CIS Throttle Position Sensor question

[Jay Laifman]

Am I missing something? I am trying to see if my throttle position valve/sensor/regulator is working. I actually have a few of them. I have tried to blow in one of the ports, and turned the throttle position, but I never get air going through.

As I understand the throttle position valve, when the throttle is turned to either end (idle or WOT), it opens up the valve and lets gas through, thus reducing pressure, and richening the engine.

So I would think that I should be able to blow through when it is at idle or WOT. I thought failure mode was the valve always letting air through.

Is this wrong. Or does it just take more pressure than I can blow with my mouth?


The reason I ask is that I currently am not using the valve. I want to start using it again. So I want to make sure when I put one on, I put one on that is working. I recognize that if it was on the car, I could use the fuel pressure gauge to see if it drops/increases based on throttle position.

[edmayo]

I've only ever done it on the car, maybe try compressed air?

[Jay Laifman]

Thanks Ed. I will try some compressed air. In the meantime, I note that the throttle position valve is adjustable in its location. That is, it can rotate a little. Do you know if there is any factory procedure for setting it?

[edmayo]

Yes, procedure is in the shop manual, dependent on fuel pressure gauge hooked up.

[Jay Laifman]

I have a number of volumes, but I don't recall having a CIS section. I'll check. Thanks. I do have the Trouble Shooting Guide. But it does not address this.

[Jay Laifman]

Well for good or bad, copyright infringement or not, I did just find it online.

This is what I found: http://www.type17.ch/downloads/Injec...p%20Manual.pdf

Here is what it says. Doesn't actually say if there is a specific intent with the few mm adjustability. Maybe it's just to make sure the throttle has full rotation, to both idle and WOT, and the valve doesn't prevent that from happening.



Warm Control Pressure WITH Throttle Activated Valve:Test warm control pressure with the warm-up regulator plug attached. Position throttle plate against idle stop.

Switch the ignition on to run the electric fuel pump. When the pressure stops increasing, read the warm control pressure on the gauge . If the warm control pressure is not within the tolerance given for idle on the test sheet, remove both fastening screws on the throttle activated valve and turn the valve in the area of the slots. If the idle value cannot be obtained, replace the throttle activated valve and readjust to the value given for idle on the test sheet.

Position the throttle plate by hand about halfway . If the pressure does not rise to the partial load value given on the test sheet, replace the warm-up regulator.

Completely open the throttle to the full load position. If the pressure does not drop to the full load value given on the test sheet, replace the throttle activated valve and recheck the idle pressure.

If the warm control pressure does not fall within the specified tolerance, test the supply voltage (approxi- mately 14 volts) available to the warm-up regulator.

If sufficient voltage is available to the warm-up reg- ulator, and the warm control pressure still does not fall within the specified tolerance, check the vacuum source for a leak.

If warm control pressure cannot be brought into specification, replace the warm-up regulator.

[Jay Laifman]

Following up. Now that the Throttle Position Valve is in, I can see that the adjustment possible in the small slots for the Valve does not impact the start or end of the butterfly. So the adjustment of the Valve is not for that purpose.

From a separate thread, I have been adjusting the CO adjustment and got it at a great spot. Everything works great now. Solid idle, smooth running. 1/8 turn either way makes it worse. The only possibly negative thing I have is at light throttle, cruising with light load, I can get a slight flutter. Since it's just off idle, I'm now thinking that the Throttle Position Valve adjustment might be to adjust just how far off idle the Throttle Position Valve makes the mixture richer. So does anyone know if that light flutter is a lean condition or rich condition? I will put on the pressure tester and see where the throttle is when the pressure goes back up.

And FWIW, I did get a smoke tester and found I had zero smoke leaks - except minor smoke out of a couple of injectors. I suspect those are built to seal under operation, where they would have vacuum, as opposed to under smoke test, where they have pressure.

[Jay Laifman]

I am circling back to this thread. I finally solved that minor flutter on light throttle. My throttle shafts were leaking. I did not notice it on earlier smoke tests. A couple weeks ago, I did notice it. And of all things, I had an extra throttle body laying around. I swapped it in and presto-chango and it made the flutter go away!

Now the only thing left is the delayed starting when warm (that is not vapor lock - after lots of experimenting, I now see it does start all the time, as long as I leave off the cold start valve and let it spin until I get any attempt at ignition, then I pull the hand throttle and it starts right up). The ONLY thing that I have not changed on the entire system is the fuel distributor. It apparently can cause hard starting issues - and my symptoms seem to match the problem the FD has. I now have a replacement and will be swapping next weekend. We'll see if that solves it.