Type4 - Temperature Sensor II Rambling

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luftvagon
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Type4 - Temperature Sensor II Rambling

Post by luftvagon » Mon Nov 25, 2013 5:57 pm

Interestingly enough, the stock location for Temperature Sensor II may not be the most ideal location for any temperature sensor.

Yesterday, after an hour of driving around, my recorded TSII temperature was 90F. The ambient temperature was 40F. When pulled over, idling at light, or parking lot, the temperature would go to ~110F. As soon as I start driving, it would drop top 90F, dipping all the way to 86F.... Rewind back to summer months, and my TSII recorded temperature was 120F or around 140F idling.

Granted, my sensor is much more responsive than TSII, however, that does not mean much....

What does it mean for the rest of the stock L-Jetronic crowd?

You may be running richer in winter, and leaner in summer. Are you? How is your MPG in summer months versus cold months?
1981 Volkswagen Vanagon Westfalia - air-cooled Type4 1970cc CV (hydraulic lifters, 42x36 valves, stock cam, microSquirt FI with wasted spark ignition)
1993 Ford F-250 XL LWB Extended Cab 7.3L IDI

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Amskeptic
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Re: Type4 - Temperature Sensor II Rambling

Post by Amskeptic » Tue Nov 26, 2013 10:28 am

luftvagon wrote:Interestingly enough, the stock location for Temperature Sensor II may not be the most ideal location for any temperature sensor.

Yesterday, after an hour of driving around, my recorded TSII temperature was 90F. The ambient temperature was 40F. When pulled over, idling at light, or parking lot, the temperature would go to ~110F. As soon as I start driving, it would drop top 90F, dipping all the way to 86F.... Rewind back to summer months, and my TSII recorded temperature was 120F or around 140F idling.

Granted, my sensor is much more responsive than TSII, however, that does not mean much....

B) What does it mean for the rest of the stock L-Jetronic crowd?

C) You may be running richer in winter, and leaner in summer. Are you? How is your MPG in summer months versus cold months?
You may be assuming that the values you recorded are an anomaly, but they are in fact merely an averaging of ambient vs combustion chamber temperatures. The factory TSII doesn't "care" WHAT the temperature is, it merely has to change resistance to reflect this one parameter for injection pulse width. The factory engineers were not idiots. They HAD to maintain HC limits at the bottom of the big cool-down hill (richen it as the engine cools!) as well as at the top of the big heat-spike hill (lean it!) and they had to address heat-soak prolonged idling (lean it!) and cold day cooling air chilling the fins (richen it!), they had to keep misfires to a minimum with cylinder walls and combustion chambers that could get too cold too quick. The factory engineers were not idiots. They got these engines to pass emissions requirements through the entire range of environmental variables, and the TSII did its part . . . as did the TSI.

All VWs cool dramatically on the downhills and warm up quickly on the uphills and the temperature of the cooling air, as you note, swings widely. Turns out, VW got caught big time with the D-Jet emissions on throttle overrun, the engines would cool so quickly during their injector shut-off period, that they would FAIL at re-light. So they reprogrammed the ECU to relight the cylinders at 2,200 rpm to get the cylinders warmed up again before you applied the accelerator for the next hill.

"my sensor is much more responsive" did you know that VW had to reduce responsiveness with the washer under the sensor as per the TSB? The TSII is just giving a relaxed reading of overall head temperatures, it is not the "combustion chamber temperature be-all end-all" reading. That is why it is carefully located for a little cooling air effect, a little combustion chamber effect, and your readings show a nice balanced overall understanding of the engine's day.

B) As a member of the stock L-Jet crowd, all I have ever asked of my stock L-Jet is that it responds to my requests for acceleration without hesitation no matter the environmental variables and give me a passable 16-19 mpg. This it does.

C) "You may be running richer in winter, and leaner in summer. Are you?" Yes . . . as intended.
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

luftvagon
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Location: Little Rock, AR
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Re: Type4 - Temperature Sensor II Rambling

Post by luftvagon » Tue Nov 26, 2013 11:52 am

Colin, thanks for the insight. I didn't say Bosch and VW engineers were incompetent. It was an observation and somewhat of a rant, because this is truly a bad place for a sensor with modern fuel injection that requires somewhat stable temperature.
1981 Volkswagen Vanagon Westfalia - air-cooled Type4 1970cc CV (hydraulic lifters, 42x36 valves, stock cam, microSquirt FI with wasted spark ignition)
1993 Ford F-250 XL LWB Extended Cab 7.3L IDI

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Amskeptic
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Re: Type4 - Temperature Sensor II Rambling

Post by Amskeptic » Tue Nov 26, 2013 12:28 pm

luftvagon wrote:Colin, thanks for the insight. I didn't say Bosch and VW engineers were incompetent. It was an observation and somewhat of a rant, because this is truly a bad place for a sensor with modern fuel injection that requires somewhat stable temperature.
It is NOT a bad place for a sensor when you DON'T GET "somewhat stable temperatures" with an air-cooled engine!

Modern fuel injection expects coolant moderated temperatures, big ol' water-jacketed moderating influence, like the gulf stream keeps Miami happy! But we of the air-cooled tribe are consigned to Siberian air-blasted cold and hot summers.
See what I'm saying? To the gulag!
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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