Fuel pressure?
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Fuel pressure? I have a quick question about fuel pressure.
I installed an aftermarket fuel pressure regulator with a gauge. When I turn the key on, the fuel pump primes for two seconds as it is supposed to. The gauge reads 41 lbs, but when the fuel pump shuts off after the prime, the pressure drops back to 0. I can start the car and the pressure reads about 38 lbs while the car is running. Runs fine, no fuel issue. But I've read the pressure should hold after the prime.
My question is...Should the pressure hold at 41 lbs after the prime or is it normal to drop back to 0? It is a brand new regulator, pump, filter etc...
I installed an aftermarket fuel pressure regulator with a gauge. When I turn the key on, the fuel pump primes for two seconds as it is supposed to. The gauge reads 41 lbs, but when the fuel pump shuts off after the prime, the pressure drops back to 0. I can start the car and the pressure reads about 38 lbs while the car is running. Runs fine, no fuel issue. But I've read the pressure should hold after the prime.
My question is...Should the pressure hold at 41 lbs after the prime or is it normal to drop back to 0? It is a brand new regulator, pump, filter etc...
How long does it take to drop back to 0? It will start to fall, but should take at least 10-15 minutes to go back to 0. If it goes back to 0 almost immediately, you need to check your lines in the tank again.
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I've swapped a 96 LT1 into a 79 Firebird. Engine didn't come with a regulator, so I bought one. This is the second one actually. The first kept leaking and couldn't get it to stop. I'll get some video of it doing what it's doing and post it.
Car starts immediately cold and runs fine. But if I kill it and try to restart, it takes pumping the gas to get it going. Thought it was an electrical problem but am now leaning toward a fuel issue. Trying to track it down.
Car starts immediately cold and runs fine. But if I kill it and try to restart, it takes pumping the gas to get it going. Thought it was an electrical problem but am now leaning toward a fuel issue. Trying to track it down.
Why answer his question with a question? 
He has one, so that is what he is using.
Other than the added expense, I prefer them b/c they can be dialed in, vs. stock which are in the ballpark but seldom exactly 3 bar or 43.5 psi.
I currently use one b/c my manifold pressure goes to 200 kPa at WOT.
He has one, so that is what he is using.
Other than the added expense, I prefer them b/c they can be dialed in, vs. stock which are in the ballpark but seldom exactly 3 bar or 43.5 psi.
I currently use one b/c my manifold pressure goes to 200 kPa at WOT.
Cool swap! Just spent a bunch of time reading the whole link. Personally it sounds as though you may have a slight injector leak. I would check and see if it blows black smoke upon hot starting it. If that happens then you've definitely got too much fuel in there. But usually the fuel pressure will be at 43-45 psi when you turn the key, then it bleeds down slowly from there (usually down to 0 in 10-15 min IIRC). Maybe try turning up the pressure at idle then go from there and see what it does.
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Ok, heres some video of what's going on. In the first video, the car is cold. First start of the day. You can see what the fuel pressure does on the gauge.
And in this next video, the car has been turned off after warming up to 170 degrees.
After attempting to start it, there is a strong smell of raw fuel under the hood. So, I'm thinking leaking injectors causing a flooded situation. Also, the fuel pressure does not "hold" unless the fuel pump is running.
And in this next video, the car has been turned off after warming up to 170 degrees.
After attempting to start it, there is a strong smell of raw fuel under the hood. So, I'm thinking leaking injectors causing a flooded situation. Also, the fuel pressure does not "hold" unless the fuel pump is running.
Last edited by BadVRod; Mar 5, 2010 at 06:14 PM.
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Many regulators do not hold pressure well after the engine is off.
You will just have to deal with this.... if the car starts OK, then don't worry about it.
You could also have an intank line or injector leak. Your regulator looks like a generic, so it could very well be the regulator unless it bleeds off in just a second or 2. Your pressure fall very fast. Block the return line & see if it holds pressure... if so it is not the regulator.
As for pressure, the mainfold vacuum will lower the pressure at idle.
Start the car, remove vacuum line & set pressure to 43.5.
Connect vacuum line back up & it will be whatever it is based on the available manifold vacuum.
