DougSilver

I've been chasing down an intermittent missing problem on my 95 LT-1 automatic for the last 6 months or so. I had change opti, plugs and wires about 2 years ago and recently installed a new IAC so I did not think those were the problem. The engine miss would happen when idling in gear and sometimes when going up a hill in overdrive (i.e., low rpm condition under load). The problem was worse the last few weeks with all the rain here in Socal. I stopped by a local mechanic who said the miss looked to be associated with the secondary ignition components (opti or plugs or wires).

Anyway, I was fooling around under the hood the other day to try and check the throttle position sensor. I unplugged the connector to try and get to the contacts to check voltage, etc. and then plugged things back (I threw a DTC 64 since I turned the key on while the sensor was unplugged but this seems irrelevant). The only other thing I did while the hood was opened was my usual check for tightness of wires and connectors that I could reach (e.g., spark plug wires).

This time, I found a wire that I had not previously checked--the lead that goes from the opti to the coil. Of course I could not reach the end that plugs into the opti but I pushed in the end that fits into the coil. To my surprise the wire pushed in a bit and I felt a click. Obviously I seated the wire more fully to its connection in the coil but I did not think much about this.

However, when I drove the car, it feels like new. The miss at idle seems to be gone and the car feels like it's on steroids. It seems amazing that the cause of my problems may have been an improperly seated coil wire but I am keeping my fingers crossed. It's been a few days of driving now since seating the wire and still no engine miss or other problems!

SilverBeast

Glad to hear it! Drive on!

Lone Ranger

This doesn't surprise me. Not that you mised it, but because of a similar experience I have had. The Moroso Blue Max wireset fits very tight. I thought the coil wire was secured but it still felt sloppy. I had pressed like hell on it with my fingers and was sure that was just the way it fit. For good measure I countered with my left hand on the back of the coil and used palm of my right to apply pressure this time and it moved some more, snapping very positively the rest of the way onto the coil terminal.

This was back when I changed the wires in the fall.

Who woulda thunk it.

DougSilver

I guess even a tiny air gap from not having the wire snap all the way in is enough to cause significant problems--it just had never occurred to me. Of course this could still be coincidence and the miss could come back but it's been 3 days now without the missing (a record) and I'm keeping my fingers crossed.

Corvette Kid

Gotta love it!

tm1995c4-LT1

I started a thread a month or two ago about my 95 having a miss. I started the thread after getting my car back from my mechanic. He changed the cap and rotor, plugs, and plug wires. The car ran fine for about 1000 miles, but then the problem came back. Not as bad yet, but it was starting to miss intermittenly agian. In one of the posts on that thread someone mentioned checking that lead wire (Nathan Plemmons. I think). I haven't got around to it yet, but I'm going to check that this weekend. Maybe (hopefully) this may be my problem too. Glad to hear your car is running well. I'll keep my fingers crossed for ya.

JAKE

I'm really glad you posted about solving your problem.

This is a perfect example of what I try to tell guys all the time. Don't over-engineer the problem. Check the basic stuff first; don't just head off to the parts store with your wallet in your hand. Often times it's something really simple.

What bugs me a little is when I make those suggestions, they sometimes get dismissed out of hand, then, 50 posts later, the guy posts he found the cause, which is something I suggested he check in post two.

I wish I'd kept a listing of all the crossed-plug wires, vacuum hoses left off, lifter preload set too tightly, rotors not screwed down tightly, distributors mis-installed, etc.

I, like many others, don't mind trying to help out, but our advice is pretty useless unless it's followed.

There IS a difference between a mechanic and a parts changer.

Just venting.

Jake

runner140*

On our LT1's its difficult to get at all the wires (opti, plugs, coil etc.) Congrats. Glad to hear you got your ride back to normal.

DougSilver

So far still good but one quick question. For engine miss problems, opti seems to be the first item many point to (along with rants about the opti--including the mechanic I visited). Then the list goes on to include crossed-plug wires, bad plugs, bad wires, etc. I am wondering what is meant by crossed-plug wires. I assume this means plug wires close to each other that somehow induce sparking across the wire insulation? Or does this mean wires that physically are attached to the wrong plugs (I would guess the engine would not even run if that were the case).

87SAM

Good score! I hope that solves it!

Thanks also for posting the resolution. It seems so often here I follow threads on particular problems, advice given and troubleshooting procedures only to have the thread die off and never hear the outcome. I can only retain about 10% of what I take in so I need as many happy endings with what solved a problem as I can get.

