Occasional dieseling problems

[Pender1]

I've got a '84 K10 with the stock 305 in it. The odometer reads ~57,000 but I don't know how many times it's rolled over (I suspect twice). I occasionally get some dieseling when I shut it off and could use some help fixing it. It doesn't do it all the time and as far as I can tell it's not temperature dependent. I put a new timing set in a couple of thousand miles ago but I wouldn't think that would cause this. I'm pretty sure I'm leaking by an oil ring or two, but not very badly. When it does it, it may only turn over one more time or it may keep trying for 10 seconds or so but at way below idle RPM. It's not really predicable or consistent.

Could this be ignition related? I have new spark plugs and wires but haven't put them in yet.

 

[Boone83K10]

It can be ignition related..or fuel..or air. I would check timing, set around 8 initial and 32-36 deg all in by 3500 rpm. Check spark. Change the plugs and wires. If you have blow by, that can cause dieseling too.

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[firebane]

Dieseling can be a cause of many things but the most common is build of carbon that remains still ignited causing the vehicle to run longer than needs to.

 

[Pender1]

It can be ignition related..or fuel..or air. I would check timing, set around 8 initial and 32-36 deg all in by 3500 rpm. Check spark. Change the plugs and wires. If you have blow by, that can cause dieseling too.

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I definitely have blowby. This motor has seen some hard use in it's life before I got it.

Dieseling can be a cause of many things but the most common is build of carbon that remains still ignited causing the vehicle to run longer than needs to.

Think some seafoam through the carb would help clean some of it out?

 

[firebane]

Seafoam could definitely help. I would go overly crazy with it but it could loosen up crap for you.

 

[glockholiday]

I had a 73' Dodge pickup with a 318 when I was in high school that dieseled pretty bad when hot. 5-10 seconds every time. It was a stick shift though so after I shut it off I would just hold the brake and let the clutch out with it in gear so it couldn't do it.

My auto shop teacher said it was because of the build up of carbon in the combustion chamber staying hot enough (cherry red) to burn any fuel left in there, which is a decent amount in the bowls of a 4 barrel carb.

We pulled a spark plug out and looked in the cylinder with a boroscope and there was definitely a lot of carbon. He told me to bring it straight into the shop the next morning and leave it running so it would be good and hot. We pulled the air cleaner off and I held it at a high idle, about 2K, while he drizzled (very slowly) a 44oz cup of water down the carb. We all thought he was crazy, especially me since it was my truck. It spit and sputtered but he would adjust the amount he was pouring so it wouldn't die.

We then pulled the same spark plug out looked again with the boroscope, it was noticeably cleaner inside you could actually see some grey bare metal surfaces. It never dieseled again. He said it actually steam cleans the combustion chamber, the steam explosion actually breaks up the carbon.

Now for the disclaimer. In no way can I recommend doing this but you have to give credit to some of these old school guys and their tricks because most of them actually work.

 

[firebane]

Using water to remove water buildup is a age old back yard trick and lots of have done it successfully and lots have not.

Essentially the water turns to steam and steam cleans the inside of your block but the caveat to all this is that you pour too much water and you could end up hydro-locking your engine since water is not compressible.

 

[glockholiday]

Yes it's a tricky procedure, oh and I did an oil change right after just in case.