well i have a stumble problem on my vette, it just chugs and falls on its face half the time. No emmisions and good vaccum. Put a fuel pressure up to it at idle and shes running about 28psi, way too low. I have an adjustable FPR and when i try to turn it, it has no effect. Sometimes it just wont start at all. Im not getting any power through the fuse to the fuel pump when i turn on the ignition. Im changing the fuel pump as soon as i can get one orderd. Could this be a problem with the relay or the pump or what? 135,000 miles on origional fuel pump, might as well change it right?
-Matt-

 

Yep, the check valve on the fuel pump is bad if it doesn't hold pressure. After 135,000 miles, your fuel pump has lived a long life and served you and the original owners as well.

 

What make of adjustable reg do you have ? Is the diaphram installed the right side up ?
The fuel delivery worked good before the rebuild, right ?

 

135K on the original pump-don't throw it away, mount it how many miles on the filter You may want to try jumping the ALDL pin G. I believe,with 12 volts just to check it out. Funny about fuel pumps, I know on another post CFI-EFI stated that the only time a check valve leaks is when the engine isn't running. Never had one apart-I just wonder about that. Basically you lose pressure 1 of 3 places, injector(s), regulator and FP check valve. I'd forget the relay, cause even if it's shot, when you get approx. 4 lbs. oil pressure she will start-and the relay has nothing to do with low fuel pressure while running.

 

Nothing you have posted indicates a bad fuel pump. Maybe it IS bad, but from what you've said there is no reason to come to that conclusion. From what you have written, I suspect the regulator. You say adjusting it has no effect, Hmmm. Does that give you any ideas? Clamp off the the fuel return line and start the engine. What is the fuel pressure, now?



Why??? All jumping 12 volts to terminal "G" does, is test the wiring, fuses, and pump. The engine runs. We already know those items are working.


Rick,
To be technical, make that "when the FUEL PUMP isn't running". You ARE aware of what a check valve is, aren't you? How could a valve be leaking if it is supposed to be open and it IS open and flowing?

RACE ON!!!

 

The way I read the post was " Im not getting any power through the fuse when I turn the ignition on" and "sometimes it just won't start at all". That's why I suggested 12 volts to terminal G. OK on the verbiage-pump Yes, I know what a check valve is-all I'm saying, and I'm not arguing the point, a valve is a valve-a pump is a pump-electrical is elcetrical and all are subject to failure. My questioning would be-if there were a flow restriction, several clogged injectors possibly, a weak pump-or failing one, including check valve could not fuel take the least path of resistance? Sometimes pumps are DOA, other times they die a slow agonizing death.

 

fuel filter just changed. I had this problem before the rebuild, so the FPR shouldnt be the problem i beleive. Funny thing is im not getting any power to the fuse when i turn on the ignition... maybe the relay??? When i get the new pump in ill clamp off the return line and see what it does then.

 

Wonder if it couldn't be a fusible link-the orange one going from the power terminal behind the battery to terminal E on the relay? or bad wireing going into the relay-mine had the insulation shrunk back and bare wires touching.

 

You said that you know what a check valve is. "Yes, I know what a check valve is-all I'm saying, and I'm not arguing the point, a valve is a valve-a pump is a pump-electrical is elcetrical and all are subject to failure." A check valve prevents back-flow of the fuel, when the pump isn't pumping. When the pump IS pumping, the check valve is wide open and fuel is flowing through it. A valve IS a valve, but it isn't subject to failure when it isn't being called upon to DO anything. What is there to wonder about?

RACE ON!!!

 

You have to be fast as it's only on for about 2 seconds

 

http://www.racetronix.com/

Try this if you need something a little better than stock. I got one for around $100 for my 87. Plug and play. 30 minute job.

 

OK, CFI-EFI, I'm open to an education here-NO side shots, OK. I'm going to try to explain myself-then you can correct me-that's fair-right?
for a simple explanation I shall use a carb as an example, or I could use a toilet in a carb you have a float-when the level reaches a certain point-the float actuates a valve thats purpose is to allow-or not allow any more fuel into the bowl-just an example,I would think that's an example of a check valve- check valves may come in different sizes and shapes-now if there's a failure in the float,or it sticks and some of them were well know to develop leaks-weighing down the float made it lose its function to actuate the valve.Valves themselves can become sticky, lose any intended bouyancy-such as the carb float-not refering to the float as the valve, just the actuator of the valve.And the old carbed cars had nowhere to dump the fuel-but into the intake, whereas our injected cars do have an alternate-may I use the word-routing source. I just happen to think a failure in the pump somewhere or in the fuel system could cause the check valve to malfuntion. OK, I'm ready.

