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Author Topic:   Fuel pressure dropping when warm
rockafellz
Gearhead

Posts: 1291
From: San Lorenzo, CA, USA
Registered: Aug 2001

posted 01-20-2003 02:33 PM     Click Here to See the Profile for rockafellz   Click Here to Email rockafellz     Edit/Delete Message   Reply w/Quote
Hey All,

Been taking the fastback for a spin every now & then and I seem to be having problems with the fuel pressure dropping off when the car is warm.

OK, when I first start the car, I get a steady 5 PSI. After the car has been taken around the town for 20 mins, I lift the hood and check it and it's down to 3.5 PSI. Yesterday I felt the fuel pump and it was HOT. I'm not sure if the power is dropping off if/when it gets too hot.

I'm using a Carter electric fuel pump rated at 100gph free flow and preset to 7PSI, running through the stock 5/16 fuel line and into a Holley 803 fuel pressure regulator. The Holley regulator has 1 input and 2 outputs. One output goes to the carb and the other output is directly connected to my Holley fuel pressure gauge (liquid filled to absorb vibration).

Please help!!

Thanks in advance.

Erik

------------------
1966 Ford Mustang 2+2
Mine - Restomod in Progress

1966 Ford Mustang Coupe
Dad's - Original Unrestored

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rockafellz
Gearhead

Posts: 1291
From: San Lorenzo, CA, USA
Registered: Aug 2001

posted 01-20-2003 02:34 PM     Click Here to See the Profile for rockafellz   Click Here to Email rockafellz     Edit/Delete Message   Reply w/Quote
Also, i'm running a rebuilt Holley 600CFM 1850-2 vacuum secondary carb.

I have a 650 double pumper that's waiting a rebuild.

Erik

------------------
1966 Ford Mustang 2+2
Mine - Restomod in Progress

1966 Ford Mustang Coupe
Dad's - Original Unrestored

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Fastymz
Moderator

Posts: 11429
From: Reno Nv USA MEM#1240
Registered: Apr 2001

posted 01-20-2003 07:54 PM     Click Here to See the Profile for Fastymz   Click Here to Email Fastymz     Edit/Delete Message   Reply w/Quote
Erik I dont know for sure,but I would think it's the pump.I cant think of anything else it could be.

------------------
SCOOP
oddly obsessed with big scoops on little Mustangs

2.26 60'S
14.9 @ 90.86MPH

65 coupe,351w,C4,Big Boss 429 hood scoop,8"3.40 TracLoc,Cragar SS,Black Suede.

https://mustangsandmore.com/ubb/Fastymz.html

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69 Sportsroof
Gearhead

Posts: 1202
From: Valley, Alabama, USA
Registered: Mar 2002

posted 01-20-2003 09:21 PM     Click Here to See the Profile for 69 Sportsroof   Click Here to Email 69 Sportsroof     Edit/Delete Message   Reply w/Quote
My guess is that the pump is working too hard. Does your pump have a regulator also? Running two regulators may be causing too much pressure on the output side of the pump. I believe the second port on your regulator is suppose to feed back to the tank. I'd also recommend 3/8 fuel line. Where do you have the pump? Is it next to the tank or in the engine compartment? It needs to be at the tank. Electric fuel pumps like to push rather than pull the fuel.

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Hemikiller
Gearhead

Posts: 384
From: Clinton, CT
Registered: Feb 2002

posted 01-20-2003 09:46 PM     Click Here to See the Profile for Hemikiller   Click Here to Email Hemikiller     Edit/Delete Message   Reply w/Quote
A friend of mine has the same thing going on with his car. Holley Blue at the tank, Holley reg, 1/2" alum line, -8 at the motor and at the sump, new tank, Moroso tank sump.

When you first start the car, he gets 6 psi, as the car warms up, the pressure gauge on the carb slowly drops to ZERO. We have tried new gauge, new pump, different regulator, checked all lines and fittings. The car runs absolutely fine. He has run 11.0's with an indicated pressure of ZERO. What's wrong? Not a clue, but there's no lean indication on the plugs, had the heads off last year, pistons look like new. Anyone have any other ideas because we're out......

