Hard start, fuel pressure questions

[DanielP]

My 1996 Tahoe with 5.7L Vortec is hard to start. The fuel pressure when I turn key on but do not crank is 60 psi. When I start cranking the engine, the fuel pressure bounces around between 48 & 52 psi. When the needle on the gauge spends more time past 50 psi, it starts. It idles at 50-51 psi and if I blip the throttle it will jump to 60 psi and then drop back down to 50 psi again even if I keep engine revved which. When I shut it off, the psi was 49 and it very slowly dropped to 41 psi after 20 minutes.

I have not yet tested for a vacuum leak. I don't believe there is an issue with the fuel filter because it has good power/acceleration/speed once running. I tried looking around the net but haven't found a clear answer on appropriate fuel pressures. There was one guide that said it needs to be above 51 psi to start though so I'm leaning towards a bad fuel pump.

I do not have any codes but do have an OBDLink MX.

 

[SunlitComet]

giving the numbers you posted fuel pressure is not really your problem. describe your hard starting in more detail please.

 

[DanielP]

It usually takes a little longer than this the first time it's started.

Skip to 00:14

 

[DanielP]

That's my video by the way, which is why I didn't try to describe the hard start in my reply.

 

[DanielP]

This is the page that says I need 50+ PSI while cranking to start: http://troubleshootmyvehicle.com/gm/4.3L-5.0L-5.7L/how-to-test-the-fuel-pump-1

The fuel system in your 4.3L, 5.0L, or 5.7L Vortec engine needs at least 50 PSI of fuel pressure to start.
The fuel pump produces much more than just 50 PSI of course.. but the bare minimum the engine needs to start is 50 PSI... so anything less and it will crank for ever before it starts or not start at all.
So, the very first thing you need to do is to verify that the fuel pump is delivering at least 50 PSI of fuel pressure while the engine is cranking. Yes... while the engine is cranking

...

OK, to get this show on the road, this is what you'll need to do:
1. <snip>
2. <snip>
3. Have your assistant crank the engine as you eyeball the fuel pressure gauge. It's important that you have someone else crank the vehicle so that you can eye-ball the fuel pressure gauge.
4. You'll get one of two results with this test:

1.) The fuel pressure gauge will register at least 50 PSI and the engine will start or.

2.) The fuel pressure gauge will register 49 PSI or less and the engine will Not Start.

I just don't know if this author is stating this as a spec from GM, from experience, or if he's just making things up. He does sound really certain that 50 PSI while cranking is a magic number though.

This is a 2nd vehicle for me so I haven't been in a rush to get it running right. Any recommendations for other tests to try?

 

[DanielP]

The problem got worse and I ran my battery a little low trying to start it a few weeks ago. I put the battery on the charger today and went to get a new fuel pump. A few hours later the battery was fully charged and I tried to start it, but no dice. I didn't even hear the old fuel pump running anymore when I turned on the ignition. Since I already had a new pump in hand, I didn't bother testing pressure. After a few hours and a couple breaks, I got the new pump installed. I cycled the key a few times to get gas through the line. Finally, I tried to start it. It took about a second to start but I believe it had to purge the air from the fuel line. It did start better than it had in a long time. If I don't post another update, consider it fixed and the information I referred to earlier a pretty reliable souce for the minimum psi needed to fire up on this era of Tahoes.