Msd 7?

[rod]

is it possible that an MSD 7 can check out good [by MSD] and fire, but still not work correctly?
my car has lost almost 3/4 of a second. the MSD is the only thing i have not changed. the car still rpms the same, just no power. i have changed or checked a lot of parts. no difference. just slow!

thoughts?
thanks rod in AZ

[buzzinhalfdozen]

I've seen the polarity of pickups magically reverse. This typically retards the ignition timing. Joe

[gsa612]

If your running a crank trigger check the wires going to it, if they are reversed the car will run, start, etc. but you will only have about half the total timing. Just went thru this on a buddys car. gsa612

[GTX JOHN]

would look at borrowing another coil and making a pass with it.....especially with one of the newer style MSD coils

[FED 387]

As far as the coils go check the resistance between the positive coil terminal and the neg coil terminal resistance should be less than about .016 or so then check the resistance between the positive coil terminal and the coil tower that should be about 30 ohms---if either of those numbers are off the coil is bad---if the numbers are close then you have problems elsewhere---also check the air gap at the pick up and make sure that the magnets in the flipper wheel are not loose too as well as the pickup wiring----do you have ANY other wires running in close proximity to the pick up??? Those pick up wires should be shielded you can get some stuff at most electronics stores to do that helps prevent any stray signals from interfering with the signal from the pick up to the MSD box---Comp

[FED 387]

Also like GTX said borrow another MSD coil see if that solves the problem---Are you using a MSD 7 that is set up for the correct engine you are using?? By that I mean a 7220 for an 8 cyl engine or a 7224 for a 4??? You cannot use a box for a 8 on a 4 or 6 and vice versa it will not function properly

[Rich Biebel]

I had an MSD 7al 2 in my Firebird Stocker. One day at the track I started to get misfiring over about 6000rpm and the tach was jumping around when it misfired. This engine had a crank trigger and most everything but the MSD box was new. I borrowed my friends identical 7al2 and the car ran perfect...no missing. I sent my box to MSD.....they said they could find nothing wrong with my box. I swapped it back into my car one day at the track....same problem returned...missed badly over 6000 and tach was shutting off when it missed....removed it and reinstalled my friends box same day....no missing. I bought a Digital 6 and matching coil and installed that. That box failed for the person who bought that car and it was no more than 2 years old when it failed. Probably got wet sitting out in the rain from waht I was told....I used to think MSD was the best ignition and boxes either worked or they didn't. I bought an MSD ignition box tester that they sell.......it allows you to fire the box without the engine running......pretty handy for testing a lot of things that are rpm triggered and to see the spark energy at any rpm. If I have a box I am not sure about...I'd replace it and MSD is not the only brand out there...Mallory has a good reputation for reliability.....


If you have an MSD distributer with mag pickup in the distributer your problem could be the small module in the distributer........I have a friend who chased a miss for months and that is what his problem truned out to be.....

[rod]

1. i was unaware that there were different boxes for different cylinders. will check that.
2. this chevy has a mallory uniliite for trigger.
3. the tach needle does, in fact, moooove towards 0 when it pops.
4 i have raced this car/engine for 37 years and never had it pop at the top of a gear. it does have an 8K top rpm chip, so it shouldn't be that as 7K is as high as i ever push it.
5. i have 2 different coils i can sub in. will try that also.
6.i am so MAD i could scream !!!!!!!!!!!!!!!!!!!!!!!

guys thanks for all the suggestions
rod in AZ

[GTX JOHN]

I have several proven MSD coils you can borrow....I am right over new bridge.

John Irving

[Robert Simpson]

Originally Posted by twrs2006

Yes it is possible under load. What coil are you running with the 7al box? If it is the MSD 8201 coil loose it or donate it to a friend! You want to run the MSD 8251 coil with the 7 al box it will get everything out of the box and it is a better match. The MSD 8201 coils heat up and looses performance from the get go. The next place to look is the Ignition On (IGN ) terminal make sure the voltage stays rock steady no drifting. The boxes will drop there output perforance as this voltage drops. Check that you have clean and tight connections to All points on the box. How old is the coil wire? we have seen an increase this year of coil wires causing issues like yours at the worst possible times. Pull off the Dist cap and check & clean out, you can use a electronic spray cleaner. Most auto parts stores carry it, it is usually marked as Alternator/ Starter cleaner.

Pat, is correct he helped me earlier this year. Took his advice changed the coil and a couple other connections, the car came around and the plugs cleaned right up. I will go back to Pat in the future for ing upgrades. By the way I had all new 7al2 box 8201 coil wires etc, chased problem for over a year changed the box and coil with another new units, wires, coil wires etc, no help until I spoke with Pat.