Sometimes, in trying to help others learn from our mistakes, one must admit failures and perhaps look less than bright.

When converting my 1986 F150 with 4.9L [originally computer controlled feedback system] to Duraspark, the aquired blue grommet ignition control box was defective. A friend who was helping just happened to have a MSD 6 AL box and said, "let me just wire that in". He had used it previously and I let him go.

From the beginning, the truck started right up and the initial timing was set. However, when the vacuum line was reconnected to the distributor, the engine would go crazy if reved to ~1800 RPMs or higher and held steady [high vacuum + centrifugal advance]. It would have a staccato rhythm. If the accelerator was quickly depressed, the engine would rev nicely, but again, when allowed to level out at ~1800 RPMs or higher, it was not happy. Obviously, it could not be driven this way.

Many attempts were made to correct this, but the final solution was to drive without any vacuum advance. Actually, it drove well and I became used to it.

To make a long story short, the leads coming from the distributor to the MSD box were reversed. For Fords, the violet colored distributor lead connects to the green wire from the MSD box and the orange colored distributor lead connects to the violet wire from the MSD box. My installation had the two violet colored wires connected. This was in October of 2013.

If it would be beneficial [if asked], I can write another thread detailing observations made immediately upon making the correct connections [Incorrectly wired MSD 6 AL 101]?

The connections were made up correctly and significant timing adjustments made and the vacuum was hooked up to the distributor. No more problems... yea!

I have written previously regarding gas mileage and some may remember that I drive a very repetitive course and maintain records. Records are good for observing patterns as I look back. Today, I did just that.

The time period for comparison will be 1/8/13 - 4/30/13 and 1/9/14 - 4/28/14. The reason is that I recently have been observing my gas mileage increasing due to milder temperatures and so have on hand this data and wanted to compare the same time period for the previous year. The only difference is that for 2013, the vacuum advance was not connected and for 2014, it is.

1/8/13 - 4/30/13 / 15 tanks / 15.51 mpg [no vacuum advance]

1/9/14 - 4/28/14 / 16 tanks / 17.62 mpg [working vacuum advance]

Having a properly operating vacuum advance has increased the mileage by 13.6% and this was during what I believe was an overall colder winter.

I hope detailing my blunder will perhaps help someone else to not make the same mistake.

 

Interesting and good info, David. That is a significant increase in MPG and it is mainly, if not completely, attributable to the vacuum advance. And, at no detriment to drivability I assume?

Are you still running the MSD?

 

No detriment to drivability. Yes, I still use the MSD.

 

David,

There are some people who feel they know everything and are right about everything and who would never admit to being wrong or making a mistake, thank you for writing what you did and trying to help others.

I'd rep you but can't.

 

Yep, that's why the vacuum advance is there. No other reason but engine efficiency.

 

Dave - Can you rep him? I'd already tried and, like Chris, can't. I'd be forever, once again, in your indebtedness......