I have a question...my car is hard to start after sitting for a period of time (usually longer than 30-40 minutes). About a month ago I had it dyno'd and it's running pretty lean. What are the possibe reasons, could the fuel pump be going bad and what's the easiest way to check the pump?

Thanks in advance
Drew

'97 Z28
MAC headers, y-pipe (with cats), Hooker cat back, SLP cai, air foil are the only mods.

 

those are some signs of a bad fuel pump.

you can check the pressure underload.

 

check your pressure first.... should be around 36 at idle and then remove vacuum line should read around 40-42... if not might be regulator...

 

I'm assuming the way to check pressure would be to use a guage that connects to a schrader valve somewhere on the fuel rail. Is this correct?
Thanks guys.

Drew

 

Yes connect fuel pressure gage to fitting on fuel rail. I dont have a fuel pressure gage, I just use an old R-12 freon low pressure gage to check pressure, it works, not sure if fuel will hurt the freon gage but dont care it is just an old one I have lying around.

 

So you're saying that when I remove the vaccum line if the reading is low then it could be the regulator and not the pump?

 

OK so I checked the pressure. It's at about 35 ish at idle, with the vaccum line disconnected it's at about 45 ish. I guess this is normal.
Anyone have any other ideas what could cause it to run lean?

 

What was the dyno A/F ratio?

Checking the pump pressures at idle is only 1/2 the job. You have to tape the pressure gauge to the windshield and take it up to max RPM/full load. Make sure the pump is able to hold the fuel pressure within 1 or 2 psi of you "no vacuum" value of 45psi.

Have you changed the fuel filter?

 

A/F ratio through the rpm range:
2600 15.2
2700 13.4
2800 13.0
2900 13.1
3000 13.1
3100 13.1
3200 13.0
3300 13.0
3400 13.0
3500 13.1
3600 13.2
3700 13.3
3800 13.4
3900 13.5
4000 13.6
4100 13.7
4200 13.7
4300 13.7
4400 13.8
4500 13.8
4600 13.9
4700 14.0
4800 14.0
4900 14.1
5000 14.1
5100 14.1
5200 14.2
5300 14.3
5400 14.4
5500 14.4
5600 14.3
5700 14.3

I have not changed the filter.

"Make sure the pump is able to hold the fuel pressure within 1 or 2 psi of you "no vacuum" value of 45psi."

Is this with the vacuum line connected or disconnected?

Thank you!!