85ZZ4TPI

The other day I tried to adjust my fuel pressure with a scanner hooked up to the computer, I started arond 50psi and would run it wide open through the gears until the volts plained out. I first got a reading of arond 960MV so I backed off some pressure thinking that would lean it down a little. It didnt work, I continued to back off pressure until my bolt in my pressure regulater was almost out and the lowest reading I got was like 933MV? I have also noticed I am dropping fuel pressure fairly fast after shutdown. I have eliminated injectors because they were redone this spring, I think the checkball in my fuel pump is bad. Any relation? Any other ideas? Thanks

TRAXION

85Z -

What scanner are you using? I noticed the same thing a LONG time ago when I use to have an AutoXRay. Then I used Diacom and found the the AXR was wrong. A few of us got together and talked with AXR and eventually found out that it was reading O2 volts wrongly.

Tim

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TRAXION's 1990 IROC-Z
Best Time = 12.587 @ 107.97mph (1.710 60ftr) on the long runner setup.
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-=ICON Motorsports=-
Moderator: PROM board at thirdgen.org

GMTech

If you have ever heard the phrase "you get what you pay for", now you know why. AXR is a low buck, cheap scantool. I'm not trying to disuade anybody from buying one, but for the best results, you have to have the best. The readings may be skewed slightly, but you also have to consider the sample rate. The scantool can't show you all the changes as they happen, or you would never be able to read them. So the O2 voltage may change several times, and you only see a few. In your case, probably the most accurate method would be to tap a DVOM into the O2 sensor signal wire, and monitor it directly.

If you are at a dragstip, you could set the AFPR by PSI and do a few runs after each change. Then you will acheive TRUE potential.

Just my rambling $.02

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If you live in Southeastern US, check us out!
South East Thirdgen

"I used to have a handle on life, but then I used it as a plunger and broke it" -The Wave

ASE Master Tech + L1
Savannah, GA
'87 Trans Am-K&N,Cold air induction, SSM SFC, Boxed LCAs, 8mm Accel wires, Flowmaster, 16" GTA rims.
'97 Bonneville SSE

Jed

You may want to consider something like an Autometer Air/Fuel meter if you do a lot of tuning. One thing I dislike about thirdgens is there is only one 02 sensor, so you only see what's happening with the left side of the engine. I use two A/F meters and two 02 sensors, so I can monitor both sides. If you don't want to buy two gauges, buy one, a toggle switch and an additional 02 sensor for the right side. Then you can switch between left and right.

The AutoXray is primative, but it is portable and easy to use, as it was designed for 'home' use. It doesn't really compare to the Tech 1 / 2 or Snap-On scanners (I don't even like the Snap-On scanner that much)because those pieces were designed for, shall we say 'industrial' use. Hence the high price tags that those units come with. But didn't AutoXray correct the 02 sensor inaccuracy? Really, it's not a bad tool if you'll only be using it on your personal vehicles and you don't have at least $2000 to spend on a better scanner. And now I'm way off-topic so...oops.

Jed

O yeah, 85Z...if you want to rule out the fuel pump check valve, clamp off the rubber part of the return fuel line w/ a pair of vise grips. If the fuel pressure still drops after you have done this, the check valve isn't your problem. Then you'd be looking at either a leaking regulator or injector.

GMTech

Actually, Jed, you have it backwards. You need to clamp the SUPPLY line, AFTER the pump stops running. If you clamp the return line, you are deadheading the pump, wich tests max pressure (usually about 80PSI), but does not test the checkvalve, the checkvalve is in the supply line of the pump.

It is the regulators job to keep pressure on the return end. Anything above 45 PSI gets bled off, anything below should hold.

------------------
If you live in Southeastern US, check us out!
South East Thirdgen

"I used to have a handle on life, but then I used it as a plunger and broke it" -The Wave

ASE Master Tech + L1
Savannah, GA
'87 Trans Am-K&N,Cold air induction, SSM SFC, Boxed LCAs, 8mm Accel wires, Flowmaster, 16" GTA rims.
'97 Bonneville SSE

RP1987GTA

after installing a new Walbro pump i'm having trouble with pump leak down ...but i also replaced the pulsator ..so it might be lealing out around that ???????

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87GTA,MAF screens removed,K&N,modified air intake,ADSchip,3:73s,3inch cat back Flowmaster,TPS.54,Bosch Plat plugs,base timing 6BTDC,Bilstiens in the rear....,don't let yer meat loaf

85ZZ4TPI

Traxion-I used a snap on scanner that I borowed.