msd 8251
 

Can a msd 8251 coil test good on a ohmn meter but still cause a misfire . I have replaced cap,rotor , coil wire,plugs, checked all grounds checked all plug wires , new batteries , alt. checking 13.6 @1800 rpm .changed carb checked fuel pressure. set float level. Plugs look dark, or damp. 7al box . really dont know to check it . going to try another dist. in the morning. Rick

Re: msd 8251
 

When I have ignition issues with my MSD equipped cars,
the first thing I do is change coils. I always have a proven
good one in the trailer. It has been the issue several times.

Re: msd 8251
 

Good morning Rick and to all,
Over the years I've had MSD troubles as well. I had two (2) #8261 coils go bad on me. One right out of the box. At the time Tech West was doing my ignition stuff and Pat said the #8261 coils were made with "offshore" components and suggested I use the #8251 coils, which I did. I have three of them including one on our engine dyno - No problems with any of these.
In the past when I had an ignition problem the MSD box was usually the problem. I have two MSD 7A's and two MSD 7AL2's. All were "tuned up" by Pat and are operating well. The last MSD box that failed - didn't miss, pop, bang, or do anything outwardly stupid. Just wouldn't go fast, went over valve springs, did a compression test, changed the converter , changed the fuel, finally Glenn asked if I had a "spare" ignition , which I did. We changed the box, coil, cap rotor and wires and PRESTO we qualified number 5. Over the next week or two changed back the coil, cap, rotor & wires without any incident.
So to make a short story long, I would suggest changing to a "known" spare MSD box and work your way from there. That was from personal experience. Ignition coils have been know to go bad , but they usually work or don't ! One other point of interest , when was the last time you replaced your coil wire? When you consider you are firing 8 spark plugs through one coil wire with the voltage we run through them you just might want to change that as well. I usually R/R mine once a season. Call it cheap insurance. That's my Two Cents and I hope that helps you.
Have a Great Day

Respectfully,
Henry Kunz 1534 H/SA

Re: msd 8251
 

Thanks for the info, new box came . Going to try it today. Worse case I will have a good spare.I did replace coil wire,did not seem to change but I have had bad ones before If anyone else is having a problem It is a good place to start. Sure not in any hurry to put out 800 bucks for a new box, but might have to. Thanks again. Rick .

Re: msd 8251
 

To answer your question about using a ohm meter to check a coil it can ohm good and be bad. The reason is that it is not under a load. We use to use oscilloscopes to look for a pigs tail showing it had good oscillation under a load.

Re: msd 8251
 

Had a miss, but only under load. Drive around pits no problem. Replaced everything we had with known good parts, except msd 7al box, tried good 6al and good coil cured miss. Msd repaired 7al box for less than $150. Of course, it is now the spare after buying a new box.

Re: msd 8251
 

Installed new coil, cant really tell if it helped or not. Going to try another set of plugs because they look gas fowled before buying a new box. Maybe try to find someone who has a good spare to try. Thanks Rick

Re: msd 8251
 

2 things to check,
make sure there isn’t any rust on the pick up coil inside the distributor.
Make sure the wires that run from the MSD box to the distributor doesn’t run close to the coil.

Re: msd 8251
 

Rick I have spare 7AL box and a digital7 box
Also have 2 different msd coils. If you want to try.
I was going to Edgewater on Sunday but you can have them
anytime to try.

David

Re: msd 8251
 

Thanks for the offer, ordered a new one. If it does not help I will use it to upgrade the Camaro. Thanks again. Rick