Dieseling help for a noob...

[elektrik]

Hi guys...I've got most of the major issues with my 1969 resolved, now I'm trying to solve the "lesser" stuff (although, I'm not sure my engine "dieseling" when I try to turn it off is considered lesser or not :|). My engine periodically diesels when I turn it off. My question is this: Could there be some sort of tune up issue involved (timing, carb adj., etc.?) with it? I had a crappy fuel tank and rusted sending unit it when it was "restored" by the mechanic and I'm not sure if he would adjust the engine to compensate...

Whew...long winded way of asking: Where do I start to try to figure this thing out?


Thanks in advance!

[Longhorn Man]

start with idle speed... too high can cause it
Check timing... too far advanced can cause it
Also, fuel grade... too low an octain reading can cause it, but not likely on an old school v-8, pinging would me more prominant

[ed2552]

what do you mean by "diesels" you mean it keeps firing a few times after turning the key off? That may be the carb, means it may be leaking into the cylinders, firing on the compression alone. My truck did that for a while, and then when it did that i threw it into gear and it stopped after a while

[elektrik]

Originally Posted by ed2552

what do you mean by "diesels" you mean it keeps firing a few times after turning the key off? That may be the carb, means it may be leaking into the cylinders, firing on the compression alone. My truck did that for a while, and then when it did that i threw it into gear and it stopped after a while

Sorry, I assumed Dieseling meant that it keeps firing a few times after turning the key off, which is the problem I have

[68gmsee]

10/4 on dieseling referring to running after ignition is turned off. Either backwards or forward. Basically it means that there's no ignition spark (like in a diesel engine) but the engine keeps running. The piston moving down sucks in more fuel from the carburetor.

As mentioned by Longhorn Man and ed2552, several things can cause this. The most common is a hot spot on the piston due to carbon buildup that can be caused by bad gas. Also timing, leaking carb and overheating are other causes of dieseling.

The hot spot ignites the fuel after you shut the ignition off and the explosion causes the engine to keep turning. It may also turn backwards depending on where the piston is when the fuel explodes.

The first thing I did on my truck was replace the spark plugs and checked timing. Then I ran the gas tank down as low as I could get it, poured in two cans of STP gas treatment and filled the tank up to the top. I did that on two tanks full before it stopped. If it's real bad, you may have to do that for a while and run the truck to burn off the carbon.

[Longhorn Man]

dieseling usually refers to an engine that fires from a hot spot, and makes the engine run backwards for a moment... or longer.

[ed2552]

Try Seafoam, is comes in a white can with a screw off top, works well in gas, diesel, engine oil. Put one can in it and when you change oil put it in in the recommended amounts, works well.

[ChevLoRay]

In the mid-70's, dieseling was common. Lower compression ratios; timing issues and the change from leaded to unleaded gasoline all contributed to the issue. Manufacturers attacked the problem by installing fuel shut-off solenoids that were nothing more than a way to positively close off the throttle.

The industry name was Ignition Run-On. This meant that the engine ran on after you shut off the ignition. But it is a combination of things that cause it. Fuel entering the combustion air stream, which is then sucked into a hot combution chamber is what it is. Shut off the fuel. Shut off the air. Alter the timing if it isn't correct.

One old school way to stop it is to simply drop the shifter (automatic) into drive after you turn off the key, or turn it off while it's still "in gear". If it's a manual, just hold your foot on the brake, and let the clutch out while it's still in gear....come on, you've never killed a stick shift by dumping the clutch?

[68gmsee]

Originally Posted by ChevLoRay

..... If it's a manual, just hold your foot on the brake, and let the clutch out while it's still in gear....come on, you've never killed a stick shift by dumping the clutch?

Did that for about a year while I had my truck parked. I was running it about once a week to keep it lubed and sometimes it dieseled so bad, the only way I could get it to stop was to put it in gear.

ed2552, what is seafoam? And why use it in the crank case?

I've heard it mentioned here but I don't believe I've ever seen it at the local autoparts.

[ed2552]

It is an additive like any other, it is designed to be used in the fuel or crankcase, it helps keep everything lubed and break up deposits

[El Jay]

Originally Posted by ed2552

It is an additive like any other, it is designed to be used in the fuel or crankcase, it helps keep everything lubed and break up deposits

You can also disconnet the vacuum line to the PCV valve, or brake booster, and suck into a running engine to clean up the intake system.

