Fuel Pressure - Hesitation

T

TurkeyLeg

New Member

Oct 14, 2007

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Oct 22, 2007

#1

• Oct 22, 2007

• #1

On my stock '88 5.0, I'm getting a little bit of hesitation on hard acceleration and I just put a fuel pressure gauge on the shrader valve on the rail. At idle, I'm getting 30 psi with the vac line on, and 40 psi with the line off. When I rev it to 4000 rpm's (with the vac line back on), the fuel pressure moves up to about 33-35 psi. Should it be higher than this? Also, when I tuen the car off, the psi immediately goes to 0. Does it sound like a bad pump or fpr, or both?

 

ShortThrow50

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Oct 22, 2006

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Pa

Oct 23, 2007

#2

• Oct 23, 2007

• #2

Last I remember it does go to go to zero with the car off. I dont know what the psi does under accel. I never really looked

 

AeroCoupe

lube between the nut and the face. I know my lubes

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Oct 28, 2001

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Claremore, OK

Oct 23, 2007

#3

• Oct 23, 2007

• #3

I have mine set or 39 psig with the vacuum line disconnected and it will go to 39 psig when I am in the throttle. It sits at about 31 or 32 at idle. At half throttle it will hit 36 or so. Sounds like you have a tired pump or bad regulator or blocked fuel filter.

Darren

 

PUNISHER RACING

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Aug 27, 2007

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Oct 24, 2007

#4

• Oct 24, 2007

• #4

Aero hit it, you should have 42 lbs with the vac off and it should fall to 38 with it back on. Start with the filter its cheapest.

 

HISSIN50

"How long does it take to get help in here?

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Nov 29, 1999

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Oct 24, 2007

#5

• Oct 24, 2007

• #5

As I recall, spec is anything over 30 PSIG is acceptable. Then stock, WOT pressure is about 38 PSI.

Your observation about the 4K RPM situation does not have enough info. We'd need to know how much manifold vac was present during this time. The fuel pressure regulator works off the manifold vacuum signal.

Good luck.

 

AeroCoupe

lube between the nut and the face. I know my lubes

Founding Member

Oct 28, 2001

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Claremore, OK

Oct 24, 2007

#6

• Oct 24, 2007

• #6

Good call HISSIN50! A vacuum check only requires a gage and a buddy or a long hose from the manifold to the driver's seat. This is a pretty cheap check too.

One other thing I forgot is the smock or prefilter on the inlet of the fuel pump. If you drop the tank to check this I would say just go ahead and buy a new prefilter and pump if you have the cash as this is not one of those tasks you like to do on a weekly basis. I would suggest either a 190 0r 255 lph unit as this will get you through a bunch of mods. I had the 255 lph unit on my car waaay before any mods and it was not a problem setting the fuel pressure. I would also suggest a Walbro unit as you can find them for a good price and they are damn reliable.

Darren

 

T

TurkeyLeg

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Oct 14, 2007

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Oct 24, 2007

#7

• Oct 24, 2007

• #7

So if I get a 190 or 255 pump, then will I need a new regulator? or is the stock one good enough for now.

 

HISSIN50

"How long does it take to get help in here?

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Nov 29, 1999

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Oct 24, 2007

#8

• Oct 24, 2007

• #8

TurkeyLeg said:

So if I get a 190 or 255 pump, then will I need a new regulator? or is the stock one good enough for now.

Click to expand...

The stock one should suffice for you. The puter will dial back injector pulsewidth accordingly (in case your FP goes up a pound or two from the new pump).

 

AeroCoupe

lube between the nut and the face. I know my lubes

Founding Member

Oct 28, 2001

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Claremore, OK

Oct 24, 2007

#9

• Oct 24, 2007

• #9

To each is their own. I would get an adjustible regulator but that is just me. If you do I have run three different ones now and I like the Kirban unit the best.

Darren

 

T

TurkeyLeg

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Oct 29, 2007

#10

• Oct 29, 2007

• #10

UPDATE: I put a new fuel pump in and now it holds fuel pressure for a while after you turn the car off. Also, when I rev it up to about 3500 RPM, the fuel pressure goes up to about 38 psi, like it should. And most importantly, no more hesitation on acceleration. Thanks for the help.