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post #1 of 12 (permalink) Old 07-13-2004, 08:14 AM Thread Starter
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Fuel Pressure

I have upgraded to a 255 LPH return-style fuel pump. This completely overpowered my stock fuel pressure regulator. Pressures were at leat 10psi high. Wound up switching to the same design used on T-Birds. Thought was fine, but I may be just over the edge with this one too.

Originally I had a fuel rail gauge. I've upgraded to an electric unit now. Also installed a vac/boost gauge next to it. Makes a difference to see it under driving conditions.

Here's what I see
30psi @ 20" vac (needle sometimes giggles up to 38psi)
38psi @ 10" vac ***I think this is my problem
40psi @ 0 vac
44psi @ 6psi


What pressures do you guys see?

I've been having real trouble getting my low end af dialed in. When I first accelerate, getting -14% fuel trim. And a second later is settles out close to 0. This happens after tip in at any speed bellow 80mph. At steady state, trims look good.


I think that the regulator is not reponding as it should. It seemed like it was at first, the fuel responds with the boost gauge in unison. Don't think its maintaining 39.5 psi across the injectors to the manifold. Have a feeling it's ramping and the wrong rate.


John

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post #2 of 12 (permalink) Old 07-13-2004, 09:01 AM
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I can confirm all your readings except the 10" of vacuum. I have never noted the pressure at that point but I have to run an erand at lunch and will check for you. I have the SVO setup with stock Tbird regulator and 190 LPR pump 30# injectors. Stay tuned

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post #3 of 12 (permalink) Old 07-13-2004, 09:04 AM
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post #4 of 12 (permalink) Old 07-13-2004, 09:12 AM
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Acording to my electric gauge at idle at 19 inches of vacuum I am making 39 psi. It stays there till I get down to around 5 inches of vaccum then it rises to 44 psi when I reach 0 manifold pressure. It then goes upto 50 -52 psi psi at 8 psi manifold pressure.
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post #5 of 12 (permalink) Old 07-13-2004, 10:36 AM Thread Starter
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I talked to Winston prior to ordering the Autometer stuff. I would have preffered the Winston & Scott monitor if it was available. I do like your display....
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post #6 of 12 (permalink) Old 07-14-2004, 04:44 PM
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John E.,

Based on the 1:1 gain rate that the stock regulator should have (another reason to get an aftermarket fuel regulator), for 6-psi of boost you have 6 additional psi of fuel pressure or 46 psi. The fact that you have 44 psi tells me something isn't right.

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post #7 of 12 (permalink) Old 07-14-2004, 10:57 PM Thread Starter
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I agree that the fuel pressures seem wrong. Think I'll datalog (video tape) the gauges. It's hard to read them and drive. At least difficult to look close enough to tell exact pressures. 20 and 10 "vac are easy, but the car is really moving between 6-8psi of boost

Johnny Langton runs a Kirban fuel pressure regulator sucessfully. Is anyone else here? AED had nothing but bad experiences to share about aftermarket regs. and they tried several of them.

Would like to resolve this fuel issue with my car. Have a set of 36#/hr injectors on the way. At least when the pressure is high, they won't add as much extra fuel. Could probably step down to a 190lph pump too. I'm currently peaking just under 50#/min of air (4.6v of 90LMAF) with an AF of 11.7, basically 256#/hr of fuel or 32#/hr per injector. So my 42's are overkill and 36's have 12% more growth available.


Thanks for the help, can use all I can get.


John

Last edited by JohnE; 07-14-2004 at 11:04 PM.
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post #8 of 12 (permalink) Old 07-15-2004, 08:51 AM
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John,

Sorry I forgot to write back at 10" I have 34psi on the rail

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post #9 of 12 (permalink) Old 07-15-2004, 10:37 AM Thread Starter
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Thanks Tim, you have the pressure I would expect to get at 10". Obviously I have fuel issues to resolve. Wish there were aftermarket options with the same quality of the OEM unit. I'm tempted to install two OEM style regulators in parallel.
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post #10 of 12 (permalink) Old 08-01-2004, 11:47 PM
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Hey, has anyone noticed the fuel pressure dropping within 30-60 minutes after turning the engine off? Jim at AED thought this was abnormal. I have a mechanical gauge installed on the fuel rail and we noticed a drop off after 45 minutes of the car sitting. Jim thought the pressure should have held longer. Is this normal?

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post #11 of 12 (permalink) Old 08-03-2004, 05:49 AM Thread Starter
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I get a bleed-down of the fuel pressure within similar time frame. Either the pressure regulator or the pump can leak pressure back to the tank. I wouldn't sweat it.


By the way, I've switched back to a 190lph pump and 36# injectors. My fuel pressures now track manifold pressures properly. Made a HUGE difference in drivability, now that the fuel calculations are correct. If I'd needed to keep the larger capacity fuel, would have added a second oem regulator.
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post #12 of 12 (permalink) Old 08-03-2004, 08:06 PM
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Thanks John E...

I was taught a little trick from a ford mechanic today...He said to turn the ignition key on to start and wait 3 seconds to turn the ignition on...He said that will increase the fuel pressure for start up and allow for proper calibration of the air/fuel mixture before start-up...I have tried it and the car starts great cold or hot...

Might want to try it John E...

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