Another fuel pressure test question
Thread Starter
Burning Brakes
Joined: Apr 2011
Posts: 917
Likes: 25
From: College Station Tx
Another fuel pressure test question
Ran a fuel pressure test on my '95 LT1. Pressure dropped from 47 psi to 0 psi in less than 1 minute. I want to try clamping the supply and return, but all I see are steel lines. Where exactly do I go to clamp off?
btw..not having starting or running issues. Exhaust fumes are pretty bad. I read here to start with the pressure test and go from there.
btw..not having starting or running issues. Exhaust fumes are pretty bad. I read here to start with the pressure test and go from there.
Safety Car
Joined: Apr 2011
Posts: 3,660
Likes: 22
Don't bother...
your problems are obvious..
Pressure drop that quick is certainly a ruptured fuel regulator or 4 shorted fuel injectors..(and IF it were inj it likely would not even start...
Pull the regulator vac line and check for wet gas. Check the oil dip stick for the smell of gas. The BIG clue is in the rich exhaust...that means the extra fuel is being sent to the cylinders somehow...either thru the vac lines OR the injectors. If you had a problem in the tank, like a bad pump it would take at least a few minutes to bleed 40 psi off...not less than 1 minute. Thats a reg diaphram.
your problems are obvious..
Pressure drop that quick is certainly a ruptured fuel regulator or 4 shorted fuel injectors..(and IF it were inj it likely would not even start...
Pull the regulator vac line and check for wet gas. Check the oil dip stick for the smell of gas. The BIG clue is in the rich exhaust...that means the extra fuel is being sent to the cylinders somehow...either thru the vac lines OR the injectors. If you had a problem in the tank, like a bad pump it would take at least a few minutes to bleed 40 psi off...not less than 1 minute. Thats a reg diaphram.
Team Owner
Joined: Jan 2003
Posts: 20,254
Likes: 220
From: Summerland B.C. Canada
I wouldn't assume anything without testing. On my 86, you can pinch rubber lines at fuel tank, after removing fuel door assembly. Maybe at front of block, also, but not sure on your year.
FWIW, I had that same quick drop in fuel pressure twice, once it was a leaking pulsator at pump, the second was a stuck check valve in pump.
FWIW, I had that same quick drop in fuel pressure twice, once it was a leaking pulsator at pump, the second was a stuck check valve in pump.
Thread Starter
Burning Brakes
Joined: Apr 2011
Posts: 917
Likes: 25
From: College Station Tx
Agent, I saw a lot of posts along that line, but most, if not all, were the earlier C4's. I wasn't sure if the latter models had the same issue a the fuel pump. I will look in the area of the fuel door before I buy a FPR. If I can find a place to pinch the hose, it will be a quick test, so no reason not to do it. I have steel hoses going from the fuel rail going back towards the gas tank. Front of the block is out of the question.
Racer
Joined: Jun 2006
Posts: 361
Likes: 6
I wouldn't assume anything without testing. On my 86, you can pinch rubber lines at fuel tank, after removing fuel door assembly. Maybe at front of block, also, but not sure on your year.
FWIW, I had that same quick drop in fuel pressure twice, once it was a leaking pulsator at pump, the second was a stuck check valve in pump.
FWIW, I had that same quick drop in fuel pressure twice, once it was a leaking pulsator at pump, the second was a stuck check valve in pump.
Same pulsator problem here also. Motor never starved for fuel but it bothered me so I replaced the pump and got rid of the pulsator.
Checking the regulator diaphragm is very easy also, just pull regulator vacuum line from plenum, start car and see if fuel comes out of vacuum line. But I also believe its either the pump check ball or pulsator. As stated above, pull fuel door assembly and clamp rubber return line on top of tank then check pressure bleed down.
Burning Brakes
Joined: May 2011
Posts: 838
Likes: 2
From: Louisville Ky
Agent, I saw a lot of posts along that line, but most, if not all, were the earlier C4's. I wasn't sure if the latter models had the same issue a the fuel pump. I will look in the area of the fuel door before I buy a FPR. If I can find a place to pinch the hose, it will be a quick test, so no reason not to do it. I have steel hoses going from the fuel rail going back towards the gas tank. Front of the block is out of the question.
the fuel smell you mentioned would not be present on tank leaks. he also said to check the oil. not uncommon for a couple gallons of fuel to be mixed in.
Thread Starter
Burning Brakes
Joined: Apr 2011
Posts: 917
Likes: 25
From: College Station Tx
Thanks everyone. I tried the smell tests, but I couldn't really smell anything on the dipstick or the vacuum tube. Pulled the vacuum tube off and ran it to a jar. Cycled the ignition a few times and gas squirted out. Getting a new FPR this afternoon. Will do another pressure test after install. Hopefully nothing else pops up. Thanks again for the help.
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Thread Starter
Burning Brakes
Joined: Apr 2011
Posts: 917
Likes: 25
From: College Station Tx
Installed new FPR. Pressured up to 45 psi, dropped to 40 psi when pump shut off and held 40 psi for over an hour. Haven't had a chance to drive it yet, but looking forward to tomorrow. Thanks again everyone.