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Dead Cylinder - Coil Overheating?
Posted by: Carburetor ()
Date: August 08, 2019 09:40AM

While driving back home from a car show, my car (’66 140/PG) started running rough, to the point where I had to put it in neutral at red lights to keep it from stalling. When I got home and pulled into the driveway, I could tell from the exhaust sound I had a dead cylinder in the RH bank (steady puff from the RH tail pipe). I didn’t have time to take a look at it so I pulled into the garage. A day or two later, I started her up, and no misfire on any cylinders. I then went on a drive, and after a couple of miles, it started running rough again and when I pulled into the driveway, I again had a dead cylinder in the RH bank. I left her running, hooked up my tach/dwell meter, and pulled one plug wire at a time from the distributor cap. I found out that #1 was the dead cylinder – however, I noticed a couple of things: (1) there were sparks when pulling the #1 plug wire from the cap, so the ignition system is trying to fire the plug, and (2) the sparks when pulling each wire from the cap were fairly weak and orange, not a blue-white color that I was expecting. I placed my hand on the coil, and wow, was it hot! So, my theory is that as the engine / coil are heating up, the spark is weakening to the point that the #1 plug won’t fire. I started her up again yesterday and pulled the #1 wire from the cap – the spark was definitely stronger (more of an orange-white color) than when I pulled the wire when the engine (and coil) was hot.

Some background info: when I bought the car five years ago, I replaced the cap, rotor, and points with new parts that came with the car – these parts have less than 1,000 miles on them (yes, I don’t drive it as much as I would like…). Last year I replaced the plugs (NGK B6HS) and the spark plug wires (Clark’s). So the ignition system is fairly new. Also, I rebuilt the carbs over the winter – was able to sync them fairly easily (a Uni-Syn makes this so much easier) but it may be idling a tad lean as I have a bit of a stumble off-idle (which wouldn’t help the #1 cylinder misfire being the furthest from the RH primary carb).

Back to my theory – I believe the #1 cylinder cutting out when hot is a symptom of the coil overheating. I’ve read plenty on here about the coil running hot if it’s running on a full 12 V instead of 6-9 V (?) through the resistor wire. I pulled out my service manual and looked at the schematic (’66 supplement page 12-7). That’s when I noticed that I appear to be missing the 20 BRN/W wire going to the negative post of the coil per the schematic – my car only has the yellow wire to the positive post and the black wire from the points to the negative post. I pulled apart the 12-pin connector in the engine compartment for a better look – the 20 BRN/W wire that is shown in the schematic is missing from both halves of the connector (not in the engine harness or body harness).

Question #1: is the 20 BRN/W wire the resistor wire?

Question #2: if the 20 BRN/W is not the resistor wire, what is its purpose? It’s MIA from my car (and has been since I’ve owned it).

But I thought I had also read that the resistor wire is cloth-covered. Taking a closer look at the wiring and schematic:

Question 3: is the resistor wire the 20 W/R/B going from the engine harness side of the 12-pin connector to the starter harness? It is present on my car.

Question 4: if my wiring is correct, is there a way to determine if the coil is on its way out, or is it just easier to replace it and see if it fixes the problem?

Any and all comments / guidance / questions are appreciated. Also, some pics for your viewing pleasure.

Jim C.
Chesterfield, MI

1966 Monza convertible (140 / PG)
2017 Chevrolet Trax (daily driver)
2017 Chevrolet Volt (wife's ride)


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Re: Dead Cylinder - Coil Overheating?
Posted by: vairmech ()
Date: August 08, 2019 09:51AM

Since you have a Monza 140 PG car you will not have the brown wire as that is for the tach on a Corsa.

The cloth covered wire you show is the resistor wire.

It looks like you have the original coil, is so then it is suspect for what you describe. Coils do run quite warm like to hot to really do more than just touch them quickly.

Ken Hand
Handy Car Care
248 613 8586

Vairmech@aol.com

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Re: Dead Cylinder - Coil Overheating?
Posted by: 66vairman ()
Date: August 08, 2019 10:32AM

What Vairmech said about wiring. The resistive wire goes to the starter pig tail harness plug because when the car is starting the starter sends a full 12VDC to the coil via the "YELLOW" wire. Once the starter releases the coil gets voltage via the resitive wire.

If the points are open (engine off) you'll see batter voltage (about 12.8VDC) at the coil positive terminal. If the points are closed (engine off), or you ground the coil "-" terminal - briefly, the voltage will drop to about 5.5VDC at the coil "+" terminal. If not then check the coil primary resistance that should be about 1.3 ohms (1.5 is O.K.).

It is possible you have an intermittent short in the cap at the number 1 terminal - look for a crack or carbon trace. Another issue is a marginal plug wire. You can use a meter to check resistance.

