High fuel pressure.....

[zapp240]

Hey all, recently purchased my 87 GN and am in the process of getting the car back to a street friendly driver. The car was pretty much clean and road ready when purchased, but was set up more as a show/ occasional strip car. I have replaced the red armstrong R106 chip with a TT chip for 93/94 octane. gave Eric the known spec as well i could, (ta 62- 3"rjc dp- slic upgrade- new tank hot-wire and fp but not sure what type- unknown internal motor upgrades- 42.5# injectors- hooker cat-back exhaust- kn intake) now the issue i am having is , as stated on the chip install, cant get the pressure below 50psi. thought it may have been the holly adj regulator so swapped out with an accufab adj and get the same results. the lines look in excellent shape. I have searched the other threads and came to the conclusion that the return line is probably the culprit, so my question i have is are there any known weak spots i can check before looking into replacing a very good looking return line?

 

[No disintegrations]

Maybe the fuel pump is overkill for your setup? Could consider smaller pump. Or has a dual pumper and both are always running for some reason? It was a show car after all.

 

[bpman1234]

That happened to it turned out to be the oring on the regulator was blocking flow wasn't properly seated or tore up check it also try to blow out the return .

 

[626gn]

Before messing with the lines I would check what pump you currently have. You're going to want to know this anyway at some point. Having said that, what specific problem are you having with the high fuel pressure or are you just trying to hit a certain number? The 43psi number was meant to be a starting point, not necessarily where every car likes to be at.

 

[zapp240]

yeah, unless i drop the tank and see whats in it, wont know the pump volume. at least it's a new tank and shouldn't be that bad. a few pics if anyone can tell by sight, i did id the howire kit

 

[zapp240]

no problems to tell, just wanted to hit the starting point. have yet to get into trying to tune it. was a big improvement on starting and idling with the new chip now want to get best performance. need to get some info from the scanmaster to see what needs tuned, but would have liked having the fp closer to 43,5

 

[626gn]

yeah, unless i drop the tank and see whats in it, wont know the pump volume. at least it's a new tank and shouldn't be that bad. a few pics if anyone can tell by sight, i did id the howire kit

Unfortunately as you know the only way to tell is drop the tank. She looks nice under her skirt though . If that's any indication it must be a very nice car.

 

[Nick Micale]

Everyone has opinions, mine is if the car runs ok, do not mess with it.

I have set 50 psi base pressure in many TR's and they run fine.

Also gauges can vary a lot, a 5-10 PSI difference in gauges is not unusual, and I prefer to have a little more pressure than too little pressure.

 

[fastblackracing]

Any time there is a fuel pressure control issue you should also
verify that you have the 1 to 1 pressure rise as the boost builds....
If your base vacuum line off pressure is 50 and you are pushing
18 pounds of boost you must have 68 pounds fuel pressure at
wide open throttle. Or add in whatever your boost number is.

I have seen pinched fuel lines both rubber and metal,
also seen the metal hard pipe to the regulator blocked
with rust inside and it was a low mile car.

As Nick stated it is not an absolute that you have to use 43# base
as you can tune around it....but you must have the 1-1 pressure rise.

You may simply be overrunning the regulator with excess fuel capacity
at idle...from to much pump for the stock return line.

Also make sure the tank has the proper plastic containment well around
the fuel pump/s as not all replacement tanks have this feature. HTH

 

[Reedogg]

Either the return line is too small for the pump or there is a restriction in the return line. The Saginaw fittings in the return line at the regulator and the flex line under the engine are really restrictive. These vary from car to car so perhaps yours are smaller than normal. My last car had a Deatschwerks pump which flowed enough that the return line couldn't return it all to the tank. The result is pressure that wouldn't fall below 48 psi. Same pressure with vacuum line on or off. This is only a problem when fuel demand is low (high return line flow rate) like at idle and cruise.

 

[zapp240]

Everyone has opinions, mine is if the car runs ok, do not mess with it.

I have set 50 psi base pressure in many TR's and they run fine.

Also gauges can vary a lot, a 5-10 PSI difference in gauges is not unusual, and I prefer to have a little more pressure than too little pressure.

Thanks Nick, yeah, I agree , if it's running good don't temp fate,,, the gauge reads spot on since that is one thing I can do well, I work in a calibration lab, all my meters , thermometers, and gauges are one thing I can count on ,,,,,,,8)

 

[zapp240]

update on this issue. Haven't had time to drop the tank, been busy chasing other issues. I put in an AEM pressure sending unit on the fuel rail and have seen the pressure start at 50 psi after initial turn on then drop to 39 psi after running the car for about 30 minutes. I am able to set up for 43/44 psi vacuum line off at this point. at WOT i see 62 psi and see the 1 psi per psi boost with my 19 psi of boost. any idea why the restriction happens with car cold, then fine after warming up.

 

[mikestertwo]

update on this issue. Haven't had time to drop the tank, been busy chasing other issues. I put in an AEM pressure sending unit on the fuel rail and have seen the pressure start at 50 psi after initial turn on then drop to 39 psi after running the car for about 30 minutes. I am able to set up for 43/44 psi vacuum line off at this point. at WOT i see 62 psi and see the 1 psi per psi boost with my 19 psi of boost. any idea why the restriction happens with car cold, then fine after warming up.

Probably because your voltage is higher on cold start up. Typically the alternator will be putting out 14.2-14.5v on cold start up then will tapper off to about 13.5-13.8v after warmed up so your pump will be running faster on cold start up.

 

[zapp240]

looks like you called it Mike, cruised this weekend with the scan-master reading the volts and at startup was 14.2 and about 15 min later saw it had dropped to 13. 8 or so and dropped to the regular FP readings. I tried getting on it when getting onto the highway and it sputtered when still reading high (about 5 minutes after startup), would the irregular high FP cause that, it seemed to not do it afterwards, only when cold. not getting to hard on it since it seems to have a third band slipping issue. Am going to contact Janis Transmission to have the transmission re-done.