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1995 Mustang GT
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Discussion Starter · #1 ·
Do not know much about the car other than what I see, 3 bar gt40 heads, tubular gt40 intake, stock tb, 19lb injectors. Not sure of cam or rr as I haven’t popped a valve cover off yet but it is not a stock cam.
Car has a idle surge I replaced the iac and tps is good I believe it was .965
Now to the fuel pressure the gauge maxes at 60lb and it’s pegged. I suspect the car had more done to it before I owned it because it has a cage, bottle holder for spray in back, and it has a nice paxton fpr that was leaking from the boost reference port so I threw a stock replacement on for now and it’s still getting too much fuel.
Not sure if it had a blower before and they took it all off and threw stock injectors back on and left a bigger fuel pump in tank??
I want to upgrade to 24lb injectors with a 70mm throttle body and calibrated MAF. Could you see this bringing my fuel pressure down? Or should I drop tank and put stock pump size in? Also will that kick me in the ass if I do the injector upgrade?

First time posting in the forums always been a reader just looking for advice and input.
 

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Discussion Starter · #2 ·
Wheel Tire Car Vehicle Land vehicle

Motor vehicle Car Hood Vehicle Automotive design
Guy I got it from didn’t know much about it and for the market prices right now it was a absolute steal at $4250 looked at vin and it was a 4cyl car originally whoever put it together had good taste minus the flames HAHA
 

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Stock pressure is 39 psi. Surging is often because it's too rich, and that fuel pressure would make it run rich. My guess is the gauge is inaccurate if you have a stock regulator. I've run 340lph on stock rails and lines, the pressure was normal. It could also be a defective regulator. Harbor freight sells a cheap fuel pressure gauge you can use to verify pressure. I think most autoparts stores also rent them.
 

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Discussion Starter · #4 ·
Before I changed the FPR with a stock replacement, beside from the fact it was leaking it would read 55psi when I turned key over then peg out when started.

When I put a AutoZone replacement on it read about 45 then do same thing once started. If driving the car when throttle is applied it will come down to 50. I’ve tried tapping the gauge but the needle doesn’t move at all i do believe it just has to much pressure and blew the diaphragm in the Paxton regulator. Just my guessumption though lol
 

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Discussion Starter · #5 ·
Stock pressure is 39 psi. Surging is often because it's too rich, and that fuel pressure would make it run rich. My guess is the gauge is inaccurate if you have a stock regulator. I've run 340lph on stock rails and lines, the pressure was normal. It could also be a defective regulator. Harbor freight sells a cheap fuel pressure gauge you can use to verify pressure. I think most autoparts stores also rent them.
^^^ sorry new here didn’t know how to reply directly
 

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Put a wideband on it and see what's going on.

I run my car at 58psi base... 4bar.
Your car has an old school tune... H/C/I 19s and jack up the fuel pressure.

It's making your 19s squirt like a 24 or close to it.
That's what's goin on
 

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Discussion Starter · #7 ·
Put a wideband on it and see what's going on.

I run my car at 58psi base... 4bar.
Your car has an old school tune... H/C/I 19s and jack up the fuel pressure.

It's making your 19s squirt like a 24 or close to it.
That's what's goin on
I was just watching a video where they were talking about doing exactly that with 19s making them act like bigger injectors. After running for awhile the car starts surging really bad and wants to stall.
Would this old school tune consist of a bigger pump? Because as of now it’s got a stock regulator and it’s not doing the job lol
You think 24lb injectors and maf could solve it?
 

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No.. you don't need 24s for a gt40 combo.. drop your pressure to 50 base.
Ideally put a wideband on and see where your at W.O.T... may be fine with stock 40psi base.. probably making 230-240 hp... 19s are plenty

The surging could be anything, bad wire, bad ground, vac leak, c&l maf, etc..
 

