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Random misfires, under load especially

Tiny
PIER2NY
  • MEMBER
  • 2000 CHEVROLET EXPRESS
  • 5.0L
  • V8
  • RWD
  • AUTOMATIC
  • 260,000 MILES
Replaced the engine with used low mileage used engine. Thought valves were sticking. Newer engine runs just as bad, so I've eliminated anything internal. There is a soft ticking sound, random, that can be heard at the top of the engine, sounds electrical, can not see any arcing in the dark. No DTC codes have set. New distributor cap, rotor and wires. Fuel system checks good. At my wits end.
John
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Saturday, June 21st, 2014 AT 3:47 PM

9 Replies

Tiny
CADIEMAN
  • MECHANIC
  • 3,544 POSTS
One of the wires is shorting out to the block or the wires are not on the cap right recheck them.
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Saturday, June 21st, 2014 AT 5:49 PM
Tiny
PIER2NY
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  • 4 POSTS
Okay, checked and double checked the wires, no short there. Replaced cap and rotor, no change. Disconnected cat converter from exhaust, no change.
Checked out the fuel pump, it's good. Still got that snapping sound, random, can't seem to isolate it. It's on top of the engine somewhere. What next?
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Sunday, June 22nd, 2014 AT 9:20 AM
Tiny
CADIEMAN
  • MECHANIC
  • 3,544 POSTS
You'll need to put it on a scope to get your answer.
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Sunday, June 22nd, 2014 AT 7:45 PM
Tiny
WRENCHTECH
  • MECHANIC
  • 20,757 POSTS
This is a different expert. I was asked to see if I could help you.

First we have to look at some basics.

You said there were no misfire codes. Were there any codes at all?
Have you completely verified the firing order. This distributor cap is very confusing because the sequence on the outside is different from the sequence on the inside.
What are you using to interface with the computer?

I can't find an image with the distributor cap order labeled but it looks easy enough to follow the wires on the following pictures.

https://www.2carpros.com/images/external/84817668.gif
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Monday, June 23rd, 2014 AT 4:01 PM
Tiny
WRENCHTECH
  • MECHANIC
  • 20,757 POSTS
Okay, I did find a better image.

https://www.2carpros.com/images/external/Firingorder0050.jpg
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Monday, June 23rd, 2014 AT 4:10 PM
Tiny
PIER2NY
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  • 4 POSTS
Thank you for the new reply. Nice wiring diagram. I have re-built engines before. I am aware of the firing order. I have since resolved the problem.
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Monday, June 23rd, 2014 AT 5:15 PM
Tiny
WRENCHTECH
  • MECHANIC
  • 20,757 POSTS
Glad to hear you got it resolved. Would you care to share what you found?
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Monday, June 23rd, 2014 AT 5:29 PM
Tiny
PIER2NY
  • MEMBER
  • 4 POSTS
The problem was with the coil. I don't know what was wrong with it, but with a stethoscope I zeroed in on the sound. Changed it out, and ran like a champ.
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Wednesday, June 25th, 2014 AT 1:32 PM
Tiny
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Thank you for posting the fix.
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Wednesday, June 25th, 2014 AT 2:27 PM

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