Late start

[68camino96tahoe]

I've just bought a 1996 tahoe it's got the 5.7, which is a replacement engine with 47,000 miles on it. The problem is that it takes about 4-5 seconds to start, but once it does it runs perfect. I've got decent repair ability just no diagnostic experience.

[2000CAYukon]

I would start with a complete fuel pressure test. One of the moderators "maxwedge" has posted these directions many times (you can search for them). You will need a good fuel pressure gauge to test (0 - 100 PSI).

EDIT: Maybe it was "MT-2500" who posted the directions (as he already has below)

//2000CAYukon

[MT-2500]

4 seconds is not much time for fuel pump to prime up.
Try key on and then off a couple of times and let the fiuel pump prime up.

Good AC plugs and fuel filter?


On fuel pressure check/hard to start cold.
The only true test on a fuel pump is to check the direct fuel pressure from fuel pump.
A quick test is to block off the return line and see if fuel pressure comes up to 75-85 lbs.
But do not run the pump at full pressure very long.
Also when testing fuel pump and pressure you need to tape a gauge to outside windshield or outside mirror and drive it on the road for 20 -30 minutes
until the pump gets has run a while to check for a pump fading out after hot.

Hard to start cold and fuel pressure testing guide line.
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.
If pump has full pressure with return line blocked and low pressure without it blocked most usually the fuel pressure regulator is leaking or not holding 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 in system.
Post back fuel pressure readings.

[j cAT]

Originally Posted by 68camino96tahoe

I've just bought a 1996 tahoe it's got the 5.7, which is a replacement engine with 47,000 miles on it. The problem is that it takes about 4-5 seconds to start, but once it does it runs perfect. I've got decent repair ability just no diagnostic experience.

If you find that the fuel pressures are lower than the spec...on start up ,, clean the fuel pump ground and also make sure the fuel pump has 12volts at the fuel pump with the fuel pump in the pime mode...

these problems on these older vehicles are common...given the cost and hassle of repair make sure its not just a bad feed/ground...

look at the fuel filter if it looks old replace...