924Board.org

[MikeDanger]

Im trying to understand what the "TPS" does.
I have always had the issue of going Full rich, just off closed throttle. The A/F would come back after a second, but this made pulling away from a stop very sluggish!

Same thing happens at idle/parked, If I hit the gas it goes rich then comes back.

I tested it 2 ways: 1 I was coasting on a slight downhill that was just enough to keep the car from slowing down with Zero throttle. then I just nudged the gas pedal and A/F immediately goes to 10.

2: I have a spare throttle switch, so I disconnected the plug to the switch and the idle jumped a couple hundred RPM, but I was no longer getting the Full rich when initiating the gas pedal.
So I plugged in the spare throttle and actuated it manually. at idle when I moved it off the Closed throttle position the rpms jump (as they did when I unplugged it)

So I have semi figured out why I get the full rich....but obviously its not supposed to work that way I assume?

I got a smoke machine an checked for leaks. I was previously getting a leak at the side cover for the BOV on the turbo, but after putting a new gasket it made minimal difference, car ran slightly better, but didn't affect the going to rich on throttle)



(side note: A long time ago I clipped the wire for the WOT position as i was also getting A/F dipping into the 9's and the car would bogged down, on boost (13psi)

heres a pic of what it looked like inside

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[924RACR]

Any chance your wiring is bad or mis-pinned? Kinda sounds like you're getting the WOT enrichment from the wrong part of the switch, no?
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[MikeDanger]

[924RACR]

Holler if you need a hand with wiring diagrams; I have seen some nice diagrams, from what I remember, in the annual service update bulletins Porsche published, but those don't tend to be as widely distributed as the manuals themselves were/are...
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[MikeDanger]

im doubting its wiring. I mean the switches work.... its just why is the system reacting that way?

im considering the mixture setting. im going more off the A/F than the pressure readings BTW.

I always forget, which is the macro effect and which is the fine tuning. the Fuel meter of the WUR?

maybe it IS supposed to get a littler richer when you Tip in, but if its too much, where is that adjusted? I mean would leaning out the mixture screw adjust that (even though it would lean the entire range out..... and then i would increase the fuel flow at the WUR?)
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It was either this or a giant box of legos

[924RACR]

The fine tuning should be the Lambda valve... even the WUR is a pretty rough adjustment IMO.

To my understanding, there would be a switch to indicate when the car is idling - so that's the angle adjustment of the TPS, so that once you reach something like 3-5% throttle that circuit opens... this will allow the lambda system to trim fuel in closed-loop while the car's idling...

Then you have a WOT switch to tell it to dump fuel hard when you're at/close to full throttle (Wide Open Throttle)...

And in-between, it's most likely running in an open-loop mode, mainly managed by the WUR... so also influenced by boost/vacuum level...

So perhaps the issue is that your WUR is leaving you very rich during open-loop running, but the lambda system is covering at idle?

Have you gone through the process to set mixture at idle including disconnecting the O2 sensor and all?

I did find, after converting my car to EFI, that my stock air intake sensor was dead, which was an interesting finding... I'd been assuming the whole time that it was fine... but I don't remember if that affects mixture or ignition...
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[MikeDanger]

Well FWIW, I shorted the wires to the "idle" switch so the abacus always thinks its closed.

now it doesnt go rich when you crack the throttle.


also btw the 965 (later 964 911 turbo) uses the same throttle switch!
_________________
It was either this or a giant box of legos