Factory Five Racing Forum banner

1 - 10 of 10 Posts

·
FFCobra Fanatic
Joined
·
616 Posts
Discussion Starter · #1 ·
I had originally posted my problem here with a complete description:

http://www.ffcars.com/ubb/ultimatebb.php?ubb=get_topic;f=1;t=007376#000016

Basically the engine sputters under acceleration and idles for a while, but will eventually die. Under acceleration you can see black smoke puff out of both sides when it sputters. I have changed out everything in the ignition and checked for intake leaks or cracked hoses. I think that my problem is in the fuel system. Here are the results of my fuel pressure test.

After turning on the key the pressure spikes to just above 40 psi and levels out at 38 psi. I can hear the regulator open as the pressure goes to 38 psi. The needle is rock solid at 38 psi so I assume that it is not a stuck or leaking injector. When the engine is running at idle the pressure drops to 34 psi. As the idle gets rougher and the engine starts to die I can see the fuel pressure drop a little. If I pull the vacuum line off the regulator the pressure increases to 44 psi. I think the Chilton's book called for 39 psi. Could this be a fuel pump problem or a regulator problem? I'm going to replace the filter and the check the pressure again. I still need to run a compression test, but every time I think about it the engine is still hot.

Sorry for the long post, but I want to give as much information to get the best advice.

Donny
 

·
Senior Member
Joined
·
6,546 Posts
Have you pulled the codes out of the computer?

Is the engine modified? If so, what's changed?
 

·
Administrator
Joined
·
9,772 Posts
Did you re-install your computer plug? Carl showed me how to use the code reader on Saturday. (Accually he showed all of us: Galt, Orange Crush, Pete Gibbs). I would be happy to see if he'll let me bring it up your way to see what's happening once and for all. That thing is trick! It will tell you all kinds of great things in just a few minutes.
 

·
FFCobra Fanatic
Joined
·
616 Posts
Discussion Starter · #4 ·
The computer diagnostic port was removed in the wire harness diet. I got one back from Roger Stein and have not attempted to reconnect it. I have a check engine light wired in and could check the codes if the port was installed.

I guess my main question is if I should be concerned about 35 psi fuel pressure at idle. The engine is completely stock and ran fine for 400 miles prior to this.

Donny
 

·
FFCobra Fanatic
Joined
·
616 Posts
Discussion Starter · #5 ·
I'll try one more time. Is 35 psi fuel pressure at idle a problem?

Donny
 

·
Senior Member
Joined
·
6,546 Posts
Without the diagnostic port on the computer you're blindly shooting in the dark.

You NEED that plug, why would it get cut out as part of the diet?!

Is the motor stock?
 

·
Registered
Joined
·
428 Posts
Just an observation, But black smoke is a to much fuel condition. Good luck
 

·
Cobra Builder/Driver
Joined
·
253 Posts
Donny:

35 psi at idle is fine. As vacuum increases (idle speed) fuel pressure decreases. At wide open throttle (Very low vacuum) fuel pressure increases to meet the increased fuel demand of the engine. So if you have set the fuel pressure to 39-40psi with the vacuum line to the fuel pressure regulator disconnected, then that is the max pressure that the engine will see at WOT. When vacuum is re-connected you will see pressure drop to 32-35psi. This is normal.

Do you have the stock Fuel Press Reg. or an adjustable one? The stock unit is non-adjustable and if it is giving 40 with vac connected then that is too high on the stock motor.

You may have a vacuum leak giving the FPR incorrect vac. and throwing off the Pressure, check your fittings and look for intake manifold vac. leaks.
 

·
Senior Member
Joined
·
6,546 Posts
Is the car stock? (I sound like a parrot)

The SD system does not handle changes to the engine very well as it has no way to know it's flowing more air.
 

·
FFCobra Fanatic
Joined
·
616 Posts
Discussion Starter · #10 ·
The engine is bone stock other than underdrive pulleys.

I have pulled the upper intake and checked all the vacuum connections as well as the intake gasket.

I still have not had the time to change the fuel filter.

I bought some electric contact cleaner and I was going to spray it around the intake with the car running to see if I could locate a vacuum leak.

The black smoke confused me as well. I thought I had a leaking injector, but the pressure test eliminated that I think.

Donny
 
1 - 10 of 10 Posts
Top