Problem @4500 RPMS

3

396LT1

New Member
Jun 1, 2004
29
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#1
Im kinda new to this site so i hope i have this in the right section.. Im posting for my service manager at the shop i work at, he has a 01 mustang Gt thats been fully built for performance but seems to have a fuel delivery or spark issue when the car reaches 4500 Rpms. Im not a mustang guy so bear with me here. Here are the mods

4.6 Dss Supermod Level 10 racing motor
kenny bell twin screw blower w/intercooler @ 9psi of boost
DSS blower cam
DSS Racing Heads
42lb injectors
Ford focus Fuel pump
K&N Cai
75mm Tb
Bassani cats & catback
Ford Racing Shorty headers
B&M 5 speed Tranny
3.73 gears w/stock rearend
Unknown Fuel Management unit
Dyno tuning & Fuel Management unit done by Anderson Motors in Clinton, IL

Codes i pulled with my Snap on scan tool are random multiple misfire after i delete that code it will return in a couple of days, Not right away... Engine appears to run ok and not be down on power it dynoed 501rwhp but when you take it up to 4500 rpms or higher it seems like it's needing more fuel and not getting it. with my scan tool the FRP(psi) is 6psi and it reads that from idle to about 4k. Now i have attempted to check fuel pressure but on the fuel lines there isnt a port to hook a guage up to. So How do you check fuel pressure with a gauge? What should pressure be on stock 4.6? What would be Optimal pressure for a setup like above? If there is anything that you recommend checking, or can suggest i look into i would appreciate it. were trying to get the car runing to it's full potiential rather quickly for the upcomming racing season.
 

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#3
sounds like he is loosing fuel presure up top. I assume you have a presure guage if you have a snp on scanner.

hook up the presure guage and see what the fuel presure is at WOT, maybe somebody with a KB can chime in on where the schrader valve is on the KB cars. with the stock rail there is a schrader valve on the rail.
 
#5
svttech76 said:
sounds like he is loosing fuel presure up top. I assume you have a presure guage if you have a snp on scanner.

hook up the presure guage and see what the fuel presure is at WOT, maybe somebody with a KB can chime in on where the schrader valve is on the KB cars. with the stock rail there is a schrader valve on the rail.
Click to expand...
I hope someone will chime in. I traced all along the fuel rail and the line leading to the rail and couldn't find anything.

Also could someone post a pic of what the stock pressure regulator looks like?
 
#7
unless this car was doing this from when you first installed the supercharger then i doubt it's the tune.

I have had MANY focus pumps go bad ( the focus did have a fuel pump recall for this problem)

If nobody speaks up on where the vavle is on a KB I will look it up my self. you do not have a presure regulator on this car, it has a fuel rail presure sensor . fuel presure in the returnless system is controled by the pcm.

another thing to look at is you might be running out of injector. not due to the sizing of the injector but because of manifold backpresure.

you have 42 pound injectors but in a boosted application you loose some of the fuel presure at the injector due to manifold backpresure. this loss is directly related to the fuel presure and boost PSI so for example at 40 psi rail presure and 10 pounds of boost you might see fuel spray out of the injector at 30 psi.

so that leads me to this question.... do you have kb's "boost a pump" installed. I would imagine you do considering the car was tuned and all.
 
#8
svttech76 said:
unless this car was doing this from when you first installed the supercharger then i doubt it's the tune.

I have had MANY focus pumps go bad ( the focus did have a fuel pump recall for this problem)

If nobody speaks up on where the vavle is on a KB I will look it up my self.
Click to expand...
Thank you I appreciate your help.
 
#9
ok now that i read some tech info from KB, you should have a schreader valve on the fuel rail unless you are using a newer fuel rail. and I would look at the fuel pump, you should be ok injector wise with the 42 pound units.

you need to check fuel presure at wot were the problem happens.

be carefull, you could blow it up if it's really low on presure.
 
