MSD 6AL Issues
 

Any input from you guys would be great! I have developed a miss under load. I can free rev the engine with no miss. My ignition combo is a MSD 85551 dist., blaster SS coil, and 6AL box. I have ruled out the dist. and plugs. In my past experience the ignition boxes work or do not work. The coil and box are hidden underneath the dash. The 6AL has developed a louder than normal buzzing noise lately. I spoke with MSD tech and they said the noise could be from the deterioration of silicone used inside on some parts, but it would not effect the box working. Before I replace everything does anyone have any suggestions. I have a lot of friends who wrench for a living and we are all kinda baffled over the miss. Thanks again for any input.

Start with the basics. I've found that the MSD cap doesn't have a long life due to the center carbon element. Check it out. Pull the plugs and see which cylinder is having the problem. Are you sure a plug wire isn't grounding out? Check the resistance of the coil to make sure it's not borderline. Since it's under load, I tend to lean towards coil, cap, plug wire, spark plug. Not distributor pickup/module.

The problem started on the way to a show about 100 miles from our home. We normally go for the whole week to mostly see friends from out of state, drink beer, etc. When we arrived I started with changing plugs. Prob still occurred. Pulled cap and found corrosion, and multiple snap ring pieces inside the cap. So I am am thinking prob found. I knew replacing the snap ring would be something that MSD would tell me I would have to send to them to fix. The cap and rotor looked awful! I would have replaced the cap and rotor only but the broken snap ring led me to think the reluctor wheel could spinning in a way to misfire. So off to the car show I go to find a dist. Found the only 85551 dist there and bought it. Once back to the hotel we checked timing, pulled dist, swapped cam gear, dropped new dist in, checked timing. She fired right up and I drove down the road, the prob was still there.

The next day another friend who arrived had brought an identical carb that was brand new to try. We wanted to rule out the carb without tearing into it. We swapped carbs and the car would not fire. Found out the carb had been used once for an engine fire up and had been placed on a shelf for the past two years. Nuff said about that. LOL. Put old carb back on and had to swap plugs again. The car ran good enough to get us home.

Here are some theories and things we looked at etc. Bad gas was ruled out with a fresh tank. There is a lot more Ethanol in gas these days. One theory was the circuit board in the carb could be gummed up from the excessive Etanol??? We also put a temp gauge on each cylinder header pipe and all pipes read within 50 degrees. Is that a huge variation in temp or is that common? Spoke to MSD and they say it isnt the 6AL or the coil???? I did not want to throw money at the problem but after seeing the shape of the dist I was convinced that was the problem. I have also looked under the hood at night with the engine running and there are no "fireworks" with the plug wires going on. I have a spare 6AL to try but I am not looking forward to crawling under the dash to swap it out. I will check the coil next.

Thanks for the help!!!!

Checking plug wires would be very high on my list.

I had a pickup coil inside the distributor do that. It even passed the test that the MSD tech coached me thru. On the plug wires you can shoot some water out of a spray bottle on them and put the engine under a load (at night) to see if there is any arching.

Yesterday evening I decided to install a spare coil I had just to rule it out. I did a twenty five mile or so round trip and she seems to be running fine. Initial start up is instant compared to before. I also did a thorough visual inspection to the plug wires, no burns etc. To summarize, it is night and day, how much better she starts and runs. Could the coil have deteriorated over a period of time? The coil is mounted under the dash away from any heat. The MSD tech I spoke with when the problem started assured me it was not the coil??? Just curious what you guys think. Thanks again for the input. :cheers:

As I recall coils can fail. The tech would have been better off telling you "it's highly unlikely, but it's a possibility."

I am no mechanic.

But i heard that you have to mount the MSD Coils upright due to liquid being inside of them..

Is your coil mounted sideways ?

Again I am no mechanic...Just throwing out something to look at..:cheers:

Glad to hear it. I bet the old coil would fail the resistance test. MSD should have the spec or you could probably use an old GM spec to get in the ball park.

I had a MSD coil go bad. Luckily Dub Renner had a spare hanging on the wall of his house.... literally.