Help !!!!! - Chevelle Tech
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post #1 of 67 (permalink) Old Jan 4th, 20, 4:18 PM Thread Starter
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Angry Help !!!!!

I have a 1970 El Camino that I have been bringing back from the dead. 454 over 030. TH400. Edelbrock performer intake,Edelbrock 750, Voodoo mild street cam with their timing chain and lifters. New MSD wires and ac Delco plugs. 2.73 10 bolt peg leg. Chinese HEI dist. with Standard coil and module. Cold Case radiator with stock BB shroud and clutch fan. American Autowire harness front to rear. New ground straps and extra ground straps. Car came from paint jail and a was running well, then all of a sudden popping out of exhaust pipes. first thought was the plug wires were shorting out on hooker headers. Nope . The GM performance looms are great.All plug wires checked and plugs pulled. Everything checks AOK. As soon as I hit 40 accelerating great let off the gas and its a machine gun. Looked at the plug wires in the dark nothing out of the ordinary. Hit gas pedal one time and she starts right up. Cold Case radiator with BB shroud and clutch fan. Never runs over 200. None of these parts have 700 miles on them. what do you guys think before I drive it off a short pier.


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Last edited by Slick87gn; Jan 4th, 20 at 4:21 PM. Reason: Forgot something
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post #2 of 67 (permalink) Old Jan 4th, 20, 4:23 PM
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Al
 
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Re: Help !!!!!

An exhaust leak could suck in air when decelerating which could cause the popping in the exhaust. Does it only pop when you let off the gas??? Is the popping only out of the exhaust???

Don't run her off the pier. Sounds like it's worth fixing.
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post #3 of 67 (permalink) Old Jan 4th, 20, 4:26 PM
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Vince
 
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Re: Help !!!!!

make sure the distributor is still secure and housing is not rotating while engine is running...
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post #4 of 67 (permalink) Old Jan 4th, 20, 4:44 PM Thread Starter
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Re: Help !!!!!

Dizzy is secure. Its raining right now but I will check for exhaust leak.


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post #5 of 67 (permalink) Old Jan 4th, 20, 5:11 PM
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Al
 
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Re: Help !!!!!

A miss could cause this. One or a couple of cylinders not firing. Raw gas in exhaust and boom when the a/f mixture gets to the right percentage in the exhaust. If you have a heat gun you can fire the engine and check exhaust temp at each header tube or manifold. Reading the plugs may narrow down the offending cylinder/s.

I'm still working under the assumption that it starts and runs fine until you let off the gas.
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post #6 of 67 (permalink) Old Jan 5th, 20, 1:32 AM
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Re: Help !!!!!

This is a dumb thing but take off the distributor cap to see if there is any moisture in side it. That can cause misfires.
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post #7 of 67 (permalink) Old Jan 5th, 20, 9:33 AM
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Steve
 
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Re: Help !!!!!

I had a problem exactly like this. Punchline - it was the pickup in the distributor (large body HEI).

What had happened in my case was that, somehow, the pickup in the distributor had come loose internally in a weird way. Once I got the RPMs up to a certain speed, if I would let off the gas, it would pop and sometimes stop firing completely. Hitting the gas would cause it to stop popping and fire back up.

The vacuum advance unit, when getting the full vacuum from letting off the gas and coasting, was pulling on the pickup and causing an internal problem with the magnetic pickup when it pulled it fully extended. Unplugging the vacuum advance unit made the problem go away.

Replacing the distributor completely cured the problem. Afterwards, during a post-mortem, you could visibly see the problem with the pickup in the distributor.

If you have another distributor to try, drop it in and see if that resolves it.
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1972 Chevelle, 454, 200-4r non-lockup, 12 bolt 3.73
1981 Camaro Z28, 355, TH350, 3.73
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post #8 of 67 (permalink) Old Jan 5th, 20, 9:42 AM Thread Starter
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Re: Help !!!!!

I was thinking of the dizzy also . I would prefer a real Delco unit instead of this knockoff.


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post #9 of 67 (permalink) Old Jan 5th, 20, 10:10 AM
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Re: Help !!!!!

Quote:
Originally Posted by Slick87gn View Post
I was thinking of the dizzy also . I would prefer a real Delco unit instead of this knockoff.
Not that expensive either: https://www.summitracing.com/parts/ado-93440806/
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post #10 of 67 (permalink) Old Jan 5th, 20, 11:01 AM
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Greg.
 
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Re: Help !!!!!

I ditched the ACCEL HEI with the Coil on Top of it after having to Rebuild it 2 years in a row

Replaced with Allstar ALL81216 Distributor & ALL81230 Ignition Coil 28/04/14
https://allstarperformance.com/hp-gm...ance-all81216/ https://allstarperformance.com/cd-ig...coil-all81230/

Over 5 years with no problems and great perf with my MSD 6AL

67 Chevelle Malibu SS Cdn
Born 283 / PG / A51
468/TH400 2,500 stall/ S60 3.70 Gs
Prev Best on M/T ET S/S #3454 street Tires/Dress 2018/05/20
60' = 1.664
1/8 = 7.532 et / 91 mph
1/4 = 11.814 et / 115 mph
NEW Best with 3,500+ Stall TC 2019/09/08
60' = 1.547
1/8 = 7.311 et / 91.76 mph
1/4 = 11.595 et / 114.28 mph


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post #11 of 67 (permalink) Old Jan 5th, 20, 12:23 PM Thread Starter
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Re: Help !!!!!

Ordered a Delco rebuilt unit from Rockauto. I'm open to all suggestions.


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post #12 of 67 (permalink) Old Jan 5th, 20, 12:44 PM
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Re: Help !!!!!

Quote:
Originally Posted by Slick87gn View Post
Ordered a Delco rebuilt unit from Rockauto. I'm open to all suggestions.

I'll almost guarantee your problem is located in the distributor. Either moisture or a malfunctioning part. The fact that it is a Chinese distributor makes me suspicious of the parts inside right off the bat. I would replace the cap with quality new one and try that. If it doesn't fix the problem, you'll have a good spare. Do you know anybody that has a good spare HEI distributor you could swap in just for test purposes?
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post #13 of 67 (permalink) Old Jan 5th, 20, 1:27 PM
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Re: Help !!!!!

Disconnect the vacuum advance and see if it still acts up.

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post #14 of 67 (permalink) Old Jan 5th, 20, 1:51 PM
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Re: Help !!!!!

Quote:
Originally Posted by bigdog454 View Post
Disconnect the vacuum advance and see if it still acts up.

Good idea. If you have a bad wire going to the pickup coil, sometimes the movement of the base plate from the vacuum advance will cause it to act up.
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post #15 of 67 (permalink) Old Jan 5th, 20, 7:22 PM
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Re: Help !!!!!

slick 87, send that rebuilt back and buy the new ZZ4 hei linked by Gary, The rebuilt won't be any good. They're usually built offshore by people who have never driven a car.

https://www.summitracing.com/parts/ado-93440806

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