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Discussion Starter · #9 ·
No.. you don't need 24s for a gt40 combo.. drop your pressure to 50 base.
Ideally put a wideband on and see where your at W.O.T... may be fine with stock 40psi base.. probably making 230-240 hp... 19s are plenty

The surging could be anything, bad wire, bad ground, vac leak, c&l maf, etc..
Thank you. What would be the things you’d look at first? The surge occurs mostly after the cars been running for a second. And will only happen at idle. If gas is applied it’ll stay alive. Also I’ve noticed oil pressure will start dropping when it’s surging. When first started it sits at 40 then will drop to 20 and bounce around almost nothing when surging. But before it starts running funky it holds 40. Not sure if that’s useful info or not but I appreciate your guys input, bit of a novice here I learn as I go.
 

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Easy stuff would be to put a vacuum gauge on it and see what it's pulling.

You could try opening your throttle stop a little ( 1/4 turn at a time) and see if that helps raise idle and smooth it some.
 

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Discussion Starter · #11 ·
Easy stuff would be to put a vacuum gauge on it and see what it's pulling.

You could try opening your throttle stop a little ( 1/4 turn at a time) and see if that helps raise idle and smooth it some.
I will update if I find anything thank you again for your input. Any info is appreciated knowledge is power!
 

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I'm not trying to start an argument but opening the throttle blade more is going to do nothing but mess things up. The computer controls idle speed. Opening the throttle more will just cause the iac to close more. More important, the computer is calibrated for the amount of air that passes through the the throttle when closed. Moving the throttle blade changes the throttle body air mass and in turn messes up the tune. You should if anything do a base idle reset to get the air mass back to original. That's not going to fix the fuel pressure. I wouldn't trust the gauge without verifing with another gauge. I've had multiple liquid filled gauges be significantly off, including the one that is currently installed on my car now which is the 3rd one i tried. I gave up and just use my aem electronic which i have verified is accurate. Start with what you know is wrong. Pull codes too. How to Manually Test EEC-IV OBD1 Trouble Codes on a Fox-Body Mustang for Free
 

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A GT40 combo shouldn't be this finicky to setup. You essentially have a ford explorer engine, with a better camshaft. Plenty of folks run them with 19# injectors and 39 psi and they run like a stock engine.

First thing I thought to myself was a blockage on the return fuel line preventing you from lowering the pressure down. I think you need to solve this issue before digging into how the engine runs. Considering the car had nitrous, i wonder if any sort of hackery was done to bump the pressure up for the spray.
 

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Discussion Starter · #16 ·
This is the first place I would look, as mentioned earlier, the fuel pump can be very large and it should still have whatever fuel pressure that the regulator dictates.
Going to check it out see what I can find. What would be best way to make sure the line is clear? Pull it down and blow air through it? Thank you guys for all the input
 

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Going to check it out see what I can find. What would be best way to make sure the line is clear? Pull it down and blow air through it? Thank you guys for all the input
I would look for a crushed metal return line under the car or a kinked return hose but you may be doing all of that for nothing if the gauge is bad...
 
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This is the first place I would look, as mentioned earlier, the fuel pump can be very large and it should still have whatever fuel pressure that the regulator dictates.
a super larger pump with a tiny 1/4 return line wont let the fpr do its job. you will get a false fp reading.

99% of drivability issues are fuel related because everyone things the throttle stop screw is idle adjustment on stock eec iv mustangs
 

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Discussion Starter · #19 ·
I would look for a crushed metal return line under the car or a kinked return hose but you may be doing all of that for nothing if the gauge is bad...
I will invest in a new gauge it is pretty old looking.. what are some recommendations? I will let you know if I see anything when I get a chance to jack it up.
 

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Discussion Starter · #20 ·
a super larger pump with a tiny 1/4 return line wont let the fpr do its job. you will get a false fp reading.

99% of drivability issues are fuel related because everyone things the throttle stop screw is idle adjustment on stock eec iv mustangs
If I’m not finding a damaged return line I will more than likely be dropping the tank to see what pump I have. There’s too much that I just don’t know about the car… the downside of getting someone else’s project lol all I know is what I see
 
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