aggravation

If the car is running and you disconnect the TempII sensor shouldn't something like the AF ratio and/or idle change?

I've checked the reading on both legs of mine numerous times, both at the sensor and at the LH and EZK connector and also both with the engine cold and hot and the resistance is always within spec but disconnecting mine has no influence on the way the engine runs.

Tom. M

When I had probs with my Temp II it manifested itself on start up only. Would fire up fine, but if not fully warmed up before shutting the car off, it would be too rich and wouldn't restart until it cooled down again.
I suspect it is out of the loop when running warmed up (controls cold start map), and the O2 is controlling the mixture.

worf928

AFAIK, the Temp-II is what feeds the warm-up enrichment map. So, once the temperature reaches a point where the maps indicates no enrichment then the temp-II should be out of the loop. IIRC it's 50-60° C on the stock map.

aggravation

That's kind of what I'm looking at. I'm assuming the ignition maps also get filtered out depending on temperature the way the fueling maps do.
In the SharkTuner, in the ignition maps, even when the car is over 90 degrees centigrade, changing the idle warm up map affects my idle. I would have thought that wouldn't be possible if the computer and sensor were really on the same page as far as the engines temperature....
I'm making assumptions here but it seems like my car is adding timing and/or fueling to the mix from maps that shouldn't apply due to the fact the engine is beyond the temperature within that particular maps range.
Maybe all the maps are always in play cumulatively contributing to the overall mix regardless of temperature.

I know this, sometiomes when I start my car, for a minute the idle is good and then there is a sudden increase in idle along with a brief puff of dark smoke out the pipe as if something took over and added fuel. The idle goes up and the O2 sensor holds the ratio in line but now I'm idling at an extra 400 rpm...

Either that or my impossible to find false air leak is on a time delay

worf928

IMO, there's no point in trying to isolate your air(?) issue with a running engine that is not at or near operating temp. There's too much "stuff" happening in all the maps until the engine's at temp.

OTOH, if your logged data shows that weird, inexplicable, things are happening during warm up with the maps not doing what you expect, then you have something to look into. Off the top of my head, I don't remember exactly what maps are cumulative with other maps and what maps supersede during warm-up/idle. I'd need to refresh my memory with the ST manual.

worf928

I don't recall exactly, but, I DO know that there's an idle ignition map that operates when the idle switch is closed. Once the switch is open control goes to the cruise ignition map. I don't recall if there are temp-dependent ignition maps.

One thing to make sure of is if the ST is getting and using the right coding plug data. You don't post the year of your 928. If it is the digital dash variety, you may need to cut the diagnostic wire to the dash to get the ST to deal correctly with the coding plug - this was the case with my '91. I installed an inline connector for that wire so that it can be plugged/unplugged when using the ST.

Or force coding in the ST UI.

John Speake

As a general rule, a short or open circuit on temp 2 will default the fuelling to the 80degC value.

This would appear to be another of Porsche's get you home modes.

WallyP

John,

I really, really didn't think that I would EVER be correcting you!

Factory Workshop Manual, Page 24-115
"In case of interruption (inf. Ohms):
excessively rich mixture, engine will not run in warm state and cannot be started.

In case of short circuit (0 Ohm):
mixture too lean, no pickup in cold state.

In case of interruption, wires could be bridged for emergency operation of the car."

This would apply to the LH side of the Temp II sensor, of course.

John Speake

Hi Wally
That page is referring to the MY 84 LH2.2. Later LH2.2 for MY85 and 86 have different software and display the same behaviour as I described above. Also, all the 87 and later LH2.3.

I went and double checked this on my test bench today, before posting :-)

And yesterday I measured the same thing on a US 85 LH to assist someone looking for a lean, no start on an '85. He thought the probelm might be a short in temp 2.

It does make more sense to have the system default to mid range, rather than go excessively rich or weak.

I beive my test bench is giving the correct answer, but I am always ready to be proved wrong !