red wire affecting idle!

cr_craig
Posts: 18
Joined: Thu Dec 14, 2006 7:19 pm
Location: San Jose, CA

red wire affecting idle!

Postby cr_craig » Tue Apr 26, 2011 9:35 pm

I have a new water temp sensor that I purchased from Race Technology, with the cable (and resistor) attached. It's installed, and I've connected signal and ground to the DL1. However, when I connect the red wire to the 5V ref out on the DL1, the car idle shifts from "normal" to almost a hunting (rpm increase from 800 to 1200, drop back, then repeat, continuously). Disconnect red wire, idle returns to normal.

I've checked the DL1: 5V is supplied correctly, 12V power and ground are good. Other sensors are working correctly. I should note that I have the CAN ECU interface connected and working properly. A Dash2 is also connected and working.

DL1 is a mark 1, serial number 701, firmware 33-4.

I'm at a loss . . .

osborni
Posts: 497
Joined: Fri Dec 07, 2007 9:08 pm
Location: USA, Michigan

Postby osborni » Wed Apr 27, 2011 12:06 pm

Everything on the DAQ system should be separate and passive relative to the motor and it's ECU. Good ground on the motor? Honestly sounds like a ground loop, but that would also likely fry the DL1.... (just guessing....)
BMW 2000 M Coupe

cr_craig
Posts: 18
Joined: Thu Dec 14, 2006 7:19 pm
Location: San Jose, CA

Postby cr_craig » Wed Apr 27, 2011 3:51 pm

Thanks, I'll have a look at the total current draw of the sensors and the possible existence of a ground loop.

cr_craig
Posts: 18
Joined: Thu Dec 14, 2006 7:19 pm
Location: San Jose, CA

Postby cr_craig » Fri Apr 29, 2011 6:42 pm

Interesting. I've got about 2.3 V constant on this wire. How the heck did that happen?

The same voltage is also present on the signal wire, so I'm guessing there's a short between the two.

osborni
Posts: 497
Joined: Fri Dec 07, 2007 9:08 pm
Location: USA, Michigan

Postby osborni » Fri Apr 29, 2011 7:29 pm

2.3 vdc is likely a short..... try taking off that pressure sensor... :)
BMW 2000 M Coupe

Support

Postby Support » Tue May 03, 2011 8:07 am

I am guessing that this sensor is also attached to the ECU. It sounds to me as if the ECU is applying a voltage to the sensor. When you are connecting the sensor to the DL1 it is applying a different voltage to the sensor which is causing the ECU to misread the temperature and so it runs roughly.

You will be able to use the sensor by just reading the voltage on the sensor as it is, but you will have do your own calibration on it to sort out which voltage corresponds with which temperature.

cr_craig
Posts: 18
Joined: Thu Dec 14, 2006 7:19 pm
Location: San Jose, CA

Postby cr_craig » Fri May 06, 2011 4:10 pm

Dr. Hill wins the prize! I took a look at the sensor and sure enough it's connected to both the DL1 and the ECU. Not what I had intended, but broken telephone works with mechanics too . . . :D


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