Msd 8973

No there are no problems with the box except for possible Electromagnetic Interference (EMI) from the high energy spark being picked up by using an unshielded crank trigger cable. If you are using a crank trigger then you HAVE to use a shielded crank trigger cable. The 8973 does not know the difference from one cylinder to another so it can't just kill cylinders 7 and 8. If the box was bad then it would mess up all cylinders. The 8973 provides the same signal for all the cylinders. The only thing that can mess up just two cylinders and always be the same two cylinders would be a bad distributor cap, bad ignition wires or bad sparkplugs to those cylinders. The EMI picked up in a crank trigger can mess up the timing.

have you set it up for any launch retard and if so how are you doing it? It sounds like it is Lauch Retarding at the release of the transbrake button. How do you have the blue wire from the 8973 hooked up?

 

Yes, the heads should be grounded to each other and then to chassis ground and should be the same ground as the coil. Swap your use a ohm meter and check out your plug wires. Compare them to each other and see if 7 & 8 match all the rest.

With a laptop hooked to the 8973 turn the power on to the ignition and look in the upper left corner where it says MONITORS and see what retards are turned on or off. You will probably need to push the transbrake button once to initiate the 8973. No need to have the motor running.

 

They other thing you can do is to email me your saved MSD file for the 8973 and I can look at it and see if anything is setup incorrectly. I doubt it but you can never tell. If you desire you can email it direct to mike.c@mindspring.com

 

Yes, it will sound different. The 8973 has a "Soft Touch" rev limiter that uses software to make sure that a cylinder(s) is not shut off for two consecutive firings so it does load up or fill up with fuel. The analog type Two Step is purely random as to what cylinders it is shutting down and can be the same cylinder(s) consecutively so it sounds harsher or as some people say meaner.

I am prety sure it was just a matter of setting up the 8973 correctly. Did you check the MONITOR on the laptop to see if everything was set up how you thought?

Did you ground both heads to each other and to ground

 

Used to compensate the Mag pickup trigger retard timing.
User adjustable as 0.0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, AUTO.
Manual is active from 3,000 rpm to 12,500 rpm range.
Auto is active from 800 rpm to 12,500 rpm range.
There is a 4 degree offset from the input signal to the
output. Crank triggers are typically 2 degrees.
Distributors are typically 1 degree.
ProMag interfaces should use AUTO.

Above is from MSD. You can see right off the bat that if MANUAL is used then the timing below 3000 rpm when set with a timing light may be different above 3000 rpm depending on what you have set in. Manual is normally only used on Mags that do not have automatic timing correction so they retard as the load is put on a mag. With the ProMag systems the standard is to set it up in AUTO because it has automatic timing compensation in the Electronic Points Box. So in AUTO if you are setting the timing when at idle of 1800-2000 rpm then what you see is going to be what you get for sure.

 

MSD back room guys told me always to be in AUTO with a promag even with a crank trigger but I will double check my memory and ask them again and get back to you. Don't want to have a "senior moment" and mess up a motor.

 

No not a MSD Tech. They have done a lot for us in the past and because of that I have a good communication with them I do them a favor and help them.

Speaking of MSD. I emailed Mr. ProMag with the question on the 8973 and the ProMag and the crank trigger and he says leave it in AUTO. There are tricks that can be played by putting it in MANUAL but it would be really confusing to most. So AUTO for MagComp with the ProMag with or without the crank trigger.

And YES to the answer if you are going to change from MANUAL to AUTO then you should check your timing.

Just a quick reminder. The easiest way to set up the 8973 is to hard wire one of the Step Retards to have 12 volts anytime the ignition is turned on. Then if you want 26* then with zero degrees in that Step Retard time it for something greater like 28* or 30*. Now if it is at 30* just put 4* retard in the Step Retard to bring it back to 26*. After you have set the timing at 30* Now anytime you check the timing or you want to change it then just change the amount of degrees in the Step Retard. Saves having to have two people and getting zapped when turning that mag to adjust the timing. Now you can adjust it in a flash.

 

few things

Take the ignition off and send to Leahy. Sounds like you have something wrong - coil, points box or generator. If you are using a tach converter, change that out too, I've seen those wreak havoc. The car has run good before or is this the first hits on a new combination?

What plug gap are you running?

You have at least changed the wires recently? Coil wire fires 8 more times than the rest...what does the cap and rotor look like? Big cap or small cap?

Does the motor sound fine and rev up in neutral? Glide or Lencodrive? If it busted a sprag in a glide should see a lot of debris in the pickup filter. If it's a Lencodrive it will drive through the transbrake if the converter sprag is busted. Been there, got that t-shirt.

I'm not a roots guy, but I have heard tale about rotors being in backwards and doing similar symptoms. Sounds great idling, but runs like crap.

If this is a new combo, need to make sure everything in the fuel system is right. If it's way too rich, it will have similar symptoms. Like a poppet being plugged with gunk, so all the fuel is going to the motor. Don't ask me how I know, but I've seen two pills in the BV block the return off, sending all the fuel into the motor.

That's the easy stuff to check...