ECU and MISSING throttle switch contacts...WHAT HAPPENS?

To all interested a/o concerned!)

Dear dr. D-Jet (Volker),
while sending you my very sincere Merry Christmas wishes I do take the chance to ....challenge you (if you will deem it interesting and useful....!) to clearly explain the...joint work of the MPS and the throttle switch during a strong, quick acceleration!
I refer to my Lancia 2000 HF coupè 1972 car, equipped with D-jetronic injection system, currently having troubles when a strong acceleration is requested, generally in 3rd gear. :the speed drops at about 3000 rpm!
It is, of course, clear to me that, when all D-jetronic parts...do work...the result is ok but what does it happen when (in my opinion the responsible....number 1!) the throttle switch .....misses 1 or more contacts (signals) to the ECU?

To me it is not only a curiosity...it could help other people when meeting with this problem....!
To me the ECU...gets confused and .....having to immediately decide what to do...(perhaps it was not prepared to such an age problem, unusual event...you know, the germans think of perfection only....troubleshooting was not practised in Germany at those times....!) does not ...tell the jnjectors to stay open a longer time!
On the contrary.....1 or more than those 20 rotary contacts missing....means (to the ECU logics!) that there is not a great fuel demand!
This would explain all....

Maybe this technical explanation, even in simple words, is not so easy to be found/made but I am sure that a good connoisseur of D-Jetronic, as you certainly are......can do it!

I do think that it would help very much....with the current knowledge of technologies, past and present, a clear and well made description of what ECU and throttle switch do perform in tandem (sequentially, contemporarely?) when such a demanding situation occurs (strong, sudden acceleration) should be possibly, hopefully available to us, poor creatures in the hands of...Bosch D-Jetronic!

By the way, thanks God, I got a nos throttle switch and a used but apparently working MPS...next year in spring..I'll know more....!

Best regards and deepest, sincere thanks in advance
Bruno
Ferrara
Italy

Hi Bruno,

that is an easy explanation. When the throttle switch signals 0-12V and 12-0V on both acceleration contacts, then it reads them and tune the pulse width modulator to broaden basic injection pulse more. When single or all such signals are missing, this enrichment won't happen. That should limit the car's acceleration but it should not lead to rpm falling down. You should be able to also run the car with the electrical connector being removed from throttle switch. All that causes is a worse idle-run and a worse acceleration performance.

What often happens is that the 2x10 contacts in throttle switch get dirty and cause more than the 10 pulses. In that case you would notice it while cruising at same speed that the car starts to have a sudden up and down in rpm. Also there it is a good idea to just remove the connector on throttle switch to verify whether it creates fake impulses.

In your case of a dropping rpm it more sounds like a wrong fuel / air ratio and the engine has no power to take the load of acceleration at all.

Wishing you also merry Xmas.

Hi Bruno,
one more remark:

The TPS is called throttle position sensor, but it only gives the position informations 'throttle closed' or 'throttle not closed' to the ECU. (On some other car models also the information 'full throttle', but not at the Lancia).
In fact, it is only a dumb switch with the additive acceleration function - I would not name this item 'sensor', just 'switch'.

As Volker wrote before, missing rotary contacts only have a short time effect at acceleration.
The ECU doesn't count the contacts or so. The ECU doesn't get any information about throttle position in real driving situation - only at idle.

Missing engine performance other then in acceleration must have another reason than the TPS.

Regards
Norbert