Manual High Idle/Advance

[ManBearPig]

The used truck I just bought has a rocker switch that the previous owner told me was for a high idle. In order to engage the high idle, I can turn the switch on, rev over 1k RPM, and the idle will stay right around 1k RPM until the switch is switched back off. I thought it seemed a little strange when it was described to me but shrugged it off.

Now that I'm reading on here, it seems as though this must somehow be tied into the high idle/timing advance? In it's original state, is this used for cold start only? What does it advance? And is it an automatic deal that is somehow based on temperature? I'm just wondering how it is supposed to work and what it really does and see if maybe I should look into getting rid of the switch assy?

Thanks

 

[79jasper]

Visit Gary's (icanfixall) recent thread.


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[ManBearPig]

Thanks for the direction. From that thread it looks as if it is supposed to be an automatic feature based on water temp. I did some poking around under the hood and found the high idle solenoid. It is wired straight into the cab to the swtich I have, so it must bypass the water temp sensor completely. Now I'm curious....How can this advance anything? Theres no ignition to advance so I assume in this context, the advance is to the IP? Although that wouldn't make much sense either... When working as intened, is there another sensor somewhere that handles whatever advance there is?
Thanks

 

[79jasper]

Nope, same temp switch behind the tstat.
And it works in the IP. (going off memory so I don't have to open my pdf's. Lol) iirc, when the timing advance is activated, it fully opens the return port, which lowers internal pump pressure, causing a advance in timing.
Is the toggle switch tapped into the factory wiring? Or have it's own dedicated wire ran?
If it's tapped in, it'll back feed power to the timing advance.
May have hooked it up like that to just use as a high idle.

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[OLDBULL8]

Some hooked up the Hi Idle like that to keep the engine cool when having the AC on in hot weather when parked with engine running. AC works better.

 

[laserjock]

I think I've also read discussions where it was used to keep them from wet stacking if it was idling for long periods. If it was done right, there is a diode to keep it from back feeding to the cold advance so that it's not messing with the timing after its warm.

 

[79jasper]

^ Correct. But how often do you see it done right? Lol

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[riotwarrior]

I am working on a manual cable high idle for winching and so forth.

I have a locking T handle throttle mounted up it is now just the IP end to contend with.

 

[laserjock]

^ Correct. But how often do you see it done right? Lol

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Doesn't everyone do everything correctly the first time every time?

 

[79jasper]

Precisely. Lol


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[ManBearPig]

I wouldn’t be the least bit surprised if this wiring weren't done "right". Coincidentally, right after I started this thread, the high idle and manual glow plug switch both stopped working. I took a look at the rats nest of wires under the dash and it looks like…well, a rats nest. I wiggled the wires around and both the high idle switch and glow plug switch started working again. I traced it back to a loose connection in the wire going to the GP relay (with is also the 12v source for the high idle switch). Previous owner just had it twisted by hand with electrical tape wrapped around the connection.

Needless to say…I'm going to rip out everything they did and start over. The high idle solenoid has been spliced into under the hood and has a single wire running back to a switch in the cab. If the switch is just going to the idle solenoid, does that avoid the IP timing advance? It would, right? Since there must be a separate temp sender that is not tied into the high idle solenoid at all, the high idle and IP advance should be separate when wired like this, right? If so I'll replace what he had done, but do a better job with the connections. Or am I missing something with my logic?

Thanks again for the info. You guys have been a wealth of knowledge.

 

[laserjock]

Sounds right. If the high idle solenoid is just connected to the switch you speak of and nothing else yes. I guess the question remains how is the cold advance hooked up? Is it still in line with the temp switch? If you wanted to put it all back "stock" and keep the high idle option in the cab, you could run a wire between the cold advance and the high idle with the diode in line so that you can't back feed to the cold advance from the high idle. There is a write up in the tech articles if that tickles your fancy. Nothing wrong with skipping it though either if that's how you want it.

 

[fuzzy1626]

This is how mine is hooked up
http://www.oilburners.net/articles/high idle override.htm

 

[ManBearPig]

I don't think the cold advance is hooked up anymore at all. I know the idle is no higher when cold than it is when hot unless the switch is flipped. I'll have to poke around more and find out. Thanks for the link.

 

[fuzzy1626]

You should be able to tell if the advance is hooked up by the sound of the engine on a cold start. It should sound like an early Power Stroke until the advance cuts out.