2000 Sonoma ZR2 High Rider

[kalyn]

Hard to start. Have replaced fuel filter, fuel pressure regulator, checked pressure with key on (57 psi). Before replacing pressure reg. truck took several tries before it would start. After pressure reg. replaced it seemed to work fine for a few days. Now truck will not start if left over night. After I allow it to sit for a while again, it starts right up. Once it's started it runs great with no hesitation. Please help.

[MT-2500]

Originally Posted by kalyn

Hard to start. Have replaced fuel filter, fuel pressure regulator, checked pressure with key on (57 psi). Before replacing pressure reg. truck took several tries before it would start. After pressure reg. replaced it seemed to work fine for a few days. Now truck will not start if left over night. After I allow it to sit for a while again, it starts right up. Once it's started it runs great with no hesitation. Please help.

What engine?
Recheck your fuel pressure cold and warm and hot.
Will it fir up with a shot of carb cleaner?

4.3 V6
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.
Full pressure with return line should be 95 -105 lbs.
engine running on road.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Depending on engine load.
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.

[kalyn]

Engine is 4.3 V6. Which line is the return? How do I block it off?

[MT-2500]

Originally Posted by kalyn

Engine is 4.3 V6. Which line is the return? How do I block it off?

The small line to or from engine intake.

Uncouple it some place and plug it and as in upper post pinch it off if it has a rubber joint in it.

Fuel pump to engine lines has 3 size lines large pump to engine middle size is return and small one is vent line.

[kalyn]

ok. fuel pressure reading with key on now is 52-53 psi. Bad fuel pump? Leak down is slow but goes to 0 psi over night. Should I find the leak before replacing fuel pump? Should I check full pressure first? Need direction. Thanks.

[MT-2500]

Originally Posted by kalyn

ok. fuel pressure reading with key on now is 52-53 psi. Bad fuel pump? Leak down is slow but goes to 0 psi over night. Should I find the leak before replacing fuel pump? Should I check full pressure first? Need direction. Thanks.

As in post 2.
Do the complete test and.

Give up all fuel pressure readings.

[kalyn]

ok here it goes...

cold start fuel pressure 52-53 psi.
engine running fuel pressure 52-54 psi. (cold/warm/hot)
have not checked running on road pressure (hose not long enough)
after shutting off - leak down slow but over night goes to 0 psi.

Disconnected line after fuel filter to connect pressure tester there. Cycling key to on and off yields same results 52-54 psi. Leak down rate fairly quick initially (drops approx. 1 psi. every 30-45 sec.) Once it drops to 50 psi. leak down rate slows a bit. After about 15 min. pressure shows 32 psi. Thanks for your help. I feel like I'm getting somewhere now.

[MT-2500]

Originally Posted by kalyn

ok here it goes...

cold start fuel pressure 52-53 psi.
engine running fuel pressure 52-54 psi. (cold/warm/hot)
have not checked running on road pressure (hose not long enough)
after shutting off - leak down slow but over night goes to 0 psi.

Disconnected line after fuel filter to connect pressure tester there. Cycling key to on and off yields same results 52-54 psi. Leak down rate fairly quick initially (drops approx. 1 psi. every 30-45 sec.) Once it drops to 50 psi. leak down rate slows a bit. After about 15 min. pressure shows 32 psi. Thanks for your help. I feel like I'm getting somewhere now.

If then direct fuel pressure at fuel filter is no 85-105 lbs the pump is bad.
You need full pressure over 10 lbs of running pressure to for the pressure regulator to hold running pressure.

Also a lot of fuel pumps fade out after running on the road when tot.

[kalyn]

I never thanked you for the help here. My problem WAS the fuel pump. Surprised my mechanic but it sure worked. Thanks for the help!

[MT-2500]

Originally Posted by kalyn

I never thanked you for the help here. My problem WAS the fuel pump. Surprised my mechanic but it sure worked. Thanks for the help!

You are very welcome for the thank you and for posting back how it went.
Also looks like you are getting some good help from Old master on you head light problem.

Good Luck