stumped on a 4.3

check for a plugged exhaust check vacuum at idle and 2500 RPM hot engine they should be the same when it dies does it just shut off or slowly die off

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Does it start right back up?

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when you come to a stop its just like you turn it off,sometimes it will restart sometimes it wont

If it stays dead for a little while, that would give you the opportunity to do the necessary testing to isolate the problem.

In order to troubleshoot the problem accurately, some things have to be tested during the actual problem. Any other time and everything will check out good. Trying to diagnose this any other way amounts to guessing and that is just not accurate by any technician.

You need to first test a few functions during the failure.

1) Test for spark at the plug end of the wire using a spark tester.If none found, check for power supply on the + terminal of the coil with the key on.

2) Test for injecter pulse using a small bulb called a noid light. If none found, check for power supply at one side of the injecter with the key on.

3) Use a fuel pressure gauge to test for correct fuel pressure, also noticing if the pressure holds when key is shut off.

Once you have determined which of these functions has dropped out,
you will know which system is having the problem.

Here's what the noid light looks like.

Images available only to Customers.

Since this is a Vortec, step 2 would be very difficult for you so just check the other 2 for now. You may have to go back to that test, depending on what you find in the other 2.

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sorry for taking so long had to order the tools,
ok,injecter has power,and fuel pres. holds at about 58 lbs.
and has great spark,(i hope my hair lays back done before work on monday)

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Power isn't what we were looking for with the injecters. we wanted to know if it as receiving a pulse signal from the computer but that is difficult with a Vortec because you can't directly access the injecter. You could weed out the correct wires from the harness but it wouldn't be an accurate test for pulse because the injecter would still be connected.

Did you check these things DURING THE FAILURE?

If you tested it when the problem wasn't present, it doesn't mean anything. We want to know what's going on while the problem is present.

Fuel volume isn't an issue with this system. It's a bypass system so in order to maintain correct pressure, 75% of the fuel is returning to the tank anyway. There's nothing wrong with the fuel pressure regulator either if it maintains the correct pressure and doesn't drop when the car is shut off.

Edited by Hammer Time on April 22 2006 at 6:34pm

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ok heres what i did,there is a plug on the harness that goes to the injector,i have another 4.3 vortec in the shed so i took the harness of of it to run this test without having to tear the other apart. i run the test again again when it shut down, it has a pulse signal,and good fuel pres. and spark

It can't have all three or it would be running.

Something is either dropping out or getting real weak.

It just has to be.

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this i know thats why i came here,could this be as simple as an air bubble in the fuel line??

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