I have been trying to eliminate a "miss" in the engine of my T for weeks. I have isolated it to number 3 cylinder, and it only happens under load. Coils are fresh. I have had the coil box apart and no signs of any breakages. I'm wondering if it's leaking under pressure through the head gasket. All cylinders seem to have compression as the car starts and runs fine until put under load. Any suggestions greatly appreciated. Chris.
What are the compression readings for each cylinder? Guessing by thumb pressure or other means is not accurate enough here. An engine with poor or uneven compression will run smoothly until under load, so it could be the problem.
Thanks John, am thinking a compression test next. Chris.
Chris,
If you have not done it my first thing to do would be to rotate the coils and see if the problem follows the original #3 coil. If still missing on #3, rotate and/or change spark plugs. Then if still on #3, switch the wires on the coil box so that another coil box position fires #3.
Then maybe make sure your timer is good. Then maybe a weak valve spring that would make a #3 valve float at higher rpm.
Other then that, just check the basics, Air, Fuel, Compression, Spark - all in the correct amount and time.
Jim
Electricity takes the path of least resistance and will go to the easiest ground under a heavier load. Try a new plug and then a new plug wire and make sure the plug wire is not close to a ground...That's my theory and I'm sticking too it.
I agree with Hal, but would add one thing. The wood in the coil box, if it has ever gotten damp, can make an excellent conductor. Once it starts to conduct it will burn a carbon track in it. Although the carbom has some resistance, it could be the path of least resistance under heavy load. Sometimes a carbon track is hard to find. Check the engine running in the dark with the hood open and see if you can see any sparks. You don't mention whether you have done any work on the timer. Sometimes the timer needs cleaning or replacement. Or if the timer is off center, it could make a bad connection.
Norm
Thanks Jim,Hal and Norman,
It has an Anderson timer and all wires seem ok.
I will compression test it later today and
let you all know what I find. Appreciate the advice, Chris
To check for a compromised coil box wood, you can shift the #3 coil and wiring to another slot and see if the miss follows.
Thanks Doug, that is next. I've compression tested the motor and all cylinders between 50 and 60psi. Will keep looking!Chris.
Turned out to be a short in the timer. Thanks for the good advice of this forum.Regards, Chris.
A short in the timer would make one coil buzz all the time.
I bet you actually had an open connection causing one coil to never buzz.
What caused the open connection?
Another thing to check if you are having a miss. Make sure the nuts holding the points are tight ( ) or/and that there is a good connection between the post and points. I just went through that last night, the car had been running fine but when I did some work one of the coils was not firing. I swapped the coils around and the problem followed the coil. When I looked the nuts holding the point were loose.
To be more precise Royce you are right. It was an open connection caused simply by wear in the timer. I replaced the flapper and the points and it runs very well. The timer has seen a lot of miles,Chris.