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454 hei starting problems

Hello out there. I'm rebulding my 1971 K5 Blazer and thought a 454 would look good under the hood, so I bought one. Tore it down, did the mandatory things to rebuild it, put in a Summit HEI distributor along with a Painless wiring harness and a Holley Street Avenger 770CFM and Hooker Headers.

Well, it ran last year- 2003- and towards the end of the year- Oct- it started to develop a backfire above 25 mph and under acceleration, so I parked it until yesterday.

Charged the batt, turned the key, engine cranked, sputtered once, and just kept cranking. So I check to make sure fuel is there, it is. Check for 12v at BATT on coil- ok, ohmed out coil per book, ok, ohmed out green and white wires to pickup- ok, had Advance auto check the module- ok. Still no spark. Rechecked timing- the old fashioned way (thumb in #1 hole, crank motor) rotor correct under cap, timing mark at TDC, still no start.

Any thoughts on what my next troubleshooting steps should be? Am I missing something blatantly obvious?

Thanks in advance.

Reply to
Carl
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Look at the cap and rotor, HEI caps can carbon track easily as well some HEI rotors burn through just under the center of the contact.

Brian

Reply to
NoSpam

I have tested a ton of BAD coils that ohmed out ok. For $15 it's worth it to replace the coil and see if she fires up. Also, the +12V connection to the coil can tend to be loose (the connector will click in ok but the wires is loose inside the connector). Last but not least, that puppy have a tach in it? If so, run a continuity test on the tach lead from the coil to the tach and see if it's shorted. A shorted tach lead will wreak havok on the ignition system.

Doc

Reply to
"Doc"

Doc- YOU ROCK! While it did cost me 15 for a coil, turns out the "new" Tach/vacuum instrument cluster I bought is the cluprit- Disconnect the tach wiring, VROOMMM!

Reply to
Carl

You're welcome. The tach wire is likely shorted somewhere between the coil and the gauge cluster. Ya didn't run the wire through the firewall without using a rubber grommet did ya? ;-)

Doc

Reply to
"Doc"

Thanks fo the input regarding the tach-

Another question- Now that it starts, the timing is set, carb is set (float, idle, etc) I have another problem-

When I accelerate, I get some backfire? Cant tell if thru carb or exhaust- Any thoughts?

Thanks, Carl

Reply to
Carl

  1. Timing set with vacuum advance disabled?
  2. Is it a true backfire or is it just header pop?

Doc

Reply to
"Doc"

HEI distributors also have problems with the mechanical advance as they age. Might want to check for binding by hand. Get a fancy timing light that can tell you total advance. Make sure to hide it from your friends and neighbors, or they'll bring it back broken.

Reply to
Eric

Reply to
Carl

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