Cold Weather Modulator

[Mark_88]

OK...timing needs vacuum line disconnected in case you're not familiar with these setups. I found simply rotating the distributor slightly often cleared up idle problems. Like my Motorcraft 5200 carb didn't idle good at 850 rpms or lower but idled fine slightly higher. No stumble and no hesitation at all but I never did nail down the exact rpm number due to not having a tachometer.

 

[bilbo]

Yep, I had it off when I set it the first time around. I'd like to see if the vac advance is doing something different when hot vs. warm vs. cold. The thing will idle beautifully after a minute or two of warmup, and when just warm from pootling around town. But after a stretch of highway or real hot weather it goes to pot. Maybe after running for a while the carb has cleaned out a bit and the mixture needs adjustment again? We did mess with it when tuning after the rebuild but it hasn't been touched since.

 

[bilbo]

I may have resolved this. Timing was ok, doing what it was supposed to. My neighbor recommending checking out the vacuum diaphragm on the solenoid that sets idle speed (I think it's called TPS in my books and TK on the vacuum diagram). I think the diaphragm is for the air conditioning system to raise idle speed slightly when the compressor is on. The diagram under the hood shows its lines as "A/C only." The vacuum line to the diaphragm comes from a thermostatic valve that seems to shut off vacuum when warmed up. I connected the TPS diaphragm to manifold vacuum and it seems to idle the same now regardless of temperature so far. I could probably disconnect it completely and just use the adjusting screw on the solenoid to accomplish the same thing. I'm still testing to see if this is really the issue.

 

[Mark_88]

Well that would be nice to add to your list of 'done' things...and if you have a chance, document it or take a few photos and post up because it's another new one to me and might help others.

I've never had A/C or even power steering on my Rangers so anything to do with those systems is beyond my current radar for troubleshooting...

Appreciate the update...