90 gt, running rough past 2500 rpms......

[HISSIN50]

all or nothing you mean there is pressure an then there is not right?

but never a low pressure from any other cause other then a bad FPR or pump?

All of nothing pertained to the FP wiring. At any given time, it generally works enough to give you full potential or it's so screwed up that the pump won't run. It's not often where you have like 6 volts reaching a pump (which would lead to low pressure, through no fault of the pump necessarily).

I mentioned leaky injectors before. There are also obvious things that could lead to low pressure like an external fuel leak, crimped fuel line, clogged line or filter, contaminated sock, etc etc. Low pressure generally comes from things like a bad pump, restriction, FPR or a huge leak.

Good luck.

 

[webslinger67]

i will check for restrictions, but as for the FPR , it works, and fuel leak is none... so.... sigh... the bottom line? fuel pump?

how hard is it to change out?

any forum instructions on how to do it?

 

[HISSIN50]

i will check for restrictions, but as for the FPR , it works, and fuel leak is none... so.... sigh... the bottom line? fuel pump?

how hard is it to change out?

any forum instructions on how to do it?

Before swapping the pump, do check voltage at the tank, and ohm out your ground back there. IIRC, you can do it without dropping the tank. You should see battery voltage minus a couple tenths of a volt at the fuel pump connector.

Otherwise, it's not too bad to do the tank. 5spd GT and Jrichker (I think) have FP write-ups that are very good (I know I recall David's; I can't remember if Joe has one - he has so many tutorials). I won't reinvent the wheel by typing up a bunch of crap that is hard to follow and not too helpful.

I'd use a Walbro pump, and be leery of overseas knocks-offs (there are a lot of 'em out there). I buy my pumps from one specific vendor whom has good prices and I trust.

Good luck.

 

[webslinger67]

what vendor is that?

 

[HISSIN50]

Dave at JD's Performance.

 

[webslinger67]

ok...update with a POLL

here is what I have done, and with all my trouble shooting the original problem points to the fuel pump... I am taking a poll to see if everyone else comes up with the same resulte..

1) tested pressure at the schrader valve..20lbs
2) pulled off vacuum tube to FPR, still only 20lbs at the schrader valve, even adding pressure to the FPR 20-lbs
3) changed out the fuel filter, still only 20lbs
4) checked and changed out the Fuel Pump relay...still only 20lbs
5) when pulled off the Schrader valve when key was on not running , no fuel squirted out the schrader valve, shows me the pump is not putting out the volume.. points to pump again.... bad pump baaaaad pump!!!!

tell me what you all think, is my last ditch effort changing out the fuel pump..... I just orderd a 255 pump from JD's Perf !!!!

 

[webslinger67]

************* UPDATE*********

for anyone that is interested on the update for my 90 GT running rough past 2500 rpms was .................... drumb roll please

THE FUEL PUMP....

James West Automotive here in Las Vegas, put the fuel pump i ordered from Jd's Perf and it now runs like a champ....


thanks again for all your help, and please, if you have fixed your mustang and asked for help in here, update your post please....

:SNSign:

 

[873Stang]

how long was it sitting for if it sits long enough gas will go bad i would either suck it out and put new gas or buy some octane booster just a thought

 

[webslinger67]

i had put new gas in it, believe me, it was the pump that was bad, it was 17years old... i would only expect it to go eventually..

 

[HISSIN50]

Glad to hear it you got it whipped.

 

[webslinger67]

yeah, so do i, now i just got to take it back tothem to fix the leak they made... sigh... is there no good mechanics any more?

 

[MattRRT]

Here we are in 2021 and this thread is helping immensely, thanks!