do i have a bad fuel pressure regulator??

[85cleangtvert]

car in question is a 91 GT automatic. it runs and drives good except for when i try to get on it. it doesnt kick down when i step on it, it just back fires through the intake and sputters... if i drive it normal or slowly press the throttle i can get it going good but on the freeway when i try to get it to kick down or when i step on it hard from a stop it just falls on its face. so far i have changed the plugs, wires, tfi module, fuel filter, put the stock injectors in (came with 24#), the MAF is stock. I just put a coil from my other mustang. i checked the fuel pressure and it was in the 40's. im thinking it is getting too much fuel when i step on it... in my mind all i can think of is the fuel pressure regulator but i havent changed one before and i havent had one go bad so i dont know exactly what it does... but if it is bad and somehow allows too much fuel to go to the injectors than that is what it feels like... i am going to change the cap and rotor tomorrow just for fun although they both look ok... any other imput, suggestions or questions to help find out what is wrong is appreciated! thanks!

 

[dcurtis]

Is the maf calibrated for the 24's or the 19's? Hows your timing?

 

[85cleangtvert]

i believe the maf is stock but i guess it is possible that it is calibrated. is there anyway to tell by looking at it? the timing is at 10* right now. i have tried it from 6 all the way to 18 and everywhere in between...the best it has ran is between 8-12* but still has problems

 

[85cleangtvert]

oh yeah i also did a compression check and they were all 135+ , not the best but the car does have 185K on it. also checked the vacuum and that was good.

 

[HISSIN50]

Even if your CEL is not on, pull codes. This issue might have stored a lean adaptive limit code.

How is fuel pressure when it bogs down?

WIth a stock regulator, you should not be in the 40's. If you pull the vac line off the FPR while it idles, does the FP reading increase or stay the same? If it doesnt increase by ~5 PSI, there's an issue. Fuel inside the vac line that goes to the FPR is also a tell (of a bad diaphram).

If that's ok/resolved, check your TPS for any breaks in the signal reading, or a WOT reading that's less than about 4.5 volts.

Good luck.

 

[85cleangtvert]

i pulled the vac line to the fuel pressure regulator off when the car was running and it sucked gas out. is this normal or is it a bad fpr? i checked the fuel pressure and it looked good it was like at 40 and when i tried it with the vac line to the fpr off it jumped up a little.

 

[HISSIN50]

If fuel came out the vac line to the FPR, the diaphram is probably bad. As a result, you have fuel in the vac system (not good) and the pressure differential between idle and WOT isnt going to be as great as it should be.

 

[85cleangtvert]

so it sounds like i should go ahead and change the FPR

 

[HISSIN50]

If gas was in the vac line, then yes. Some aftermarket FPRs can be rebuilt, though finding parts can be tough. If stock, I'd grab a known good stocker or a quality aftermarket piece.

 

[85cleangtvert]

i didnt see gas in the vac line probably because it would get sucked up or evaporate . when i tried to pull off the vac line when the car was running it sucked fuel out and it sprayed out the top of the regulator.

fuel is not supposed to be able to come out of the vac. port on the FPR correct?

 

[HISSIN50]

fuel is not supposed to be able to come out of the vac. port on the FPR correct?

Correct.

 

[85cleangtvert]

i changed the fpr. my car was still not running right finally found out what it was and it was a different maf than stock. i dont know what it is but it is not a stock one. i put a stock one and it runs great now. as it should after i changed a lot of parts.

 

[D-SLO]

Check the wire on the sensor of the MAF you took off. Check ito see if there's any debris or dirt blocking it. It may still be good and if it is one calibrated for the 24's you'll want to use it if you decide to reinstall them. MAF sensors are calibrated to work with only one specefic size injector. The stock MAF is designed to work with 19lb's not 24's