How much pump advance is too much?

[dieselbegreat]

(1) I am getting some surging on the highway under very light throttle conditions and (2) I always thought the truck sounded and ran better when the cold advance was on, so I advanced the pump so that the mark moved from about 1/8 inch to not quite 1/4 inch to the driver side. It puts out a slight amount of black smoke for the first 30 seconds when cold now and puts out more black smoke when full throttle than it used to but it feels better off the line and about the same at high rpm. The surging seems slightly better actually but I'm beginning to think I may have small air leak in fuel supply line or a bum injector. I think fuel mileage is about the same or slightly less at just under 18mpg. It is noisier but not "objectionable." Did I turn it too much?

[CleviteKid]

A few years ago Jim Allen did a series for "Four Wheeler" magazine using the 6.2L engine in his Blazer. He found that it IS possible to crank in too much advance to the point that the power actually dropped.

It "sounds" like you have NOT gone too far. My rule of thumb (or rule of ear) is if your truck is not quite as noisy as a 7.3L PowerStroke, you have it advanced just about the correct amount.

Stay tuned for Britannic to give you a better answer, based on instrumentation and theory and all kinds of other good stuff. If he volunteers to bring it all to your house and tune it for you, accept that offer :D !

Dr. Lee :cool:

[britannic]

The only way you can be sure is to get the timing set with a meter and baseline for future experimentation.

Surging and variations in timing can definitely be caused by air leaks, so eliminate those first before changing your timing.

[dieselbegreat]

Thanks. I think I'll just drive it some more first. smile.gif