Hard starting 2005 Impala

[scherp]

I have a 2005 Impala with 207,000 miles on it, that start hard/rough/sputers, but once running the engine runs fine. I have not tested the fuel pressure yet, but an interesting note, if I manually pull a vacuum on the fuel pressure regular to 12-15 psi and re-hook up the vacuum line the engine starts immediately. Any thoughts?

[maxwedge]

Yeh, bad pump or regulator. Check for fuel in the hose, what is the fp key on. Good fuel filter?

[scherp]

I just replaced the filter. Check for gas in the fuel pressure regulator and non came out and possibly I could smell gas. Did this after 15 minute drive.

Fuel pressure test

key on/engine off: 24 psi (but did not cycle the key, just turn on and checked meter)

engine running: 51 psi

engine running, vacuum off the fuel pressure regulator: 58 psi

leak down test: pressure started to drop slowly immediately after engine turned off.

Bad check valve in pump?

[maxwedge]

I would say the pump and reg. Seem ok. Possible leaking injector or two.

[jyount]

I'm with him, sounds like injectors to me as well. If you stick a mechanic's stethoscope on each you might be able to hear fuel flow. Has to be quite alote though. The worst part is where they are on this engine it takes atleast 4 out of that option. They are in the lower manifold. Maybe able to acess the two nearest the belt end, but doubtful...

Usually if the valve in the pump is bad the pressure leak down is rather quick, not slow like you say. Suprised its not throwing rich codes, that would narrow it down. I don't think there is any soft parts of the lines you could clamp and watch the gague, rule the pump out all together.

[scherp]

Sorry, what I should have said the pressure started to drop by the time I got back to the gauge from shutting off the motor. The pressure drop steadily from the 51 psi to 10 within 5 minutes. It wasn't like the needle went from 51 to 0 immediately.

[Tech II]

I doubt it's the injectors.....leaning towards the f/p regulator...

[scherp]

Tech II, why do you feel it is the the f/p regulator?

[Tech II]

Because of your first post:

if I manually pull a vacuum on the fuel pressure regular to 12-15 psi and re-hook up the vacuum line the engine starts immediately.

You say your fuel pressure is 51psi.......once running, you don't mention any problems....

[scherp]

I finally got around installing a new fuel pump that solved the hard starting. I went to my local library and accessed Alldata and printed out GM fuel pressure testing procedure and it pointed to the fuel pump.