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Old 07-29-2013, 12:41 PM
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LOUD popping from exhaust

My engine has been 'afflicted' with this issue for some time now, and in the past I just figured it was from the fouled spark plugs and pretty much just ignored it, since I don't actually 'drive' the car. .I just start it and idle around the shop, let it warm up from time to time so it doesn't 'get stiff' from sitting.. anyway

The popping has more or less gone away for some time.. but last night I was working on cleaning up the wiring around the engine. I pulled all 8 plugs off the cap (I marked #1) and removed the cap to make room. I noticed some buildup on the terminals in the cap, so I gave them a light scrape with a scraper and a quick rub with some 150 grit paper (it's an MSD cap with brass terminals)

put it back together, double and triple checked the firing order 1-8-4-3-6-5-7-2

and now it's popping like CRAZY. at random intervals and random cylinders. I know it's random cylinders because I have dual exhaust with no crossover of any kind.. left cylinders come out left side pipe only.. and standing behind the car, it's popping from both sides.

I'm wondering if this is just a matter of fouled plugs.. and that I'm running an MSD 6-AL box, and the multi-spark is just causing the fuel to ignite in the pipes instead of the cylinders? The other reason I suspect it's a side effect of the Multi-spark, is that it goes away above 3000 rpm. which coincidentally, is where the MSD stops doing multi-spark, and goes to a single long spark.

I'm going to throw some new plugs at it when I can and see if that helps...

Has anyone else seen something like this?

btw.. when I say 'popping'.. I don't just nice little 'fluffs'.. I'm talking M-80, hurts your ears, feel in in your chest, echoes off the house down the street KA-BANGS.

exhaust is 1-5/8 headers into 2-1/2 pipes with basically straight through mufflers and 2-1/4" tail pipes..

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Old 07-29-2013, 04:36 PM
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Well, by the firing order, it's a SBC. If you've double and triple checked the firing order, and the popping is random, I can't see it being plugs...I have seen an MSD box cause problems. I installed one for a customer a while ago and it was giving me a similar problem right out of the box. The one I had would leave 2 cylinders dead all the time. I brought it back, replaced it and problem solved. Now I'm not saying that replacing it will solve your problem, just that I have seen the MSD product be defective when new...but that can happen to any manufacturer.

Ray
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Old 07-29-2013, 05:05 PM
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Have you ever had one of those moments, when you've just realized you've done something very stupid... and look around HOPING that no one else noticed?

I pulled the plugs out, they were all pretty nasty, didn't realize I had 5 Acell shorties and 3 Delco's in there..

Replaced 7 of the plugs with brand new R44TS's. Cylinder #6 the exhaust primary is so close to a standard plug I can't even get the boot on the plug so I had to reuse a shorty. .I cleaned up with a wire brush and some lacquer thinner.. regapped it.. I'm not exactly sure what I was thinking last time I gapped those plugs.. I had them set somewhere around .050

I set all the new plugs to .035.

fired it up.. same thing... this time it kicked a big fireball back through the carb.. so I checked the firing order for a 4th time...



I had #6 and #8 wires switched around.

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Old 07-29-2013, 05:06 PM
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btw... it runs sweet as a cherry now with 8 good plugs in it

I leaned the carb out as far as I dare go with it while I'm just idling around the yard.. hopefully it won't foul them out again.

(it has it's winter tune when it got parked, rich idle, lots of choke)
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Old 07-29-2013, 10:58 PM
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did you use dielectric grease?

wrong gap and no grease,sometimes you get a cross fire in the cap
look for what looks like pencil lines in the cap.
with a .050 plug gap and MSD,there is going to be a spark somewhere! The spark will take the path of least resistance
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