My DeVille (429cu.in.) after I shut off the ignition, will continue to sputter, sometimes for several minutes. I can pull the coil wire and it still does it, so I think ignition is ruled out. I know it is not acuratly timed due to a stuck advance (the new distributor is ordered) but my mechanic says it could be carbon deposits on the pistons. He dumped some water in the carb while running to "boil" out the motor and that did not help. It is a 67 motor and it is all stock. I am sure that it being out of time is part of the problem, but is there anything else I should be checking? I have never had this problem before.
How hot is it getting? What is the timing at? Does it sound like a diesel after the ignition is turned off? A couple of simple things to look for.
Definitly sounds like a diesel. It does get hot, but on the gauge it does not show in the danger zone. I can't get an accurate read on the timing because the advance is not functioning, so it could be rather off, but I am not sure.
I should note too that the car has a slight miss due to a bad plug wire arcing the dipstick. I ordered a distributor, cap, rotor, wires, and plugs so I can completely rule out the spooks in the ignition and get it timed correctly.
In my experience, run-on was caused by mr truck overheating. Sounded just like you said. But i had a friend tell me that his firing order was off by 2 cylinders and it did the same. I say, get the new parts, install, time it, and try again. That guage could be VERY off to. Get/borrow a multimeter with the temp function and check it for yourself. Just so you know it is acurate.
I did notice the other day that the upper radiator hose is about to burst, which a replacement is ordered. It did puke a little coolant after a 30 minute drive today too. Guess I should flush the radiator and check the thermostat when I do the hose.
This was a noted problem when this car was new. You can simply stop this by turning the car off while still in gear then put it in park.
Check to make sure that the distributor is not loose and then set the timing again, Check stuff like the throttle cable is not getting stuck open too. It may be getting hot spots in the combustion chamber .A complete tune up would be the best thing to do before pointing fingers at anything really wrong with the car though. It might be more than one thing wrong
It will still diesel when I shut it off in gear. Distributor is tight. Throttle cable is not sticking. Since this car had an air conditioning cooler in front of the radiator, and since it sat a while, ill see if I can blow out the space in between with an air hose. It may be a combination of getting too hot and off timing. Like I said, I am going to replace the ignition parts to insure that the timing can be set accuratly, and flush out the cooling system and put in a new thermostat and hoses. Hope I can get this thing figured out. This car is my driver. I have also heard that there is an anti-dieseling solenoid on the carb. Is there a test procedure for it, or would I benefit from replaceing the carb all together?
Reasons for doing this: Running too hot Too much timing too much compression lower than needed octane used Possible: too hot a spark plug carbon deposits on piston idle set too high
Fix the advance and set the timing by the book. Then see if the problem persists. If you have jacked the timing around because the advance is not working then you probably have it advanced too far causing it to diesel.
If you have an anti-dieseling solenoid on the carb the idle screw should be set to hold the plates open only enough to prevent sticking and the idle speed adjusted at the solenoid. The solenoid is used to set the curb idle speed and when the engine is shut off it drops to close the throttle plates. This prevents fuel mixture past the plates and prevents run on from detonation.
Does the caddy have an alternator and electric fuel pump? There is a rare but known problem with GM alternators backfeeding. I lost the engine on my Willys last year when it overheated due to a hairline crack in the radiator losing coolant under load. I shut off the ignition - it still ran. I shot off the master cut out switch - it still ran. I pulled all the plug wires and it still ran. it took me ten minutes to shut it off by pulling the supercharger blow through plumbing and suffocating the carb with rags. The GM alternator was backfeeding to the electric fuel pump despite everything being switched off. Painless Wiring has an $80 kit to prevent this backfeed situation.
Or you can put in a $1.98 bulb in the feed line to prevent the same thing. I'd spend the $80.00, because the economy needs the boost. Cosmo
Man I thought that you meant that it wouldn't shut off like in keep running forever and I was going to say that it is a better problem than one that won't start. It could still be carbon deposits. They get hot and glow. Try speeding up tour idle and throwing a handful of rice (uncooked) down the carb. But you can't rule out the distributer one that is timed fast will run on. You may also check the running temp they also run on when hot. Or it could be a combination of all of the above. Those old cad motors are good motors by the way. My experience with them is that they run forever and very seldom give any problems. It will be worth your while to get it sorted out. I didn't want to say this but if the dizzy and the rice doesn't cure it you may have to pull the heads and de-carbonize it. There was a time that mechanics actually offered that service. Folks would lug them around town and get them "all cobbed up." Sometimes a good run down the highway at highway speed will cure it also, keep the revs up say around 3K for a dozen or so miles. This is confusing isn't it. Well the meds must be kicking in my back quit hurting about 10 minutes ago. You can sort it out right?
