1996 Chevy Cheyenne Intermittent crank over but no firing

Tiny
RAP
  • MEMBER
  • 1996 CHEVROLET CHEYENNE
  • V8
  • 4WD
  • AUTOMATIC
  • 144,000 MILES
Hi, I tried to start my 96 truck this morning but it would not start. It turns over intermittently(hesitates) but will not fire or start. I changed the starter and battery but still no luck. The fuel pump hums when I turn the key and their is pressure at the schrader valve. Can you help me? Thanks, Bob
Tuesday, March 11th, 2008 AT 4:53 PM

9 Replies

Tiny
MASTERTECHTIM
  • MECHANIC
  • 4,750 POSTS
Check to see if it has spark, if it does spray starter fluid into intake and see if it starts then get back to us.
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Tuesday, March 11th, 2008 AT 5:00 PM
Tiny
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  • MEMBER
  • 7 POSTS
I'm not sure about spark and how to check for it. I did try starting fluid but no luck. The truck wont turn over consistently. It turns over then hesitates. Turns over and stops etc.
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Tuesday, March 11th, 2008 AT 5:05 PM
Tiny
MASTERTECHTIM
  • MECHANIC
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Ok I get you now. Do not try cranking it over anymore. You need to replace the crankshaft sensor. When they go bad it advances engine timing 50 degrees causing the locked up cranking symptom you haqve. If you continue to try to crank it you will break starter motor. I have seen this a lot on this engine. The crank sensor is located on the front of engine near the harmonic balancer. Hope this helps
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Tuesday, March 11th, 2008 AT 5:13 PM
Tiny
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Tim, Is this a sensor that I can replace myself? Do I have to tear into the front of the engine? What will need done once the sensor is replaced? Timing? Thanks for your help. Bob
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Tuesday, March 11th, 2008 AT 5:18 PM
Tiny
MASTERTECHTIM
  • MECHANIC
  • 4,750 POSTS
Its fairly easy to replace with simple hand tools. Nothing needs to be reset when done. Once your done hold the gas to the floor to put it in clear flood mode and immediately release pedal when it starts and you might have to hold idle up a little until it clears out(plugs are probably starting to foul).
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Tuesday, March 11th, 2008 AT 5:20 PM
Tiny
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I'll give that a shot Tim. Thanks and I'll let you know what happens. Bob
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Tuesday, March 11th, 2008 AT 5:25 PM
Tiny
RAP
  • MEMBER
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Hi Tim, I tried the sensor and that didnt fix it. It still cranks over with hesitations and no start up at all. I do notice that tthere is no smell of gas during all this. I turn the key and hear a hum from the gas tank momentarily and then it stops. I pushed in on the schrader valve under the cap on the line on top of the intake while the key is on and I get a little gush of fuel that sprays out and then quits. Should that be a high pressure force of fuel that sprays out? I dont have a press. Guage to check it. Would a bad fuel pump be causing this abrupt cranking problem or a clogged filter? Thanks, Bob
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Wednesday, March 12th, 2008 AT 1:25 PM
Tiny
MASTERTECHTIM
  • MECHANIC
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No I doubt it. We might have fouled plugs now. If you crank a engine over without correct spark it dumps raw fuel into cylinders. Next step is to remove all spark plugs and replace them if they are gas soaked
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Wednesday, March 12th, 2008 AT 2:29 PM
Tiny
RAP
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Hi Tim, I just got done troubleshooting some more. I pulled the cap and rotor and found the tip of the rotor not looking too good and the cap had some carbon buildup on the contacts. I changed these about a year and a half ago. I went ahead and changed the cap and rotor and she started right up. Thanks for your help and time. Bob
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Wednesday, March 12th, 2008 AT 4:48 PM

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