Fuel pressure too high?

all motor 5.0

New Member
Jun 18, 2005
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I've been watching my fuel pressure lately and have noticed it is around 38psi at idle and 43-44psi at WOT. I have an FRPP AFPR on the car. My mods are:

Ed Curtis .547 lift cam
TFS TW heads
1.6 roller rockers
75mm Holley TB and EGR spacer
Edelbrock IM
24# injectors
80mm Pro M MAF and intake
MAC headers
Bassani catted X
Flowmasters

Should I drop my pressue down a bit here? At the track, my trap speeds seemed low to begin with at only 101mph, I know running too rich can cause part in that too. Would it be better to run 38psi at WOT instead? Thanks in advance.
 
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all motor 5.0 said:
I've been watching my fuel pressure lately and have noticed it is around 38psi at idle and 43-44psi at WOT. I have an FRPP AFPR on the car. My mods are:

Ed Curtis .547 lift cam
TFS TW heads
1.6 roller rockers
75mm Holley TB and EGR spacer
Edelbrock IM
24# injectors
80mm Pro M MAF and intake
MAC headers
Bassani catted X
Flowmasters

Should I drop my pressue down a bit here? At the track, my trap speeds seemed low to begin with at only 101mph, I know running too rich can cause part in that too. Would it be better to run 38psi at WOT instead? Thanks in advance.

The ECU will adjust for the lower pressure over time - it's better to get the MAF set up correctly. OTOH, there is no reason to run other than stock 39-40 psi with vacuum line disconnected. If you change it and see a temporary boost in power you will know for sure it's running too rich.
 
I made an appt. to get the car tuned at MD Motorsports here in Cincy. They agreed the car had MUCH more in it still. We'll see how it goes, Thursday April 6th. It's getting the SCT chip as well.
 
The injector pulsewidth shouldn't vary at WOT, and that's where he is feeling that he is sluggish. At all other times, the adaptive strategy should kick in.
Good luck.
 
all motor 5.0 said:
Fuel pressure is varying at different RPMs which shouldn't really happen that I know of.
It will to a degree. Crudely stated, fuel pressure is inversely proportionate to manifold vac.

If you had a manifold vac gauge, you would see that when the vac reading drops, the FP would increase a hair. WHen vac is high, FP is lower. If you are doing a little canyon carving, you would see the vac and FP reading move about a good little bit, but the FP shouldnt fall out of the acceptable specs (FP shouldnt drop below 30 PSI, nor go higher than your vac-off setting).

Good luck.
 
Thanks for the input, I have a VAC gauge in the car too and read it all the time. The pressure on idle is around 37psi and under WOT it's at 44ish psi, should it vary that bad? Should I try to set the FPR with the vacuum source plugged and see where I'm at then?
 
all motor 5.0 said:
Thanks for the input, I have a VAC gauge in the car too and read it all the time. The pressure on idle is around 37psi and under WOT it's at 44ish psi, should it vary that bad? Should I try to set the FPR with the vacuum source plugged and see where I'm at then?
That range of idle vs WOT pressure-delta is normal IMHO. I have an 8 PSIG spread one on stang and 7 on the other.

Me thinks that there is very little difference in setting the FP with the vac line plugged vs unplugged (just venting). I would do it plugged (just leave your finger over the end of the line).

Without datalogging/wideband etc, it gets to be hard to fine tune the ideal pressure IMHO. The other smart folks will be able to help in that regard (I am one who is willing to run a little rich vs getting every last ounce of performance). But with your nice mods, I bet you're leaving a nice little bit on the table without a tune. (OOPs, you know that and have an appt. :nice: ).

I would just ask them what base fuel pressure and timing they want the car at (I bet they want stock FP and stock timing - they will change as needed for FP and the chip will take care of timing and the rest of the changes).

A 94-95 guy just had Don do an SCT chip on his ride and got some nice gains and better drivability out of it (the AODE 5N95 U4 computers are real real finicky though, unlike the A9 puters).

Good luck!
 
I'll definitly post up the dyno sheet when I get it all done, what shift points would you think to shift at? Powerband rated from 2600-5600, the stock dyno chart was dropping off at 5400 so I was shifting at like 5500 at the track.