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Old 02-02-2008, 02:36 PM   #1
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Question Hard Starting fuel pressure situation.

Greetings,

My 1995 Z28/M6 takes two turns of the key to start. I hooked up a fuel pressure gauge and turned the key on(without starting the engine.) I get 43 psi or so, which is in the acceptable range (41-47psi) according to my Haynes manual.

The problem is that the manual says my car should hold this pressure. Mine immediately drops back to zero.

I left the gauge hooked up, started it and drove it around. At idle, it is around 36-38psi, again withing spec (33-40psi or 3-10psi lower than pressure with engine not running.) As I give it more throttle and the vaccuum drops, the pressure goes up as it should.

The concern I have is it generally takes 2 turns of the key to start the car. Does anyone else's pressure drop immediately after turning the key (but not starting the car)? This car has lots of bolt ons on it, but it was modded by the person that was two owners ago...and the last owner did not know anything about the car. In other words, I may have a cam, an aftermarket fuel pump... or any other number of mods without being aware of it.

The car runs strong at all rpm's with only one other wierdness to it. After coming to a stop, the idle hangs at 1500-1800 rpms for a few seconds before it drops to idle. I have my idle at around 1000 rpms at this point and the hanging idle leads me to believe it might be lean as this is what my bike tuning experience tells me.

Any suggestions on the pump not holding pressure or on the car being slow to drop to the set idle speed?

Thanks,
Ben

P.S. The car is reliable and I trust it to always start, I just have these two annoyances with it. The hanging idle wouldn't be so bad if the car was not mega-loud (full headers/full exhaust with what must be very old/blown out mufflers, or maybe flowmasters?)
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Old 02-02-2008, 04:01 PM   #2
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My car does the same thing. It's the fuel pump check valve. You can either replace it or live with it. It is f'in annoying though.

Your other problem could be you need a tune. Dunno about that one.
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Old 02-02-2008, 04:14 PM   #3
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Thanks for the quick reply. I guess I can live with double cranking since it is known why it happens and it is not like it is just a symptom of a bigger problem. I guess this is just another way that the car feels more than a tad rough around the edges.
*Shrug*

If I ever end up going with nitrous kit, I will get the other issue t-shot on a dyno. Until then, I will just drive it as is.

Ben
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Old 02-08-2008, 01:39 PM   #4
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I had the same issue almost to the T. Shortly after deciding to live with it, my fuel pump died.

In my case another reason to beef up another OEM component. Granted that was a v6, not my formula.
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Old 02-08-2008, 03:02 PM   #5
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Most likely it is the fuel pump as said above, but your regulator could be leaking. Pressure up the system and after the system is pressure up block
to return line and see if it still drops. If so then it is your fuel pump.
Good Luck
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Old 05-15-2008, 04:36 PM   #6
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Default hard starting

i have a 94 trans am.LT1
new fuel filter and new fpr.
hard to start, i have 0 psi when turning on the car engine off-at the same time i hear the fuel pump turn on i hear a hiss sound. with engine running i have 38psi- when i turn the car off the psi drop back to 0 psi

no signs of leaking fuel.

after the driving the car and parking it for more then 10 mins or so it takes couple of cranks to start up again, im able to start it with no problem within those ten mins, the pressure gauge rises to 45 then drops to 0 psi, could i have a faulty fuel pump?
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Old 05-15-2008, 08:02 PM   #7
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It could be a bad injector, a leaky fuel pressure regulator, or a defective pump. I just replaced my regulator last weekend due to the same symptoms and now it starts great again. Pull the vacuum line off the regulator and pressurize the system and see if fuel leaks out the back of the regulator. If it does, get a new one and your all set. read this courtesy of shoebox.
http://shbox.com/1/4th_gen_tech2.htm...essure_testing
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