Hi folks,

Well, after several months of driving my poor Lancia Y10 around after never having quite fixed the problem (I posted a thread about this a long while ago), I finally took it in to a Fiat dealer for diagnosis. 1 hour of work and he'd found the problem - the butterfly potentiometer (at least that's the translation from French).

The symptoms were:
1. poor idle, especially in cold weather... means it could stall often before warmed up... the little solenoid to raise the idle when cold on the injection block (sorry donno the name) wasn't doing anything, unless it got a little push with the finger...
2. a nasty acceleration hole after travelling for 20+ minutes on the highway... or after having driven and then stopped for 5 to 60 minutes. Sometimes this problem would show up, sometimes not at all... very pesky! Closer inspection revealed that the injector's spray became very non-uniform (yukky) in this region of rpm.

So experts, does the butterfly poteniometer seem like a suitable cause for these symptoms?? I'll never quite trust a mechanic if he's not my friend first!

They say only the whole injection block can be replaced... which costs 900 Euro!!! I'll trash the car before that... but can only the potentiometer be replaced?????

A little info: it's a 1990 Lancia Y10, 999cc Fire engine, about 150000kms on the car, the engine has 125000kms cause we swapped it out with another (which by the way had the same problem... a defect in Fire engines???)

Any help would be apprechiated!!!!!!
Thanks!
Fatnote.

FatNote said:

They say only the whole injection block can be replaced... which costs 900 Euro!!! I'll trash the car before that... but can only the potentiometer be replaced?????

Click to expand...

My understanding of the throttle body potentiometers is that the official view is that they are set in position on the body during manufacture.
So I expect you'd have problems getting it/them as a separate new part.

Despite that, I think the Italian website mentioned in your earlier post does give some detail of setting it up, or checking if it is correct, and how to verify that it is OK. At least for the Bosch unit.



it might be worth seeing if we can find someone here who can do a technical translation.


In terms of symptoms caused by the potentiometers, think about what they are doing:
providing a steadily increasing voltage as you press the pedal, so that the ECU knows how much fuel to feed in.

If you get a noisey spot (think grotty volume control on an old radio) or a section where there is no voltage, consider what the ECU is going to make of it:
throttle goes suddenly shut - no fuel for you then!
throttle goes well open - lots of fuel...

I couldn't say if the faulty section would change with warm up, although I'd expect heat to have some effect on mechanical parts which are (barely) touching.

I don't know enough to say how the stepper motor is driven, but I thought I'd read somewhere that its position on a cold startup was determined largely by coolant temperature - is the stepper motor "sticking"?.

Perhaps they want to change the throttle body because it is the stepper motor, injector, and the potentiometers - all in one lump.


You can see from the picture that the two potentiometers work on different portions of the travel (with some overlap).
The second one is basically trying to be second choke on a twin choke carb..

Consider investing a few Euros in a voltage test meter, and introduce a couple of very thin bits of bare cooper wire into the socket, remake the connector and measure what is actually happening when the pedal is gently pressed (from one of your bits of wire to earth, then the other one).

For this kind of testing my preference would be an analogue meter, as it's not stunning accuracy in the voltage you're interested in, but sudden changes or variations.
IME cheap digital meters can be misleading in this situation, as they sample and hold, then resample and hold, etc, on something like a once or twice a second basis, and display the "held" voltage, rather than being a continuously updated display - so you might miss a small disturbance completely.


Regards


John H

Thanks John H!

Don't worry, i speak Italian, or at least a little. Otherwise my Italian buddies can do so.

I'll give it a try with a volt meter... no prob, i work in a lab so it's easy to get my hands on one.

So I guess the stepper motor is the thing I called a solenoid?? It's like a little rod that protrudes to boost the idle lever when cold. Ya, it seems it might just be a little sticky... maybe I can fiddle with it.

Ok. I'll let 'cha know!
Grazie!
D.

FatNote said:

So I guess the stepper motor is the thing I called a solenoid?? It's like a little rod that protrudes to boost the idle lever when cold. Ya, it seems it might just be a little sticky... maybe I can fiddle with it.

Click to expand...

Yes.

On my CLX you can hear the stepper motor run, on turning the key prior to a cold start.

The throttle pedal goes down a bit too (as the cable is a bit too tight).

I think the ECU just pulses the supply when warm up is under way, to alter the fast idle setting in "steps", from this "cold start" postion.

There is a lot of detail on that site, if you have the translation skills you'll be well ahead of the average mechanic

You can buy the potentiometer on its own for slightly more reasonable €60.

Mmm...that intake manifold doesn't look like the Y10's 1000 one :nono: ...anyway...if anyone needs a quick translation I'll be glad to be of (little) little help .

That potentiometer applies to the later and larger Y10 ('92 onwards) engines -for the Panda this is a better pic.

Hi Martin,

I think your first posting relates to the microswitch which is "throttle closed".

This is a different part of the throttle body assembly, and not the "butterfly potentiometer".

Post number 8 is the one to look at:
if you look closely at part 4 (the body itself) the line from the number 4 nearly points at the potentiometer socket.

John H said:

My understanding of the throttle body potentiometers is that the official view is that they are set in position on the body during manufacture.
So I expect you'd have problems getting it/them as a separate new part.
John H

Click to expand...

is almost the case, in that you can get stepper motor, injector, ATS, microswitch, etc, but the body comes with the potentiometer.

The item "sensor" at the bottom of post 8 is the air temperature sensor - it plugs onto the top of the injector.


Regards


John H

John,

You have shown up my ignorance of the SPI system. I have updated the picture above.

The price new is very steep.

Thanks for the update, Martin.

That price is horrific - I bet Bosch don't charge that much for them.

I suspect this sort of pricing is to kill off the repair of older cars, and/or make some profit, as the margins on news cars seem a bit slim. (you can get a brand new 1108 Panda for about 5300UKP if you shop around).

Here's hoping the throttle body on my Panda holds up a bit longer...
on my (2 year old) CD I've finally navigated my way down to the relevant section, and the body (same part 9944564) comes up as 525.10 UKP including VAT.