When I shut off my truck it continues to fire ad sputter. Is this because of using too low of octain fuel or a timing problem. It only hapens if the truck runs for more than ten or fifteen minutes. Any coments are welcome. Thanks - Nick

 

Sounds exactly like what you've mentioned. Although, it sounds like more of a problem with bad gas instead of too low octane. Try getting from somewhere else next time.

 

My '69 F250 and my dad's two '70 Fords will all "diesel" if the idle is too high. In fact we had to drop the idle a bit lower than the factory specifications to about 500 RPM to keep them from doing that. It is rare that they do it now, and if they do, it is only for 1 or 2 revolutions. We tried changing the timing and the grade/brand of gas but that did nothing.

I have heard that using colder spark plugs may also help, but I have yet to try that.

I had a neighbor whose Chity, oops, I meant Chevy, had a severe case of "dieseling". His would go like that for a good 10 minutes if he shut off the key without having the auto tranny in gear. I once laughed and said, "Hey Roy, is that The Heartbeat of America I hear pounding away?" He moved not too long after that.

 

hey Nick...

you didn't say how many miles are on the current engine, but if there's alot--believe it or not, excessive carbon deposits in the combustion chamber can actually heat to the point of "glowing" and cause the run-on ignition after you shut off the key (much like a glow plug in a diesel engine).

The only way to clean it out permenantly is to take apart the engine, but I've heard of, and tried, a trick to pour a half cup of water (yes, water!) down the carb throat with the air cleaner off, holding the throttle open to a faster RPM than idle. Whether this actually works is not obvious but there IS a risk in trying it---if your carbon deposits are very bad, it's possible for a dislodged larger piece of carbon to wedge between the valve and valve seat when the valve closes, and possibly bending the valve stem! (try it at your own risk, but I've done it on a lower mileage engine with carb as a maintenance routine thing).

cw

 

I don't know about the water, sems like pouring water into a hot engine could cause probs. I had an Auto Mechanics instructor in high school tell us to pour automatic tranny fluid into the carb(about a cup) and take it out on the interstate for 10-15 miles. It helps burn off the carbon. It will smoke a-lot at first but it will clear it up.

 

First off afford premimum gasoline, then advance your timing beyond factory specs, do not use a timing light, on V8s turn distributer CLOCKWISE, WITH VACCUM ADVANCE CONNECTED, until you get the highest rpm you can, then test drive truck, and IF engine pings on acceleration back off timing just a hair until it just barely does not ping, you will probably need then to adjust the idle speed down on carb, also adjust air/fuel screws to obtain maximum engine rpm, your engine will run better, and have more power, & even get better gas mileage.Good Luck

 

Motors that continue to run after the key is turned off usually have a problem with carbon deposits in the head. The idea to introduce water into the cyl when running is correct. The water will remove the carbon deposits and help with this. Though it is not recommened to poor a lot of water at one time into the motor as water increases the combuston and could cause a piston failure. In the 70s and 80s there were componies that sold a water injecton system for Carb motors. This worked according to the acceleraton of the motor, the harder the acceleration the more water added. They had a small resovoir on the fender that you would fill when getting gas or checking the engine. This worked very well for my vehicle, which was a 1975 Ford with a 400 motor. I had this problem in 1980 and when we removed the heads found large carbon deposts, after we installed the water injector, 2 years later we removed the heads and found them to be almost completly clean.

If you cannot locate one of these water injectors, and you want to use water to clean you heads, use a spray bottle and do not poor into the carb, with a small to med mist, and engine running about 2000 rmps, spray the mist into the carb. Clue, engine must be at running temp.

Dave

 

Everyone's right - you probably have carbon deposits that are getting hot and acting like glow plugs. The throttle plates are also open just slightly too much, allowing fuel to be sucked-in even though the ignition is off.

The easy (and potentiall dangerous) solution I heard of is pouring a mixture of 1/2 cup water and 1/2 cup brake fluid slowly down the carb throat when the engine is warm. Raise your idle a bit and pour it in slowly enough so the engine doesn't stall. After it's all in let your truck sit overnight. The water turns to steam and helps the brake fluid get into the carbon. The brake fluid will work on the carbon and break it free when you start the motor the next morning. If this was me, I would disconnect the coil wire and crank the engine for a few minutes before starting it, so I could get most of the carbon out without abusing the engine. Crazywoman is dead-on - the carbon deposits will fall off and if they are too big you could damage the valves (a piece of carbon prevents a valve from closing and the piston hits it) or a piece could become wedged between the piston and head and damage the piston. If you have catalytic converters the carbon will most likely mess them up so you may have to replace them.

The best solution is to remove the head(s) and scrape off the carbon.

I have an '81 F-100 with a 300 cu 6 that diesels. I now just slightly engage the clutch when I turn-off the motor to stop the dieseling.

A year ago I found a web page posted by a petrochemical engineer. He addressed the issue of carbon build-up. He stated that pure fuel would cause little carbon buildup. It's the additives that do not burn completely and cause the carbon buildup. Every brand of gasoline uses different additives. He switches brands every 5,000 miles and this stops the carbon from building up.

Water injection is also a great idea. It not only helps keep the carbon from building up, it cools the incomming ari/fuel thus giving you the equivalent of a slight increase of octane rating. It really helps on hot days. I'm considering it for my '71 F-350.

Hope this helps.

Bruce

 

OK these all tell me to do the same thing, one more question. Where can I get a water injection system. Thanks everyone.

 

Water Injection Packages are very expensive and usually intended for use in higher compression engines where detonation can be a problem--like turbocharged engines. Water injection supresses detonation and frankly, to address the concern of carbon build-up is overkill--most engines using decent brand-name petrol will only build up carbon over the period of time in which an engine rebuild is required anyway (bearing clearances worn, compression too low).

Pouring water into a healthy engine is *only* intended as a maintenance or routine method of avoiding carbon build-up....to hope it will "clean out" a dirty combustion chamber is a misunderstanding. It may help; but most likely an engine tear down is required as the most stubborn carbon is not going to be removed without abrasive methods anyway.

If you truly want to look into purchasing a water injection system, be wary of systems that claim to allow extended mileage using very little water--those systems may not inject enough water to do much good at all. Edelbrock: 213-781-2222 (commonly available at mail order and auto parts stores) manufactures something they call "Vara-Jection" kit which is both load and speed sensitive in calculating water injection. Also another manufacturer is Spearco: 818-901-7851.

Incidentally, since I posted my orignal message about carbon build-up, another thought came to mind. Check your spark plugs and make sure you are using the correct ones. If the plug threads are too long, they extend into the combustion chamber and the sharp edge of the exposed thread can actually overheat and cause run-on ignition. As I think someone else suggested, plugs that are too hot of a heat range can also glow red!

cw

 

your problem is cuased by the throttle plate of your carb left too open when shutting down. on late model cars w/carbs the idle is adjusted with
a solonoid and the idle stop screw on the carb is
usually set so that the plates are almost all the way closed. adjust the idle mixture as rich as can be set for smooth running and adjust idle speed with solonoid. dieseling is caused by carbon in combustion chamber glowing enough to cause ignition if idle plates are open enough to alow mixture to pass in sufficient quantity to burn.

 

If you have'nt solved the problem yet, water injection will work but I advise caution for all of the reasons already mentioned.
The best solution if it's carbon build up is to
add carbon cleaning additive to the fuel tanks
over a couple of tanks worth.
This process cleans carbon at a moderate rate and
causes no damage.