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Old 02-23-2013, 12:49 PM
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will crank but not start

1998 Chevy1500 Z71 5.7 v8. This first started about a month ago, truck would crank but not start then went out after work and it fired right up ran great for about three weeks thensame thing except I couldn't get it to start for about a week then ran great for a couple days and now its back to not wanting to start. I'm lost, coil,cap,rotor all fine. Wires good. Plugs little fouled but not to bad. Checked for spark on a plug and had spark. Shot some starting fluid in intake while a helper tried starting and nothing so ruled out fuel pump. Ideas please!
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Old 02-23-2013, 12:54 PM
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Dont rule out fuel untill you verify actual pressure and injector pulse. Big mistake.
Spraying with starting fluid can be a quick presumptive test, but many misdiagnosis is due to presumption.
Verify CORRECT fuel pressure.
Also you need to verify spark at the plugs, not the coil wire, not sure if you did that . Spark shoul be blue and jump 1/2 to 3/4 inch without problem.
Your setup is A Vortec ?
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Old 02-23-2013, 01:01 PM
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Yeah I tested spark at the plug and was sufficient enough, I have to stop and get a fuel pressure gauge to test fuel pressure, what psi do they normally run? And yes a vortec
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Old 02-23-2013, 01:01 PM
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I'm not sure when the manufacturers started using theft deturrent keys, but my 2000 won't start if the key is defective. Not trying to be a smart a**. The theft protection keys have been known to go bad.
You said it has spark. Is it blue(yellow equal weak)? If you do and you use good starting fluid, it should fire up for an instant. Try turning it over while a timing light is on the plug wire and using starting fluid. Put a fuel pressure gauge on it while its cranking.
Air, fuel, and spark equal fire.
ssmonty
I see LAtech beat me to it.
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Old 02-23-2013, 02:45 PM
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How bad are the plugs fowled. Did you pull them all or just 1.
As LA mentioned fuel pressure is critical on those. It is odd that it didn't even try to fire on starting fluid.
Those trucks also had a ground braid near the bottom of the engine that rots out and would give weird issues.
I am thinking electrical connection somewhere because you said it ran fine for a while then would not start again.
I would verify spark and fuel pressure again and go from there
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Old 02-23-2013, 03:56 PM
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sounds like a fuel pump .does it have the 2 second prime sound comming from the tank ?
when key is turned on does fuel squirt out fuel rail test valve when depressed ? good luck hope this helps
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Old 02-23-2013, 03:57 PM
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some times i bang on the botttom of the tank and they will start if it does get a pump
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Old 02-27-2013, 01:44 PM
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Finally got a tester for fuel pressure. Put on rail turned key on and let pump prime, had 56 psi then just let it sit to see if it dropped. After about five minutes it was down to 50 psi
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Old 02-27-2013, 03:10 PM
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Spec is 60-66psi KOEO(Key On Engine Off). These things are finicky with fuel pressure. Quiote often you will see pressure bleed like you are. Either leakiy poppets, fuel pressure regulator, or pressure backflowing into the tank.

If I have a no start I dump a bit of gas down the t-body and start.

Since youa re getting pressure, you could have an intermittent pump issue. I have had to do a fuel pump even with the gauge reading 60psi.

If its a fuel injection spider issue, I suggest swapping to the MPFI conversion GM introduced in response to fuels in certain states being incompatible with the 1966-2002 CSFI spiders.
CSFI to MPFI - Vortec Engine Fueling Fix - Fuel Injection - Off-Road Magazine

Cleaning poppets
http://www.acdelcotechconnect.com/pd...sb_05D-105.pdf

Whats the fuel pressure when the pump is actually priming? You have to mount your gauge so you can read it as you cycle the key, or have someone else cycle the key for you as you read the gauge.

If you have to do the pump, be sure to inspect well.

peace
Hog
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Old 02-27-2013, 04:35 PM
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I believe that 56psi would be enough to make it fire up. May have some drivability issues, but it should still fire up briefly anyway.
I have a 2000 Silverado with the 4.3 V6 and it would run on 50psi.
Are you sure the injectors are getting a signal from the computer? Like someone mentioned dump about a table spoon of fresh gas into the throttle body after removing the air filter assy.
Don't press the throttle and try the key. If it tries to run then stops, check your fuel system/injectors/computer. May not be getting a signal to the injectors or to much fuel causing it to flood. If its flooding you should smell it. If not then check your ignition system. May have a bad crank or cam sensor that triggers the ignition/computer. I don't know what your engine uses to signal the ignition to fire.
I swapped my Central FI system for a MPI system and it runs much better FWIW
ssmonty
PS Are you losing coolant. May have gasket thats gone bad letting coolant get into cylinders. I did thanks to Dexcool or whatever they called it.
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Old 02-27-2013, 06:35 PM
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I shot starting fluid into it and nothing different. But when it does rarely start it runs perfectly and don't believe I'm losing coolant
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Old 02-28-2013, 08:18 AM
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sounds to me like the camshaft position sensor, or a crankshaft position if it doesn't have a camshaft position sensor. if this sensor is bad it tells the injectors when to fire. had a gmc van with a 5.7 in it that did the same thing it was a 2000. I tried starting fluid one time and it backfired through the intake and blew the plastic intake pieces apart.
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Old 02-28-2013, 09:32 AM
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Dumb question; is it throwing codes?

Here in the northeast, as TBucket alluded to; we have lots of issues with wiring and grounds because of corrosion or plain old body rot.

Only other thing I can add is be careful using ether all the time to tinker with this; it can damage things. Be careful when you add gas, I would use some kind of squirt bottle; my father has a friend who used a Gatorade bottle to pour some gas in his motor; it backfired and he jerked his hand back, spilled gas all over and burned his hands REAL bad, not to mention wiring etc
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Old 02-28-2013, 03:21 PM
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Quote:
Originally Posted by prumora1 View Post
sounds to me like the camshaft position sensor, or a crankshaft position if it doesn't have a camshaft position sensor. if this sensor is bad it tells the injectors when to fire. had a gmc van with a 5.7 in it that did the same thing it was a 2000. I tried starting fluid one time and it backfired through the intake and blew the plastic intake pieces apart.
Those will run without the cam sensor I believe. It is possible the crank sensor is bad and the spark could be coming at the wrong time. If you have spark you may be able to check ignition timing while cranking.
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