Trying to Understand Slow Cranking Caused by Too Much Ignition Advance
 

Lifted from another thread, so as not to hijack that one:

https://www.ford-trucks.com/forums/1...start-hot.html

I'm trying to get a feel for the symptoms of a slow cranking starter caused by excess ignition advance. I'd like to use this info to update my write-up on using a voltage drop test to diagnose a slow starter. I've only got a quick mention of this, and would like to make it more accurate and helpful.

https://www.ford-trucks.com/forums/1...t=Voltage+drop

Does anybody have any experience with slow cranking caused by too much ignition advance? If so, was the cranking speed okay for a half-turn or so and then quickly dropped off? Or was it just slow from the get-go? I'd think the former, but I don't really know. I'd suspect there'd be no extra resistance until some fuel/air mix could be drawn in and then ignited. A spark plug firing with nothing to ignite would not change anything, at least the way I'm thinking. That's why I suspect the initial cranking speed might be okay, but that's strictly conjecture on my part.

In addition, if the fix was to correctly set the ignition advance, had there been other symptoms besides slow cranking? Pinging or knocking come to mind.

Also, is too much ignition advance very likely with a TFI ignition system? I could certainly see it happening with DuraSpark, as the timing is mechanically and vacuum controlled. I suppose anything is possible with TFI's computer control, but this does not seem very probable the more I think about it.

Begin the abuse ;)

You are correct, you don't hardly see it on a computer controlled ignition. You see it a lot on GM with the HEI, the advance weights like to get rusty and the springs are not strong enough to pull them back.

It may ping, it may not. The problem is just a little too much advance during cranking on a hot engine. When the engine is cold, if it's borderline it will crank ok, and then give problems when it's hot when you try to crank it.

Sometimes it's hard to tell if it's a starter, cable or timing problem. When it cranks over and the timing is too advance you get a turn over-almost stop-turn over-almost stop type of cranking. If your battery is not very strong, it won't take too much till it doesn't have enough to turn it over.

I've done it plenty of times. Do a motor install/swap whatever replace distributor and get it where you want it what you think is the sweet spot using your ear eyeballs timing light vacuum gauge manual timing spec whatever. So everything is hunky dory you got it all dialed in and decide hey let's take a ride.
So you hop in it and go somewhere, shut it down and a few minutes later you go to start it and you get a big ol wwwwwuuuuuuuuummmmmmmp sump wwwwwwwuuuuuummmmmp like Franklin said slow with intermittent speed up. No chance in hell of it starting until you back it off a little (if this isn't your first rodeo and you brought your distributor wrench) or you wait until it cools down. Otherwise your not going anywhere.
If you need to understand this concept then imagine pushing someone on a swing and instead of waiting for them to get all the way back you want to push while they are still coming back. Won't work too good.

Thanks gentlemen, lots of helpful info in these replies. I'm learning a lot.

Re: Sticky advance weights - that's a big factor I hadn't considered. At engine shutdown, what happens to the centrifugal advance? Wouldn't the upper portion of the distributor shaft briefly try to keep rotating, even though the lower part stopped? If so, couldn't this inertia from the upper portion 'backdrive' the centrifugal weights and push them out against the springs? If everything was in good condition, the springs would quickly retract the weights, but not if there was any binding.

Don't mind me talking out loud. I'm just trying to get a handle on a possible failure mode. That is, if I'm thinking through the inertia scenario correctly.

It only rotates like 1/4 of a turn. Not much rotation. You can grab the rotor with the engine off and the dist cap off, and see how much it rotates and how the springs fight it.

Some racers will run a lot of initial advance, so much that it won't turn over in a high comp. engine. The fix is a cutout switch that disables the ignition while cranking, the engine is then turning fast enough to light off and the switch is released, engine starts, etc.

Some of the hot rod aftermarket ignitions have a start/retard function. When cranking it retards the timing. Many people don't realize that a true Motorcraft Duraspark ignition box also has a spark retard feature to it. That's why there is a red/blue wire going to the ignition module.

ive got this problem on my ‘68 460. thinking about putting an electric vacuum shut off valve inline with the vacuum advance and hooking positive to the s output on the starter solenoid, thats usually used for more amperage for ignition during cranking. theoretically, it should crank fine until she fires and the starter stops and than it runs better… right?

If you have the vacuum advance hooked up like most are, there is no vacuum at idle to the distributor, only when the throttle is pressed open.