1996 5.7 Vortec starting problem

[79Malibu]

I have an Isuzu NPR commercial truck with a GM 5.7 Vortec. I noticed over the last couple of weeks that it was having trouble starting. No check or service engine light on. Today was the worst. It took about 2 minutes of intermittent cranking to get it to start. for the first time I noticed it was sluggish and seemingly trying to die if I accelerated a little hard from a light. I got to my destination, shut it off and 45 minutes later it would not start. As it was trying to start, it had that odor like it was lean. Being a service truck, I had tools and pulled the fuel filter, it was easy to blow through. I rigged my air conditioning gauge and measured the fuel pressure at the engine. It did not climb above 55. It would vary between 50-55. I finally got it to start and it ran ok, other than poor acceleration. The 55# pressure occurred when I quickly pressed the throttle.

Any ideas on this? It may be a bad fuel pump from what I have read here since the pressure is a little low, should be 62??

Any help is appreciated. Thanks.

[MT-2500]

Welcome to AF
On a 96 GM pickup the fuel specs is 60/66.
You need to check with a good accurate gauge.
Even a couple of lbs low will give you a hard start.
Starting pressure should be close to 64/65 lbs of fuel pressure.
Some parts places rent or loan fuel pressure gauges.

Hard to start cold.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak.
Post back fuel pressure readings.
MT

[79Malibu]

Thanks. I did measure and it was in the low 50s. I loosened my gauge connection and let some fuel out which dropped the pressure and I could get the engine to start sputtering around 45#. I did get 60# at one point after purging the line pressure after engine shut down. The pressure does bleed down, but takes a while to do so. I wouldn't think the injector pressure would be lower on this truck vs. a regular 350 Vortec would it?

[MT-2500]

If it is a 96 GM vortec engine it needs 64-65 lbs of fuel pressure to squirt the fuel injector on a cold start an 60/66 lbs lbs of pressure to run it right
Run the test as outlined and post back pressure readings and we can help you..