Long start up on LT1 - NJFBOA - Home of New Jersey's Camaros and Firebirds

NJ346 · 03-18-2010, 05:17 PM

My buddy's LT1 camaro has developed a long start up problem. I checked pressure at the rail and noticed that it was taking a while to build up. I figured the pump was on the way out so on tuesday I replaced the pump with a Walbro 255LPH pump. When I took out the old pump I noticed that it had a pin hole in the feed line so I figured I had found the source of the problem...I was wrong.

Problem right now:
Brand new Walbro pump
Long initial crank
Fuel pressure is not holding at the schrader valve when key is turned off.
If I cycle the key to the run position anywhere from 3-5 times, I will hear a quick humm and then there is pressure at the schrader valve and the car starts right up.(Note: I hear the pump turn on everytime I turn the key to run so the pump is not the problem, there is an initial humm that has to happen for it to build fuel pressure)

I need to figure out why the fuel rail is not holding pressure shortly after the key is turned off. It sounds like some type of solenoid or possibly a fuel pressure regulator to me...any ideas?

This is definitely a fuel issue. I checked for spark and it has spark as soon as you crank.

deadtrend1 · 03-18-2010, 05:32 PM

I would look into the regulator, but first, put a actual guage on it and see what the pressure is. I run mine at around 40-43 psi (cant remember off the top of my head). Same as stock.

NJ346 · 03-18-2010, 05:36 PM

Quote:

Originally Posted by deadtrend1

I would look into the regulator, but first, put a actual guage on it and see what the pressure is. I run mine at around 40-43 psi (cant remember off the top of my head). Same as stock.

Put an actual guage on the regulator or schrader valve?

Pressure at the schrader valve when the car is running is ~43psi. I just did a search over on LS1tech and it seems to be either a leaky fuel pressure regulator or evap purge solenoid.

sweetbmxrider · 03-18-2010, 05:40 PM

take the vacuum line off of the regulator and see if any gas comes out. sounds like the regulator to me though. i have an adjustable one i don't want if your buddy desires one. hit me up.

03-18-2010, 08:52 PM

my g/fs car does the same thing, she just cycles the key twice every time she wants to start it. ill probably figure out what it is when i come home. let me know how you make out

NJ346 · 03-18-2010, 09:16 PM

Quote:

Originally Posted by JerzLT1

my g/fs car does the same thing, she just cycles the key twice every time she wants to start it. ill probably figure out what it is when i come home. let me know how you make out

I've gotta do some more research/ diagnosing before I buy a fuel pressure regulator because the kid doesn't want to have to spend more $$ than he has to. I plan on spending some time on the car saturday to try and get to the bottom of this.

BarneyMobile · 03-18-2010, 09:18 PM

I'll bet money its the fuel pressure regulator. theres 2 things in the fuel system that holds pressure after the key is turn off, 1: the fuel pump check valve,(you have a new pump so that rules out the check valve), and 2: the fuel pressure regulator. For an extended crank, 4 out of 5 times, its usually the regulator.

BarneyMobile · 03-18-2010, 09:20 PM

Also, double check to make sure you have no fuel leaks any where in the system.

S.J.SLEEPER · 03-18-2010, 09:27 PM

fpr & check vacuum line for fuel as said above.
also:
I still want those manifolds, just been so busy w/work have been leaving @ dawn and getting home after dusk

RamAir95TA · 03-20-2010, 10:38 AM

You will also want to check to make sure you don't have any leaky injectors (hasn't been mentioned yet). Remove the rail from the intake manifold and turn the key to ON and look for the (possible) stuck injector.

NJ346 · 03-20-2010, 03:04 PM

Quote:

Originally Posted by RamAir95TA

You will also want to check to make sure you don't have any leaky injectors (hasn't been mentioned yet). Remove the rail from the intake manifold and turn the key to ON and look for the (possible) stuck injector.

yea, I found that while reasearching on the the net...I'm going to go look at the car in a little bit, I'm gonna pull the vacuum line off of the regulator and if I smell gas, it's getting replaced.

