Do you have a crank trigger on the car?

When I switched to a grid a few years ago I was using the Distributor as the pickup just like normal and was having the same issue. I put a new pick up in the dist and it worked for a week or 2 then the same thing happened.

Broke down and added a crank trigger and never had the problem since.

Just a quick update:

Rewired the pickup leads from the distributor to the MSD box using shielded cable and re-routed away from everything else. Shield wire is grounded at the MSD box. Tested Friday night - no change, still breaks up at the top of high gear. On the fence between adding a crank trigger setup or buying a brand new ignition box. The racing season is over for us but I'm going to try to make a decision and test again before it's time to store for winter.

High RPM break up,could indicate weak valve springs.....check valve spring pressure

I had a slight miss a few years ago wehen I got an APD alky carb. They recommended I use a spark plug with an extended tip. This fixed the issue I had.

Since you have now spent 3 months chasing this issue, might I suggest you load up your engine, ignition system, spare parts and take it to an engine dyno. If it doesn't show up, then you know the issue is in the car ( fuel supply, wiring), if it does, then a good dyno operator should be able to isolate it quickly. Or there is always all of next season to look for it.


Joe
PS full disclosure, I own and operate a dyno and have found dozens of issues that owners have wasted 1/2 a season chasing.

I've chased "ignition issues" numerous times over the years, and I don't think it's ever actually been a problem with the ignition system.

It sounds like the ignition box is bad and it looks like you have changed the wiring but not the box?

HAVE YOU CHANGED IT OUT WITH A GOOD KNOWN WORKING BOX?

Very first thing I would do because of stupid BS MSD put me through. Had motor doing that and I had tested it with one of their ignition testers. They kept telling me the box is good if it tests good try this. Or this. or that. Blah, blah, blah, wild goose chase.

Finally I got another box and tried it any way and car ran perfect, I spent a lot of time and money and a few lost rounds of racing because of the bull from MSD.

Trying to save you the wild goose chase, change the box. I can tell you this if you put it on a dyno that would be one of first things they do is try another box. Takes a few minutes and will help you narrow it down.

Upon review I'll add these points.

The 7-AL2 is the only MSD ignition that I have ever seen malfunction while still operating. Just my experience. I found it while monitoring the timing light. It would scatter spark randomly and caused misfiring issues.

Put a 6-AL on it for a test.

I'm not a big fan of the digital stuff, even though I "upgraded" my 6 series to the Digital + this season out of feeling guilty, and being convinced that the 2-step action is superior to the old plug in Soft Touch module. Meh.

Clean the air bleeds on your carb.

To the OP, adding a crank trigger is a wise upgrade that offers the best firing resolution, but honestly, I doubt that there is anything wrong with your brand new distributor. If you decide to upgrade ignitions and need to save some money, consider the MSD Grid 7730 and use your existing 7al2 and coil. At least you’ll have data acquisition of the Ignition IN /OUT to review to help locate the problem.

I think the newer Analog and Digital MSD boxes are very good. I prefer Digital because of the programmable options. My 7730 Grids are over 10 yrs old and have been in several other cars troubleshooting problems. Both work perfect as I switch between them every other year to confirm working properly.

You had stated prior that “ I get breakup before the shift as well but it's most notable after the shift”. My EFI shows the leanest AFR during rpm dip after flash stall at launch and the rpm fall back after the shift to high gear. EFI is correcting for this by adding fuel during these periods. Perhaps you need more fuel.

My MSD tester showed my box was fine. Changed the box and problems gone.

I've got a crank trigger and digital 6al2 box coming. My spare 7AL2 that I bought second hand was DOA and no one I know has a spare laying around. Air bleeds have been inspected. It will be a few weeks before I'm back to the track for testing but will follow up again hopefully with resolution.

I appreciate the replies.

quote:

Originally posted by Cashflow:
My MSD tester showed my box was fine. Changed the box and problems gone.

Very common, and I use the MSD ignition tester but have little faith in it. It is good to verify shift point, rev limit, shift lights etc.

I have had 3 of the 7AL-2 boxes go bad. Now one of first things I check. Also since a carb is so easy to change I would swap it out for a known good one before spending much time on it but I am pretty sure it is the box.

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This message has been edited. Last edited by: CAD,

Just to put a bow on this topic. I finally got to test last night. This was with a brand new Digital 6AL2 and a crank trigger setup. The engine ran clean in 4 passes.

Unfortunately, on the 5th pass, I got into some antifreeze that one of the street cars dropped on the track and put my car in the wall. Fixable but disappointing to say the least. The track confronted the leaker and apparently they got combative. Sigh...

Seems my "quiet" off season just got filled up by some repair and body work.

Really sorry to hear that happened. I'm glad you are okay and not hurt though.

Good to hear that you’ve solved the engine miss problem, you are ok and your car repairable.

I know the venue you were at and doesn’t surprise me. Their event is billed as “Fun Racing”.