Timing setting for 305E

[GMCNUT]

Hey guys - until I bought my 64 2500 series I had never really got to drive a 305E equipped truck any real distance and have been racking up the miles on this one since it runs like a top. However, it seems to be idled up more than it should be and will "cadillac" some when you turn it off occasionally, so I think the timing must need to be adjusted - I have no idea what the timing is supposed to be set to though - can someone tell me? its completely stock if that matters - Thank you for your help

[raycow]

I have never before heard the term "cadillac" used to describe what I think you are talking about. Does the engine continue to run (very roughly, and with loud splitting or cracking noises) after you turn off the switch? If yes, this is usually caused by carbon (or other deposits) building up in the combustion chamber and being heated to the point where it serves as an ignition source.

This is not a timing issue, because, if you think about it, there is no spark with the switch off. If the engine is idling faster than normal, it couldn't hurt to reduce the idle speed and see if that helps. The next step would be to pull the plugs and see what they have growing on them. If they look bad, a plug change MIGHT make the problem go away for a while. If nothing else works, you will have to pull the heads and clean out the offending deposits.

If you have a manual transmission, it is a lot less work to just put it in gear and engage the clutch with the engine idling and your foot on the brake. It is a real problem only if you have an automatic, because then you have no easy way of killing the engine.

Ray

[FetchMeAPepsi]

You can try cleaning your plugs if they have deposits on them. It can cause that too. And make sure your gap is right.

You might pour some b12 chemtool in it too to clean it out more in spots you cant reach.

[ghoff]

The plugs should tell all....do a compression check before removing heads.....gas is really yukie compared to back in the 60's....some additive or even octane booster run through a couple tank fulls....google can give you timing setting

[GMCNUT]

Thanks guys - I do not know what is causing it so I will try changing the plugs - its due for that anyway. Do you guys know what the gap setting is for V6's? I would still like to check the timing and make sure its right - what is a 305E supposed to be set at?

[GMCNUT]

Originally Posted by raycow

Does the engine continue to run (very roughly, and with loud splitting or cracking noises) after you turn off the switch?

Ray

yep - I kill the switch and the engine continues to try and run supposedly from late spark occurring at the time I kill the power - I was told if the timing was off it would cause this....maybe not. I do not know what the official name of this is, always heard it called cadillacing. Never heard anyone say it was caused by engine deposits that's for sure....hmmmm

[raycow]

Originally Posted by GMCNUT

I do not know what the official name of this is, always heard it called cadillacing. Never heard anyone say it was caused by engine deposits that's for sure....hmmmm

The names I have heard most frequently for this behavior are "running-on" or "after-run". There really is no spark once you turn off the switch and the fuel-air mixture has to be ignited by something. Well that something is a hot spot in the combustion chamber, and most often that hot spot is a deposit that has been heated to the fuel ignition temperature.

Don't forget to try reducing the idle speed. This can often be enough to fix the problem.

Ray

[ghoff]

Originally Posted by GMCNUT

Thanks guys - I do not know what is causing it so I will try changing the plugs - its due for that anyway. Do you guys know what the gap setting is for V6's? I would still like to check the timing and make sure its right - what is a 305E supposed to be set at?

The plug gap is .030----ignition timing degrees----7.5B------idle speed 525rpm

[GMCNUT]

Originally Posted by ghoff

The plug gap is .030----ignition timing degrees----7.5B------idle speed 525rpm

Thank you - will check this on mine

[George Bongert]

Hello GMC Nut!

What you are describing, (engine run on after switching off) is also, and more commonly known as "Dieseling" which can be caused by, or contributed to by engine idle speed being too high, and/or carbon deposits in the engine reaching a point of incandescence which will be hot enough to ignite the fuel. High idle speeds exacerbate this problem. Usually, reducing idle speed fixes the problem if hot carbon deposits are not a factor. Ignition timing has no bearing on "Dieseling" or "Cadillac" as you put it.