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RicardoJM
12-03-2008, 08:15 AM
The engine of the FJ40 does not turn off right when the ignition is turned off and key removed. The engine turn off takes a long time (5 seconds or so) and sounds like a real slow diesel engine. I'm really not clear on how long I've had a run on issue, but it has become much more pronounced and consistent since yesterday afternoon.

Have any of you ever encountered this issue? What debugging process of ignition components did you follow?

My FJ40 is a 1971 with an F engine. I have a gear reduction starter from a 60 Series, generic 12v coil, points in the distributor and the ignition switch in the dash.

Often times (maybe too often) I can find a strong correlation between a problem and something I recently did, but am coming up blank on this issue. My gut tells me to focus on electrical, i.e. coil has to be getting power for spark the engine to run. At the same time, it has been a several months since I did timing, points and such.

nakman
12-03-2008, 08:29 AM
two ideas- one is you have excess carbon buildup, which is causing your dieseling. Have you done any kind of carb cleaning/carb adjustments? The other idea is you have a timing issue. In both cases, there's still stuff in the intake that wants to burn, after you've shut off the juice, and you need to get it to where you have fewer leftovers. And you did cause this with something you recently did- you've been driving the 40 a lot.. good for you! :)

subzali
12-03-2008, 08:32 AM
The coil gets power when the ignition switch is on. Sometimes these switches get worn out and cause this issue. I have the same thing going on with mine, also on mine sometimes if the engine doesn't fire right away then it will keep cranking when I am trying to start it and turn the key back to the off position.

Uncle Ben
12-03-2008, 08:33 AM
two ideas- one is you have excess carbon buildup, which is causing your dieseling. Have you done any kind of carb cleaning/carb adjustments? The other idea is you have a timing issue. In both cases, there's still stuff in the intake that wants to burn, after you've shut off the juice, and you need to get it to where you have fewer leftovers. And you did cause this with something you recently did- you've been driving the 40 a lot.. good for you! :)

Ditto!!! My guess if I had to pick just one would be timing.

treerootCO
12-03-2008, 08:48 AM
Watch the fan and see if she is running backwards when dieseling. My low compression engine is fun to watch running backwards with the key off:hill:

Electric fans without a diode inline will act like generators and keep an engine running with the key off as well.

MDH33
12-03-2008, 08:52 AM
Does your carb have a fuel cut-off solenoid on it? Might have gone south or it might be disconnected.

Edit:

Also, pull a couple of plugs after running it and see what they look like. A good indicator if your carb is out of tune will be the carbon buildup on the plugs. What octane fuel do you run in it?

leiniesred
12-03-2008, 08:53 AM
The Big healey used to do this too. (1963 Austin Healey with a very similiar cast iron I-6)

It was never ignition. It was always carbration.

If the engine loaded up, (extended idling would do it) it would diesel on shutdown. I would just kill it with the clutch.

I took the time to balance the dual carbs and tuned it. I ened up much leaner and the dieseling problem went away. Starting was better, driving cold was much better (no more backfiring flames out the carbs under load.)

Carb tuning tip (especially this time of year):

One thing I learned is that I had to tune it HOT. I could get it tuned to run great on the driveway, idling for 15 minutes, and it would suck on the road. (terrible bog). If I hot rodded around the neighborhood, whipped into the driveway and started tuning it right away, With the engine still HOT, I had better results. If the engine ever got loaded up, (you'll hear it) I would have to stop, drive around again to clear it out, then back onto the driveway for more hot tune. The hot engine tune was VERY different than the driveway idling tune. It still ran great on the driveway cold or hot, but it also ran great on the road if I tuned it HOT.

I have a feeling you will be able to tune your rig leaner. There will be less raw fuel condensed on the intake walls and the dieseling will go away.

subzali
12-03-2008, 09:41 AM
Can the fuel mixture be adjusted on these carbs? I thought it was only the idle mixture that could be adjusted...

MDH33
12-03-2008, 10:05 AM
Depends on which carb he's running. Most have the high and low speed idle adjustment and also a separate fuel mixture adjustment.

