It Keeps Running And Running And ...
Q. I have a '36 Ford with a '70 Chevy 350 engine. The distributor has a PerTronix module in it and the engine has about 1,500 miles on it. It runs fine; however, when I turn off the key, everything shuts off but the engine, which runs on for three or four seconds. Any ideas as to why this is happening?
Bill Bean
Via the Internet
A. This is a surprisingly common issue with electronic ignition systems, not just the PerTronix. The problem is the ignition system is being "back fed" from some electrical device, which means that the energy the PerTronix needs to operate is coming from somewhere other than the ignition switch. In your case, we'll bet you have an electric engine-cooling fan that's doing it.
An electric fan will actually act like a generator as it coasts to a stop and create the very problem you have. Usually this happens when a toggle switch is used to run the fan. The fan continues to spin briefly when the engine is shut off; as it does, it acts like a generator and creates a small amount of current, which feeds backward through the electrical system. That current is just enough to make the ignition system function even though the key is off. When the fan stops, so does the engine.
The same situation can crop up when the fan switch has an automatic/manual option. To energize the fan on our Model A pickup we used a single-pole, double-throw switch, which has two "on" positions and one "off"; it allows for manual or fully automatic operation. In one "on" position, an internal, thermostatically controlled switch controls the Flex-a-lite fan; in the other "on" position, the thermostat is bypassed and the fan comes on. While this does add the ability to manually control the fan, it can also cause the engine to keep running for a short period after the key is turned off.
Fortunately, the cure for either scenario is simple. One solution comes in the form of a device called a diode. Basically a one-way electrical valve, a diode in the feed wire to the fan will cure the problem. Another option is one of the temperature-sensitive fan controls from one of our advertisers.
Where's Dr. Phil When You Need Him?When looking at an engine from the front of the car, the crankshaft turns in a clockwise direction. That means, when installing a U-joint in a driveshaft, the zerk fitting should be positioned as shown so it's in compression rather than tension. So, in reality, is it a big deal, one way or the other how the U-joint is installed? Maybe, maybe not. It probably depends on the amount of horsepower involved and how the car is driven. However, we did in fact collaborate on a driveline story with one of the tech advisers at a U-joint company who had been a drag racer and was also into off-roading. Needless to say, he had seen his share of broken U-joints and passed the installation tip along. It certainly makes sense, so we've been installing U-joints that way ever since.
Q.I know you've settled arguments before, so here's another one for you. My brother has a '40 Ford with a 350/350 and a 9-inch Ford rear. We were replacing the U-joints in the driveline and we got into a discussion as to how they should be installed. He says it doesn't matter, but I say it does and that the grease fitting should be placed so it's in compression when the driveshaft turns.
I'm counting on you to back me up on this for two reasons. One is the loser has to pay to renew our subscriptions to STREET RODDER, the other is I read this in a tech story you did years ago so I figure you owe me a subscription if he doesn't.
Al and Ken Hobbs
Via the Internet