fuel pressure question
02-08-2005, 10:36 PM
#1
Drifting
Thread Starter
fuel pressure question
OK, this may be a stupid question, but better safe than sorry when dealing with fuel. Here's what I have...Walbro gss340m intank fuel pump, racetronix harness, aeromotive LT1 adjustable fuel pressure regulator, autometer fuel pressure gauge (in car, with electric sender on fuel rail), new fuel filter --- all new. 5 fresh gallons of 93 octane in the tank, new setup has not been fired up yet at all. I decided to check the fuel pressure (key on, engine off). The gauge seems to work fine, it went to 60 or so psi, then quickly dropped down. I soon realized there was fuel at the back of the intake. I saw drops of fuel on the fitting for the gauge sending unit. A quick tightening of the fitting eliminated this. Then, with the key on, the same thing happened. That's when I realized the regulator was wet. After careful inspection, I found it was leaking at the extra pressure port on the back. The plug was very loose, so if you get one of these and don't plan to use that port, don't assume that it came from the factory pre-tightened. After tightening the plug, I turned the key on again, and still, the pressure drops. I can't tell you what it does with the engine running, because I have not fired it up yet. My question is...after you turn the key on, and the fuel pump runs for a second or two to build up pressure, how long does that pressure stay in the fuel rail? I can't find any more wet spots, anywhere around the rails, or even the lines under the car. I don't think it should be dropping to zero in a few seconds, should it? Or is this a characteristic of the walbro pump, or maybe the electric gauge and sender? I would think as long as the key is on, the gauge would be powered up to show current pressure. Any advice would be greatly appreciated. 
02-09-2005, 01:58 AM
#2
Melting Slicks
Hey polo,
If you are not holding pressure there is something wrong...
I do similar I also have a extra inline fule pump as well...
It should go to say 60 pounds or whatever ... and usually with mine it may drop slightly lower say minimum of 40 psi.... it willl hold for quite some time... I'm thinking at least 30 minutes... I really never timed it, however it will drop to zero over night.
My fuel pressure gauge is manual with a transducer so it reads whether the car is on or not.
Is there a possibility that when you turn the key off the gauge is also shutting off? ( thought I'd ask...)
If in fact you are still dropping to zero in say less than ten -15 minutes or so, I would say either your regulator is set too low, or you have a leaky injector?
You can fire it up and see what your fuel pressure is showing, it sounds like you stopped the leaks.... if the pressure is too low it will stall too high the injectors will adapt with the PCM.... and you will see it with the gauge...
Hope this helps,
Mo
If you are not holding pressure there is something wrong...
I do similar I also have a extra inline fule pump as well...
It should go to say 60 pounds or whatever ... and usually with mine it may drop slightly lower say minimum of 40 psi.... it willl hold for quite some time... I'm thinking at least 30 minutes... I really never timed it, however it will drop to zero over night.
My fuel pressure gauge is manual with a transducer so it reads whether the car is on or not.
Is there a possibility that when you turn the key off the gauge is also shutting off? ( thought I'd ask...)
If in fact you are still dropping to zero in say less than ten -15 minutes or so, I would say either your regulator is set too low, or you have a leaky injector?
You can fire it up and see what your fuel pressure is showing, it sounds like you stopped the leaks.... if the pressure is too low it will stall too high the injectors will adapt with the PCM.... and you will see it with the gauge...
Hope this helps,
Mo
02-09-2005, 11:25 AM
#3
Race Director
Member Since: Sep 2000
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Originally Posted by Mo_Bandy
Hey polo,
If you are not holding pressure there is something wrong...Is there a possibility that when you turn the key off the gauge is also shutting off? ( thought I'd ask...)
If in fact you are still dropping to zero in say less than ten -15 minutes or so, I would say either your regulator is set too low, or you have a leaky injector?
You can fire it up and see what your fuel pressure is showing, it sounds like you stopped the leaks....
If you are not holding pressure there is something wrong...Is there a possibility that when you turn the key off the gauge is also shutting off? ( thought I'd ask...)
If in fact you are still dropping to zero in say less than ten -15 minutes or so, I would say either your regulator is set too low, or you have a leaky injector?
You can fire it up and see what your fuel pressure is showing, it sounds like you stopped the leaks....
If the regulator were set too low, he wouldn't see 60# fuel pressure. Which is way too high, by the way.
I'd suggest cranking the engine with the plugs out, to clear the cylinders of raw, liquid, gasoline, to prevent a hydrostatic lock before trying to start it. This is the classic symptom of leaking injector(s).
RACE ON!!!
02-10-2005, 01:22 AM
#4
Melting Slicks
CFI-EFI I agree, missed the key on comment.
Polo is supercharged, 60 pounds fuel pressure when you just key on and the system pressurizes is "normal", it returns to 40 ish once the engine fires...
Mo
Polo is supercharged, 60 pounds fuel pressure when you just key on and the system pressurizes is "normal", it returns to 40 ish once the engine fires...
Mo
Last edited by Mo_Bandy; 02-10-2005 at 01:29 AM.
02-10-2005, 05:59 AM
#5
Safety Car
Polo The regulator is designed to not hold fuel for more than 3 seconds and then it drifts to 5 or 10 lbs
Be careful the vacum nipple sometimes has to many threads and needs to be ground down to take the presure off the adjustment spring.
In theroy the fuel presure drops so the engine will not start at first ,you crank the key and oil presure builds and then a second or two later the engine fule presure comes up and engine starts.
Be careful the vacum nipple sometimes has to many threads and needs to be ground down to take the presure off the adjustment spring.
In theroy the fuel presure drops so the engine will not start at first ,you crank the key and oil presure builds and then a second or two later the engine fule presure comes up and engine starts.
02-10-2005, 04:22 PM
#6
Drifting
Thread Starter
REDC4,
So you are saying my specific regulator, the Aeromotive LT1 regulator, is designed that way? The other people are saying an injector may be leaking. Do some regulators hold pressure, and others let it bleed off? If this is the case, then I have nothing to worry about. Let me know for sure.
Darren
So you are saying my specific regulator, the Aeromotive LT1 regulator, is designed that way? The other people are saying an injector may be leaking. Do some regulators hold pressure, and others let it bleed off? If this is the case, then I have nothing to worry about. Let me know for sure.
Darren
02-11-2005, 04:00 AM
#8
Safety Car
GUARENTEE NO PROBLEM.
That regulator is designed that way .
They are for racing and the worst thing in the world is to start a motor and rev it up.
Their design is set so when you turn on the key and dont crank the engine,after about a few seconds the presure will drop.
Then you start cranking the engine and oil presure builds and then the car starts.
That is why you don't crank the key when you first turn it on .
You can over ride it if you turn the key and crank the starter as soon as you turn the key on.
Keeps the crank shaft and bearings from dry starts and prolongs the engine life.
I love mine!
That regulator is designed that way .
They are for racing and the worst thing in the world is to start a motor and rev it up.
Their design is set so when you turn on the key and dont crank the engine,after about a few seconds the presure will drop.
Then you start cranking the engine and oil presure builds and then the car starts.
That is why you don't crank the key when you first turn it on .
You can over ride it if you turn the key and crank the starter as soon as you turn the key on.
Keeps the crank shaft and bearings from dry starts and prolongs the engine life.
I love mine!