Odd Miss

[Detroit Bill]

Originally Posted by A98Coupe

Check the connections onto your ignition switch. I had the same issue once. Turned out to be a loose connection.

Will do I have a suspicion it is something like that where power is dropping out.

[Detroit Bill]

I had limited time last night.

I pulled the cap looking for anything odd, nothing.

Checked timing at full advance was 36 as expected.

Pulled all the rev limiter plugs and turned them up well over red-line.

I noticed that the 4-6-8 dial on the MSD was not really at 8. It was somewhere between 4 and 8. I dialed that in exactly. It did not appear to have a lot of tension on the "dial"

I checked the 7-8 plug wires they were separated, I rerouted them so they were more separated.

I took it out for a ride the stumble, miss, cutout was gone for several high 5,000 rpm shifts. Stumbled once. The difference between this and other tests was that the car was not as hot as usual. I thought I saw the tach take off once, hard to pay attention exactly at that RPM.

So far tonight I am going to:

Do a first to 4th shift to see if I can get the clutch to slip.
Check resistance in the plug wires.
Check the connections on the ignition switch.

What else?

[Tim7139]

Originally Posted by Detroit Bill

That test is Ohm meter looking for 0?

No, depending on the wires it's something like 50 ohm/foot. Once you pull a couple you will get a baseline and if you have a bad one it will jump right out at you.
At the same time it is a good opportunity to make sure you have a little dielectric grease on the plug ends which will only help the whole equation.
I've found, most often if there's an issue it is right at the plug boot getting bent/forced onto a plug and they fail right at the metal connection.

[patrickt]

Originally Posted by Detroit Bill

I took it out for a ride the stumble, miss, cutout was gone for several high 5,000 rpm shifts. Stumbled once. The difference between this and other tests was that the car was not as hot as usual. I thought I saw the tach take off once, hard to pay attention exactly at that RPM.



What else?

It does not happen very often, but it does happen: the feedback from the tachometer itself to the MSD box can cause a misfire. Obviously, the way you test this is to just pull the tach wire out from the MSD box and run it up to where the misfire occurs with the tach completely disconnected from the box. Now, mind you, this is a "low probability" event, but it's very easy to check assuming your misfire is relatively consistent and your ears are attuned. If you don't trust your ears, rely on your speedometer to tell you when the misfire occurs. For example, 60MPH in second gear. That will act as your RPM measuring device while your tach is disconnected.

[Jaydee]

Another thing you could try. Make up a ht wire from the center of the dizzy tower and place clear tubing over the wire so that the spark will jump a half inch gap to the coil wire, and then clamp a usb inspection camera near, so that whilst your driving, you'll see if the sparks stops momentarily.
JD

[Jac Mac]

Another play on that theme... grab your timing light, tape the trigger in the 'on' position and fit it to the Coil/Cap HT lead and have someone hold/watch it while you drive, if the light stops flashing your losing ignition.

Originally Posted by Jaydee

Another thing you could try. Make up a ht wire from the center of the dizzy tower and place clear tubing over the wire so that the spark will jump a half inch gap to the coil wire, and then clamp a usb inspection camera near, so that whilst your driving, you'll see if the sparks stops momentarily.
JD

[Detroit Bill]

Had a second test drive and the miss appears to be gone. I think it was the 4,6,8 dial.

[Jac Mac]

Originally Posted by Detroit Bill

Had a second test drive and the miss appears to be gone. I think it was the 4,6,8 dial.

That would do it, MSD thinks its on a 4cyl, rev limiter would cut in at 3500 for a 7k chip on a V8.