Fuel Pressure supercharged '95 - Ford Mustang Forum
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post #1 of 16 (permalink) Old 06-03-2019 Thread Starter
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Fuel Pressure supercharged '95

Car wont idle when warm, but it runs down tbe road.
I noticed black smoke out the tail at WOT so I checked the pressure at the rail and it was 50 psi with and w/out the vac line connected to the regulator. I replaced the regulator and it was around 40 psi with and without vacuum.
Still black smoke at WOT, and now there is black liquid coming out.
I checked the pressure again several times and it gave several different readings. Sometimes the KOEO pressure would either be lower or around the same as KOER, but never higher. One time it was around 25-30 psi when it primed and then it slowly crept up to 40 psi at idle. Sometimes it would prime up to around 40 and stay there idling. Removing the vac line seems to have little affect and after changing the regulator it never got above 40.
I don't know what the fuel pressure is supposed to actually be, but shouldn't it always be the same? To muddy the waters, It has an inline pump as well, and also I'm using an FMU. When I saw black smoke I thought that would be indicative of high fuel pressure, and when I saw it was 50 I thought I was on to something, and was thinking bad fuel reg or clogged return line.
But now it's not that high but it still smokes and it won't idle after it's hot. Sometimes the rubber line that connects to the inline pump and filter squeals similar to that of a ballon with the air coming out.
What does it mean when pulling the vac line off of the regulator doesn't cause pressure to rise, and what does it mean when the pressure is higher KOER than it is KOEO. Isn't it supposed to be the other way around?
How about the pressure being higher sometimes than others when it primes, and the slowly raising? But then sometimes it'll shoot right up to 40 and hold.
This is awful..

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post #2 of 16 (permalink) Old 06-03-2019 Thread Starter
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Other drawings

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post #3 of 16 (permalink) Old 06-03-2019 Thread Starter
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Sorry, it would only let me upload one file
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post #4 of 16 (permalink) Old 06-05-2019 Thread Starter
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Ghost town
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post #5 of 16 (permalink) Old 06-07-2019 Thread Starter
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I think it's the flux capacitor.
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post #6 of 16 (permalink) Old 06-08-2019
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Thats a tough one man.Not to get off topic,but was the charging issue straightened out,since voltage to the fuel pumps can determine how they run or what amount of fuel they output??

91 LX 342ci (10.5:1)
TFS 190cc (stage ll)
GT40 (tubular) intake
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post #7 of 16 (permalink) Old 06-10-2019 Thread Starter
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Originally Posted by wbrockstar View Post
Thats a tough one man.Not to get off topic,but was the charging issue straightened out,since voltage to the fuel pumps can determine how they run or what amount of fuel they output??
Nah man. The volts were/are still jumping at the distribution box. I assume it still is anyway. After I replaced the box and harness and it was sill messing up I didn't mess with it for awhile. Then the smoking occurred and I got off on that and I hadn't looked at the box again.
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post #8 of 16 (permalink) Old 07-02-2019 Thread Starter
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I think it's going to be a stuck FMU or clogged fuel return line. So I think I can disconnect the return line that runs from the fuel rail to the FMU and have the fuel empty into a container while it idles so I can check the pressure. If the pressure responds when I pull the vacuum line off of the regulator I think I'm on the right track.
What I'm not sure is how much fuel comes out of the return, and if it'll be a trickle or a fairly high pressurized squirt.
Y'all think the gas out return line will be like 40 psi, or a slow drain?
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post #9 of 16 (permalink) Old 07-03-2019
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Yeah the return line is also under pressure.The end of the return line on the hanger assembly also has that orange colored reed valve on it,with a slit cut in the bottom of it, which is a restriction in and of itself.The following is a great video from ProM that shows whats happening inside the tank at the return line.6/8 AN lines are being used,which will output more fuel than the smaller oem lines,but the effects are the same.A portion of the tank has been cutaway in the video so you can see a clear view of whats happening.



91 LX 342ci (10.5:1)
TFS 190cc (stage ll)
GT40 (tubular) intake
Lunati 61011(.549"/.565")
QA1 Coilovers
Weld ProStar XP's

Last edited by wbrockstar; 07-03-2019 at 01:59 PM.
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post #10 of 16 (permalink) Old 07-03-2019 Thread Starter
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Quote:
Originally Posted by wbrockstar View Post
Yeah the return line is also under pressure.The end of the return line on the hanger assembly also has that orange colored reed valve on it,with a slit cut in the bottom of it, which is a restriction in and of itself.The following is a great video from ProM that shows whats happening inside the tank at the return line.6/8 AN lines are being used,which will output more fuel than the smaller oem lines,but the effects are the same.A portion of the tank has been cutaway in the video so you can see a clear view of whats happening.


https://youtu.be/Ium8jf4Jm04
Thanks man. Dang, it's shooting out.. Maybe I'll pull the fitting off that hooks to the rail and hook it to a long piece of hose so I can have it run into a container a little distance a way.
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Thanks man. Dang, it's shooting out.. Maybe I'll pull the fitting off that hooks to the rail and hook it to a long piece of hose so I can have it run into a container a little distance a way.

