1997 3.0 V6 Throttle Cable

[Bitwise]

Recently took a 2000 km trip this February the day after a 50cm snowfall and through -26 C weather through much of the journey in my 1997 Ford Ranger 3.0 V6. Only issue was at one point the throttle cable got caught and stuck half open. Sometimes when it's cold it sticks at just a little bit of throttle but quickly tapping the pedal fixes it.

This time I couldn't unstick it so I had to pull it over. I had some WD40 with me so I sprayed that on the cable from the top and the bottom, and through a crack in the sleeve over the cable about halfway down. After working it back and forth manually for a while it unstuck and I was on my way. The WD40 fix worked fantastic for a while but it gradually started sticking a little like it usually does. I'd like to take care of this just in case. Looks like they don't sell new cables anymore for my generation. Anyone know if one for a newer generation can be made to fit? Not too many of these in the junkyards around here. I might be able to find one, but since my cable isn't actually broken lubricating it properly might be the better option (and covering the crack in the sleeve). Anyone got any tips for how to best lubricate the cable?

Thanks!

 

[RonD]

Use silicone spray, WD40 dries out

Remove throttle cable at engine end and raise it up, spray the lubricant in and let gravity do its job, and work it back and forth same as before

Also check the back of drivers side head, there will be a ground strap from head to firewall, this is often left off after engine work, if its there make sure both ends are clean, no corrosion
Its the Main Ground for all cab electrics
If its not there then add a ground to firewall, from engine is preferred
What happens is the throttle cable inside the sheath can be used as a ground path and that dries out any lubricant over time

 

[Bitwise]

Finally got a chance to look at this again. Lubed throttle cable with silicone spray. Worked it back and forth a while and kept spraying more down the top. Cable moves very smooth now.

Didn't fix the problem entirely though. Noticed that if I slowly close the throttle, either using the pedal or manually via the throttle mechanism, it sticks partly open. The mechanism the cable connects to closes fully and can't be forced further, but the rpms don't drop down. Sounds like maybe the throttle plate isn't closing all the way. Tapping the throttle gets it to close again.

Anybody have any experience with this?

 

[RonD]

Could be the TPS(throttle sensor) is holding it open
Warm engine, shut it off
Unbolt TPS but leave it connected
Then start the engine and see if it REVs and then idles back down, no sticking
It will stumble when REVing, that's normal with no TPS
But you are looking for/at full throttle closure, not the REVing part


TPS is there to give the computer a "heads up" when driver steps on the gas pedal, the MAF sensor is way to slow to react to give instant throttle response
TPS does what the "accelerator pump" did on a carb, tells the computer to spray in more fuel instantly for instant REVs

 

[Bitwise]

Alright. Did that today. I have a bone to pick with whoever decided to use phillips head machine screws somewhere that will be exposed to the elements for years.

Was not able to reproduce sticking by reving the engine with the TPS unbolted. Drove it around like that all day without issue. Normally sticks just about every time so I'm pretty confident this narrows it down. Engine ran fine without the TPS. Maybe a little more sluggish that's it.

From what I can find online the procedure for testing the TPS involves probing the voltages. I'd prefer not to damage the wires so I measured the resistances and did a few calculations to get approximate results at fully open and closed throttle. Closed throttle is 593 ohms, which would be around 0.753V. open throttle is 3760 ohms which is about 4.78 ohms. Closed throttle should be 0.2-0.9V and open should be 3.5-4.5V. Looks like my open throttle is a little out of spec, but since I found it indirectly I don't think that's much to be concerned about. The resistance varied smoothly as the sensor was opened. The sensor also springs back closed very strongly so I'm not sure what the issue is. I'm willing to just replace the sensor if that's most likely the problem, but I'll also reinstall it and make sure it was installed correctly for a couple days to see if the issue comes right back.



593 3.76

 

[RonD]

Spec for closed Throttle is .69 to .99v
Wide open is 4.5-4.8v

The computer learns TPS voltage when its new or you reset computer, also learns IAC Valve voltages again

TPS is used for a few things
Its used like an "accelerator pump" on a carb, MAF and MAP sensors are too slow to use for instant throttle response
TPS gives the computer an instant "add more fuel NOW!!" when you step on the gas pedal, lol, so without it, yes, the throttle response will be sluggish

When coasting with foot off the gas pedal(TPS under 1v) the computer will shut off fuel injectors until RPMs are below 1,400 or so, then it will restart them at idle levels
This is actually one of the bigger fuel savings EFI offers over carbs, injectors can be shut off when not needed
Coasting in Neutral was OK with a carb, but with EFI its better to leave in gear with foot off the gas pedal, 0 fuel use

Computer does inject some fuel to keep the Cats hot but it ain't much

I use sewing pins to pierce wires to test voltages, doesn't hurt insulation at all

 

[Bitwise]

Used some pins to pierce the wires. Thanks for the tip. I measured 66.6 mV from sensor ground to the battery negative so looks like the ground is fine. All other voltages are measured with respect to the sensor ground and are within normal ranges.
* reference voltage is 5.03V
* closed throttle signal I originally measured 0.932V but when I moved the throttle open and closed each time it came back to 0.968V. Both are within spec for closed.
* I also measured signal voltage while running (vs just key on) and got 0.979V consistently at closed throttle. Also within spec.
* open throttle measured 4.58 V
* voltage varies smoothly between closed and open throttle
* TPS unbolted measured 0.47 V

This indicates that the throttle position sensor is functioning normally. I was not able to reproduce the sticking while testing it. This might have to do with the temperature being much hotter than usual today. The sticking seems to be worse in cold weather, and especially worse on first startup on a cold day. it usually seems to get better after a while but does not fully disappear. I first noticed the sticking in the fall (I got the truck at the end of summer)

Besides the TPS which seems to be working correctly, and the throttle cable itself which I confirmed to not be sticking and is fully closing is there another possible cause for the apparent sticking? I doubt it's something like a vacuum leak since it ran great with the TPS unbolted. No CEL is on either.