What kind of carb do you have, Ricardo?

subzali
12-03-2008, 10:15 AM
I'm pretty sure he's running an Aisian. I am too and have the problem, maybe my timing is too advanced.

On the Aisans, though, the fuel mixture screw only really has an effect at idle right? When the throttle plates open the jets control the fuel mixture right?

RicardoJM
12-03-2008, 11:05 AM
Wow, a bunch of stuff to digest. It seems like a reasonable first step would be to go revist the timing and carb adjustments (http://forum.ih8mud.com/40-55-series-tech/26635-carb-works-great.html). Interesting that the carb adjustment procedure also recommends doing it at operating temperature.

I'll need to get a new vacuum pump. I managed to lose the seal when using my Harbor Freight special when I was using it to bleed the brakes. Is there a "gold standard" brand/model for vacuum pumps?

Regarding the last time I checked these details, it was early this year. I had the carb rebuilt this spring. The guy that did it for me noticed many little things that were different than what was documented in the FSM. I suspect I have a frankencarb. Also this spring (with Jeff Zepp's guidance) I adjusted my valves and set the timing. IIRC we started the timing a 7 but ended up advanced it significantly before finding sweet spot. The truck runs great; good power, no ping, no backfire - just doesn't stop running smoothly:D.

I may have carbon build up as I had been running without a thermostat until very recently. I'll have to get the BoomBoom to help me see what the fan is doing, I don't have an electric fan. I'll check the cut-off selenoid on the carb to make sure it clicks and has the wire connected. I'll look at a couple of plugs. I am running the low octane, 85.

I am running an Aisin carb. My understanding of the adjustments for the carb and how the mixture is controlled is aligned with Subzali. I am not aware of my carb having anything other than the idle mixture screw.

Of course, I can't eliminate the electrical being a contributor. Thanks all.

MDH33
12-03-2008, 11:38 AM
...I am running the low octane, 85.

...

Try running some higher octane gas in it. You might be surprised. Your older engine was probably designed to run on leaded gas (I think '72 was the last year). Higher octane fuel will help with preignition and run-on. Better for your valves too.

RicardoJM
12-15-2008, 07:30 AM
A quick update on my diseling. A tune up is in order, an inspection of the plugs showed 3 of them with carbon build up and the other three good. My timing is way advanced, I backed it off a bit but did not see an improvement in the diseling. I did start running the mid-grade gasoline and that eliminated the diseling.

Uncle Ben
12-15-2008, 07:32 AM
A quick update on my diseling. A tune up is in order, an inspection of the plugs showed 3 of them with carbon build up and the other three good. My timing is way advanced, I backed it off a bit but did not see an improvement in the diseling. I did start running the mid-grade gasoline and that eliminated the diseling.

If your plugs are carboned up the combustion chamber looks the same if not worse. Sounds like your running to rich.

Rezarf
12-15-2008, 08:19 PM
Ricardo- Your 40 is just telling you it wants to be driven more!

:D

Air Randy
12-15-2008, 08:45 PM
A quick update on my diseling. A tune up is in order, an inspection of the plugs showed 3 of them with carbon build up and the other three good. My timing is way advanced, I backed it off a bit but did not see an improvement in the diseling. I did start running the mid-grade gasoline and that eliminated the diseling.

Since you didn't have to do any major work to yours, that means you might have time to come down and help me pull the head on mine.............;)

RicardoJM
12-15-2008, 09:17 PM
Since you didn't have to do any major work to yours, that means you might have time to come down and help me pull the head on mine.............;)

I've not ever pulled a head, but would be up for working in a heated shop. When are you thinking about pulling it apart?

Air Randy
12-15-2008, 09:33 PM
Probably pretty soon since I'll need to send the head somewhere to get rebuilt. With Xmas coming up if I don't get it in pretty quick it might not come back until after the holidays.

I'm still shooting to try and get this thing on the road for one of the club activities right after the new year.

I do have an engine hoist so getting the head off wont result in a hernia:thumb:

If you or anyone else wants to come down, I always appreciate the help. Even if it's just for moral support and wise a** comments, it beats working alone:D