Sounds like your throttle blades are open to far. Try turning what ever you have on your carb to idle it up all the way out. Look inside and see if the blades are fully closed or just barely open, you want them just barely open at idle. Turn your idle mixture screws out to get it to idle if you have to. If someone opened your blades too far the carb. will be receiving a vacuum siginal from air being pulled under the throttle blades causing fuel to be pulled out of the idle passage outlets and cause run on.
A large build up of carbon on the pistons will do this as well ,I used to run water through the carb when the motor was hot and running, but if you don't know what you are doing you will have more problems. GM use to offer an upper cylinder cleaner for this that you did the same way also I agree with the anti dieseling solenoid, hence the name. if you don't have one you might want to get one
Does this car have an electric fan? My sbc in my 3window used to diesel over as well.....one day we were messing around with moving wiring and forgot to put the fan wire on...the car didnt run on when we moved it in the garage.... pluged in the wire and it ran over again.... so we found the problem....
UPDATE: I flushed the radiator today an put in a new thermostat. The old stat was a 198 or 196 degree, and the new one is a 180, so it is not getting as hot. I also flushed out a butt load of stuff from the cooling system. It does not run on as much, but I do not have the new ignition parts yet so it is still way out of time. I have no idea what it is set on, cause I broke the light in my timing gun and had the local mechanic dicker with it. They should not have. It runs worse now, but the advance is stuck. I have never heard of the rice thing. May try it, but I gotta problem with rice burners!
oh, i should mention that it will still diesel if I pull the col wire off, so I don't think it is backfeeding, no electric fan, no electric fuel pump.
----------------- It's not timing because dieseling happens with the ignition shut off . What's going on is auto ignition caused by too much heat and compression for the octane of the the fuel being used. Try using using a higher octane fuel - or if you're already using the best available pump premium in your area. try blending a quart of either Xylene or Toluene to about every 8 or 10 gallons of good unleaded pump premium. Xylene and Toluene are available from paint stores and industrial supply places in 5 gallons pails and is sold as a solvent and as a paint thinner and stripper. It's also the main ingredient in most commercial 'octane boosters' too, but it's a heck of lot cheaper when you buy it in 5 gallons pails as a 'solvent' from an industrial supply or paint place - instead of in little bottles as "octane booster" from a gas station or discount store! A couple other things that have been previously mentioned. Make sure your idle is set as low as possible, If you're running a 190 decree or higher thermostat, going to a 180 degree or cooler thermostat might help - as well as a step or two colder spark plugs and/or a bit richer overall fuel mixture. Mart3406 ================================================
Reminds me about the time my brothers elk would not turn off . all of a sudden everybody is a expert mechanic . I sitting there while it goes ka putt putt ka putt ka putt like for I don't know for how long just dieseling . some guy says just put er in gear . OK Ill try it , ka putt ka putt . then another guy says put yur foot in it that will kill it , OK ka putt ka putt ka putt putt . then I flip the ignition to ON accidental or just because everybody was giving me orders and I am trying everything like a jerk and it starts burning rubber and smackers in to the car in front on me. I knock it six feet out of its parking space ! security guard standing there , this crap is funny after wards not when it happens .
My thoughts...this was a common problem with many older models. From my experience, it's caused by above normal engine temperature, idle too high (that's why the solenoid was designed...it shut the air off when ignition was turned off...no air - no run) or glowing carbon deposits. Personally, I don't like the rice idea because if you accidentally pour it in too fast, you're gonna create real problems. I like to run the engine RPM's up and "drizzle" automatic transmission fluid down the carb. Keep the RPM's up high enough to prevent the engine from dying and don't be surprised if the neighbors call the fire department...just tell them you're part of the mosquito control agency.
I was going to suggest this as well. I would not even mess around until you get the timing right. Then get some premium in it. The 429 is a fairly high compression engine. 10.5:1 If i'm not mistaken.
Check the plugs and make sure you are not running too lean. If you are too lean you'll get hot spots in the combustion chamber. Often this is very localized and will not cause the temp gauge to rise. As others pointed out, idle speed is also a common cause. Try letting it idle for a few minutes. This should let the combustion chambers cool down if your running a vacuum advance. If you're not running a vacuum advance it will likely get hotter.
The Jalopy Journal