Usually when a coil starts to go bad the mis-fire will be random, not always the same cylinder, but it may be a combination of things.

If you replace the coil buy a quality aftermarket coil for a 1965-6 Chevy Impala SBC V8 engine. DON'T use a six cylinder coil from Flamethrower - WRONG COIL.

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Re: Dead Cylinder - Coil Overheating?
Posted by: stitch ()
Date: August 08, 2019 10:49AM

Coils are pretty darn cheap, considering. Try a new repop...

"If you can't fix it with a Hammer, you have an Electrical problem."
Stitch...
Schertz, Texas.
(Smallish town/burg 17 mi. NE of San Antonio)

'Ms Penny'
!967.. 4th body
8th off the line

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Re: Dead Cylinder - Coil Overheating?
Posted by: stitch ()
Date: August 08, 2019 11:31AM

Advance Auto $24.99!smileys with beer

"If you can't fix it with a Hammer, you have an Electrical problem."
Stitch...
Schertz, Texas.
(Smallish town/burg 17 mi. NE of San Antonio)

'Ms Penny'
!967.. 4th body
8th off the line

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Re: Dead Cylinder - Coil Overheating?
Posted by: MattNall ()
Date: August 08, 2019 11:34AM

Jim.... first thing...

Move the coil to the verticle bracket behind the license plate.. wires reach easily.

And plug the hole under the coil, if there is one.

MODERATOR
Sea Mountain, between Charleston Harbor and Coos Bay! SW Oregon Coast
Click HERE for My Website...Click HERE for My TechPages!
..............................110-PG.................................................Webered-Turbo

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Re: Dead Cylinder - Coil Overheating?
Posted by: Bob65 ()
Date: August 08, 2019 01:34PM

I mounted a 12 volt fan near the coil to help with coil overheating.

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Re: Dead Cylinder - Coil Overheating?
Posted by: joelsplace ()
Date: August 08, 2019 02:51PM

Also a coil can't be selective on one cylinder misfiring unless that cylinder is harder to fire than the rest and the coil is barely managing to fire the easy cylinders but this is unlikely. If you have a #1 misfire and the compression is good you need to look at the plug, wire and cap.

Joel
Northlake, TX
5 Ultravans, Lost count at 100 Corvairs...

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Re: Dead Cylinder - Coil Overheating?
Posted by: 66vairman ()
Date: August 08, 2019 03:18PM

Bob65 Wrote:
-------------------------------------------------------
> I mounted a 12 volt fan near the coil to help with coil overheating.

Creative, but not as effective as mounting the coil on the rear bulkhead bracket as was done on A/C cars. If you need a longer coil to dist. wire you can get one from Seth Emerson as he makes them up for A/C equipped Vairs.

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Re: Dead Cylinder - Coil Overheating?
Posted by: Carburetor ()
Date: August 08, 2019 05:02PM

Ken - never occurred to me that the Corsa tach lead would have to be connected to the negative post of the coil (this being my first Corvair). Interesting that on that same page of the schematic they show other wires as being specific for Corsas (thermister) but didn't call this one out. Nice to know my wiring appears to be correct. I thought this was the stock coil too (my parts book shows 1115202 - stamped 202-12V) but it's a Delco-Remy coil stamped 293-B-R which I believe is a later coil for points equipped Chevys (1115293) per GMPartsWiki.


66vairman - I took the following measurements:

Battery (key off): 12.6 V
Battery (key on): 12.2 V
Old coil, points open (key on): 12.1 V
Old coil, points closed (key on): 5.8 V
Old coil, primary resistance: 2.0 ohms


stitch - I had the same thoughts, so I grabbed a new coil from AutoZone.

Here are the same measurements with the new coil:

New coil, points open (key on): hmm, swore I wrote that down. Think it was 12.0-12.2 V
New coil, points closed (key on): 5.0 V
New coil, primary resistance: 1.4 ohms

Matt - I may move the coil later. I did plug the hole underneath it where the shrouds come together (Gorilla tape).

With the new coil installed and idling in the garage, it appears to idle better with the new coil (or its just my imagination). I pulled the #1 wire off of the cap and I believe the spark is stronger than with the old coil. Won't be able to take it for a shakedown run until tomorrow after work, fingers crossed!

Edit: I don't disagree that the steady misfire on #1 when hot (which has hopefully gone away with the new coil) points to something amiss. I did check the cap and everything looks good. I'll pull the plug and wire and check them tomorrow.

Jim C.
Chesterfield, MI

1966 Monza convertible (140 / PG)
2017 Chevrolet Trax (daily driver)
2017 Chevrolet Volt (wife's ride)





Edited 2 time(s). Last edit at 08/08/2019 05:06PM by Carburetor.

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Re: Dead Cylinder - Coil Overheating?
Posted by: MattNall ()
Date: August 08, 2019 07:09PM

You're getting there!