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jsracingbbf
Gearhead

Posts: 1677
From: Batesville,MS. , U.S.A.
Registered: Mar 2002

posted 01-20-2003 11:31 PM     Click Here to See the Profile for jsracingbbf   Click Here to Email jsracingbbf     Edit/Delete Message   Reply w/Quote
Back when I ran a carb on the strip I used to have the fuel PSI gauge where I could see it BECAUSE 6-7 lbs at idle was only 3-4 on the big end of the track at WOT ( wide open throttle). EVEN with 1/2 inch fuel line. I wound up setting mine at 10lbs. As long as it isn't blowing gas by the needle and seat of the carb, it's not bad to have more fuel pressure. At least that's what I remember.

------------------
Jerry
69 Mustang Pro ET Drag
70 Mustang retired former footbrake car
"Even a Blind Hog can find an acorn every now and then"

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65_302
Gearhead

Posts: 239
From: Bixby, OK
Registered: Jul 2001

posted 01-20-2003 11:32 PM     Click Here to See the Profile for 65_302   Click Here to Email 65_302     Edit/Delete Message   Reply w/Quote
Maybe the location of the pressure gauge?

If it runs when the gauge says zero, the fuel must not be getting to the gauge.

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69 Sportsroof
Gearhead

Posts: 1202
From: Valley, Alabama, USA
Registered: Mar 2002

posted 01-21-2003 08:05 AM     Click Here to See the Profile for 69 Sportsroof   Click Here to Email 69 Sportsroof     Edit/Delete Message   Reply w/Quote
Another thing to consider is that pressure doesn't equate to volume. A large diameter fuel line will give you more volume at a lower pressure.

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blown 351
Journeyman

Posts: 64
From: Seattle, Wa. 98258
Registered: Dec 2001

posted 01-21-2003 10:49 AM     Click Here to See the Profile for blown 351   Click Here to Email blown 351     Edit/Delete Message   Reply w/Quote
I doubt that your fuel pressure is dropping.
Liquid filled gauges usually read low after the liquid in the gauge heats up. This is particularly evident when the gauge is close to an aluminum intake manifold.
I bet if you moved the gauge to a cooler environment, it would read accurately.

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rockafellz
Gearhead

Posts: 1291
From: San Lorenzo, CA, USA
Registered: Aug 2001

posted 01-21-2003 11:24 AM     Click Here to See the Profile for rockafellz   Click Here to Email rockafellz     Edit/Delete Message   Reply w/Quote
Morning Fellas,

OK, here's the fuel pump I have.

http://store.summitracing.com/partdetail.asp?part=9882

And here's my current fuel pump configuration.

1. New OE Style 16 gallon tank/sender/gasket kit.

2. High flow cintered bronze Earl's fuel filter 4 inches away from the fuel tank. Input/Output pointed correctly.

3. Carter fuel pump CRT-P4600HP directly connected to outlet of fuel filter 1 inch away.

4. Stock 5/16" fuel line. (not planning to upgrade since SteveW ran 12's with a 351W using 5/16" line, I've only got a built 302 )

5. Holley Fuel pressure regulator http://store.summitracing.com/partdetail.asp?part=7733 5-6 inches away from the end of the 5/16" fuel line. It is located at the bottom of the engine compartment where the windshield washer pump and bag should be.

6. Fuel pressure gauge http://store.summitracing.com/partdetail.asp?part=11820 directly connected to one of the outlets of the regulator.

7. Fuel line run from the regulator to the Holley 600cfm 1850-2 carburetor.

The car runs fine except when doing short bursts of the throttle (running it up to 5000rpm) then coming to a stop light. It tends to idle a little more wobbly than normal. I worry a little at that point, but when I look to the side of me, the person in the other car keeps looking at my hood/frontend. Takes all my worries away for that moment and I get a fat smily grin.

Thanks in advance.

Erik

------------------
1966 Ford Mustang 2+2
Mine - Restomod in Progress

1966 Ford Mustang Coupe
Dad's - Original Unrestored

[This message has been edited by rockafellz (edited 01-21-2003).]

[This message has been edited by rockafellz (edited 01-21-2003).]

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jsracingbbf
Gearhead

Posts: 1677
From: Batesville,MS. , U.S.A.
Registered: Mar 2002

posted 01-21-2003 09:30 PM     Click Here to See the Profile for jsracingbbf   Click Here to Email jsracingbbf     Edit/Delete Message   Reply w/Quote
Can you mount the fuel pressure guage where you can see it? I mean during these short bursts you are speaking of. I would do that first. I am not trying to be a smart guy here but I think you really need to be looking at it WHILE it is acting up. I always mounted my fuel pressure guage on the cowl when I ran one. You could even do it temporarily until you sort it out. I really think you need more line ( bigger) and pump myself, but thats just my .02
Jerry

