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malcolm2 |
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Advanced Member ![]() ![]() ![]() ![]() Group: Members Posts: 2,747 Joined: 31-May 11 From: Nashville Member No.: 13,139 Region Association: South East States ![]() ![]() |
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) 914LTD.com ![]() ![]() Also found on RATWELL (scroll down to WORKAROUNDS)http://www.ratwell.com/technical/TempSensorII.html#parts |
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TX914 |
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Alan-B ![]() ![]() Group: Members Posts: 176 Joined: 27-July 14 From: USA Member No.: 17,689 Region Association: None ![]() ![]() |
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. |
pbanders |
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#3
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Senior Member ![]() ![]() ![]() Group: Members Posts: 939 Joined: 11-June 03 From: Phoenix, AZ Member No.: 805 ![]() |
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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Lo-Fi Version | Time is now: 26th June 2024 - 05:57 AM |
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