Fuel Pressure Question

[dave from mesa]

Have a fuel pressure gauge under the hood. When I turn on the key the pressure goes up to about 40#'s for about 3-4 seconds and then drops to zero. When I hear the ticking sound of the pump stops the pressure goes down. When I hit the starter the engine won't start till the pressure gets to 40 again.
Shouldn't the pressure stay up when the pump stops? Car is getting harder and harder to start when it's cold. This only happens when it's cold.
Give me some ideas on what to look for.
thanks

dave from nevada

[Danr55]

Look for a new motor!

Seriously, is this a system that returns un-used fuel to the tank or is it constant pressure?

[mikiec]

Dan,

He has an EFI system. It returns un used fuel.

I have one word................ Carburator.

[Gaz64]

Dave,

Your non-return valve within your pump is faulty or you need to add one to your pump if it doesn't have one internally.

[RedSnake351]

Dave, I have only one answer for you, come back up to Illinois and I'll take you and Judy back to Giarardo's for some more Chicago style pizza!!!
Ralph

[Danr55]

Dave, ..Mikie...What he said!

[vettestr]

Dave,
I sent you a PM a couple of days ago with a few points and questions. What generation or year/group is the ECU or computer. Depending on the generation of your donor you may or may not have an issue with pressure going to 0 after key is left on for 5 seconds without a tach signal or engine started.

The complaint is hard starting when cold... right? We need a bunch more info too help nail this one down. Is cold starts the only symptom? Does she puff a little smoke when it does start, is mileage and power down, do you have a miss in ignition at any RPM, what have you tested, any other clues beyond what he said?

[Car Nut]

If I remember right, he using a stock Ford ECU.

Most of these keep pressure in the line for while after they are intially pressurized.

[bobcowan]

It all depends on the fuel system you're using. Generally, the pressure regulater is simply a bleed valve. Think of it like a hole with a tapered rod. Turning the screw moves the tapered rod in or out, making the bleed hole smaller or larger.

When the pump is pushing fuel through the hole, pressurer will build up behind the bleed hole. When the pump stops pushing fuel, the pressure bleeds off.

Turn the key to Run and you'll hear the pump run. If the computer doesn't see any nrpm's after a couple of seconds it will shut off the pump. I have an A1000 pump outside the tank, so it's really easy to hear. Turn the key to Start before the pump shuts off. The pump should run while the engine cranks.

[Car Nut]

Dave,

I double checked the Ford Service manual, it clarifies "When fuel injected engines are turned off, fuel in the fuel lines remains pressurized for long periods of time to provide quick start ups."

As I remember, you are using the Ford SEFI systems, probably from a Mustang and you have a stock regulator providing for no adjustment. The regulator mounts on the fuel rail and has a rubber diaphram.

If you don't have any other leaks, I would suspect the fuel regulator, the diaphram could be leaking internally or the seat is worn out allow fuel to return to the tank or into the intake manifold (if the diaphram is leaking). Anyway, its the cheapest to replace.

A fuel injector could be pissing into the cylinder after it is shut off. Check your plugs immediately after shutting the key off and pressure drops.

The fuel pump itself could be worn and is leaking back preventing fuel pressure to be maintained when it is not running.

If none of the above are it, then its Don's fault as he is full of leaks.

[Danr55]

This is all beginning to sound very familiar. Didn't we do this in Kingman? Fuel pressure issues there also or something for the Route 66 run?

[John-Tucson]

Dave from Mesa, Where did you find "COLD" in the Phoenix area ? My gosh man it's July and you found "COLD". What happened, did it get below 90 degrees ? From what Jeff, car nut, and Bob have said so far you should be able to find the problem. Good luck.

[vettestr]

I spoke to Dave yesterday, he does not have easy internet connection so is a little hit n miss. He is driving to a location to check his email and going back to home base to ingest the messages. BTW... his cold start problems are @ 65 to 70 degrees burrrrrrrrr !!!

Engine is getting hard to start after sitting overnight or first time but seems to RE-start if up to temp without issues. He is using the car as his main transportation and towing it behind the motor-home so can't take his house to grab dinner etc..

Ford Guru's help needed here. This is a STOCK-ish early 80's injected 302 engine in a Cobra. He is running a typical donor/stock set up. Very limited diagnostics have been done but here some hints to his problem. Engine cranks over but does not start easy if it sat or not up to temp already. Thinks it is fuel related (lack of) on cold start up. When it does start no black smoke or signs it was flooded. No smell of fuel after shut down from dripping injectors (like he had on another engine once before) Does have a pressure gauge mounted under hood .... it shows 40 PSI when running. He hears pump run on key activation but seems to time out after about 4 or 5 seconds without cranking engine and takes a few seconds to build to 40 PSI with key activation. Gauge is found at zero on cold start up or drops to zero after time out or as soon as running engine is shut off?

I told him .... I think pump time out is normal without cranking the engine. I don't know if pressure should drop to zero when shut down or if it should keep system pressurized at least for a reasonable time after shut down??? I suspect temp sensors ---- not adding fuel for cold start up or something ECM related between cold temp and operating temp as it starts easily if up to temp already?????? What do the Ford Gods say??

[Gaz64]

Refer to post 4.

Fuel pressure will fall to zero with a faulty pump outlet check valve.

[Fitz]

Time for a 408 with a blower

[vettestr]

Originally Posted by Gaz64

Dave,

Your non-return valve within your pump is faulty or you need to add one to your pump if it doesn't have one internally.

Gary,
Thanks for the reply. I don't work with the 5.0 much so I am riding the short bus here.

You mentioned if the pump does not have one installed I should add one.... Did they all have a check valve but some were internal and some external ?
How much pressure should I expect to see after shut down and about how long will it hold that pressure? thanks Jeff C

[Mike Brasfield]

Let me add some information for Dave. He has a stock 302 Ford block, EFI with in tank fuel pump and return line. He running Edlebrock RPM performer heads, with 1.6 roller rockers and Ford Cobra Intake system. Stock distributor with MSD ignition. He has 19lb injectors and a Summit Racing adjustable fuel regulator (35-65psi) on stock fuel rails. Fuel pressure at last veiwing by me was 41 psi when running or with key on. Did not return to zero, at least I don't remember seeing it drop to zero. All injectors were recently checked as well as the "O" rings on each. No leak in the fuel rails were visiable. Was running smooth and probably still is when he get's it started. Did not "miss" while running at idle or while accerating to 5-6K. Hope this helps a little.

[dave from mesa]

What Mike said.
After Jeff left me a message saying something about the computer I decided to disconnect the battery and see what happened. Seems to start a little better now but the fuel pressure gauge still goes up to about 40#'s and drops to zero. Guess when we get home will have to change/add/check the pump outlet check valve. Thanks Gary.
Car does stumble (miss) under normal (read NORMAL) exceleration (sp?) when cold but clears up when it is warm. Starts fine once the engine reaches a decent temp.
Hopefully it keeps running till we get home as this is our only mode of transportation.
Have internet now but it's slow and doesn't work all the time. This is the second time I wrote this.

thanks again

dave from Morgan Hill, ca

[Mike Brasfield]

After some discussion with others I think the problem is with the in tank fuel pump. I just happen to have a near new fule pump in my "bag of tricks" so we'll pull out his old one when he gets home and try that. Last summer I coverted from EFI to CARB and still have some parts left over from the change. Thanks to all of you who tried to help Dave with the problem and solution.

[Positraktion]

Well I'm with Mikie on this one......simple and looks period correct...can you spell..........C-A-R-B-U-R-E-T-O-R....."Those were the days my friend...."....geez these would be good lyrics for a song.....Posi......