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steve'66
Gearhead

Posts: 6522
From: Sonoma,CA,USA
Registered: Mar 2000

posted 01-21-2003 09:57 PM     Click Here to See the Profile for steve'66   Click Here to Email steve'66     Edit/Delete Message   Reply w/Quote
Erik,

I've been avoiding this thread because you're worried about a fuel pressure reading. Not worrying about actual results. The truth is the '66 has never had a fuel pressure gauge on it, and still doesn't! It doesn't fall off at the end of the 1/4 and that's all I care about. The fuel pressure might be down to 0 psi, but as long as the bowls on the 850 Holley are full who cares?
Just my opinion and of course I could be wrong.
But "the last time I was wrong, I thought I was wrong but I was really right".
Is this a real problem or what?

SteveW

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jsracingbbf
Gearhead

Posts: 1677
From: Batesville,MS. , U.S.A.
Registered: Mar 2002

posted 01-21-2003 11:56 PM     Click Here to See the Profile for jsracingbbf   Click Here to Email jsracingbbf     Edit/Delete Message   Reply w/Quote
I don't run a fuel pressure gauge at all now. No need to. However, If his fuel pressure is falling off on the big end ( he didn't say this was the problem ) it just means the needle and seat are opening up and the bowls are requiring more fuel, IF you have ZERO pressure at the guage on the big end of the track fuel MAY not be going into the bowls fast enough. I've seen this first hand. Not saying you are wrong Steve, I just really think this would be a place to start. I never really liked those Holley regulators myself even though I used to run one alot. A good constant fuel regualtor has some sort of return line. When I ran that C & S specialties/Holley Alcohol 950 I used a return line bypass type regulator with NO GUAGE. This may not be necessary for his application though. I'd still move the guage if I was concerned about the fuel PSI Just my 02.

------------------
Jerry
69 Mustang Pro ET Drag
70 Mustang retired former footbrake car
"Even a Blind Hog can find an acorn every now and then"

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steve'66
Gearhead

Posts: 6522
From: Sonoma,CA,USA
Registered: Mar 2000

posted 01-22-2003 12:19 AM     Click Here to See the Profile for steve'66   Click Here to Email steve'66     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by jsracingbbf:
IF you have ZERO pressure at the guage on the big end of the track fuel MAY not be going into the bowls fast enough. I've seen this first hand. Not saying you are wrong Steve,

It's cool Jerry, because I don't have a f'n clue what the fuel pressure is!

Maybe I should but.... I try to keep it simple for my driver, and I sure couldn't feel any let up when I drove it! All I'm trying to say is that too much information can "snow you with the facts while ignoring the obvious".
How does it run? That's the obvious.

Maybe I should upgrade the fuel system, it's just a Holley red in the rear feeding 3/8" s.s. tubing to a stock mechanical up front thru 3/8 s.s. to the dual feed lines of the Holley 850dp'r. I know it's weak for a 10 second car, but I wanted to see if it realy needed a mega fuel system!
I really don't think that it'll pick up much from going to the fuel cell in my garage and 1/2" lines and a 300+ gpm pump, with regulator and a return line. But if you guys think it will I'll give it a try.


SteveW

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jsracingbbf
Gearhead

Posts: 1677
From: Batesville,MS. , U.S.A.
Registered: Mar 2002

posted 01-22-2003 02:17 AM     Click Here to See the Profile for jsracingbbf   Click Here to Email jsracingbbf     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by steve'66:
It's cool Jerry, because I don't have a f'n clue what the fuel pressure is!

I really don't think that it'll pick up much from going to the fuel cell in my garage and 1/2" lines and a 300+ gpm pump, with regulator and a return line. But if you guys think it will I'll give it a try.

SteveW


If your not having a problem I bet the fuel is OK. Your probably right, it wouldn't do much different. I think the car is running great from the pics I've seen and the times hey if it ain't broke why fix it?

------------------
Jerry
69 Mustang Pro ET Drag
70 Mustang retired former footbrake car
"Even a Blind Hog can find an acorn every now and then"

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rockafellz
Gearhead

Posts: 1291
From: San Lorenzo, CA, USA
Registered: Aug 2001

posted 01-22-2003 10:15 AM     Click Here to See the Profile for rockafellz   Click Here to Email rockafellz     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by steve'66:
Erik,

I've been avoiding this thread because you're worried about a fuel pressure reading. Not worrying about actual results. The truth is the '66 has never had a fuel pressure gauge on it, and still doesn't! It doesn't fall off at the end of the 1/4 and that's all I care about. The fuel pressure might be down to 0 psi, but as long as the bowls on the 850 Holley are full who cares?
Just my opinion and of course I could be wrong.
But "the last time I was wrong, I thought I was wrong but I was really right".
Is this a real problem or what?