JAKE

Most of the time crossing plug wires involves putting a wire on the wrong spark plug. Many times it's flip-flopping 5 and 7 since they're so close together and five fires right before 7. So, someone would put the #5 plug wire on the #7 plug and #7 on #5.

Cross firing occurs when voltage from one wire jumps to an adjacent wire. Mis-firing occurs when the spark jumps to ground. You can best tell this is happening in a darkened area. When a plug wire has bad insulation you can sometimes see a blue halo around the wire in the dark. Spark may not actually be jumping (yet) but voltage is leaking.

Spark is like water and takes the path of least resistance. If it's easier to jump to ground or to another wire, rather than jump the gap at the spark plug, that's what the spark will do.

Plug wire should be separated by AT LEAST 1/4", preferably more.

Jake

DougSilver

Cross-firing is what I was thinking of as a Chevy mechanic once blamed my opti problems on cross-firing so they replaced the wires along with the opti. I have all the right looms on the wires but there are still a few locations where I see plug wires that are near or touching other plug wires. It seems this is unavoidable with all the various small passages and obstructions that the wires have to go through as they get near the opti. My guess is that if the wires are in reasonably good shape, they should be resistant to cross-firing even if one wire is touching another--am I wrong?

JAKE

For a while you'll be able to get away with it, but over time, well, that's another story. Remember, not all problems immediately jump out and bite you.

It's heat that has the primary effect on the plug wires: the insulation breaks down over time from being exposed to the high heat of the engine compartment.

A plug wire should never actually touch another one or anything else (except the wire separators) for that matter. If it touches, say, metal, constant engine virbation can cause the insulation to wear through.

There are lot of after-market wire separators available. There are also several heat resistant insulators available for both the wires and the plug boots. Jesel even has some that are ceramic. I use to always shrink-sleeve the plug wires (MSD stuff) on the race engines.

A little creative routing can keep all the wires where they should be.

Jake

DougSilver

Jake--do you or anyone else know if the wire loom/separators are available from GM or other aftermarket sources? If so, are these bought individually or as a set. I found one that was broken (one that has slots for 2 wires) and was wondering if I could get a replacement.

JAKE

Most of the parts suppliers that many of us use sell them. Summit, JEGS, Performance Automotive Warehouse, MSD, etc. They're offers for specific setups too, center bolt or perimeter vvle covers, etc. Many of them come in different colors too, to match the color wires you have and to fit different diameter wires.

Moroso sells the separators in pairs and some of the auto parts stores, like AutoZone and Pep Boys have them hanging on the rack.

If you're bucks down, you can make them out of plastic cable ties.

Summit and JEGS have websites that list their stuff.

Jake

DougSilver

The one that broke is OEM and has a plastic slot that snaps onto a metal clip (attached to some bolt on the head) that serves to hold this in place. Being a purist I was wondering if it was possible to get an exact replacement. I'm checking GMPartsdirect. The separators sold by Mid-America look pretty similar so I may opt for that set which is about $10.

kwik_ta

sweeeeet!!! It's always cool when the problem is rather miniscule, but always a PITA when it is something so silly. Now she's running on steroids... can we call it Canseco???
of course we will need pics of a monster burn out now

JAKE

Since you want the original GM type, you'll have to hit the dealer or a wrecking yard or, as you said GMPARTSDIRECT.

Jake

eschoendorff

Damn! Sounds just like my dad! And the worst part is that after I had screwed around with a problem long enough, I would finally come to the conclusion that good 'ol dad was right!!! Time to eat some crow... I have been guilty of all of the above

DougSilver

Well the car drove well for several days but I noticed the miss coming back a bit. So today, instead of just jiggling the wire to the coil I removed it and was amazed to find a bunch of greenish powdery stuff completely coating the fitting on the coil as well as inside the boot of the wire. It looked like there was not actual metal-to-metal contact at the coil wire. So I took some steel wool to clean off the fitting on the coil and cleaned the inside of the boot as best as I could so now I can at least see clean metal on both parts. I did not get a chance to drive the car yet (raining in LA area today) but I assume this was the source of my problem. I just hope similar corrosion is not at the other end of the wire that plugs into the opti (too difficult for me to remove and reinstall) but I will have the mechanic maybe totally replace this wire when I bring the car in for service.