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View Full Version : Why won't the #3 cylinder FIRE!!!

243
06-01-2002, 06:02 AM
I've pulled my hair out trying to figure this problem.

I have a new MSD Blaster TFI coil, distibuter cap with brass terminals, rotor, wires, ac/delco plugs (.040"); and as of this morning, a new Edelbrock 1406. The guys at O'Reillys did me right and exchanged it even without my receipt.

I had an internal leak which was most of the problem with the rich idle condition.

When I ground my 12V tester, and poke the needle through the top of the distributor wire and into the terminal, I get a noticable drop in engine rpm at each wire with the exception of #3.

I pulled the plug wire and put a plug in it to verify spark at the plug which it has.

I believe low voltage at the plug is part of the problem but don't know why.

Could it be the distributor?

BTW, I've swapped plug wires at #3 and even bought a brand new wire and swapped plugs several times.

Distributor...what else could it be???
Rande
06-01-2002, 06:16 AM
Perhaps the distributor cap has a bad terminal. May be a manufacturing defect. Have you tried a different cap?
jeepbob
06-01-2002, 06:29 AM
You are not telling us which rig but I would suspect either worn dizzy bushings or a bad cap. remove the rotor and move the dizzy shaft back and forth, if it moves it is time for a new dizzy. Or you could have bad valves or bad lobes on the cam in that cylinder.
RichCal
06-01-2002, 02:52 PM
If you've proven you have spark at #3 plug, and grounding it does not lower the rpm - as do all the others - it may be time for a compression check. Evidently #3 isn't contributing much to begin with.
243
06-02-2002, 12:06 AM
I had it re-inspected yesterday and low idle HC dropped to 1820ppm from 1850ppm, still 3X the limit so the carb had nothing to do with the problem. I bought a new brass terminal distributor cap and rotor last week. I don't think it is the cap; when I pull the #3 wire from the cap, the spark will jump 1" to my grounded test probe.

The distributor was pretty corroded so I bought a new one along with new wires. It had no effect whatsoever so I pulled the drivers side valve cover. All the valves visually appear to be operating fine, the rocker arms all travel the same distance.

The motor shakes at idle and it's very apparent when in drive; however, I have 20hg of vacuum and it's steady, no fluttering.

If low compression is the problem, I am SOL. I cannot buy a motor right now.

[ June 02, 2002: Message edited by: 243 ]</p>
Rande
06-02-2002, 03:59 AM
Yup, at this point, I'd recommend a compression test. :(
PhilSine
06-02-2002, 04:46 AM
Is the plug even wet when you remove it? Can you verify that the cylinder is even getting fuel? Even though the valves may appear to be opening, #3 intake may not be. As others have suggested, a compression check is definately in order to help pinpoint the source.
greenchero
06-02-2002, 05:54 AM
If the compression checks ok look for a vacuum leak. Something on the #3 runner of the manifold.
jeepbob
06-02-2002, 01:16 PM
Check the vac port on the front of the intake for cracks and check the hoses for cracked or broken hoses or even being unhooked. This port draws off #3 cyl. When you checked the rocker movement did you eyeball it or did you actually measure it? It is very easy to miss a worn lobe by eyeballing it.
243
06-02-2002, 02:14 PM
#3 plug was not wet and looks good very light but not completely white.

Yes, I used the eyeballs and it was late...I don't have a dial indicator, is there another method?
RichCal
06-02-2002, 02:31 PM
How does that compare to #1,5 & 7?
Lindel
06-02-2002, 11:14 PM
How many miles do you have on the engine? Could be a bad lobe on the cam (intake), and you're not getting any mixture to fire. That would explain the plug looking so nice, not being wet, hard miss, etc.

It'll even pass a compression test that way, too, but still won't fire. Pull the valve cover, and look to see if maybe you broke a rocker, or a bridge. Could be you've bent a push rod, or you have a collapsed lifter, as well.
Gary Holmes
06-10-2002, 02:26 AM
I had the same problem (#3 also) on the Camo Cow and it turned out to be a bent pushrod. That's what started me on the rebuild road.
steven79
06-10-2002, 03:29 AM
243 if you want come on over and we can put two heads together on this, we can even do a leakdown test on it if you want. smile.gif
243
06-10-2002, 05:04 AM
Steven~

I am going to the waiver station to plead my case on the 13'th. If they don't put a sticker on it, I will take you up on your offer. Pulling Red out of the garage is not high on my list.

Do you have a compression tester as well?

Gary~

I will check for a bent pushrod(s), it's an easy task and I need to replace the valve cover gaskets anyway.