DanielRicany

Hi guys, I have a 1985 Corvette with a Miniram, 58mm throttle body, AFR 195 Eliminator Heads, flat tappet ZZ409 cam, Hedman longtube 1 5/8" headers, Dynomax true dual 2 1/4" exhaust, 1.6 Comp cam roller rockers, D.U.I. distributor, MSD 6AL2 ignition box, Descreened MAF sensor, no cats, and a few other mods.

My fuel pressure is supposed to be at 60, because I am running 24 lb injectors and need it for the injectors to keep up. Me and my tuner have been tuning off of 60. Anyway, when I connect the fuel pressure gauge, the needle flutters violently. This happened with the old gauge I had to, but I always thought that was just because the old gauge had a small leak. It jumps back and for from like 55 - 65 PSI. I don't think it does it on other cars either.

Does anyone know what could be wrong? I wanted to hook it up to see if fuel pressure drops off at high RPMs to see if I had an insufficient pump, but now I can't even set the fuel pressure accurately.

Thanks!

cumbercr

Close off the vacuum line to the regulator and see what happens.

DanielRicany

I did that and it was still fluttering but only slightly less.

cumbercr

Mine also flutters but not with +/- 5 psi swings. A certain amount is to be expected because the pump pulses.

DanielRicany

Okay. Can I set fuel pressure with the car off and the fuel lines primed? Or will that not work?

cumbercr

No, that won't work. I thought your goal was to see if your pump is undersized. I thought we had the conversation that you could find out by data logging at WOT and then looking at O2 voltage.

DanielRicany

It is. But I had some problems getting the car started yesterday after getting the trans in, and I had played around with the fuel pressure to see if maybe there was air in the fuel lines, to try to bleed it out. I had spark, fuel pressure, injector pulse, and timing set properly and it wasn't starting. Started up on starting fluid. Turns out the gas went bad after only 2 months. Drained it out and put fresh gas in and it fired right up. But since I messed with the FPR I'm trying to set fuel pressure again.

Tom400CFI

You're a "mechanic"...think about what you just said. How could there be air in the fuel lines, after the pump runs for more than a couple seconds??

powerpigz-51

Did you install the "washer" under the cap that goes with the spring? I tried leaving mine out, and it did the same thing. Ran fine, though.

DanielRicany

Because air rises to the highest point.

Tom400CFI

Really. And where is that point, in your fuel system? How does it do that when it's being circulated (pushed through the system) at a fairly high velocity?

And even if air were trapped in the "highest point"...who cares? What's it going to hurt? How? Think.

EDIT: My point is, once again, you're chasing your tail trying to resolve problems that don't matter, don't exist or both. The goal was to test your fuel pressure. Test your fuel pressure.

DanielRicany

Because it was sitting for 2 months with no circulation. And the fuel rails are higher than the return line. The reason why I was trying to bleed it out is because it wouldn't start. During that process I had adjusted the FPR to try to allow more fuel into the return line to try to bleed it out. I never thought that gas would go bad after only 2 months.

DanielRicany

Under what cap and what spring? In the FPR?

Tom400CFI

So? You think the fuel drained out past the regulator that holds ~40 PSI? And even if it did...lets say your regulator leaks, what do you suppose happens as soon as you turn your key on?

Chasing "problems" that don't exist.

DanielRicany

I wasn't chasing problems that don't exist. I was going through diagnosis procedures. If I have spark, fuel pressure, fuel injector pulse, timing set properly, compression, and injectors that ohmed out okay, what do you think is causing it not to start?

Especially for the fact that it was just running the same day for about 10 seconds until it shut off.

DanielRicany

Enough with this debate, Tom. What I really would like to know is what could cause the fuel pressure tester needle to flutter? Thank you.

cumbercr

You've been give a couple of suggestions. 1. Did you install the washer under the fuel pressure regulator cap? When you turn the screw to adjust pressure, the screw should be pressing on the washer. 2. The fuel pump pulses. There is a pulsator located in the fuel line coming off the stock pump. When you install the new 255 lph pump (and I know you will), throw away the pulsator and install a piece of 3/8 fuel line in its place.

In any case, the flutter is not causing operability problems. When adjusting the fuel pressure just adjust for the middle of the needle swings.

powerpigz-51

Yes. And fuel does not go bad in 2 months. I believe any air in the lines, ends up in the "air space" of the fuel tank in milliseconds after the pump comes on.

Tom400CFI

Fair enough. As you were...and good luck!

DanielRicany

This was the fuel that drained out after sitting for 2 months. It was Shell V Power 93 octane.