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Aseem, before you close your TPS back up, maybe consider adding a mechanical connection to those solder joints. After I had already re-sealed mine, it occurred to me that I should have wrapped a strand of fine copper wire around the joint and then flowed it with solder. Maybe I would get more than 31 years out of it this time!
“.As I vaguely recall the input terminal for each switch is on the same side as the final elements for that function- trust I have that correct.but would not bet my life savings on it. There was something that seemed a bit strange about the layout but for the life in me I cannot remember what it was.”
Fred, your memory is good regarding the electrical connections. I specifically added the picture with the correct labeling as a result of reading a thread mentioning a labeling error in the WSM. Now if MY memory serves me correctly, it was Rob Edwards who posted that info.
For those interested, here is a picture of the capacitor which is installed between the legs of the WOT switch.
Roger,
Excellent input- I could not tell from reading the wiring diagram which terminal was for the WOT and which for idle! The common earth cable was easy to fathom out!
My memory is such that I cannot remember where I put the damned thing I sectioned! Never spotted the capacitor and dare say I would not have known what it was even if I saw it. I only opened up the box to see what was in there rather than make any attempt to repair anything. Fortunately one of my ST2 mentors spotted my comment about the WOT switch seemingly not working and educated me as to the workaround. I had a spare switch and fitted that but on my ST2 fettled system I disengaged it in the software and use the cruise map for full throttle readings as it seems impossible to operate in that part of the map without being on full load. The ST2 software analysis programme "Sharkplotter" that Jim wrote tells us when the switch is engaged as it presents the data point with a bigger "dot".
Why they did not fit the micro switch to both sides is beyond me but so are most things when it comes to electronics. They must have had a solid reason for wanting a mechanical switch rather than rely on the rpm and load signals- maybe they thought they would get a slightly quicker response not using a feedback signal?
Why they did not fit the micro switch to both sides is beyond me but so are most things when it comes to electronics.
The single microswitch already presents extra complexity in setting up the cables. Imagine trying to adjust pedal and plate cables to trigger both microswitches. You’d likely have to have an adjustable pedal stop to avoid mashing the WOT switch into oblivion. And then you’d probably get to repeat the setup process every few years as cables stretched.
The single microswitch already presents extra complexity in setting up the cables. Imagine trying to adjust pedal and plate cables to trigger both microswitches. You’d likely have to have an adjustable pedal stop to avoid mashing the WOT switch into oblivion. And then you’d probably get to repeat the setup process every few years as cables stretched.
Interesting thought.
I take the point of view that they are both mechanically actuated and the critical thing is the accuracy of the span built in to the switch itself- neither of which is independently adjustable but a critical factor nonetheless given the need to ensure correct adjustment of the system before fitting the manifold when a new switch is installed. I consider the entire throttle adjustment system is non too clever given the switch is "non adjustable" once the manifold is fitted and as you rightly say cables do stretch eventually- thus the type of switch is academic and given a choice I would go for the one that is most reliable - personal experience suggests that is the micro switch contact- maybe your considerable experience is different?
I take the point of view that they are both mechanically actuated and the critical thing is the accuracy of the span built in to the switch itself- neither of which is independently adjustable but a critical factor nonetheless given the need to ensure correct adjustment of the system before fitting the manifold when a new switch is installed.
If I understand you, then yes. The arc the throttle plate must travel determines the location of the switches. The as-new plate cable could be adjusted to trigger both switches, then the variables become pedal cable adjustment, pedal stop and cable stretch.
I consider the entire throttle adjustment system is non too clever given the switch is "non adjustable" once the manifold is fitted and as you rightly say cables do stretch eventually-
But, the switch doesn't need to be adjusted except the one time, after that you never need to do it again, and it isn't that hard to do. The biggest issue seems to be that folks forget to do it. (But, they only forget once...)
thus the type of switch is academic and given a choice I would go for the one that is most reliable - personal experience suggests that is the micro switch contact- maybe your considerable experience is different?
There are two micro switches that I have to replace in my refrigerator every four years. So...
Also, do we know for a fact that the switches (WOT in particular) are the dominant failure mode? Above it was the solder? Yes?
Have we, without sufficient data, decided that since the WOT-side of the circuit dies first that it must be the switch?
We need a dozen or more WOT switch autopsies so as to get some data before deciding why the switch sucks donkey *****. The conclusion is not in dispute, just the mechanism of suckage.
Apologies but for whatever inept reason on my part I can never get the multi quote thing to work.
