special tool

Luis - I beleve that Loren is developng a system for 944/951.
He is dong research by attacking the pride of TT (what better source) - whom he guilts into giving VALID informaton because TT feels sorry for him.

I don't like the way he does this, and I have seen him do it before in other forums.

These are just my opinions, of course. Time will tell...

Luis de Prat

And valid opinions they are, from a respected Rennlister. Good to know.

Lorenfb

"We appreciate your expertise. Specifically, when "we" say Throttle Position Switch or TPS, we are referring to the part pictured below. What do you call it?"

That appears to be a standard idle & WOT switch unit as used on most Motronic systems, i.e. 0 ohms when closed (a click), & infinite ohms when open.

944

This uses an idle switch & WOT switch combined into one unit as shown.
The outputs from these go to the DME pins 2 & 3, respectively.

944S

This uses an idle switch & WOT switch combined into one unit as shown.
The outputs from these go to the DME pins 52 & 53, respectively.

944 Turbo

This uses an idle switch & WOT switch and a TPS combined into one unit.
The outputs from these go to the DME pins 2 & 3, respectively. The TPS
outputs go to the KLR pins 21, 22, 23.

968

The TPS input is DME pin 53. No need for a idle or WOT switches as on the early
cars, as all info comes from the TPS element.

"I told you, I have your number." - special tool -

Really! Please. So who's this guy who hides behind a "no name" from nowhere.


Bottomline: The DME has a switch inputs element and the KLR has a true TPS input,
i.e. a varying voltage input

special tool

I do not understand this recent post.

Everyone on this forum refers to 120 400 as "tps" - which clicks.

If you are the minority, then please use the same language to elliminate confusion.

Lorenfb

Please read the Porsche Manual (944S - WKD 494 121) page 2-22.
Porsche refers to the idle switch and WOT (pins 52 &53) switches as "The Throttle Valve Switch"
and NOT a TPS. This is as I mentioned above.

Then read 944 Turbo Porsche Manual (WKD 453 920) page 19.
Porsche refers to a real TPS as "Throttle Valve Potentiometer" which
also has switch contacts for the idle switch & the WOT switch.

After that, read the 968 Repair Manual (WKD 482 820.06) Sheet 5.
There you'll see a true TPS as the DME input to pin 53. The TPS
is called a "Throttle Valve Potentiometer".

Finally, read the Bosch Motronic Technical Instruction Manual
"Combined Ignition & Fuel Injection System with Lambda Closed-Loop Control"
page 9 and see element (same as image posted above) #15 designated as
"Throttle-valve Switch".

Check out this web site ( www.systemsc.com/glossary.htm ) under TPS.
Again, a true TPS is NOT a switch type element, it's a throttle position sensor
(TPS - as used by most/all OEM car manufacturers)!

Call it by it's true function; TVS - Throttle Valve Switch or TBS - Throttle Body Switch.
Reserve the TPS for the KLR element used to provide throttle angular position.

hmd

my BAD its pin 22 on the KLR white/green.

pikey7

Guys, Look, I think we can safely say that everyone on here calls it a TPS, even though Porsche may refer to it as something else. The bickering is not helping though!.

All TPS' that I've seen have a click right at the end as a switch to definitively turn off the unit to give 0 output, this is why the "click" should be as close to the on/off mark on the throttle as possible. Once it gets over this "click", then it acts as a potentiometer sending the correct throttle position (hence TPS) to the ECU so that it can work it's magic with the right fuel/Air/spark/advance etc settings.

HMD, thanks for the graph. It seems I'm not far off. Does your Idle wander at all. I'm only talking maybe 100rpm.

jimbo1111

The click that everybody hears is a micro switch that closes a contact to the isv. Without it the engine would stall or drop below desirable rpms when the gas peddle is released and throttle closes. The Idle maps are referenced through the tps but it's not on the same circuit as the isv.

Lorenfb

"The click that everybody hears is a micro switch that closes a contact to the isv"

So if you're checking the idle switch, pin 2 of the DME, don't rely on a "click" as
an indication of the switch's closing. Use an ohmmeter to make sure. When checking
for the proper functioning of the TPS input to the KLR, use a voltmeter to to check
the voltage at pin 22. It should increase from about .40-.50 to over 3.5 as the
throttle linkage is moved from idle to WOT.

You can check the functioning of the DME idle switch input by grounding
pin 2 and then accelerating the engine, the RPM should not increase over 1200 to 1300 RPMs.

hosrom_951

Loren: I understand you're point about the "switch" vs "sensor" and the clicks, but the clicks are just for alignment purposes, NOT for testing, voltage and resistance readings

I understand that you are basing the TPS (both switch and sensor) from an electrical backround, but they need to be properly aligned physically to the throttle body

AL951

I think Loren is correct.....In oder to adjust it correctly you would need a voltmeter to get it right. And yes it is a TVS and a TPS in one unit, and they are their to perform diffrent fuctions.

Lorenfb

"I understand that you are basing the TPS (both switch and sensor) from an electrical backround, but they need to be properly aligned physically to the throttle body"

Agree! But the electrical fuctionally needs to be tested & not assumed.

hosrom_951

By both testing the actuat switch for resistance (0-10ohms when throttle is closed and infinity when open) and from the KLR as well

When the switch on my car failed, it still clicked, thus it was physically aligned correctly, but was giving incorrect voltage/resistance (didn't check then).

The most common fault for the throttle switch is due to mis-alignment, again, this is the most common, not always the case as you (and several others) stated

shaheed

it's pretty transparent special tool, you aren't the only one that's noticed. i think most people in this forum are aware of the depth of TT's knowledge about the 951 electronics.

Lorenfb

A good text for many to read is the "Bosch Fuel Injection & Engine Management"
by Charles Probst (SAE member). Also, the Bosch "Automotive Handbook" (3rd edition)
is very informative. For those interested in more recent Porsche technology, the Porsche
DME 7.2 Manual - OBD II (WKD 483921) is another good read.

For those that are DIY types, get an old DME unit and apply power
to pins 18 & 35, ground to pin 17. Then use a sine wave signal generator
to apply a speed signal to pins 8 & 27. Use a differentiated square wave applied
to pins 25 & 26 (ref signal), and you'll have a functioning DME unit to "play" with.

Use this approach to fix your own DME problems.

For those software types, "read" the EPROM as a binary hex file
and save it on your P.C. Then use the MS DOS DeBug program and
you can disassemble (list the 8051 code) it and figure out what
the DME is doing in your 944.

No real mystery to the 944 DME, it's very very simple technology you
might find in a high school electronics class. So let's not over rate
those that appear to be knowledgeable about the DME operation.
The 996's technololgy with OBDII and the immoblizer gets a little
more involved.

Bottomline: The 944 DME design is over 20 years old now and many
(like lots) have "hacked" it. So there ain't any real 944 DME gurus,
just some who think they are, as is obvious from this forum.