Yeah I was surprised myself to see just how fast & forceful the fuel was coming out.I would think a stock 88lph pump would be a bit less forceful than the 255lph pump they were using,but since youve got a (if I remember correctly) stock 88lph pump in the tank plus a T-rex inline pump,you'd probably have the same amount of force,as shown in the video,occurring inside your tank also.Im kind-of surprised people don't experience driveability issues related to the turbulence thats caused at the return line.This seems especially true once the fuel level gets somewhat low in the tank.With that much force coming out,it seems like the fuel would literally be pushed away from the pump inlet at the bottom,unless maybe the filter/strainer (attached to the pump inlet) calms the waters enough to prevent this.

91 LX 342ci (10.5:1)
TFS 190cc (stage ll)
GT40 (tubular) intake
Lunati 61011(.549"/.565")
QA1 Coilovers
Weld ProStar XP's

Last edited by wbrockstar; 07-04-2019 at 03:11 PM.
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post #12 of 16 (permalink) Old 07-05-2019 Thread Starter
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Quote:
Originally Posted by wbrockstar View Post
Yeah I was surprised myself to see just how fast & forceful the fuel was coming out.I would think a stock 88lph pump would be a bit less forceful than the 255lph pump they were using,but since youve got a (if I remember correctly) stock 88lph pump in the tank plus a T-rex inline pump,you'd probably have the same amount of force,as shown in the video,occurring inside your tank also.Im kind-of surprised people don't experience driveability issues related to the turbulence thats caused at the return line.This seems especially true once the fuel level gets somewhat low in the tank.With that much force coming out,it seems like the fuel would literally be pushed away from the pump inlet at the bottom,unless maybe the filter/strainer (attached to the pump inlet) calms the waters enough to prevent this.
Yeah, I have the stock pump and a inline. I think the inline is rated at 100 and some odd psi. I kind of think the videos results are exaggerated a little because the fuel in their rig doesn't have to travel as far as if it was on the car. They're only circulating a few feet where as the return line on the car is probably like six feet. But for my test I guess it'd be similar to their results since I'll be removing the line closer to the rail.
I was thinking about disconnecting the line that feeds the fmu since it's easier to get to. But if I did that I wouldn't know if gas was going through and out the bottom of the fmu like it should. So I guess I'm going to have to rig up long hose coming out of the bottom of the FMU and into a gas can.
Do you think it'll up a gas can pretty quick?
I'm hoping the FMU line is messed up because it'd be the cheapest and easiest. It's plausible. The fmu line that goes from the rail to the fmu leaked so I replaced it with a home made job. I can't find the stock hoses so I'm going to have to pull the fittings off of the fmu hose and attach them to a length of hose like I did the other.
A new FMU is $200. I found a set of 6 42# injectors and I think singles were sold for like $30 each. I'd have to get a re-tune which would be around $300. If it turns out to be the fmu I would like to take it off and get larger injectors. But I don't know if money will allow. Here's the injectors. They're knock-offs I do believe, and a lot cheaper than others I've seen, so I'm not sure about them either. Are these stock style? Are the stock ones "fat" or "skinny?"
Parts Geek Part Number: 5473-02034550


https://www.partsgeek.com/gbproducts/AC/5473-02034550.html?utm_source=google&utm_medium=ff&utm_ content=TTC&utm_campaign=PartsGeek+Google+Base&utm _term=1986-1995%2C+1997-2004+Ford+Mustang+Fuel+Injector+Kit+Replacement+90 2-118-K6+86-95%2C+97-04+Ford+Fuel+Injector+Kit+1994&fp=pp&gbm=a&utm_sou rce=google&utm_medium=ff&utm_campaign=PartsGeek+Go ogle+Base&gclid=EAIaIQobChMIvKamxqaS4wIVyrrACh2R4A d4EAQYBCABEgKIHvD_BwE
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post #13 of 16 (permalink) Old 07-08-2019 Thread Starter
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I hadn’t messed with the mustang yet, but ordered a new FMU because the one for a ‘94/‘95 is back ordered forever. If I don’t need it they said I can return it. I found the OEM fuel return hose that connects to the rail and the line by the shock tower. So now I’ll be able to bypass the fmu for testing without using a bucket.
Maybe I’ll get the ole gal back on the road yet.
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post #14 of 16 (permalink) Old 4 Weeks Ago Thread Starter
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Well the fmu wasn’t so back ordered after all because it arrived. When I called and ordered it they said that they’d have to make one first. They must have grabbed whatever they had lying around and slapped it together because they sent me a black one. The one that came with the kit is blue and so are all the other ones I’ve seen. I like the black bettter though because I think it’ll blend in better visually and not stick out like a sore thumb.
I guess next weekend I’ll do some testing to see if I need it or not. Has anyone ever ran the motor with the return fuel line squirting into a container?
I bought a fire extinguisher just Incase.
Is it going to run well enough to do a fuel pressure test with that line off?
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post #15 of 16 (permalink) Old 3 Weeks Ago Thread Starter
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Fuel Pressure Fixed

The FMU was bad. The fuel pressure now rises without vacuum to the regulator and the rich condition is fixed. No more black smoke, no more fuel smell.
However it still stumbles when the electric fan comes on and it still doesn’t want to idle after it’s been running awhile. It runs down the road well though. I still think the alternator is getting abnormally hot. I measured the temp and it was 165*. The supercharger was 134* and I think the upper manifold was like 120 some odd I think. Is 165* normal? I’m about ready to set it on fire.

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