1997 5.7 Vortec intermitant slow start revisited.

[Steven_R]

1997 5.7 Vortec intermittent slow start revisited.

 

Short version:

 

I have a 1997 Express with a 5.7 Vortec and the CSFI system. It has 130k miles.

It is hard to start after sitting. If I pulse each of the fuel injectors with an injector tester then it starts right up. Problem description is mostly in next post. The test procedure that makes it start is in the third post.

 

[Steven_R]

1997 5.7 Vortec intermittent slow start revisited.

 

Long version:

 

I have a 1997 5.7 Vortec with the CSFI system. It has 130k miles. This is a continuation of the problem in an earlier post.

https://www.gm-trucks.com/forums/topic/238081-1997-57-vortec-intermitant-slow-start/#comments

 

I thought I had it fixed when I replaced the rotor, but no. The symptoms are more consistent now. I suspect that's because with the new rotor it only has one problem. With the testing I do, it always takes about four or five tries to start. Injector testing causes the engine to start. See next post.

 

Symptoms:

 

It is hard to start after sitting for more than a day. It cranks fine. It cranks and cranks and finally starts. Once it starts it runs fine.

 

New parts (AC Delco):

• Plugs, wires, cap and rotor (6+ months ago)
• Fuel pump and filter (also 6+ months ago)
• Rotor again 1 month ago. A plastic piece broke and the tab was loose.

Testing:

• Fuel pressure is at 60 before start, drops to about 50 when running.
• Connected scan tool but saw nothing wrong before it starts.
• It always has good spark.
• The injectors all have the same resistance.
• All injectors work when pulsed with an ALLOSUN Injector tester (the cheap box from Amazon).
• A shot of starting fluid makes it sound like its going to start, but it doesn't start.

[Steven_R]

Testing procedure and starting:

I have tested it four times since replacing the rotor with the same results.

1. It doesn't start, so I check fuel pressure. 60 psi before cranking, 50 psi when cranking.
2. Pull a plug wire (#8) and check spark with a spare plug. Cranking shows good spark. A couple of times I did the same with #6 - also good spark.
3. Pull the injector harness connector. For each injector, connect the tester. Cycle ignition to get fuel pressure. Pulse it injector twice while observing the fuel pressure gauge. It drops the same amount for each injector.
4. Reconnect the injector harness connector. Now the engine will start up immediately.

Note that one time I tried giving a shot of starting fluid. That made it sound like it wanted to start for a moment, but did not start.

Also, the last time I tried this I only pulsed injectors 1-4, with the same results.

It seems like the injectors or regulator are the problem, but I don't know what could be wrong to cause this problem.

If it were a stuck poppet, I think it would start anyway since I know the engine will start easily with 6 plug wires.

 

Edited May 31, 2020 by Steven_R
Edited for clarity.

[GMTfour100]

So is it fixed now? After you replaced the injector harness connector?

 

 

 

 

[Steven_R]

No, it is not fixed.

 

Sorry that previous post was not clearer. I did not replace the injector harness connector. I reconnected it. What I meant is that after testing the injectors with the pulse box, and reconnecting everything, the engine fires right up.

 

Now the problem is getting worse. It is bad enough that it will not start without a lot of cranking (unless I test with the pulse box). It is almost consistent now, so I should be able do some productive testing today.

 

Also the pressure only come up to 56 of 58 PSI. I ordered an adapter for the fuel return line, which should be in this morning. I intend to route the return through a rubber fuel line into a gas can, and restrict the return while powering the pump from the test port. This will clearly show whether the pump is strong enough to produce 60 psi. If the pump is good than the regulator is bad. So if the problem doesn't go away during testing I will know the culprit.