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> CHT sensor extension, Curious, does it work? Who uses one?
malcolm2
post Oct 25 2016, 09:11 AM
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I want to cover all my bases here. I have purchased the new GB CHT sensor from 914Rubber to try.

So, I think I will buy a spacer from Brad Mayeur to have the option. From what he says it should:

"Porsche 914/4 Cylinder Head Temperature Sensor Extension.

This little device slows down the heating of the sensor and improves warm up drivability.
"

I do have "warm up drivability" problems = Low idle RPM until the VDO CHT hits about 250*F. So it seems like my problems don't need the warm up to slow down, it needs to SPEED UP. (IMG:style_emoticons/default/WTF.gif)

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Also found on RATWELL (scroll down to WORKAROUNDS)http://www.ratwell.com/technical/TempSensorII.html#parts
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TX914
post Oct 29 2016, 08:19 AM
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Very nice. This seems closer to being realized. I gather Spoke’s revised UI switch still allows for adjusting lean and rich circuits.

I’m curious about the Isolate switch as you say the car would not run when open. What would be the effect of grounding the ECU CHT sensor lead on hot restart?
I recall long ago when experiencing some intermittent bucking on acceleration, to test for a bad CHT sensor (engine hot) my mechanic simply disconnected the ECU lead and grounded it to neg. battery terminal
(or was it just to ground – can’t remember), and the car ran fine.
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pbanders
post Oct 29 2016, 05:35 PM
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QUOTE(TX914 @ Oct 29 2016, 07:19 AM) *

Very nice. This seems closer to being realized. I gather Spoke’s revised UI switch still allows for adjusting lean and rich circuits.

I’m curious about the Isolate switch as you say the car would not run when open. What would be the effect of grounding the ECU CHT sensor lead on hot restart?
I recall long ago when experiencing some intermittent bucking on acceleration, to test for a bad CHT sensor (engine hot) my mechanic simply disconnected the ECU lead and grounded it to neg. battery terminal
(or was it just to ground – can’t remember), and the car ran fine.


Surprisingly, you could actually do that, because the CTC circuit in the ECU's response to the value of the CHT resistance flattens out below 300 ohms, so anything under 300 ohms has the same effect, including a short. As the CHT gets down to 50 ohms or so when the engine is fully warmed up, a short would act the same.

You can see all of this in the analysis of the CTC circuit in the ECU on my web page.

http://members.rennlist.com/pbanders/ecu.htm#CTC

This behavior is by design so that once the engine is warmed up, the mixture doesn't go all over the place as the head temperatures rise and fall, which anyone with a CHT probe will tell you is commonplace. What we think is happening (as of yet unproven) with the hot-start problem is that the CHT is cooling off enough that it's getting to more than 300 ohms, and leaning out the mixture. By having the test point in the circuit and the isolate switch, I'll be able to see if this is really what's happening, or like with many things we've thought we understood with these cars, we had no idea of what we were talking about (IMG:style_emoticons/default/smile.gif) .

Remember, experimental results always trump theoretical musings.

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Posts in this topic
malcolm2   CHT sensor extension   Oct 25 2016, 09:11 AM
bretth   If I understand it correctly it is meant to keep t...   Oct 25 2016, 09:22 AM
Mikey914   Exactly. I have one also and may reproduce these.   Oct 25 2016, 09:26 AM
BeatNavy   I do have "warm up drivability" problem...   Oct 25 2016, 09:28 AM
pbanders   The possible downside, which is probably attribut...   Oct 25 2016, 04:22 PM
BeatNavy   The possible downside, which is probably attribu...   Oct 25 2016, 05:39 PM
pbanders   [quote name='pbanders' post='2415735' date='Oct 2...   Oct 25 2016, 06:15 PM
malcolm2   I have checked what I understand to be the other c...   Oct 25 2016, 09:36 AM
BeatNavy   It doesn't slow down the engine warming. It s...   Oct 25 2016, 09:45 AM
pbanders   OK, I have one of these and have been using it for...   Oct 25 2016, 04:19 PM
malcolm2   From this and other research it seems that I may j...   Oct 25 2016, 06:52 PM
TX914   I wish some clever guru would create a way to modi...   Oct 26 2016, 06:13 AM
BeatNavy   I wish some clever guru would create a way to mod...   Oct 26 2016, 06:47 AM
Philip W.   i have dealt with same issue with my 2.0 d-jet tha...   Oct 26 2016, 07:15 AM
pbanders   i have dealt with same issue with my 2.0 d-jet th...   Oct 26 2016, 01:42 PM
Mikey914   Well a rheostat would give you the ability to have...   Oct 26 2016, 10:20 AM
pbanders   See my edited response above. BTW, it's nearl...   Oct 28 2016, 04:32 PM
BeatNavy   What worked best was to start with key off, then ...   Oct 28 2016, 04:46 PM
pbanders   What worked best was to start with key off, then...   Oct 28 2016, 05:59 PM
porsche913b_sp   I will have to keep you all's suggestions in m...   Oct 28 2016, 04:46 PM
pbanders   Here's the schematic for using a DPDT switch a...   Oct 28 2016, 06:02 PM
pbanders   I never was worth a crap as an EE, I was more of a...   Oct 28 2016, 06:06 PM
pbanders   OK, here's a circuit version with two pots, on...   Oct 28 2016, 06:35 PM
pbanders   OK, I can't stop, here's one more circuit ...   Oct 28 2016, 06:48 PM
Spoke   OK, I can't stop I know the feeling. Here...   Oct 28 2016, 08:37 PM
pbanders   [quote name='pbanders' post='2417044' date='Oct 2...   Oct 28 2016, 09:47 PM
pbanders   One thing I always know for sure: If I draw a circ...   Oct 28 2016, 09:52 PM
TX914   Very nice. This seems closer to being realized. I ...   Oct 29 2016, 08:19 AM
pbanders   Very nice. This seems closer to being realized. I...   Oct 29 2016, 05:35 PM
timothy_nd28   Instead of a switch, why not a small circuit that ...   Oct 29 2016, 09:02 AM
pbanders   Instead of a switch, why not a small circuit that...   Oct 29 2016, 05:36 PM
timothy_nd28   RE: CHT sensor extension   Oct 29 2016, 07:17 PM
TX914   I'll take 2 of those. :)   Oct 29 2016, 09:21 PM
pbanders   Tim, thanks, I've got all those components exc...   Oct 30 2016, 07:28 AM
timothy_nd28   Sorry, I know it wasn't helpful but I happen t...   Nov 1 2016, 11:28 PM
nine9three   I have the extension and it transformed my car whe...   Nov 2 2016, 11:07 AM
Mikey914   I have the extension and it transformed my car wh...   Nov 3 2016, 11:31 AM
porsche913b_sp   I have the extension and it transformed my car wh...   Nov 3 2016, 11:44 AM
Mikey914   What I'm getting at is you installed a new CHT...   Nov 3 2016, 11:55 AM
pbanders   I have the tester box all put together, not wired ...   Nov 3 2016, 11:24 PM
pbanders   OK, I got it all together and installed, and went ...   Nov 4 2016, 06:59 PM


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