I used to work for repair shop that handled small equipment. The techs would use "Deep Creep" (Sea Foam in an aerosol can) to clean the carbs and intakes on small engines. It smoked the livin' dickens out of the shop, but it cleaned everything up real good.
I forget exactly how it was billed, but it was something like, "chemically clean intake and exhaust system."
I can't say exactly with whom the shop was contracted nationwide (about 1000 stores), but Tony Stewart might be able to tell you.

[ed2552]

I dumped the clutch on it for a while after i drove it when it did that and it stopped after a while, idk why

[ed2552]

Ask for it, they should have Seafoam, never been to one that didn't have it

[Longhorn Man]

I real good way to get rid of carbon deposits, is with a spray bottle of water, or a bottle of dextron ATF.
Warm up the engine, remove the air filter and air cleaner assembly. Fire up the engine and either have an assistant hold the throttle, or crank up the throttle to about 1500 - 2000 RPMs. With water, put it in a spray bottle and put the nozzle on stream. Start squirting it directly in the carb. You can spray it as fast as humanly possible.... there is no physical way for you to do damage.
I prefer the dextron. You do the same thing as far as set up, but you slowly pour the dextron into the carb. The best way I can describe the rate of pour, is to dump it slow enough that it is a steady pour, not dripping. However, not so fast that it is a thick stream. We've all played in the sink as a kid, tried to get the least amount of water out with a steady stream... THAT mauch.
The water cleaning method will make steam out the tail pipe, the ATF will make it smoke. but it all clears up.
If your vehicle is equipped with a catilittic converter... DON'T do this. Chunks of carbon can, and possibly will shoot out the tail pipe. If you have cats, this WILL clog the cats.
Seafoam does nothing more than this. (when poured down the carb) And I garuntee you have water or dextron in your house already.

[elektrik]

Originally Posted by Longhorn Man

If your vehicle is equipped with a catilittic converter... DON'T do this. Chunks of carbon can, and possibly will shoot out the tail pipe. If you have cats, this WILL clog the cats.

Ugh...so this leads to another noob question-how do I know if I have catalytic converters? Can I tell just by looking? My mufflers just look like mufflers LOL

[jhow66]

Uhh, I don't believe they had cats' back in the days our trucks were built. L'man was talking about late model stuff on the cats'.

[Longhorn Man]

that is correct. I wanted to throw in that disclaimer so no one on here would go and do $1000 damage to there lateer model car. 74 and up for cars had cats. Trucks were kinda hit and miss.

[SCOTI]

Originally Posted by Longhorn Man

that is correct. I wanted to throw in that disclaimer so no one on here would go and do $1000 damage to there lateer model car. 74 and up for cars had cats. Trucks were kinda hit and miss.

Still might be worth taking a look just to make sure someone tree-hugger didn't put some 'cats' under the old iron (engine swap w/the entire donor vehicles exhaust....). Anything's possible.

[Longhorn Man]

I can't remember is the San Antonio area is a smog area or not (been a while since I was in Tx) but in all reality cats would be required per federal smog laws if it got a late model engine swap.
The reality of it is though, don't ask don't tell. Passes the sniffer, no need to vonentier info to the smog cops.

[elektrik]

Originally Posted by Longhorn Man

I can't remember is the San Antonio area is a smog area or not (been a while since I was in Tx) but in all reality cats would be required per federal smog laws if it got a late model engine swap.
The reality of it is though, don't ask don't tell. Passes the sniffer, no need to vonentier info to the smog cops.

It's not a smog area, but remember I'm a CA native (and so is the truck)

...That said, how would I be able to tell what it would look like? Should I take pix of under the truck and submit?

[Longhorn Man]

I highly doubt you have them. Even one in cali would not need it for 99% of the engine swaps.
However, if you want to verify 100%, look under at your pipes, and count the mufflers. If you have one muffler per pipe (most of these trucks have true daul exhaust) If you have one muffler per side, you're golden. If there's two mufflers per side (best way to describe it to someone who doesn't quite know) then get us a photo.

[elektrik]

Just one muffler per side - two total

[twouvakind]

Let me resuscitate this dead thread by saying Sea Foam is available at my local WalMart, about $8 a can.

[ChevLoRay]

Man, I've seen older threads revived, but it's been a while.

If anyone has this dieseling problem, one thing that hasn't been mentioned is that for those who are running an old QuadraJet....the plugs in the float bowls may leak fuel into the intake manifold and fuel the hot engine with a fuel/air mixture that keeps on keeping on. Rebuild kits should include thick foam-type piece that fits into the well of the throttle plate and keeps those plugs in place after you rebuild the carb and/or use plugs that also have an o-ring.

[elektrik]

Actually I'm glad this thread was revived-I forgot to actually *do* this to the old gal. I'll have to try it.