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Discussion Starter #1 (Edited)
My #2 cylinder's exhaust is warm, but not hot, and a skip/non-fire at idle, and backfiring out of the exhaust on deceleration. What gives? Backfire is likely timing/fuel tweaking, but the dead cylinder is a mystery!!

Inventory (All New and stock):
- Crate Vortec L31 350 long block
- Eddy intake/carb
- Summit distributor and wires

Check #1 - Plugs are good (E3) and have fire.
Check #2 - Wires' resistance is within specs
Check #3 - Compression is good at 145-150psi on all cylinders
Check #4 - Valve train is moving as I would expect during manual crank

Vacuum Leak? - I would think that would make things hotter as it would lean out mixture?

Intake Gasket? - I read this elsewhere, but would a leak or runner blockage be possible?

Dist Cap Arcing? - Not familiar with this, but with all new electrical and connections, could be possible?

Valve Train? - Outside of the visual test I did, is there anything else I could torque/see/check?

Any other ideas? Thanks for any help!!!!
 

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Discussion Starter #4
Thanks for the reply!

neils63ss - I did swap wire/plug to another and seemed to skip in both. I will retry this to confirm, as it was a little late the other night and memory is fuzzy. If that was true, I would think I have two problems..

seventynovaSS - I visually checked the cap, but have not taken it off. Is carbon tracking the arcing I've read about? Would this be in between two of the terminals on the inside of the cap?
 

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Retorque your intake manifold bolts.....not likely but possible

Purchase a inline spark indicator... one where you can see the spark. I just used mine to troubleshot nd discovered My #6 spark was fading in and out, resulting in misfire and idle changes.

E3 plugs, ...I have heard they can cause issues...but I have no first hand knowledge, just something to consider.

Gl
 

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Discussion Starter #6
Will do on the intake bolts. I'm trying not to have to pull too many things off, so i'll try and retorque to be sure.

If there is a problem with the intake (maybe gasket/seal), am I correct in thinking it would cause a vacuum leak..and likely hotter exhaust temps?

It sounds like a spark plug tester would be better at mimicking CC pressure/spark strength? Probably better than me just putting the plug next to the frame to watch the spark.
 

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Bad spark. (If you've checked everything else, it could just be cold/weak.)

Bad valve.

Mis-ground cam.

Plugged head/header/manifold.
 

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Discussion Starter #8
Thanks Squigie. Being that the wire resistance is good, a bad/weak spark could be the plug OR the cap..just on that cylinder? Is that what arcing would do, if I find evidence of it?

Given it is a crate GM long block, I would hope the valves/cam would be alright.

Is there something on the valves (outside of visually looking at them) that I could measure to see if the intake is opening up all the way?
 

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Mike - 74 Nova Baltimore, MD
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I did swap wire/plug to another and seemed to skip in both.
When you stated "seemed to skip in both", did you mean that after you moved the plug/wire from the #2 cylinder...
*The skip stayed in #2 PLUS you gained a new skip in the cylinder with the plug/wire that were originally at #2?
- or -
*The skip moved to the new cylinder with the plug/wire that were originally at #2 AND #2 (with a different plug/wire) was now firing properly?

You might want to check all of your spark plug gaps (should be looking for around .034"-.035" gap on all plugs). A larger gap could produce a weaker spark in the cylinder when trying to fire in a "compressed air environment".
 

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Discussion Starter #10
RifRaf, I believe it started skipping in both cylinders when I swapped wires. Again, I "believe"...though it was late at night...

If it did, which I will check this weekend, that would mean I would have a couple problems I'd imagine, but it would likely center around the electrical.
 

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Mike - 74 Nova Baltimore, MD
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It might also be helpful to know what specific distributor, coil, and spark plug wires were used for your set-up (links, part #s, etc).

If you converted to an HEI unit... or some other type of electronic distributor, did you run a 12 volt power source to the distributor/coil (bypassing the original resistance wire)?
 

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It's a stock Vortec L31.
Which Eddy manifold?

Which manifold gaskets? I used the Mahle MS16167P gaskets on my engine with Vortec heads. They're spendy, but they're well made and they seal well.

What torque specs did you use? Vortec intakes require VERY low torque on the bolts, inch pounds instead of foot pounds.

I know this only addresses one of the points raised in a previous reply, but if an intake gasket lead is contributing to your problem, this might help.

Gerry
 

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Discussion Starter #13
It might also be helpful to know what specific distributor, coil, and spark plug wires were used for your set-up (links, part #s, etc).

If you converted to an HEI unit... or some other type of electronic distributor, did you run a 12 volt power source to the distributor/coil (bypassing the original resistance wire)?
Thanks RifRaf,
Distributor - SUM-850205 Summit Billit Distributor
Coil - SUM-850500 Summit HO Coil
Wires - SUM-868858R Summit 8mm wires

No HEI, as I think I tried it, but had fitment issue to the firewall.
 

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Discussion Starter #14
It's a stock Vortec L31.
Which Eddy manifold?

Which manifold gaskets? I used the Mahle MS16167P gaskets on my engine with Vortec heads. They're spendy, but they're well made and they seal well.