NJ346 · 03-20-2010, 04:31 PM

OK UPDATE
I just checked the FPR and it checked out fine. I hooked up a mighty vac to the fpr and it held vacuum so it's good. The high pitched noise I have been hearing is just the air pump turning on, so I think that it's just coincidental that I sometimes get fuel pressure when I hear the air pump turn on. Even when it gets to the fuel ~43 psi in the run position(motor off), the pressure leaks down in a matter of 2 seconds tops. This is all pointing to a bad injector I believe in less someone else has any other insite?

RamAir95TA · 03-20-2010, 04:48 PM

There are four possible causes for the pressure to bleed down so fast:

-Leaking fuel pump check ball.
-Leaking fuel pump flex pipe.
-Leaking valve/seat within fuel pressure regulator.
-Leaking injectors.

So it's definitely one of those.

Good luck!

NJ346 · 03-20-2010, 05:11 PM

Quote:

Originally Posted by RamAir95TA

There are four possible causes for the pressure to bleed down so fast:

-Leaking fuel pump check ball.
-Leaking fuel pump flex pipe.
-Leaking valve/seat within fuel pressure regulator.
-Leaking injectors.

So it's definitely one of those.

Good luck!

I just looked up a few more ways to check the fpr again. I never did a running fuel pressure test while unplugging the vacumm line on the. I guess the only way to test the fuel pump flex pipe would be to take the pump out of the tank and turn the key to run and see if there are any leak downs. The original pump had a leak so maybe that is the problem, but the clamps I used were pretty tight so I doubt that that is the problem.

NJ346 · 03-20-2010, 07:59 PM

additional tests on the FPR showed that it is still working. So either leaking injectors or leaking lines at the pump. I may call up walbro during the week and see if they have any idea on the possibilities of a bad check valve on a brand new pump.

RamAir95TA · 03-21-2010, 04:35 PM

Have you checked for leaking injectors yet? That's something you can do in 5 minutes. Just remove the four bolts holding the lines down, pop it up, and turn the key.

NJ346 · 03-21-2010, 06:54 PM

Quote:

Originally Posted by RamAir95TA

Have you checked for leaking injectors yet? That's something you can do in 5 minutes. Just remove the four bolts holding the lines down, pop it up, and turn the key.

no I have not. This is for a friends car, so I don't have 24hr access to the car. I'll be able to look at it again on tuesday and if it doesn't turn out to be a leaky injector I'll be pretty stumped on what it is since the fuel pump is brand new.

Zero4488 · 03-25-2010, 01:07 AM

Try hooking up the mighty vac to the FPR while the car is running with the gauge on the rail and see if you can regulate the pressure....I'd still suspect that regulator.....if not your leaking somewhere....

NJ346 · 03-30-2010, 10:03 PM

Quote:

Originally Posted by Zero4488

Try hooking up the mighty vac to the FPR while the car is running with the gauge on the rail and see if you can regulate the pressure....I'd still suspect that regulator.....if not your leaking somewhere....

yea, that test was done when i said "additional tests" were being done. FPR is in perfect working order. It's most likely a leaky injector, i just haven't had time to get my hands on the car to take off the rail and look at it.

Pampered-Z · 03-31-2010, 09:55 AM

How old is the fuel filter? I'd change that and see if the presasure comes up quicker.

WildBillyT · 03-31-2010, 09:57 AM

Forgive the stupid question, but in the really off chance that it may be applicable:

What fuel level is the tank at?

NJ346 · 03-31-2010, 11:30 AM

Quote:

Originally Posted by WildBillyT

Forgive the stupid question, but in the really off chance that it may be applicable:

What fuel level is the tank at?

problem occurs no matter what the level of fuel is in the tank. I will change the filter next time I have the car, but like I said, pressure will shoot up and then drop within a matter of a second or two, so there is a leak down somewhere.