C2: L36 Keep missin' the miss

[Dan Pepper]

I've been working on hunting down a persistant miss that's most noticable around 1500 RPM, then smooths out with more revs. I can still feel that it's there, it's just less noticable with higer RPM's.

So far I've:

-Checked/changed plugs (old plugs clean, #4 was a bit dark/oily... hmmm)
-Checked wires: replaced all boots that looked suspect (Lectric Limited wires)
-Rebuilt/recurved distributor-HD points, condensor, new cap & rotor, etc.
-Checked vacuum from the AC port: vibrates between 13-15 inches @ idle
-Checked the heat riser: was sticking a bit, so I wired it open
-Checked the fuel system/filter/pump - all okay
-Carb seems to be functioning a-okay

After all of this, the engine is a lot happier (rear tires aren't), but the miss is still perceptable.

I am my no means an expert at turning wrenches, so I'm at a loss on what to do next. Could this be a valve or lifter problem? Maybe the stuck heat riser contributed to burning #4 valve? How can I tell if it is? Can a shop with a machine diagnos the problem without tearing it down?

Advice appreciated.

[Craig S.]

Re: C2: L36 Keep missin' the miss

Dan - I have had this type of problem in the past on chevy V8's, and it was related to camshaft lobe wear (but could be a lifter/valve problem as you suggest). Step 1, I would accurately measure the lobe lift at each lifter with a dial indicator, to verify you have correct lift at each lobe and one is not going away. This is easy to do with a cheap dial indicator from someplace like Harbor Freight if you don't want to go expensive, and will help pinpoint any problems. Since you mention number 4 is running a bit dark, I would also run a full compression test of the cylinders, and, better yet, a leakdown test. This will go a long way to diagnosing any weak areas without teardown. Good luck!...Craig

[Dan Pepper]

Whoa! Light show...

I just took a spin and pulled into the garage, kept it running popped the hood and shut off the lights - you guessed it. EVERY plug was arching into the plug shields.

The wires are about one year old so I didn't really suspect them. I did check for arcing a couple days ago, but missed it because it was so faint. I couldn't tell exactly where the arcs were emitting from as the bluish light was very faint. The arcing looked like it was radiating from inside the plug tunnel, rather than making a distinct, sharp arc in plain sight. I'm using Delco Rapidfire #4 plugs and stock Delco 232 coil - just wondering if the new fangled Delco plugs may be contributing to the problem.

Don't think I damaged the wires - but it's odd that every hole was arcing. This is the second set of Lectric Limited braided wires with which I've experienced this problem. I used dielectrick (sp?) grease on the boots this time around too.

Other than replace the wires (again - arghh - expensive), is there anything that can be done to eliminate the problem? And if no, anybody suggest another source correct braided/dated wires?

[Jack H.]

Re: Whoa! Light show...

Have seen this (plug wire arcing) on even brand new, off-the-shelf, reproduction, sheilded/braided, BB plug wires. Sorry I don't have a solution other than to contact the supplier/mfgr and complain. Could be quality control taint all that great in repro-land....

[John Lokay]

Re: Whoa! Light show...

How often should spark plug wires be changed, every 5+ years, etc?

[Duke W.]

Re: Whoa! Light show...

Depends. Wires degrade primarily from exposure to heat. The type of wires used on our vintage Corvettes should probably be changed about every 60K miles. For a daily driver this is about 5 years, but since most of us just drive our cars a few hundred to a few thousand miles a year they should last much longer than five years. Modern cars generally have higher quality insulation that has considerably more life the the wires from the sixties.

Regarding evidence of blue light, it may not necessarily be an indication of a leak, especially if the light is very faint. Jack or some of the other EEs may want to comment on this, but there is a phenomenon called "corona discharge" that can create a faint blue light due to the rise and fall of the magnetic field surrounding the wire. An actual leak that causes an arc will be a very bright blue when viewed in a dark garage.

Duke

[Dan Pepper]

Jack, so what about...

...this "corona discharge" that Duke mentions?

My only experience with it has been in a restroom just south of Puerto Viarta. But seriously folks, could there be any visible electrical "leakage" that wouldn't disrupt firing, thereby causing miss?

[Duke W.]

You actually used a RESTROOM? *NM*

[Jack H.]

Re: Jack, so what about...

Corona is unmistakeable. Similar to the seafarer's phenomon, St. Elmo's Fire.... It glimmers and radiates in a circular fashion surrounding the current carrying element (plug wire) in an undulating mode with the rise/fall of magnetic field strength (byproduct of electrical current flow).

What I was talking about was bona fide arcing. Crisp blue discharges from the braided jacket of the plug wires in random radial lines (like lightning bolts) seeking various ground points on the engine block.