Wot switch

[Porsche 935]

I ohm'd my wot switch out. It shows contact about 7/8 through the range but the ohm readings fluctuate badly after contact. I took it apart, cleaned and adjusted contacts. Ohm readings are good now. Anyone ever use the jumper to set idle but rev the engine to 2000 rpm and check fuel mixture? I was told using the jumper is the same as the wot switch being engaged at idle, which would be normally be impossible unless you were driving the car. So, the jumper in the test port bypasses the idle valve and maybe the o2 sensor but this also puts the car in the wot fuel map. Now with the wot switch plugged in I seem to be in the wot fuel map all the time. Fuel mixture in neutral at 2000 rpm is 12.5, but remove the plug from the sensor and fuel mixture at 2000 rpm is 14.7. I think the wot switch is bad even though it ohms OK or maybe shorting to ground because if you drive the car for awhile you can plug the sensor back in and the fuel mixture will return to 14.7 at 2000 rpm and work fine until you park car for a few days and restart it, and after warm goes back to 12.5 unless you unplug sensor again. I don't see any new sensors for sale, anyone know if the wot switch for the 944 can be used as a substitute? Our host says there is a small circuit board in the sensor but all I saw was a set of points. Any help is appreciated.

[Porsche 935]

Lots of views but no answers. Anyone running a wideband sensor in addition to the regular o2 sensor willing to put in the idle jumper wire and tell me what air fuel mixture they get at 2000 rpm. This would help me rule out a problem with the DME unit. And can anyone tell me if the wot switch part number changed between 84 and 89. Appreciate any help.

[E Sully]

According to the Bentley manual, the full throttle switch should show no continuity from pin 3 to ground till full throttle position is reached.
There is no circuit board, just a set of contacts.
I would also check the cylinder head temperature sensor if mixture seems incorrect.
I'm not sure how testing with the jumper in and revving to 2,000 works since this might be affected by opening the idle switch on the throttle plate.

[Porsche 935]

Thanks for the reply but all the necessary tests have been done and all other sensors work perfectly or have been replaced. Down to the final issue which is the wot switch. Really need someone with a separate wideband o2 to confirm my findings. I spent many years as a Porsche tech, but never ran into this issue. If you ever tested the fuel map change over you would know why I need this test done on another car to confirm my suspicions. Anyone confirm the wot switch part numbers or have one sitting on a shelf?

[Porsche 935]

Still looking for wot switch. Don't see one in classified. I have a few parts laying around, maybe someone wants to trade. PM me!

[Porsche 935]

Also it would helpful if someone could help me with the part number. Can't find a wot switch with part number the same as the one on my car and replacements seem to start with 944. Maybe they are available again but I'm looking under the wrong part number. Maybe they are all the same new for both the 944 and the 911.

[76FJ55]

Per PET the WOT switch on the 3.2 was 944-606-113-01 (84-86) and 930-606-119-02 (Bosch 0-280-120-309) (87-89). I would have guessed them to be interchangeable however when searching Pelican they do not list them associated with the opposing year ranges. I believe all the other parts of the throttle body assembly are the same so it would surprise me if they truly aren't interchangeable, but more research on that would be necessary before saying definitively.

Edit: for reference some of the 924, 944 and 928 also rant that same 944 part number.
It is interesting on the 911 it only uses that switch for the WOT contact and has a separate idle switch, where as the 928 (im not familiar enough with the others to say)uses both the idle and WOT contacts in that switch.

[Porsche 935]

When I spoke to pelican they said the wot switch had a small electronic board inside. But after taking mine apart all I found was a set of points and a diode inside. I also noticed the return spring wasn't really working either. If I unplug the connector from the wot switch I have no issues. But plugging it back in causes the ecu to switch into the wot map. It could be grounding out internally but not indicating that when doing the ohm testing. Trying to rule out the wot switch as an issue before sending ecu off for testing. I always wondered if the 84-86 was compatible with the mod made to the ecu to accommodate the Steve Wong chip. Maybe the 01 wot switch is no longer available and has been superceded by the 02 switch.