You will just have to deal with this.... if the car starts OK, then don't worry about it.
You could also have an intank line or injector leak. Your regulator looks like a generic, so it could very well be the regulator unless it bleeds off in just a second or 2. Your pressure fall very fast. Block the return line & see if it holds pressure... if so it is not the regulator.
As for pressure, the mainfold vacuum will lower the pressure at idle.
Start the car, remove vacuum line & set pressure to 43.5.
Connect vacuum line back up & it will be whatever it is based on the available manifold vacuum.
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Verdad Gallardo That quick of a bleed down is certainly a bad leak. If the smell is under the hood, check the following:
Turn the key the the "ON" position and pull the vacuum hose off the regulator, and see if it is leaking out that hose. If the diaphram has a leak, it usually exits there.
If not, pull the fuel rail and turn the key to the "ON" position. Just leave the injectors mounted in the rail. You will be able to see if the injectors are leaking.
You will also be able to see if it is leaking at the o-ring where the regulator mounts into the fuel rail, and inspect the junction between the gauge and the schrader valve.
Turn the key the the "ON" position and pull the vacuum hose off the regulator, and see if it is leaking out that hose. If the diaphram has a leak, it usually exits there.
If not, pull the fuel rail and turn the key to the "ON" position. Just leave the injectors mounted in the rail. You will be able to see if the injectors are leaking.
You will also be able to see if it is leaking at the o-ring where the regulator mounts into the fuel rail, and inspect the junction between the gauge and the schrader valve.
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Lonnie...the regulator is an inexpensive Professional Products unit. The car does start and run fine. I've driven it a few miles and had zero fuel issues. I read into the routing of the fuel lines and found that the regulator was to be placed after the fuel rails, on the return side. I thought this to be counter-intuitive, but it seemed like more people were doing it that way so I ran with it. Could this be why the regulator drops to 0?
Koolaid...My FPR is mounted to the firewall behind the fuel rails, but I have 3/8 braided fuel line connecting it to the rails and fuel tank. I had 6-an fittings put on the rails to accept the braided line. I have no leaks anywhere in or around the car.
I'm going to do an injector leak test as soon as I get a little more time in the shop. I hope that's the problem. It's an easy fix. I'm so close to being able to drive this thing I can taste it. Just need to kill these little gremlins!
Koolaid...My FPR is mounted to the firewall behind the fuel rails, but I have 3/8 braided fuel line connecting it to the rails and fuel tank. I had 6-an fittings put on the rails to accept the braided line. I have no leaks anywhere in or around the car.
I'm going to do an injector leak test as soon as I get a little more time in the shop. I hope that's the problem. It's an easy fix. I'm so close to being able to drive this thing I can taste it. Just need to kill these little gremlins!
Block the return port on the regulator. (a -6 plug is cheap.)
Cycle the key, pressure will build.
If it holds, it is the regulator... if not, look elsewhere.
Also regulators have been known to leak internally through the diaphragm.
This can cause hard starting, wierd idle etc. pull the vac line & see if it is wet.
There are numerous potential issues.... you need to start a process of elimination & many of the above mentioned ones that both I & Koolaid_kid mentioned are worthy of trying. It does not take a lot of leakage to make pressure drop quickly.
Cycle the key, pressure will build.
If it holds, it is the regulator... if not, look elsewhere.
Also regulators have been known to leak internally through the diaphragm.
This can cause hard starting, wierd idle etc. pull the vac line & see if it is wet.
There are numerous potential issues.... you need to start a process of elimination & many of the above mentioned ones that both I & Koolaid_kid mentioned are worthy of trying. It does not take a lot of leakage to make pressure drop quickly.
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I got to work on the car today. Started off checking the FPR and it checked out ok, held pressure no problem. I pulled the fuel rails with injectors attached and put pressure to them, 3 of them were leaking. Went ahead and pulled all the injectors and bench cleaned them with pressurized injector cleaner, a battery, and a starter button. Put them back on, retested them and they held. Reinstalled the fuel rail, started the car and let it warm to 180 degrees. Killed it and it restarted immediately. Completely solved the problem.
Thanks for the advice guys. Made today a really good day!
Thanks for the advice guys. Made today a really good day!
