Fuel Pressure Problems
Thread Starter
Instructor
Joined: Sep 2016
Posts: 129
Likes: 16
From: Milwaukee WI
Fuel Pressure Problems
I've got a 1987 Corvette that has some cold start problems. It takes a solid 5 seconds or so before it'll start up. To diagnose this, I started looking at the fuel system (just replaced injectors). When I pressurize the system, it quickly rises to 40 psi and then drops to 20 psi within a few seconds. It'll hit 0 psi with 30-45 seconds after that. I clamped the return line, then the supply line, and then both lines - the pressure drops in the same fashion each time. Finally I took the top end apart so I could test the injectors. Since I have some Bosch 3's (no retaining clips), I lifted the fuel rail up, placed some thin lint free clothes under each injector, and then put the rail back on. I did pressurized the system twice, then took it off and didn't see a single went spot. For fun I did it a second time with some new cloth, still nothing.
I've pressurized the system a solid 40+ times tonight and figured if I was leaking somewhere else I would be able to see it on the floor, but I'm not seeing (or really smelling) any gas.
Any thoughts? I'm at a loss. :-(
*I've driven it for about 500 miles since putting the injectors in. For what it's worth, I don't smell any gas in the oil.
Nevermind! The new gauge I got has a longer hose and I was able to watch it as I clamped/released the flex hose at the tank. The fuel pressure is definitely slower while the supply line is clamped and drops immediately when I release the clamp. I must have just not been clamping it down enough to stop the flow entirely.
I've pressurized the system a solid 40+ times tonight and figured if I was leaking somewhere else I would be able to see it on the floor, but I'm not seeing (or really smelling) any gas.
Any thoughts? I'm at a loss. :-(
*I've driven it for about 500 miles since putting the injectors in. For what it's worth, I don't smell any gas in the oil.
Nevermind! The new gauge I got has a longer hose and I was able to watch it as I clamped/released the flex hose at the tank. The fuel pressure is definitely slower while the supply line is clamped and drops immediately when I release the clamp. I must have just not been clamping it down enough to stop the flow entirely.
Last edited by slhawkins; Mar 1, 2017 at 11:48 PM.
Racer
Joined: Nov 2015
Posts: 294
Likes: 40
From: Massachusetts
I went through this with my '96 and you are basically where I was. It's time to pull the fuel pump. Luckily on these cars its very easy. My problem was that someone eliminated the fuel pulsator between the fuel pump and sender line and didn't clamp it down. It was dumping the fuel back into the tank, which is why I couldn't find a leak. For you it could be the pulsator, possibly the fuel pump. I ended up replacing my fuel pump while I was in there and a new strainer sock, which I would recommend doing. I used the Delphi replacement pump, clamped the new hose down tight and my PSI is right at 40.
Team Owner
Joined: Jul 2004
Posts: 28,472
Likes: 3,290
From: Hartford WI
Replaced the injectors with what? Did you also have the cold start valve cleaned and tested? Those are often overlooked.
My under, which is standing is that you lose fuel pressure in spite of the clamping of the return line? IF so lets go backwards. Assuming the injectors are good, is the diaphragm leaking and good? This is a 2 man job. Pressurize it and clamp on the return line. Before it drops, clam off the feed line. If it still leaks, you have a problem in the regulator.
If not, are you sure that the dampner is in good shape? I'd replace it with fuel hose rated for submersion.
My under, which is standing is that you lose fuel pressure in spite of the clamping of the return line? IF so lets go backwards. Assuming the injectors are good, is the diaphragm leaking and good? This is a 2 man job. Pressurize it and clamp on the return line. Before it drops, clam off the feed line. If it still leaks, you have a problem in the regulator.
If not, are you sure that the dampner is in good shape? I'd replace it with fuel hose rated for submersion.
Thread Starter
Instructor
Joined: Sep 2016
Posts: 129
Likes: 16
From: Milwaukee WI
Replaced the injectors with what? Did you also have the cold start valve cleaned and tested? Those are often overlooked.
My under, which is standing is that you lose fuel pressure in spite of the clamping of the return line? IF so lets go backwards. Assuming the injectors are good, is the diaphragm leaking and good? This is a 2 man job. Pressurize it and clamp on the return line. Before it drops, clam off the feed line. If it still leaks, you have a problem in the regulator.
If not, are you sure that the dampner is in good shape? I'd replace it with fuel hose rated for submersion.
