Electric fans are very common...
Electric fans are very common on street rods, they’re affordable and effective. However, their permanent magnet motors can also act like a generator in the right circumstances.
After five years I’ve just about finished my ’40 Chevy coupe. The last step was the wiring, and I’ve got to tell you it’s been the most difficult part of the project because of my complete ignorance on the subject, but boy have I learned a lot lately.
You may not remember, but a few months ago I wrote you about a problem I was having with the gauges. You emailed me back and gave me several suggestions to get them working properly, one was to make sure everything was grounded properly. That in fact turned out to be the problem.
Based on your advice I checked all the grounds and added several. I grounded everything, the battery to the engine, the engine to the frame, the body to the frame; now there are grounds everywhere. In fact, I even made a ground from the trunklid to the body and now the license plate light is bright because it’s not grounding through the powdercoated trunk hinges. Like I said, I’ve learned a lot.
The car has a 350 small-block Chevy and a Camaro five-speed. I’ve got everything working like it should, except for one thing. Now the engine won’t shut off. I turn the key to the off position and the engine keeps running, the only way I can shut it off is to kill it in gear. Evidently, I still have a lot to learn about electricity. Can you help?
A. Engines running after the key is shut off can result from a number of things. There are several mechanical issues that can contribute to this problem, individually or in combination with others, such as: fuel with too low an octane level, excessive engine operating temperature, excessive idle speed, vacuum leaks, improper ignition timing, and high intake air temperatures. Of course there are also electrical gremlins that will make your car act like the Energizer Bunny.
When electric fans are simply...
When electric fans are simply wired through a toggle switch there can be problems with the engine running on after the ignition switch is shut off. A relay, like this example from Painless, will cure the problem.
According to our friends at Painless Performance here are a few electrical issues that may cause the problem:
Faulty alternator/regulator. GM 10si and 12si alternators sometimes feed voltage back into the exciter wire even when the engine is shut off. This causes voltage to feed into the ignition circuit, which causes the engine to keep running. Remedy this issue by installing a diode PN 276-1661 from Radio Shack inline with the alternator exciter wire. Make sure to install the diode with line or band around the body closest to the alternator. By installing this diode you have introduced a one-way gate in which voltage can only flow through the exciter one way to the alternator and not back the other way.
An electric fan wired into the ignition circuit without a relay. Electric fans must be wired with a relay if they are spliced into any of the ignition hot circuits of any chassis harness. Without a relay the fan will act like a generator as it winds down. When the ignition switch is turned off, the fan, which is still spinning, will feed voltage back into the ignition circuit and the engine will continue to run.
A faulty ignition switch. An ignition switch can wear out and break apart internally. If any of the brass parts inside the switch break off and wedge themselves across the terminals within the ignition switch that can cause the engine not to shut off.
Metal parts/fragments lodged in the back of the fuse box. Depending on how they are mounted, fuse blocks with an open back are susceptible to foreign objects. Anything that is a conductor of electricity, a metal upholstery staple or a scrap piece of wire as examples, could short across the ignition and battery circuits of the fuse box, which would make the engine continue running.