#10
svttech76 said:
ok now that i read some tech info from KB, you should have a schreader valve on the fuel rail unless you are using a newer fuel rail. and I would look at the fuel pump, you should be ok injector wise with the 42 pound units.

you need to check fuel presure at wot were the problem happens.

be carefull, you could blow it up if it's really low on presure.
Click to expand...
Ive done some seaching on the site, and i see alot of guys are recommending dual cobra pumps and tank when running over 450rwhp. Do you think this is something that should be considered?

I also believe the random misfire is caused by a fuel issue but i really don't have anything to back up that theory until i can check the pressure, But Like i said before im pretty sure that the rails do not have a port on them to check pressure Jim (Owner of car) & I have checked and couldn't find anything.

Now if it doesnt have a port how would you guys normally check pressure? at the filter?
 
#11
396LT1 said:
Ive done some seaching on the site, and i see alot of guys are recommending dual cobra pumps and tank when running over 450rwhp. Do you think this is something that should be considered?

I also believe the random misfire is caused by a fuel issue but i really don't have anything to back up that theory until i can check the pressure, But Like i said before im pretty sure that the rails do not have a port on them to check pressure Jim (Owner of car) & I have checked and couldn't find anything.

Now if it doesnt have a port how would you guys normally check pressure? at the filter?
Click to expand...


at my work we have a adapter we can plug in to the fuel line just before it plugs into the rail and test from there.

we really need a KB owner with a 99-up 2v to post on this. I have worked on a KB 2v before but that was 3 years ago.

I do agree about the cobra pumps, I think he needs to do this upgrade. remember you also need the tank from a 03-04 cobra.
 
#12
Hmmm... My car has a very similiar problem! I have basically the same mods, including DSS shortblock, fuel injectors, etc. However, I do have dual cobra fuel pumps (just removed the baffle in the tank) on my 00 GT. And I have a Vortech S/C instead of a Kenne Bell.

On my last tune, they noticed at 4500rpm both fuel pumps would go into full duty cycle and then I would start losing fuel pressure. I called up a shop that did the fuel tank conversion and pump install (Murillo Motorsports in TX), and original tune and they are almost sure that it is a "fuel rail sensor". I'll provide the part number tomorrow. I bought one from Ford for ~$70. It is a cinch to replace.

Unfortunately, I don't know yet if this fixed the problem. I'm anxiously awaiting to get it checked out, but won't know for a couple weeks yet. I'm crossing my fingers, and I hope this is your problem too!
 
#16
The ford part number for this sensor is 3R3Z9F972AA.

My car was not throwing any codes, although I would hope that a sensor like this would be smart enough to throw a code. I guess the jury is still out on this being the guilty part.

My tuner was able to test it with his laptop while he was tuning my car (SCT XCalibrator), so I guess it was some sort of data logger that showed the duty cycle of the pumps and the drop in fuel pressure.
 
#18
ok so this may sound retarded - but did he make sure to get the SVT focus fuel pump? Someone on this site with a blown '99 GT bought the regular Focus pump (non SVT) and only when he started having fuel delivery issues did he realize that he got the wrong pump. Sorry if I'm no help, but definitely tell your friend to cross-check Ford P/Ns to make sure that isn't the problem. Good luck!
 
#19
stangGT97 said:
ok so this may sound retarded - but did he make sure to get the SVT focus fuel pump? Someone on this site with a blown '99 GT bought the regular Focus pump (non SVT) and only when he started having fuel delivery issues did he realize that he got the wrong pump. Sorry if I'm no help, but definitely tell your friend to cross-check Ford P/Ns to make sure that isn't the problem. Good luck!
Click to expand...


good point. there is a pretty large flow difference between the regular focus pump and the SVT focus.
 
#20
svttech76 said:
best way to test the sensor is using live data watch the FPS ( fuel presure sensor) and with a guage see if there is a difference between the 2.
Click to expand...
I can do that with my scan tool.. In the scan tool it reads that the frp is 6psi. But im still looking for a way to hook up a gauge when the rail has no service port.

Thank you Stang GT we will look into this tomorrow. It's a easy mistake that could of been made.

Would anyone happen to know the cost of the dual cobra pumps and the fuel tank?
 
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