 

The carb fuel bowl valve is not a check valve. It is opened and closed by an independent (the float) force. I wish I could make a drawing. Picture a brass fitting, with a ball, inside of the tube, with a small amount of spring pressure pushing the ball to cover the opening and block the flow, through the hole in the brass fitting. This is our check valve. The fitting and ball are on the inlet side and the spring is at the outlet end. When the pump is running, the flow, unseats the ball off of the opening of the fitting and compresses the spring. Fuel flows freely through the (check) valve on toward the engine. Because of the regulator, there is pressure in the system. When the pump is running, the pressure is fairly equal from the pump to the injector nozzles and the regulator, which bypasses the fuel back to the tank. When the pump shuts off, the pressure drops at the pump. As the fuel tends to flow toward the lower pressure area at the tank, the flow pushes to ball to cover the hole in the fitting, preventing back-flow. THAT is what a check valve is. A check valve freely allows flow in one direction, but prevents flow in the other direction. You SAID that you knew what a check valve was, but given your carb example, is seems you didn't. Failure of a check valve could involve erosion or cracks in either the ball or the ball seat that would allow flow to leak back past the check valve when it is closed.

Does a better understanding of what a check valve is, help your "wondering about that"? The only time a check valve is closed is when the pump isn't running. It can't hardly leak if it isn't, or isn't even supposed to be closed.

RACE ON!!!

PS. Since I wrote the above, I've spent too much time looking for an example or a cutaway of a check valve to post or link, here. Although the "fluid" is different, and the construction is all different, the flapper valve at the end of your dryer vent, outside of the house, is a "check valve". When the dryer is running, it is open, and allows the moist air to exit the house. When the dryer shuts off, it closes to prevent the outside air from entering the house. Do you wonder about the dryer vent flapper valve leaking, while the dryer is running?

 

Very nice explanation-thanks for the education. Let me ask you one other question then, "failure of a check valve could involve erosion or cracks in either the ball or ball seat that would allow flow to leak back
past the check valve when it is closed" could the spring fail also? I thought the carb illustration was fine-infact you could say the float was for explanation purposes on my side-the spring. Now that you have described the check valve to me-with great accuracy I might say,
it did bring back a check valve experience I had. My last boat had a check valve on the tank. I had been stupid enough to use another boaters 50 gal. drum and pump to put gas in my boat-his tank contained all kinds of debris-which of course I didn't see,while boating later-of course I ran into problems, the debris clogged the check valve, now that check valve was to keep fuel from siphoning into the motor while not running-somewhat like you described-this check valve didn't fail-it just became clogged.And therefore prevented me from getting any fuel.Great explanation CFI-EFI, and discription-weird thinks happen-sorry, but I retain my reservations.

 

i tell ya what guys, ill have a new pump and relay on her by monday, ill let ya know if either one was the problem.

 

Your boat had a check valve that prevented fuel from flowing from the fuel tank to the engine??? What did that engine run on? And why did you bother with a fuel tank?

Of course any fuel system can become clogged and contaminated with foreign objects, but I maintain my position "that the only time a check valve leaks is when the engine isn't running", because that is the only time the check valve is CLOSED. How can a valve that is supposed to be open and IS open, be determined to be leaking???

A fuel line check valve did NOT prevent fuel from reaching your engine. Debris may have accumulated near or at the valve, and caused a blockage. But a valve that is supposed to be admitting fuel to the engine doesn't fail in it's purpose, by LEAKING. Obviously my explanation wasn't so great. Your response indicates that you still don't grasp the concept of a "check valve" Think of it as a "one way" valve. If you are familiar with electronics, think of it as a diode.

RACE ON!!!

 

I meant to type this yesterday, but I think you are throwing money at the problem, replacing the fuel pump without testing it. No power at the fuel pump fuse has nothing to do with the pump. Adjusting your regulator had no effect, so I suggested clamping off the return line and rechecking the pressure. You responded with "When i get the new pump in ill clamp off the return line and see what it does then.". The whole point of clamping the line is one step to see if the pump is bad. Maybe the pump IS bad. Maybe it isn't. To me, that is a lot of money to throw out there on a crap shoot.

RACE ON!!!

 

well i was planning on getting a new fuel pump anyways. Im making alot more horses than what it was stock. Bigger injectors, more fuel consumption... The relay was shot, well at least the wires going into it. The wires were stripped back and it looked like they were barley connected. If it wasnt bad now, it may soon be.

 

Without waiting to see if the old pump would meet the demand?


So did you fix the wiring or just order a new relay?


And so, may be the engine. Have you ordered a new one? How about the whole car?

RACE ON!!!

 

i repaired the wiring, and bought a new relay, total cost was $17; preventative maintenence. Quick question, should there be what appears to be some sort of silicone sealent around the stock relay and its little cover?