96 350 vortec back firing and loss of power

Asked by Dec 26, 2014 at 02:26 PM about the 1996 Chevrolet C/K 1500 Cheyenne Standard Cab SB

Question type: Maintenance & Repair

i have a 96 chevy 350 vortec. just changed the motor in it and cant get it to run right..it will
sit there and idle great when its it park...when i get out on the road it starts to loose power   
and back firing alot but only when i get to about 25-30 mph. help me under stand this.
took it to a shop they said i had a air leak in the intake,now there saying that  valves are
too tight...what is the problem?  you can email me at dustinjboshell@gmail.com...

5 Answers

56,845

Is it running hot as well? If so it's going to be a knock sensor problem. Sounds like the knock sensor is retarding the ignition timing. HTH. -Jim

no its not running hot at all... like i said i just bearly replace the motor with a long block from city motor supply in dallas tx...so its been at the shop for a week no and they keep telling me that its this and that but when the replace that part and put it back together its the same way as when i drop it off to them..... just trying to get some answers to why its doing this.... i read also about the cam retard offset... wouldnt that give them false codes if that was not set right???

56,845

It could give false codes but not necessarily. If the computer thinks that the engine is pinging it will retard the ignition timing. I had that happen to me on my '93 Caprice when it got old and develop a valve tap. HTH. -Jim

1 out of 1 people think this is helpful.

So your saying that it's the kn ock sensor.

56,845

It could very well be. The knock sensor is like a microphone. It "listens" for the engine pinging and retards the ignition timing until the pinging stops. If you have other noises going on near the knock sensor it may pick them up. On my Caprice the valve tap was right next to the knock sensor. With extremely retarded ignition or valve timing you'll get loss of power, popping back at the intake/throttle body, late transmission shifting (older models), and heat soaking. HTH -Jim

1 out of 1 people think this is helpful.

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