Popping under acceleration

Tiny
M144ME
  • MEMBER
  • 1998 CHEVROLET TRUCK
  • 5.7L
  • V8
  • 4WD
  • AUTOMATIC
  • 210,000 MILES
I had very high idle. I changed the intake gaskets and plastic upper intake, put new distributor cap, wires, plugs, started engine and it starts easy idles fine, but under acceleration it hesitates starts popping. I let off and take it easy and it does not do it. It is like the timing is slow but the crows foot locks distributor so you cannot turn it. There are no timing marks on timing cover. Just a pointer with a notch in it. Any help would be appreciated. Thanks
Tuesday, February 27th, 2018 AT 7:20 PM

7 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,796 POSTS
Good evening.

Did the engine do this prior to this repair?

Did you verify the wires were in the correct location in the distributor cap?

Roy
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Wednesday, February 28th, 2018 AT 5:51 PM
Tiny
M144ME
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  • 4 POSTS
No it did not do this just idled at 1200 rpm after changing just about every sensor I could I changed intake gaskets fixed idle problem. Yes I checked wires twice it idles smooth no miss unless it is under hard acceleration it pops through intake. This weekend I am going to change crows foot that holds distributor down to old style so I can move it. I think timing chain has slack do to high mileage and distributor needs advancing. This had 195,000 when I got it. What do you think?
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Wednesday, February 28th, 2018 AT 6:17 PM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,796 POSTS
Okay, you cannot adjust the timing. The distributor is actually the camshaft position sensor. The timing is controlled by the PCM. Moving the distributor will not change the timing at all.

Another issue the older Chevrolet's had was a worn camshaft. The lobes wear down and the valves do not move enough and it ends up backfiring through the intake under load. To confirm, you would need to remove the valve covers and run the engine and watch the valve movement.

Roy
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Wednesday, February 28th, 2018 AT 6:25 PM
Tiny
M144ME
  • MEMBER
  • 4 POSTS
Thanks for the response. If I have a worn lobe would I have a ticking from rocker arm out of adjustment? I am not ASE certified but have a 1968 Nova race car I built myself and race, but do not know much about computer cars. The engine runs smooth and no noises I am baffled as to why you cannot adjust timing. My buddy says computer does it, but there is no advance in the distributor how does that work? So it is useless to put a timing light on it? I have not done that because there are no timing marks on timing cover? How do I find out where the timing is at?
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Wednesday, February 28th, 2018 AT 6:35 PM
Tiny
ASEMASTER6371
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  • 52,796 POSTS
You need a scan tool that can read the timing. It is under total control of the ECM.

There will be no ticking from a lifter due to the fact only the lobe is worn, not the base of the cam.

Roy
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Wednesday, February 28th, 2018 AT 6:38 PM
Tiny
M144ME
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  • 4 POSTS
Thanks for the information. I will try to get checked out and get back with the results. Your help is greatly appreciated. Travis
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Wednesday, February 28th, 2018 AT 6:40 PM
Tiny
ASEMASTER6371
  • MECHANIC
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You are welcome.

Keep us updated.
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Wednesday, February 28th, 2018 AT 6:41 PM

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