I think of the WOT switch as a weak link because mine failed and have seen what seem to be a good number of failures failures on the list. The idle contact micro switch have been to known to fail but they just do not seem to come up anywhere near as often as the WOT failure thus I wondered if you might have a different take on that having seen a lot more than DIY oiks such as myself do. I fully support the numbers option but we just have to run with whatever data we have- modest as it may be.
Indeed folks do forget to adjust the new switch- ask me how I know! Fortunately I had just plonked the manifold into position and was adding the grommets and nuts when I realised my mistake- 5 minutes later and it was all done and dusted.
The throttle system adjustment in general seems very fickle. Lost count of the number of owners I have advised to go check the cable adjustment when they had a idle issue- that or add a few drops of sewing machine oil where the cable enters the bulkhead- that often "works wonders".
Seems to me you need a fridge made in Japan- they last forever and nothing goes wrong them.
Even Porsche turned to Toyota for lessons in quality management and every time GB talks about his "measuring tools" the name sounds remarkably Japanese. Their flutes are also wonderful- I have a Miyazawa professional model flute- had it many years and it still plays perfectly with a minor service every decade- the same cannot be said for the flautist!
On the other hand a Japanese tool company once sent the British Aerospace Engineering Division a couple of drill bits claiming to be the smallest drill bits in existence. The Brits sent one back with a hole drilled through the middle of it- the other one is in their museum at Hamble [or was when I last saw it]!
Way expensive, for sure, but limited use part on a portion of years on a low production number car. Be glad it’s even available.
On the other hand, a pair of external microswitches might have worked (sorry, I guess they did that at one point).
I may have found a more cost effective alternative - working with Sean to see if it will do the job.
__________________
Does it have the "Do It Yourself" manual transmission, or the superior "Fully Equipped by Porsche" Automatic Transmission? George Layton March 2014
928 Owners are ".....a secret sect of quietly assured Porsche pragmatists who in near anonymity appreciate the prodigious, easy going prowess of the 928."
Aseem, before you close your TPS back up, maybe consider adding a mechanical connection to those solder joints. After I had already re-sealed mine, it occurred to me that I should have wrapped a strand of fine copper wire around the joint and then flowed it with solder. Maybe I would get more than 31 years out of it this time!
I think of the WOT switch as a weak link because mine failed and have seen what seem to be a good number of failures failures on the list.
Uh huh. Like I wrote: they suck donkey *****. Indisputably. Although some might think 12 years or 60k-miles (seemingly) mean is good enough.
The idle contact micro switch have been to known to fail but they just do not seem to come up anywhere near as often as the WOT failure thus I wondered if you might have a different take on that having seen a lot more than DIY oiks such as myself do. I fully support the numbers option but we just have to run with whatever data we have- modest as it may be.
Yes. I'd opine that 9 times out of 10 it is the WOT functionality that ceases to function.
However, I've always $h1+-canned dead idle/WOT switches. There was never a point in understanding the failure. Now that they've gone stupid-expensive it makes sense to understand the failure mode. And it makes sense to attempt repair, rebuilt, bionic enhancements.
Seems to me you need a fridge made in Japan- they last forever and nothing goes wrong them.
Find me - new - a small micro switch that isn't made in China. Then you can heckle.
Interesting post! While my intake is removed, I thought I'll check my TPS while it is accessible.
I do not appear to have a Bosch TPS. Mine has no branding, accept for a # 5078 08B and Made in Italy.
It also appear to have no resistance, whether for closed throttle or open. I measure by attaching my multi meter and turning the selector fully from one side to the other. It makes no difference whether I measure across2 and 18 or 3 and 18. I measure no resistance.
When the TPS is attached to the intake, I hear a click when the throttle closes fully.
My TPS
So two questions:
Any idea what this TPS is? And, am I measuring for resistance correctly?
From the post I would expect to read a resistance of under 10 ohm across 2 and 18, and over 10 across 3 and 18.
Any thoughts and advice will be appreciated before I open this up for a look.
With our injection systems, there's not many signals for the computers to change fuel and timing.
This switch provides some important signals to the computers.
If the idle side fails, the LH and EZK has no idea that the car is at the idle position, so it will never switch to those maps.
This makes for a unstable idle, usually always too rich.
If the 3/4 throttle side fails, the result is very lackluster performance, due to a lack of signal to the LH and the EZK, limiting fuel and timing.
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
03-31-2020, 01:52 AM
George Layton March 2014