SteveW


Hey SteveW,

Thanks for the reply. You're probably right, I guess i'm just overly cautious since this is my first project car and I'm learning as I go. I wouldn't mind taking that damn thing off. It would be one less thing I have to worry about.

But, the only time I notice a problem is when I go for a drive and come to a stoplight. The rpms bounce from 500-900rpm. If I put it into neutral, rev it a little, then back into drive it's back to it's usual 700-800 idle. I thought maybe my bowls are low or something. I also think my converter is too tight since it wants to "scoot" as i'm waiting for a light.

Thanks in advance.

Erik

------------------
1966 Ford Mustang 2+2
Mine - Restomod in Progress

1966 Ford Mustang Coupe
Dad's - Original Unrestored

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rockafellz
Gearhead

Posts: 1291
From: San Lorenzo, CA, USA
Registered: Aug 2001

posted 01-22-2003 10:24 AM     Click Here to See the Profile for rockafellz   Click Here to Email rockafellz     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by jsracingbbf:
I'd still move the guage if I was concerned about the fuel PSI Just my 02.



Thanks Jerry,

I'll take it for a better spin this weekend. The car has never "fallen" on it's face when driving. I've been on the freeway and took it to about 80mph without a hitch. That reminds me, i've got to get a speedometer gear for transmission. My speedo was reading 110mph+ when I think I was doing about 80mph.

Any info on that by any chance before I start another thread? I went from a 3.00:1 rear to a 3.55:1 rear with help from SteveW.

Thanks again.

Erik

------------------
1966 Ford Mustang 2+2
Mine - Restomod in Progress

1966 Ford Mustang Coupe
Dad's - Original Unrestored

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Ryan Wilke
Gearhead

Posts: 1501
From: Stanton, Michigan 49707
Registered: Oct 2000

posted 01-22-2003 12:14 PM     Click Here to See the Profile for Ryan Wilke   Click Here to Email Ryan Wilke     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by rockafellz:
I thought maybe my bowls are low or something.

Erik,
Did you say that you checked the float levels to ensure they were correct?

A quick, easy & cheap check would also be to install a loop of fuel hose between the two float vents with a 'bite' out of the center-top of it; this is an old band-aid trick to reduce the chance of any splash-over that may be occuring out of the vent tubes...

-- just my 2 cents worth,
Ryan

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itlbrnmoff
Gearhead

Posts: 746
From: Indianapolis,IN.USA
Registered: Nov 2002

posted 01-23-2003 03:49 AM     Click Here to See the Profile for itlbrnmoff   Click Here to Email itlbrnmoff     Edit/Delete Message   Reply w/Quote
Hey...guess what...it's just the liquid filled gauge dropping...
I bought a liquid filled gauge and it did the same thing...returned it for a non-liquid gauge and PRESTO...consistent reading at any temperature...junk that gauge...

------------------
Mustang Lover...
Blue Oval Bleeder...
I've got the scars to prove it...
Society's whipping post...
Low Dollar 1983 Mustang GT W/T-tops...
306 4bbl. T-5 3.45 trac-loc...it'll burn 'em off
1988 Lincoln LSC
5.0 auto full power

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Glens67
Gearhead

Posts: 325
From: Petaluma
Registered: Mar 2002

posted 01-23-2003 06:39 PM     Click Here to See the Profile for Glens67   Click Here to Email Glens67     Edit/Delete Message   Reply w/Quote
Just mount it out side of the engine compartment like on the hood with flex line or mount it to the cowl grill with copper line.

------------------
Glen
67 GT 390
65 Galaxie 500 XL 4 Speed
It was not a Red Light they gave me a Slow Tree

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clevelandstyle
Gearhead

Posts: 638
From: Connersville, IN
Registered: Jul 2001

posted 01-23-2003 10:19 PM     Click Here to See the Profile for clevelandstyle     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Glens67:
Just mount it out side of the engine compartment like on the hood with flex line or mount it to the cowl grill with copper line.



Mine is mounted on the cowl and it drops in the heat of the summer when the sun is beating on it.

------------------
Ben
Grabber Green '70 Mach I 351C 4V
Robbin Egg Blue '79 Fairmont 351C 4V

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