MODERATOR
Sea Mountain, between Charleston Harbor and Coos Bay! SW Oregon Coast
Click HERE for My Website...Click HERE for My TechPages!
..............................110-PG.................................................Webered-Turbo

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Re: Dead Cylinder - Coil Overheating?
Posted by: American Mel ()
Date: August 08, 2019 11:30PM

Hopefully it is an electrical issue.
I had an intermittent miss in one of my 140's.
It would come and go.
Turned out to be a dropped valve seat.
It would pop in and out of place.
Sometimes holding the valve open, and other times allowing it to close.
It finally got worn enough that it stayed out.

.
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
WA. state, 1 mile south of the Canadian border,
I am not at the end of the world, but you can see it from here.
'66 Monza Coupe - 4spd, 140 Daily driver beater
'67 Monza Vert. - PG, 140 Daily driver beater
'67 A/C Moredoor Monza - 140 4-spd. driver
.
non-vair
'04 Dodge Cummins Quad Dualy, approaching 400K
17'Terry

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Re: Dead Cylinder - Coil Overheating?
Posted by: JimBrandberg ()
Date: August 10, 2019 06:46AM

I hate to go off on a rabbit trail but can't help myself. I can't get past only having one cylinder affected. Have you considered lifter adjustment? Perhaps some are at the bottom of their travel and get tighter when warm?

Jim Brandberg
Isanti, MN
CorvairRepair.com






Edited 1 time(s). Last edit at 08/10/2019 06:47AM by JimBrandberg.

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Re: Dead Cylinder - Coil Overheating?
Posted by: Brizo ()
Date: August 10, 2019 08:37AM

Jim, I think a tight valve misfire sometimes goes away when the engine expands ?

Dan Brizendine,
'64 8door Greenbrier 140 PG. "In beautiful Wanamaker Indiana...with one stop light and 5 pizza shops"

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Re: Dead Cylinder - Coil Overheating?
Posted by: TerribleTed ()
Date: August 10, 2019 11:49AM

Brizo Wrote:
-------------------------------------------------------
> Jim, I think a tight valve misfire sometimes goes away when the engine expands ?


I would think this is possible and would certainly readjust the valve or valves running and warm to see,

---------------------------------------------------------------------------------------------------------

Avid Corvair hobbiest since 1984.
I have personally performed ground up restoration on over 20 Corvairs.
I currently work full time at restoring and repairing Corvairs.
Located in the Atlanta Georgia area.
[www.facebook.com]

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Re: Dead Cylinder - Coil Overheating?
Posted by: Carburetor ()
Date: August 10, 2019 07:54PM

Unfortunately I didn’t have a chance to take her for a shakedown run before my wife and I left for a week’s vacation. Not sure how the valve adjustment could have gone awry so suddenly but it’s something to keep in mind. We’ll see what happens in a week from now when I get back home.

Jim C.
Chesterfield, MI

1966 Monza convertible (140 / PG)
2017 Chevrolet Trax (daily driver)
2017 Chevrolet Volt (wife's ride)


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Re: Dead Cylinder - Coil Overheating?
Posted by: DaveO90s4 ()
Date: August 11, 2019 04:53AM

Could the ‘one cylinder only affected’ issue possibly be caused by a less than good connection between spark plug lead and top of spark plug? My engine was misfiring recently. Replaced plugs same problem. Found on one lead the plug connector had ‘retreated’ too far and when rubber seal was covering spark plug hole in tinware the lead was not quite reaching the plug. Adjusted lead length through rubber spark plug connector and all is now OK. Just a thought...

Cheers

DaveO

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Re: Dead Cylinder - Coil Overheating?
Posted by: JimBrandberg ()
Date: August 12, 2019 05:52AM

Dan presented the theory that a tight lifter gets looser as the engine warms. That makes sense to me as the engine expands when warm. I was looking for possibilities affecting a single cylinder.

Jim Brandberg
Isanti, MN
CorvairRepair.com



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Re: Dead Cylinder - Coil Overheating?
Posted by: MtnVairMike ()
Date: August 12, 2019 06:26AM

Jim,

This being a 66 is there the smog pipes opening cut in the shroud under the coil?
That took my coil out intermittently.
If so you need to block that hole and get a new coil.
Some folks move it to the back near the hood latch like on AC cars.

That opening is a hot hair dryer straight on the coil when running.

Search my posts and you'll see my story.

Thanks,

Mike

1966 Monza Convertible, 140HP-4 speed, Ermine White

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72 Corvette Stingray, 58K miles, owned since 86
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Re: Dead Cylinder - Coil Overheating?
Posted by: kenzen ()
Date: August 13, 2019 06:45PM

Bad plug? Swap and see if the problem moves.

kenzen
66 Monza Coupe 110/PG
Bel Air, MD

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