My under, which is standing is that you lose fuel pressure in spite of the clamping of the return line? IF so lets go backwards. Assuming the injectors are good, is the diaphragm leaking and good? This is a 2 man job. Pressurize it and clamp on the return line. Before it drops, clam off the feed line. If it still leaks, you have a problem in the regulator.
If not, are you sure that the dampner is in good shape? I'd replace it with fuel hose rated for submersion.
I updated the original post, I redid the clamp down test of both lines and found that a clamped down supply line would slow down the loss in pressure considerably. So it looks like it's either the fuel pump or pulsator. New parts come in on Saturday.
Safety Car
Joined: Sep 2001
Posts: 4,157
Likes: 554
From: Glenbeulah Wi
Injectors were replaced with Bosch 3's from Jon. I read about some people from the frozen North removing their cold start valve so I went ahead and did the same since mine was leaking - I'll be moving to San Diego in a few short months. :-) It's now blocked off at the rail and runner.
I updated the original post, I redid the clamp down test of both lines and found that a clamped down supply line would slow down the loss in pressure considerably. So it looks like it's either the fuel pump or pulsator. New parts come in on Saturday.
I updated the original post, I redid the clamp down test of both lines and found that a clamped down supply line would slow down the loss in pressure considerably. So it looks like it's either the fuel pump or pulsator. New parts come in on Saturday.
Thread Starter
Instructor
Joined: Sep 2016
Posts: 129
Likes: 16
From: Milwaukee WI
Will it be fine in 60 degree weather? It sits in the garage otherwise.
Safety Car
Joined: Sep 2001
Posts: 4,157
Likes: 554
From: Glenbeulah Wi
I do not know, you will have to try it and find out. If it still starts poorly have a new chip burned. You could try a stock chip out a 1989 and see if it starts better, those cars were designed without the cold start injector and added in the additional fuel through the fuel injectors.
Team Owner
Joined: Jul 2004
Posts: 28,472
Likes: 3,290
From: Hartford WI
Injectors were replaced with Bosch 3's from Jon. I read about some people from the frozen North removing their cold start valve so I went ahead and did the same since mine was leaking - I'll be moving to San Diego in a few short months. :-) It's now blocked off at the rail and runner.
I updated the original post, I redid the clamp down test of both lines and found that a clamped down supply line would slow down the loss in pressure considerably. So it looks like it's either the fuel pump or pulsator. New parts come in on Saturday.
I updated the original post, I redid the clamp down test of both lines and found that a clamped down supply line would slow down the loss in pressure considerably. So it looks like it's either the fuel pump or pulsator. New parts come in on Saturday.
Not sure how to fix that issue short of a reprogrammed chip.
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Thread Starter
Instructor
Joined: Sep 2016
Posts: 129
Likes: 16
From: Milwaukee WI
For those that I read, it was due to it leaking and they were wondering whether they actually needed it (same thing I was wondering!).
Looking back, I agree that the hard start was likely caused by the lack of the 9th injector. I am glad to have found out about the fuel pressure though, in theory the new pump will fix that.
And thanks to you guys, a shipment from Moates will be on its way today so I can program a chip for it. :-) One way or another, this will be fixed and I'll feel better about putting the wife's car up for sale!
Looking back, I agree that the hard start was likely caused by the lack of the 9th injector. I am glad to have found out about the fuel pressure though, in theory the new pump will fix that.
And thanks to you guys, a shipment from Moates will be on its way today so I can program a chip for it. :-) One way or another, this will be fixed and I'll feel better about putting the wife's car up for sale!
Team Owner
Joined: Jul 2004
Posts: 28,472
Likes: 3,290
From: Hartford WI
For those that I read, it was due to it leaking and they were wondering whether they actually needed it (same thing I was wondering!).
Looking back, I agree that the hard start was likely caused by the lack of the 9th injector. I am glad to have found out about the fuel pressure though, in theory the new pump will fix that.
Looking back, I agree that the hard start was likely caused by the lack of the 9th injector. I am glad to have found out about the fuel pressure though, in theory the new pump will fix that.
Not sure how it will. What exactly is wrong with the fuel pressure now? If the leak is at the tank area, you should get the kit from Racetronix that has all the necessary hardware to replace the hose. Or just a new pump with the kit
Last edited by aklim; Mar 2, 2017 at 02:52 PM.
Thread Starter
Instructor
Joined: Sep 2016
Posts: 129
Likes: 16
From: Milwaukee WI
It's leaking back to the tank. I only discovered it because I was diagnosing the cold start issue (which we agree is a lack of a cold start injector). Now that I know it's there, it'll be fixed. I have a Racetronix FPA-011 kit coming in to replace the original pump.