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Temp2 sensor unplug and runs.
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binger59
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PostPosted: Fri Oct 22, 2021 11:01 am    Post subject: Temp2 sensor unplug and runs. Reply with quote

Hey folks looking for some help. 84 1.9 slowly lost power after driving for 176 miles. Unplug the temp 2 sensor and fires right up. Plug in and it dies. Currently in VT rt17 at the Vermont skydiving adventures. Currently dead in the water.
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hdenter
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PostPosted: Fri Oct 22, 2021 11:22 am    Post subject: Re: Temp2 sensor unplug and runs. Reply with quote

What is it that you're looking for? Diagnostic advice, second pair of hands, some tools, a place to work...

Hans
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binger59
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PostPosted: Fri Oct 22, 2021 11:46 am    Post subject: Re: Temp2 sensor unplug and runs. Reply with quote

Sorry for being vague. I wanted possibly a workaround… having owned one of these things for the last 25 years it was just wishful thinking I guess. I have a friend bringing a brand new sensor from Burlington. Fingers crossed, I’m confident that’s the problem consider the trouble shooting I’ve done. Thanks for letting me vent I suppose.
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jlrftype7
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PostPosted: Fri Oct 22, 2021 12:19 pm    Post subject: Re: Temp2 sensor unplug and runs. Reply with quote

binger59 wrote:
Sorry for being vague. I wanted possibly a workaround… having owned one of these things for the last 25 years it was just wishful thinking I guess. I have a friend bringing a brand new sensor from Burlington. Fingers crossed, I’m confident that’s the problem consider the trouble shooting I’ve done. Thanks for letting me vent I suppose.
If you can a spare resistor that's the right value, you could wire it in as a substitute Temp sensor value for a hot engine spec. But, since you have a new actual sensor on the way via that friend, let us know how you make out.
A Decade Box is starting to look like a nice tool to keep in my Vanagon if I lost a temp sensor suddenly. [Decade box is a premade set of resistors wired up on a board with switches, you can select or add values to create your own resistance value for testing. Handy for Gauges or other troubleshooting]

Just one example out there for a Decade Box: This one has its own alligator clips and wires, so you only need pins that match what ever connector pins you're trying to tap into, or even paperclips unfolded in a pinch

https://www.tequipment.net/ElencoK-37.html?Source=...=3d4effdd6
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danfromsyr
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PostPosted: Fri Oct 22, 2021 12:29 pm    Post subject: Re: Temp2 sensor unplug and runs. Reply with quote

I'm not exactly sure but iirc you can unplug the sensor and GND the signal
ie. cross the 2 terminals with a paperclip
and it'll run rich but will run..

would have to possibly unplug the O2 as well so it won't try to over/under compensate and create a bucking scenario.



here's the test values if you have a VO meter
https://web.archive.org/web/20150225033333/http://www.vanagonparts.com/sensor_tests.html

Coolant Temperature Sensor
Application: Measure resistance between terminals No. 2 and 7.
Temperature °F (°C) 122 (50)
Ohms 800-1000

Temperature °F (°C)176 (80)
Ohms 250-350

Temperature °F (°C) 212 (100)
Ohms 100-200

page 27 of the digijet manual

http://www.gmac999.com/Downloads/digijet_fi.pdf
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binger59
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PostPosted: Fri Oct 22, 2021 2:08 pm    Post subject: Re: Temp2 sensor unplug and runs. Reply with quote

Sensor didn’t work van just turns over. Not flat bedding it to Craig’s vw repair.
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Wildthings
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PostPosted: Fri Oct 22, 2021 3:06 pm    Post subject: Re: Temp2 sensor unplug and runs. Reply with quote

It didn't sound like the sensor, as a bad sensor and a disconnected sensor should run the same. I think you have something that is making the engine run lean. A bad vacuum leak or maybe low fuel pressure. Remember that vacuum leaks often occur on the under side of a hose or boot so you may need to do more than a casual visual check.
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djkeev
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PostPosted: Fri Oct 22, 2021 3:11 pm    Post subject: Re: Temp2 sensor unplug and runs. Reply with quote

Spark?
At coil?
At plugs?

Fuel?
Pressure?
Volume?
Injectors spraying?

Clogged exhaust?

Massive vacuum leak?

Clogged air filter?
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binger59
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PostPosted: Fri Oct 22, 2021 3:13 pm    Post subject: Re: Temp2 sensor unplug and runs. Reply with quote

Getting fuel, injectors are pulsing and there’s spark. So I’m not sure check the vacuum as best I could. Its getting dark out now
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Howesight
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PostPosted: Fri Oct 22, 2021 4:00 pm    Post subject: Re: Temp2 sensor unplug and runs. Reply with quote

binger59 wrote:
Hey folks looking for some help. 84 1.9 slowly lost power after driving for 176 miles. Unplug the temp 2 sensor and fires right up. Plug in and it dies. Currently in VT rt17 at the Vermont skydiving adventures. Currently dead in the water.



The Temp 2 sensor is a Negative Temperature Coefficient (NTC) thermistor. That means at low temperatures, it provides high resistance, and at high temperatures, it provides low resistance. The ECU is programmed to add fuel to the base fuel map when the resistance is high and vice-versa. So, if you were losing power, and adding fuel reduced the power loss, then you very likely have a vacuum leak as another poster suggested above. Unplugging the temp 2 sensor leaves the ECU with infinite resistance which results in the ECU adding a substantial amount of fueling over the base fueling map. This is likely why the engine ran with the Temp 2 sensor disconnected.

Common sources of vacuum leaks include:

1. The corrugated rubber pie between throttle body and Air Flow Meter (AFM) which must be removed for a proper inspection;

2. The diaphragm inside the breather tower;

3. Cloth-covered rubber pipes joining intake plenum to the intake runners;

4. Brake vacuum hose;

5. Breather hose;


Finally, don't discount the possibility that the extra fuel injected with the Temp 2 disconnected has flooded the engine and wetted out the spark plugs. Older spark plugs will wet out more seriously since the carbon acts like a sponge. If you end up pulling the spark plugs, a compression test would be a good idea (for better diagnosing)while the plugs are out.
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