karpetcm

Ok i have 96 Z28. The car will without a doubt it will start each and every time. Its when you first go start it after sitting for more then 10 minutes it will take 15-20 cranks. If you turn it off and turn it on immediatly then it turns on after the 4-5th crank but no matter what it will always start. This is what ive checked so far wether its correct or not.

1: Fuel pump primes and makes noise when ignition key in ON Position
2: I pulled the vaccum hose off the FPR and ran it, no leaks also put my finger to plug the hole on the vaccum hose still not on the FPR and FPR did not leak. There is vaccum sound coming from the vaccum hose and its strong.
3: When i had a Fuel Pressure Gauge put on the Fuel Rail after the FPR with vaccum hose off to immitate Wide Open Throttle it showed 25psi not rising or dropping even after 5 minutes. Slso there was snother clear hose connected to the fuel pressure gauge were it would route the fuel out and it was a slow flow out the hose it seemed like your pour water through a straw snd the speed that it comes out on the other end is just how it flows because if gravity no real pressure just a downward flow.

i just dont get whats going on. I will say and rare because i dont drive the car that long often. But if you drive it more then 20 or so minutes it will have trouble idling and wants to stall. This car has a new Opti, wires, MSD Coil, furl pumps bern changed all by prior owner. Brand new MAF as well.

Injuneer

You have ruled out a leaking fuel pressure regulator diaphragm.

Confusing - was the engine running when you did this?

What does "on the Fuel Rail after the FPR" mean? - You put the fuel pressure gauge on the Schrader valve, which is on the fuel supply side hardline. You do not connect it to the line with the FPR.... that is the return line.

Here's what you want to do. Leave the vacuum hose where it belongs, on the FPR.

Turn the key to "run" (do not "start") and note the maximum pressure reading on the fuel pressure gauge when the pump shuts off. Should prime to at least 40psi. Watch the gauge to see how fast the pressure drops off. If it drops rapidly, it will cause extended cranking times, and can be the result of several problems.

Now start the engine. Take the vacuum line off. The "correct" fuel pressure is 43.5psi. GM accepts anything within the range of 41psi to 47psi as within tolerance. If you have 25psi at this point, you have a problem. Reattach the vacuum line with the engine still running. Fuel pressure should drop proportional to intake manifold vacuum. A stock cam will typically drop the pressure about 8psi. 43.5 - 8 = ~35psi.

Now tape the pressure gauge to the windshield, take the car out on the road, and take it up to at least 5,000 RPM. Watch the fuel pressure. At WOT it should not drop below 40 psi.

Never saw a fuel pressure gauge like that. Are you sure it isn't just connected to a leaking bleeder valve to relieve the pressure in the system before you disconnect the pressure gauge? Post a picture of the gauge.

Have you ever scanned it for codes?

karpetcm

Hi Injuneer,

sorry for the confusion and appreciate the advice for sure.

I have never scanned it for codes.

The fuel pressure gauge was hooked up to the shrader valve and car was running

shoebox

If the pressure gauge you were using has a relief valve and hose and fuel was leaking into it during your test, the valve on the gauge is leaking and will skew your pressure reading.

karpetcm

Hi Shoebox,

when we saw a low reading of 25psi he opened the relief valve to see what the pressure was like and it just kinda poured out like ur just dumping water through a straw using just gravity. I think i really need to invest in just buying a fuel pressure gauge anyway and will just buy one and retest, before i do anything.

Injuneer

If the hose connector wasn't screwed on tight to the Schrader valve, it may not have depressed the valve core fully.

karpetcm

[QUOTE=Injuneer;6983515]If the hose connector wasn't screwed on tight to the Schrader valve, it may not have depressed the valve core fully.[/QUO


I think what needs to happen is i need to test it again. Funny thing is once the car is running and i go through the rpm's all the way to the top car pulls nice. This starting issue is just got me baffled for a long time and finding someone who knows how to work on these cars is like trying to win to lotto.

David94TA

Sounds like a problem I had. Turned out to be leaking injectors causing a "flooding" condition. Here is my write up:
https://www.camaroz28.com/forums/lt1...inally-867642/

karpetcm

Today i went and ordered the Fuel Pressure Gauge Test Kit. So ill be getting that soon to re test. I had the car on today as well, now what it does in the last couple of times starting is it will try to quickly start the motor on the first crank then dies, cranks over a few more times then it starts up.

It didnt try to start up right away it would take 10-12 cranks before now it tries to start up on the first crank dies a second later cranks a few times and then starts. Also i noticed after 20 minutes of idle the battery gauge starts to drop lower and lower and i hear a tiny sputter like a tine puff from the exhaust or a hick up if that make sense every couple of seconds. Its super hard to explain it and im probably not very exact but in the vid and my exhaust is a tad loud you can hear it sputter a bit if you listen carefully. This car has new battery and alternator as well. Hissing noise is the A/C being turned off by me. When i go to the bottom of the car you can hear a clank or thump, hick up, sputter something of that sort.

Injuneer

Videos really don't seem to do it for me. Listening with my Sennheiser over ears, with total isolation from the outside world didn't help.

Just curious.... you still haven't retested the prime/leak down fuel pressure with a gauge that isn't leaking? Couldn't you just borrow one at a local auto parts store?

karpetcm

Hi Injuneer,

I actually havent really left the house back is really bad. I ordered one since there so cheap and hopefully when i get it in a few days i feel better to go down to check it.

karpetcm

Ok finally got the fuel pressure gauge on and went to test it. In the video i pulled the vaccume hose off to immitate WOT which went up from 30psi to 39PSI. I also revved the motor with the vac hose on the regulator till 4000rpms which looked like it didnt move from 30psi. Also i turned the car off with the vac hose on the regulator and off and the pressure dropped to zero right away. So with the vac hose on the regulator it stayed at 30spi at WOT and with it off went up to 39PSI. Seemed to me that it didnt hold pressure at all but this could be normal. I did it several different ways in the vid as i pulled the vac off you can hear it hissing.

Injuneer

When the fuel pump shuts off the pressure should not drop more than 5psi in 10 minutes, per the factory manual.

karpetcm

Ya i wish i think the fuel pump is toast or something with fueling is wrong it pretty much drops off right away. Holds no pressure at all.

Injuneer

Rapid loss of pressure:

-FPR not fully shuttling off fuel return
-faulty check valve in pump
-leaking injectors
-leaking fuel line, including the flex line in the tank

You already checked for a leaking diaphragm in the FPR.

But, your fuel pressure is slightly low. You need to test the pressure with the engine under load to determine if the pump can pump adequate fuel. See my post #2. Free revving the engine at 4,000 RPM does not do that. I would have expected more movement of the gauge when you revved it, but if you were moving the throttle slowly, it won't move much at all.

FPR not shutting off fully, and leaking lines can cause low fuel pressure. Faulty check valve in the pump will not, just extend cranking time.