Cold Timing Advance not working

[ManBearPig]

I haven't noticed any adverse symptoms from this, but I've determined my IP timing advance is not working. I didn't even know the truck was supposed to have an advance until I started digging around these forums....dangerous place!!!

I replaced the thermostat in the truck yesterday and realized that would be a good time to mess with the temp switch/sender. I had already confirmed that with the ignition an and engine cold, there was no power to the advance plug on top of the IP. I figured that pointed to a bad switch so I was going to replace it while it was easy to get to with the stat housing out of the way. I pulled the old switch out and tested it, and to my surprise It tested good. The two poles of the switch have continuity when cold, but lose continuity when heated over a boiling pot of water. After the switch cooled down continuity returned. I did this several times to make sure. So I put everything back together and I'm still not getting power to the plug on top of the IP. Weird. Bad connection at the switch? I'm getting power to both wires coming from the switch. The only logical explanation could be a bad wire connecting the switch to the plug atop the IP, right? I gotta say I'm not thrilled about this because that harness is encased in a nice factory loom, and difficult to get to. I guess my question is this....There are other wires intertwined within that harness. I'm wondering if the same wire that powers the cold advance runs anything else that I could test? The previous owner rigged up a manual GP switch and I'm wondering if they somehow intentionally (or unintentionally) disconnected (or screwed up) the timing advance? Is there any other testing I can do before I cut this harness apart looking for a damaged section of wire?

Thanks

 

[MTKirk]

You should only have power to one of the wires that connect to the switch. The other is connected to the advance and is hot only when the temp switch is closed (when engine temp is cold). The wires must be shorted to each other somewhere. I would un-plug the engine harness from the chassis harness, then test for continuity between these two wires. If you still have continuity, your short is in the engine harness.

 

[ManBearPig]

You should only have power to one of the wires that connect to the switch. The other is connected to the advance and is hot only when the temp switch is closed (when engine temp is cold).

Right. Truck sat overnight and engine is cold. With the ignition on, both terminals at the switch should be hot (which they are) and the connector at the advance on the IP should also be hot (but its not).

I think we're saying the same thing, or do I have it backwards?

Also, when you say engine harness and chassis harness.....I haven't traced anything that far back. Where are these at?
Thanks

 

[MTKirk]

Follow the wiring from the glow plug controller to the passenger fenderwell. There should be an 8 pin connector there that connects to the chassis harness.

But reading your latest post I think you should run a temporary wire from the switch connector (the one that is not hot when the temp switch closes) to the advance terminal. Then run another temporary wire from the always hot wire at the switch connector to the switch. If this temporary set up works normally, then I think you need to fix the wire inside the harness, you'll have to un-loom it to do it.

 

[laserjock]

I think I mentioned before, jump the cold advance from a key on hot somewhere else. This rules out any actual problem with the pump. Be careful though and make sure the wire doesn't get hot. It's conceivable there is a short in the solenoid that caused the wire to burn if in fact that's the problem.


You've got a bad wire or connection somewhere. Question is where and why.

 

[icanfixall]

That sender you found that works sends power to 2 areas at the same time. The cold electrical advance in the pump and the fast idle solenoid on the passenger side of the pump. Also found in that engine wire harness run is the wires to the tach sender found in the drivers side of the injection pump gear housing. It has the 2 black wires feeding it.

 

[ManBearPig]

I temporarily repurposed a switch I have in the cab to run the timing advance. It sounds slightly different when it advances so I guess it works. I expected a more dramatic change in sound based on what I've read. But it does something....guess I need to cut open that factory harness and find out what's going on.

 

[compressionignitionrules]

wow cold timing advance? all I have ever seen on the 6.9 7.3 idi motor is the power wire to the fuel on/off, and the cold high idle speed switch/solenoid. I learn more here the longer I stay . now I want to go back and read my 89 EVTM.

 

[icanfixall]

wow cold timing advance? all I have ever seen on the 6.9 7.3 idi motor is the power wire to the fuel on/off, and the cold high idle speed switch/solenoid. I learn more here the longer I stay . now I want to go back and read my 89 EVTM.

Look at my post count and imagine what I have learned over nearly 25,000 posts... And yes I continue to learn something new to me all the time reading the posts here.

 

[ManBearPig]

I've been in here a few weeks and have already learned more than I really ever intended...I didn't even know there was a timing advance either. It was only once I started poking around with a test light that I learned there is supposed to be one, but mine wasn't working.

I'm still surprised it isn't more noticeable. When testing mine I could flip the switch back and forth and hear a slight change in sound, but if not for that I'd never notice when it is or isn't advanced. I still intend to fix it anyway.

 

[ManBearPig]

Guess I should update this in case anyone comes across this thread while searching in the future.


I found out what was going on. I had to dig into the factory loom a little bit but not too far into it. The previous owner had rigged up a manual high idle switch, and completely cut both wires going to the high idle solenoid. It turns out, one of these wires is how the timing advance gets it's power. One I figured out how the harness was supposed to be wired, I put everything back to how it should be, but also tied in my high idle switch so I can also run it manually. I added a diode in the mix to prevent the timing advance from being triggered with the high idle switch, so I'm happy with how it turned out. The high idel and timing advance come on automatically each morning and stay on for about a mile. What is surprising, though...is that the high idle/timing advance do *not* come on after sitting at work all day. I guess 8 hours heat soaking in the 100* weather keeps the water temp over 120* all day, but it cools down below that at night. I'm sure that won't be the case in the winter...

 

[icanfixall]

Glad you were able to cut in and find what the previous owner fubared in the harness. It amazes me reading what some owners do thinking they are "improving" the wire harness in any rig.

 

[MTKirk]

I've been in here a few weeks and have already learned more than I really ever intended...I didn't even know there was a timing advance either. It was only once I started poking around with a test light that I learned there is supposed to be one, but mine wasn't working.

I'm still surprised it isn't more noticeable. When testing mine I could flip the switch back and forth and hear a slight change in sound, but if not for that I'd never notice when it is or isn't advanced. I still intend to fix it anyway.

If you lived where it got REALLY COLD, you would definitely notice a HUGE difference in how well it starts.