Working on get my Caddy ready for a road trip off the Island next week and just changed out the points with a pertronics kit.It is a 472 and it had engine run on with the points and it still has it with the pertronics in it.So that never fixed it!! Thought it might of been bad fuel but I have put a few dollars in it and let it run it through,still no difference. What kind of problems should I look for that will cause a engine to run on after you shut it down??
Many cars from the period your engine was made had a electric solinoid that dropped the idle speed to stop run on due to deiseling
Well, I'll try to give you a start....... I ***ume it is run on due to detonation - not the ignition system. I've seen some problems with faulty wiring back-feeding the ignition, causing it not to respond to the key. If it's detonation, you have something running hot in the cylinder causing "dieseling" - glowing carbon, spark plug too hot, etc. Check timing carefully for too far advanced, plugs for correct heat range, then take it out and 'run the carbon out of it'! Also check for idle set too high. If that fails, turn off the key with the car in "drive" Good luck !
my guess is your wiring is feeding back voltage to the coil, is the supply tapped off another source like the alternator? if it isn't isolated you need a diode installed to do that. i ran into the issue when i converted farm tractors years ago and used diode, proplem solved.
Yep. A common problem, rarely has anything whatsoever to do with the ignition components. Inherent with higher compression motors of yesteryear, where anything that supports the dieseling occurrs. Like g***erjohn points out, check out the idle speed first. Sometimes it's due to carbon buildup in comb chamber, but was quite common with those old motors, even when they were new, if the idle was too high. Another trick is drop it in gear to lower the idle before turning off the switch.
Diode in alternator? I remember something about the ignition being fed off the alt after shut off and keeping it going. Try disconecting it.
Rx7 13b used to fry the diode on occasion drove us nuts. Perhaps a bit if time with the timing light too?
Do you have an electric fan? They can act like an alternator and back feed voltage.If you have an electric fan try unplugging it and see if it still does it. If that fixes it you need a diode on the cooling fan to prevent the back feed or put the fan on a switch and shut the fan off before you shut off the engine.
Its dieseling..which means as the ignition is shut off, the engine is continuing to draw fuel thru the carb, and ignite it with glowing carbon deposits, or hot steel in the combustion chamber.DROP IDLE SPEED, LEAN OFF IDLE MIXTURE. basically try to get the motor to run at as low an idle as is practical.idle cut off solenoids help by closing the throttle ****erflies as you switch off, and they can be retrofitted to most carbs. Nothing to do with ignition at all.
Had a quick look today and the dieseling switch is always on and keeping the idle up. I unplugged it and the idle dropped and the engine shut off.I was thinking of unplugging it and removing it all together and set the carbs idle with the carb idle screw.What is your take on this??
Try it but unless you can live with a lower idle speed than you have now ,most likely you will want to get a new solenoid.
It's a true story. Get a working solenoid and set it up right and your problems will be over. If it was possible to avoid the dieseling with out that part, then you can bet yer **** GM would have ditched it and and saved money on every 70's -80's carbed engine they made.
The solenoid is working. Unplugging it has proven that. It's not connected to the correct power source, should de-energize when ignition sw is shut off. Chase the wiring problem down, you have the problem solved.
Yes,I have been doing more thinking about this.These switches are new to me,anyway I am going to have to see if the power is shutting down when the key is off. The switch does work but it is in need of adjustment I am wondering if it is sticking open when I shut it down.I`ll have a look at it tomorrow.Thanks for everyone help.
You are on the right track. Also whilst you're in there, check the automatic choke adjustment, the fast idle stops related to that also. They're all related.........
Make sure your engine temp hasn't crept up a bit higher than normal. This can make matters worse for dieseling. You're probably better off if you can get the idle stop solenoid adjusted and working properly. In effect there might be as many as three "idle speed" settings that can be made. The lowest should be the base or "curb" idle made with the idle speed screw. Next highest would be the idle stop soleniod speed set possibly by turning the plunger of the solenoid with a wrench or turning the solenoid itself if it's threaded into its bracket. This is set with the solenoid energized, and depending on the specs for your engine it might need to be set with the engine idling in gear. Finally there's the fast idle or cold start speed setting. This is set with a screw against a specified step of the fast idle cam connected to the choke linkage and picks up the idle speed for cold starting. Check the shop manual if you have one for the settings and the sequence to make them in. If the car is mostly driven in town at low speeds it may have some carbon deposits in the cylinders which can cause hot spots and lead to dieseling as mentioned already. Some highway driving may help clean things up or you might consider running some combustion chamber cleaner thru it. If you do, you might consider having a fresh set of plugs ready as you might have some carbon fouling issues after you "blow the gunk" out of it.
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