What torque specs did you use? Vortec intakes require VERY low torque on the bolts, inch pounds instead of foot pounds.

I know this only addresses one of the points raised in a previous reply, but if an intake gasket lead is contributing to your problem, this might help.

Gerry
Thanks Gerry

Eddy Performer EPS (Vortec specific) and Eddy intake gaskets.

I will check torque on the intake tonight. Thank you all for the posts! Hope I can solve this soon!
 

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Discussion Starter #15
I'm trying to think through this before I take off the top part of the motor...

If there was an intake issue (seal/torque/gasket), wouldn't either:

1. I have compression issues? On compression stroke, valves should be fully closed, right? So, if there was a bad seal, wouldn't I see an impact on compression?

OR

2. Vacuum leak on intake would suck in more air, leaner mix, and hotter exhaust temps..not cooler like I'm getting?

I'll still check the torque specs, but I'm thinking (which a few of your have suggested) spark or intake block of some sort.

Will rent a bore scope and inline spark tester tonight...we'll see!

The dizzy cap looks good to me?...

 

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What does the spark plug look like on the cylinder that is missing. Spark plugs are cheap. Before I took anything a part I'd change the plugs in it. I know everybody is different but I've been running auto lite spark plugs for many years. I have had a few over the years that were bad out of the box. Another thing I would check that is very easy to do. Turn the lights out in the shop and crank it up at night. Open the hood and see if you can see fire jumping from spark plug , wires or distributor. I recently had a coil wire fail. I drove my car and parked it one night and the next morning was messing around and noticed the coil wire boot didn't look right. When I touched it to look it fell completely apart in my hand.
 

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Mike - 74 Nova Baltimore, MD
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Distributor - SUM-850205 Summit Billet Distributor
Coil - SUM-850500 Summit HO Coil
Wires - SUM-868858R Summit 8mm wires
I am not familiar with the Summit 850205 Distributor (kinda looks like an MSD "Ready to Run" Distributor).

Did Summit provide detailed instructions on how to wire their 850205 Distributor?... Did the installation instructions specify to run a full 12 volt feed wire to the + side of the coil?... or did they state to run some type of a resistor feed wire to the + side of the coil.
NOTE: I tried to find installation instructions online for the Summit 850205 Billet Distributor, but the wiring portion about what type of voltage feed should be run the + side of the coil was unclear from what I was able to find.
https://static.summitracing.com/global/images/instructions/sum-850050.pdf
*See page 3 - Top of page.

Also... where did you attach the ground (black) wire from the Summit Distributor to?
 

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Discussion Starter #19
I am not familiar with the Summit 850205 Distributor (kinda looks like an MSD "Ready to Run" Distributor).

Did Summit provide detailed instructions on how to wire their 850205 Distributor?... Did the installation instructions specify to run a full 12 volt feed wire to the + side of the coil?... or did they state to run some type of a resistor feed wire to the + side of the coil.
NOTE: I tried to find installation instructions online for the Summit 850205 Billet Distributor, but the wiring portion about what type of voltage feed should be run the + side of the coil was unclear from what I was able to find.
https://static.summitracing.com/global/images/instructions/sum-850050.pdf
*See page 3 - Top of page.

Also... where did you attach the ground (black) wire from the Summit Distributor to?
Thank you for digging on it RifRaf, I really appreciate it. It's been so long since I installed it, I will have to check on the wiring, but that PDF is the instructions I utilized.

From last night's work, had some success:

- CARB GASKET - Should my carb gasket have material on the middle divider between the two planes of the intake? Eddy 1406 and Performer intake and just have the square gasket with no material on the divider. I didn't think this was needed unless you were getting hard start issues in the heat?

- CARB STUD - One stud was loose and partially stripped (on the corner of the dead cylinder). I removed the stud, cleaned threads and it seemed to snug back in pretty well. I will check it and put some threadlocker if it loosens.

- INTAKE RUNNER SCOPE - Bought a scope and threaded it down the runner of the dead cylinder. Looked good and no blockages.

**- CRACKED PLUG - Bought a spark tester and noticed the dead cylinder's brand new spark plug had a loose insulator. Brand new E3. Swapped for a spare and seemed to run again!

Checking tonight: Coil wiring, timing, fuel mix. I am still getting some backfiring, and the skipping made it run like it had a cam, so hopefully if I can get timing/fuel right, I can confirm it is running like it should!
 

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Mike - 74 Nova Baltimore, MD
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Do you know what type of cam profile (lift/duration) was installed in your engine?

Once you check the timing, can you post some numbers.
- Initial (no VA)... and at what RPM
- Total Mechanical (no VA)... and at what RPM
- Initial + VA* (* is VA connected to a full time vacuum source, or a ported vacuum source?)
- Total Mechanical + VA
-What is your vacuum level at idle?

NOTE: Sometimes if the spark plug socket slips off the hex head of the spark plug while tightening, the socket may slip and crack the spark plug's insulator.
It might be a good idea to pull all of the spark plug boots and recheck all of the plug's insulator by trying to "wiggle" them.
 
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