Attn: PKRWD more fuel Q's

Hyper92GT · 07-25-2002, 09:42 AM

I read your reply about checking Fuel pressure.
Recently I have have backfiring and overall loss of upper range power, it seems to fall flat in 3rd gear at 4000rpms (hard to tell in 1st and second but more evident on highway roll ons)
So, I clamped the fuel line and the F/P still fell.
Then clamped return line, same effect, both with Key on eng off.
Went from 38psi right to 20psi and slowly over 5-10sec fell to zero.
Is this normal. I have an AFPR and 19lb injectors with 190lpr in tank.
thanks

PKRWUD · 07-25-2002, 01:52 PM

Your description sounds more like a mass air problem, but your fuel pressure issues are typical for leaking injectors. If you clamp off both the source of the fuel, and it's ability to return to the tank, the injectors are the omly place left where the fuel has to bleed down.

Take care,
~Chris

Hyper92GT · 07-25-2002, 02:01 PM

Sorry but on this topic i am fairly ignorant. What exactly would be wrong with the injectors (ie technically). I will be replacing next year for the blower setup but would like to drive the rest of the year with what i have. (only drive weekends). I know you cannot diagnose over the net, but other things being equal would it cause damage even if pressure stays up under load (ie engine running).
I will look at the mass air also , thanks for you help!!!!
PS what size injectors should I purchase for an S-trim, with existing ported TFS heads, crane cam (.533/.544 i think 270/276) and edlebrock intake, forged pistions etc.
Thanks again.

ultraflo · 07-26-2002, 03:02 PM

I've noticed that alot of people run 42lb injectors with an S-trim... ask around and see what you come up with

...can't help you with your other issues... I'll leave that to Mr. PKRWUD

jimberg · 07-26-2002, 03:33 PM

There are some other possibilities for the location of your leak. Some AFPRs are sensitive to fuel additives, especially injector cleaner or octane boost. Fuel can leak from the vacuum port into your intake. This would also cause the backfiring. This happened to me.

Pull the vacuum line off of the AFPR and then have a friend turn the key on and off a few times to pressurize the fuel lines. See if fuel comes out of the vacuum port.

Another place to look is the seal at the top of the injector where it meets up with the fuel rail. This is less likely since you would notice fuel pooling on your intake unless it's happening under the plenum. Does your engine compartment smell like gasoline?

07-25-2002, 09:42 AM	#1
Hyper92GT slow like mud Join Date: Mar 2000 Location: toronto Posts: 180	Attn: PKRWD more fuel Q's I read your reply about checking Fuel pressure. Recently I have have backfiring and overall loss of upper range power, it seems to fall flat in 3rd gear at 4000rpms (hard to tell in 1st and second but more evident on highway roll ons) So, I clamped the fuel line and the F/P still fell. Then clamped return line, same effect, both with Key on eng off. Went from 38psi right to 20psi and slowly over 5-10sec fell to zero. Is this normal. I have an AFPR and 19lb injectors with 190lpr in tank. thanks __________________ 1992 DECH GT Not stock, still slow.

07-25-2002, 01:52 PM	#2
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	Your description sounds more like a mass air problem, but your fuel pressure issues are typical for leaking injectors. If you clamp off both the source of the fuel, and it's ability to return to the tank, the injectors are the omly place left where the fuel has to bleed down. Take care, ~Chris __________________ Webmaster: Rice Haters Club Jim Porter Racing Peckerwoods Pit Stop Support Your Local RED & WHITE!

07-25-2002, 02:01 PM	#3
Hyper92GT slow like mud Join Date: Mar 2000 Location: toronto Posts: 180	Fuel injectors Sorry but on this topic i am fairly ignorant. What exactly would be wrong with the injectors (ie technically). I will be replacing next year for the blower setup but would like to drive the rest of the year with what i have. (only drive weekends). I know you cannot diagnose over the net, but other things being equal would it cause damage even if pressure stays up under load (ie engine running). I will look at the mass air also , thanks for you help!!!! PS what size injectors should I purchase for an S-trim, with existing ported TFS heads, crane cam (.533/.544 i think 270/276) and edlebrock intake, forged pistions etc. Thanks again. __________________ 1992 DECH GT Not stock, still slow.

07-26-2002, 03:02 PM	#4
ultraflo NX dealer-man Join Date: Sep 1998 Location: Peoria, Illinois Posts: 977	I've noticed that alot of people run 42lb injectors with an S-trim... ask around and see what you come up with ...can't help you with your other issues... I'll leave that to Mr. PKRWUD __________________ RLS Racing! 93 LX 9.20 @ 147mph 03 Mach 1 12.39 @ 116mph

07-26-2002, 03:33 PM	#5
jimberg Registered Member Join Date: Oct 1998 Location: Rogers, MN Posts: 2,089	There are some other possibilities for the location of your leak. Some AFPRs are sensitive to fuel additives, especially injector cleaner or octane boost. Fuel can leak from the vacuum port into your intake. This would also cause the backfiring. This happened to me. Pull the vacuum line off of the AFPR and then have a friend turn the key on and off a few times to pressurize the fuel lines. See if fuel comes out of the vacuum port. Another place to look is the seal at the top of the injector where it meets up with the fuel rail. This is less likely since you would notice fuel pooling on your intake unless it's happening under the plenum. Does your engine compartment smell like gasoline? __________________ 351W 89 Mustang GT Convertible

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