76 2.0, 118,000 miles, engine runs perfectly, all equipment functioning, (thermostat, auxiliary air regulator, no vacuum leaks, but engine runs on for several seconds or more after shutdown. The motor does have a Crane Fireball ignition system. From what I have read here, and ruling out a vacuum leak and an unlikely leaky injector as the cause of the run on, the Crane ignition is often mentioned in the forum as a possible cause of engine run on. If the Crane ignition is the cause, the fix mentioned is to install a diode on the lead to the generator light. I am going to follow these instructions at this link:
http://www.mgexperience.net/article/mgb/ignition-run-on.pdf
I have ordered the diode named in the article and I just wanted to check in this forum that my plan is sound before I do the diode installation. I'm not sure if this will fix the problem, but I don't see a downside to trying this next. Does anyone else have a comment on this next step?

See if the diode helps. I had a similar problem with the SDS efi and ITB's on my car, but the run on was forever. You could turn the key off, pull it out, and the car would keep running until you pulled a battery cable. If yours is a run on for a couple seconds, might be another cause, but you've got to start somewhere.

Very interested in this, let us know if it works. My solution is much more low-tech, I just put the car in gear, clutch in, put my foot on the brake hard, then shut the car off and release the clutch enough to stop any run-on.

When you turn the key off, all power to the FI should be shut down as well. So there should be zero fuel going in, unless something is feeding power back into the ignition circuit. (Which is what is used to send power to the FI.)

With no fuel, it shouldn't matter if there are hot spots enough in the combustion chamber to light off a fuel-air mixture, there should be zero fuel.

That says to me either that you have a ton of fuel built up in the intake, or you have something feeding power back into the ignition circuit.

I had the latter; it was because I put a single-filament bulb into a rear turn-signal socket. When the turn signal stalk was down, the "parking light" circuit would feed back through that wrong bulb and into the ignition circuit, keeping the car running.

--DD

Hi Dave, I just recently cleaned the whole upper intake and throttle body, and I haven't changed anything electrical other than the Crane unit. I read somewhere that these electronic ignitions can stay firing after shutoff due to some kind of electrical feedback loop. Do you see any downside to trying the diode before the generator light approach?
thanks

Hopefully not a dirty combustion chamber creating preignition / "dieseling", or whatever you want to call it.

High idle speed is the first thing that'll lead to this.. Whats the idle RPM?

As I said, feedback into the ignition circuit from somewhere. (Hadn't heard that the Crane could do that, but who knows?)

The alternator light should have current able to flow through it in either direction. One of its functions will not work if you put a diode in line with it. You might wind up disabling your charging system...

--DD

Who is the "Jake" clown, spewing nonsense?

LOL. Kidding of course. Nice to see you posting. A good reminder to look up what you're up to now......

I had a similar run on problem after my conversion to EFI and found this:

http://forums.pelicanparts.com/porsche-914...l-not-stop.html

The diode mod works as far as it stops the run on issue. I havn't run my engine long enough yet to know if it charges or not....I think I measured 13,3 volts on the battery with the engine running at idle. Alternator is newly rebuilt.