Plug wires
 

I'm running MSD 8.5 super conductor wires (new this year). I've been chasing a miss so I've been testing some things. At what ohm reading per foot of length would you consider a plug wire needs to be changed. MSD says 50 ohm's per foot is normal. What number higher would there be a problem. I'll tell you what I read after I here some others chime in. I'll also call MSD but I'd like to get some races input. Thanks Robbie

Re: Plug wires
 

Are the **new** plug wires following the same routing path that the **old** wires did---

have you installed or rerouted any sensitive wiring since the old wires were replaced???

are all wires the same length as the wires they replaced???

are the boots OK do they have carbon tracking inside them???

MSD suggests that 40-50 OHMS per wire foot COLD is their recommended number----

is it the same cylinder or does it move around???

have you thoroughly checked the distributor/cap rotor/wiring and coil ---how old is the coil do you have a **powerful** enough coil for the application

do you have a MSD box and has it been checked out-- did you try a different box

was the coil and or coil wire replaced??

have you checked for a cracked porcelain or other possible defect of each spark plug??


what else was changed??? If you have the **old stuff** put it back in see if the miss goes away

does it happen on humid days or dry days-- cool days or hot days or does it happen almost any time??? low RPM or High RPM ??


FED 387

Re: Plug wires
 

[QUOTE=FED 387;573841]
If you have the **old stuff** put it back in see if the miss goes away

Best advice there is, right there. It ran fine, you changed some things, now it misses. Put all of the "old stuff" back on and if you lose the miss, starting replacing old pieces with new, one piece at a time. Obviously, the piece that brings back the miss is the culprit.

Re: Plug wires
 

Id replace the coil wire at a minimum, and possibly the coil.
Also, did you run the MSD ignition box positive and negative straight to battery?

Both of these issues (engine misses) happened this season on 2 different cars. Fixes were immediate when corrected.

We have a MSD tester and the ignition boxes tested fine on both cars during the issue.

Re: Plug wires
 

I fought a miss with the same wires, found one wire with 2K ohms, other 7 were less than 200 ohms, changed wire still had miss, checked rotor to coil button in cap distance, was to low, adjusted it with gauge that came with MSD cap and rotor and miss was gone. Another racer with a dirt modified told me he was fighting a miss, I checked his rotor, set his distance, miss gone. If metal tang looks like it has been arcing tang is to low.

Re: Plug wires
 

I've noticed that MSD has added an instruction sheet with their rotors lately that include the specific rotor tang height.

Re: Plug wires
 

Thanks for the response's. I looked for signs of arcing in the cap and rotor button (looked clean) but I'll check rotor button height. The miss just developed it had been running good but I tried changing over to alcohol and had issues. I blamed the miss on that so I went back to gas and it still had a miss. One thing of note the miss on alcohol seem to be more a fuel system issue (very bad missing would not go down track) the miss on gas seems to be a single cylinder. I ohmed the pick up coil (MSD dist) and it read good but unless it failed completely I guess it could read good? I'll start changing some of the old parts and see what happens. Thanks again I'll let you know what I find.

Re: Plug wires
 

Hi Robbie,
Since you mentioned alcohol I'll share an experience I've run into a few times in the last several seasons. A few seasons ago I picked up a dragster to bracket race with. It was a typical BBC run on methanol when I got it, and I raced it exactly the way it was, never changed a thing. I had no prior experience with running alcohol. I had good luck with it right off the bat. Anyway after a while it developed a miss. It wasn't terrible, I was still able to race with it. But after checking all the expected things (crank trigger, rotor, wires, wiring, coil, ignition box etc) with no success another experienced alcohol racer asked me if I had changed the plugs. I had changed the plugs recently but it was a short time before the miss developed so I really didn't think the plugs could have anything to do with it. A few mins later he showed up at my trailer with a few boxes of new spark plugs and insisted I change them. He ended up being right... the miss was gone. Since then, it has happened again and a spark plug change was the fix. What he told me was that with alcohol plugs don't seem to last as long as when running gas. Give that a shot. Good luck.

Re: Plug wires
 

Don't overlook the coil wire. -Al

Re: Plug wires
 

if you are running a crank trigger then you may want to change the pick up.
also make sure the gap is correct.
Fought the same deal several years back and bingo.