[Porsche 935]

And I would like the wot switch to work as designed so if there is ever another owner he won't have to figure this out or wonder why it is unplugged.

[Porsche 935]

Still looking for the switch. Auto Atlanta has a replacement unit for just over $100. The dealers want $600 plus. Need the one for 84 911 but no knows if later model unit is interchangeable. Any thoughts? Anyone have a used one laying around that doesn't have 200,000 plus miles on it?

[Porsche 935]

Anyone have any luck with a generic one, claims they fit all years, plus multiple Porsche's. But I find that hard to believe. On the other hand, if it's a on off switch, part number shouldn't matter. Ant thoughts or experiences?

[Porsche 935]

Pulled my wot switch off to verify part number and found it is a Bosch 0 280 120 309. So must have been replaced before because this is for the 87-89 cars. Don't know how old it is but I've had car 10 years. Can't find original under $600 so might take a chance with the same one. Anybody out there swap theirs with the Bosch one?

[Porsche 935]

After doing more research, found the 93060611002 has superceded back to the 94460611301. Can anyone verify if the Bosch number for the 94460611301 is 0280120308? Appears to come on certain year 944 and 928's. And still don't know what the change was and why they converted back. Pretty sure my Bosch 309 did not originally come on the car.

[scarceller]

If the WOT switch is the first gen type, then you can remove the cover and clean the contacts and possibly do minor repairs. What is actually wrong with the switch? Is it always making contact?

[scarceller]

And to answer your question on WBO2 testing. If the idle switch is open/unplugged and the WOT switch is closed/0homs the DME will always be in the WOT maps and you will see rich mixture across the board.

But if the idle switch is closed and the wot switch is closed this is special calibration mode for the Idle Control Valve. It parks the ICV at 10% open so you can set base idle speed at 900RPMs using the TB air bypass screw.

Hope that helps.
Enjoy!

[scarceller]

The WOT switch has 3 pins but only 2 are used. One is brown wire and that is always ground, it gets grounded at the main ground screw on intake runner #1.

The other pin goes to the DME and should ALWAYS read +5vdc if the harness is disconnected from the switch. Internally in the DME that signal line has a 5volt pullup resistor that pulls the voltage up to 5vdc. With the signal line at 5vdc the DME considers this as not in WOT mode.

What the switch does when it closes is it puts a solid ground 0vdc on that DME signal line. It pulls the voltage down to solid 0vdc. when this happens the DME goes into WOT maps.

So the very best test is to connect the switch and pull back the boot on the harness and measure voltage at the signal line. It should read 5vdc with switch open and 0vdc with switch closed. If you read from 1-4vdc at anytime in between that's an issue.

The voltage test is much preferred to just ohm testing the switch. You want to know exactly what the voltage is doing on the signal line. When not at WOT, throttle closed it must read 5vdc. Then slowly open the throttle till around 75-80% and the switch closes, the moment this happens signal line should read 0vdc or at least less than 400mv.

Enjoy!

[Porsche 935]

Sal, if I have my engine at 2500 rpm (idle switch open) and wot switch plugged in or open I have a rich condition across the board. If I unplug the wot switch I have normal fuel mixtures or 14.7 at 2500. But after driving it for awhile I can sometimes plug the wot switch back in and still retain normal 14.7 mixture either at cruise rpms of 2500 or in neutral reving to same 2500 rpm. Do you think my problem is with the wot switch or dme? Your help is appreciated.

[Porsche 935]

I did that test as per instructions from another member and the one wire had 5 volts and the other homed good as a ground. Started car and everything was working well. Next day started car and mixture back to richer across board again. So lost as to what is happening to ecu when sitting for awhile.

[Porsche 935]

I see no issues with wot switch.

[Porsche 935]

Can't seem to post photos.