Fuel Pressure

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   Hey all. I finally got another day on the car and here's what I found:

My adj. pressure reg was set to 'off'. Ha. 
I tested it by pulling the upper plenum, hooking up a fuel pressure guage (Tested as per 2 other guages and +-1psi, so calibration is ok), then jumpered the fuel pump on and the pressure read about 52psi.

I cranked down on the reg...no change...cranked some more...no change...the again, finally the pressure started coming down. At the same time the sound from the fuel pump changed to a much smother tone. It had kind of a rattle to it before.

So, don't let anyone tell you the fiero won't run on a returnless system!

Anyway, my question is about the 52psi with it blocked up..it seems a little low to me...expected more like 70psi? Maybe it was bleeding by a bit...not sure. When the vaccuum goes down the rate should rise I think..there is not much room for this to occur. Tuning will take care of it in any case I think.

Opinions?

Chay

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CFoss Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 13 February 2007 Location: Canada Status: Offline Points: 580	Post Options Post Reply Quote CFoss Report Post Quote Reply Topic: Fuel Pressure Posted: 16 June 2009 at 9:35am
	Hey all. I finally got another day on the car and here's what I found: My adj. pressure reg was set to 'off'. Ha. I tested it by pulling the upper plenum, hooking up a fuel pressure guage (Tested as per 2 other guages and +-1psi, so calibration is ok), then jumpered the fuel pump on and the pressure read about 52psi. I cranked down on the reg...no change...cranked some more...no change...the again, finally the pressure started coming down. At the same time the sound from the fuel pump changed to a much smother tone. It had kind of a rattle to it before. So, don't let anyone tell you the fiero won't run on a returnless system! Anyway, my question is about the 52psi with it blocked up..it seems a little low to me...expected more like 70psi? Maybe it was bleeding by a bit...not sure. When the vaccuum goes down the rate should rise I think..there is not much room for this to occur. Tuning will take care of it in any case I think. Opinions? Chay
	86 SE 3.4

Dr.Fiero Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Post God Joined: 12 February 2007 Location: Canada Status: Offline Points: 1726	Post Options Post Reply Quote Dr.Fiero Report Post Quote Reply Posted: 16 June 2009 at 5:32pm
	Yeah, you must have SOME bleed past.... I think I blocked mine off totally once, and it pegged the 100psi gauge off the end while it was dead ended. The fuel maps are scaled for 'x'psi/'x'in hg. So if you screw with the pressure, you're effectively changing the whole fuel table.

Capt Fiero Members Profile Send Private Message Find Members Posts Add to Buddy List Admin Group Founding Member Joined: 12 February 2007 Location: Canada Status: Offline Points: 4039	Post Options Post Reply Quote Capt Fiero Report Post Quote Reply Posted: 16 June 2009 at 9:08pm
	Chay it sounds like you one of the old regulators that you have to have the plenum off to adjust. If thats the case, look into the Holley regulator, it has a large at least 2" diameter wheel on the top of the regulator so you can reach in with a finger and adjust it with the plenum on the car and engine running. As for pressure, forgive me I don't totally remember what setup you have, but idle with engine running and vacuum applied, 35psi is good for 15# injectors on a semi stock motor or 17# injectors on a 3.4. However if your car is modded to hell, 40psi idle 50psi WOT is acceptable. When I was running my 19# injectors on my 2.8 with the Nitrous I ran 40psi idle and 50psi WOT, which on any regular non nitrous 2.8 would run horrible.
	Capt Fiero 88 Fiero GT 5spd V6 Eight Fifty Seven GT V8 5spd.

CFoss Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 13 February 2007 Location: Canada Status: Offline Points: 580	Post Options Post Reply Quote CFoss Report Post Quote Reply Posted: 17 June 2009 at 12:36pm
	I agree with what you guys have said. I have a 3.4 bored.5mm over, intake and exhaust ported, but nothing else right now (Stock injectors). At 50+ psi my blms were a little high (Lean) at low load values, but low (Rich) at higher load and I was at 11.5:1 at wot through the range, so I knew I was rich...now I need to redo the blm reads and see where I'm at. Hopefully I'm in the ballpark. A little wot highway time souds good ! It may take a bit though..I seem to have a tank leak and I want to get my rear suspension dialed in after the poly change etc.etc. Chay
	86 SE 3.4

CFoss Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 13 February 2007 Location: Canada Status: Offline Points: 580	Post Options Post Reply Quote CFoss Report Post Quote Reply Posted: 24 June 2009 at 2:59pm
	The tank leak is fixed. I have to find an excuse for a road trip to check the BLMs again. Man, did I have fun ripping around town though. I almost forgot how much fun the car is when it's right. Chay
	86 SE 3.4