in the fuel lines. I would suspect the filters before I would the regulator.

 

[BigRed]

Ken's right there will be a sock filter on the pump which you pbly would have NOT gotten just by buying the pump. (Later model GM's have em not early)

Next is follow the fuel line ALL THE WAY from the tank. Make sure you are not leaking anywhere.

Your going to run into the filter now...change it

Keep following the line looking for folds/bends/leaks/corrosion

Should reach the fuel rail now at the fuel pressure regulator. Check your pressure before the rail AND after you may find your pump is bleeding down and the regulator is fine OR the pump holds pressure but the regulator won't adjust.

Now follow the rail and make sure your injectors aren't leaking internally or externally.

Everything checkout? ok

Make sure your computer system is running good (scan it) Ok?

Verify your spark power. Ok?

Now heres the kicker that everyone misses, do you have Cat Converters? Make sure there is nothing stopping your exhaust flow via plugging.

Hope that help you.

 

[Bruce Huey]

Many thanks to Ken, Big Red and ZR-1 for your tips on my pressure problem. Will try all new suggestions as soon as I can get free. Also, will post solution or solutions asap.

Appreciate your help a lot.

Bruce

 

[Bruce Huey]

Sorry, C5d....didn't mean to call you ZR-1

Bruce

 

[Bruce Huey]

Update on my 86 with low fuel pressure....Pretty much tried all suggestions from members and still haven't solved problem of only 20# pressure after initial warm-up. Hooking directly from battery source to pump and sender unit still only produces 0 to 20 # pressure. Do have a strong voltage reference signal to pump. So now have sent for a new $400+ sending unit as last resort. Sure as hell hate throwing expensive parts at unknown problems but this is a last resort attempt. Will stay in touch.

 

[vettenick]

Hi Bruce!
Just a thought...What is your pressure when you turn the key to the "ON" position? Also, does the pressure hold, or drop down to zero? If it drops immediately, then block off the return line and recycle the key to the ON position. If pressure holds then the regulator is suspect. If it still drops, then either your injectors may be leaking, or the check valve in the pump could be bad. One other option could be the rubber coupling from the pump inside of the tank to the fuel line could be leaking.
One other thing, take a look at the vacuum nipple to the regulator to see if it's leaking fuel.

 

[Bruce Huey]

Thanks, Vettenick, for your input. Before we change the sender, I'll go through all of your suggestions that I haven't already looked at, especially the key recycling and rubber coupling leak when I can get back to the Vette. Appreciate your trying to help me and when this thing is finally figured out, I'll let you know.

Bruce

 

[rrubel]

When you're checking the pressure, are you disconnecting the vacuum line from the pressure regulator? According to my Haynes (and instructions with an adjustable regulator), you need to do this.

When you replaced the regulator, did you just replace the spring, or the diaphram as well? What about the seal under it where it meets the fuel rail assembly?
[RICHR]

 

[vettenick]

Bruce, just remember that you may have to cycle the key a couple of times in order to fully pressurize the system, especially if it's bleeding off. Just turn the key on for 2 seconds, turn it off for about 5 seconds, and then turn it back on.

Good luck!

 

[Eagle85C4]

You may want to read through the posts by 69myway as he was rebuilding "Frankenvette"
One of his posts provided info on the fuel rail...in that he was surprised to find there is an orfice hole on the input rail where fuel enters. It could be that a piece of dirt or something has plugged the hole and is not letting sufficent fuel through.
But as already mentioned I believe the strongest possibility is a leaky injector.

 

[Bruce Huey]

Again, thanks Vettenick and both rrubel and Eagle 85C4 for your input. In response...this fuel problem started about 15,000 miles ago. The first time was in the mountains. I limped into Denver and had fuel pump and filters changed. The 86 ran fine for about 10,000 miles more before losing pressure. This time had it towed to a good mechanic who rebuilt the regulator, changed filters and pump again. I'm not sure about the diaphram or gaskets used. Car ran great for another 4500-5000 miles. This last time when it quit, I bearly could get it off of the interstate. Car was towed to a good mechanic who has been trying to solve the problem. (I will give him your suggestions.)
I may sound a bit ignorant but I do know that the pressure off of the back of the tank right at the sender and pump is not holding. 20# max is all it can produce. This is after trying 3 different pumps...last one was a Delco. Wouldn't the fact that the pressure reading off of the tank would eliminate fuel rail, filters, injectors, regulator....everything ahead of the actual tank? That's the reason I had decided to order a new sender...thinking that perhaps one of the two wires in the sender was faulty. Anyway, will have my mechanic go through all new suggestions before changing the sender.
Thanks a lot for all of the suggestions. I realize that everyone of them has been a solution to somebody else's problem and they certainly all are valid and worthy of consideration. Bruce

 

[Bruce Huey]

Solution to fuel pressure problem

After a long time and a lot of mistakes a good mechanic didn't give up and solved the low pressure (0-20#) pressure problem on my 180,000 '86. After trying 3 different pumps and two different pulsators, checking every other filter-option, voltage drops, oil pressure senders and every kind of known kind of fuel restriction possibility, he again changed to another pulsator and immediately got 45# pressure. Hard as it is to believe, it took three pulsators to rectify this problem. Guess it is true that new parts aren't fail-safe. Thanks again to everyone who offered their advice. I'll try to get back with the brand name of the pulsator which worked.

 

[Bruce Huey]

pulsator replacement

An update on the pulsator problem on my high-mile '86. Thought that my mechanic had replaced the pulsator for the third time. He replaced the pulsator with fuel hose and completely eliminated the pulsator. He told me that he used the idea from other GM tanks, similiar to the Vette, which didn't use a pulsator in the first place. For some reason after the original pulsator failed, by replacing the fuel pump at that time the car would run for several thousand miles before failing again. As stated before, each interval to failure grew shorter until replacing the pump or pulsator did no good at all. Only after eliminating the pulsator altogether did the car build correct pressure. Mileage, performance and smooth engine operation are back!
Also, I was lucky enough to have the sender that I had ordered put on back order and cancelled it before it arrived at Eckler's.
Just really appreciate member's suggestive help and the Corvette Action Center for being 'out there.'