Printable Version of Topic

Click here to view this topic in its original format

914World.com _ 914World Garage _ CHT test

Posted by: MarkG Dec 13 2004, 06:04 PM

when testing CHT I get the correct ohm readings, but get no reading when putting Ohm meter to the CHT harness wire to the 'brain'. Should there be a reading to the box also or just to the CHT/head itself?

p.s. who has the sky blue/red stripped 'LeMans' 914 I saw SB I-25 @ Colorado Springs last Sunday?

Posted by: vsg914 Dec 13 2004, 06:06 PM

Don't think you get a reading at the brain, just the sensor.
What did it read?

Posted by: jwalters Dec 13 2004, 06:09 PM

Dude, it has been my befuddled experience to never -ever---ohm check a brain box---this is not to say it cannot be done on models that have the proper protections / design for doing so. But I do know from experience on gm, ford, chrysler, bmw, mercedes, and porsches (944) that once you actually ohm check it--you most certainly killed it----all those teensy tiny circuits and diodes cannot take it..

Hope yours is the "safe" model

Posted by: dmenche914 Dec 14 2004, 01:33 AM

Never run an ohm check to the brain, it could blow the brain. An ohm meter actually sends a voltage (via the battery in the ohm meter) thru the circuit you are testing. This voltage can ruin sensitive components in the brain.

To check the Head Temp Sensor back to the brain, you can remove the brain cable connector, and read ohms from the connector (off the brain) to the ground wire on the same connector. This will give the total resistance, head sensor to the brain connector. Then check the resistance just at the sensor, the values should be the same, as the wires to the connector at the brain should add almost no additional resistance to entire circuit.

You can probe all the sensors, injectors, trigger points, etc... from the brain connector after it is removed from the brain, by using an ohm or volt meter depending on which wires you are checking.

Again, never run the ohm meter thru the brain, damage might result.

dave

Posted by: DJsRepS Dec 14 2004, 04:37 AM

On that ECU plug I ran a feeler gauge through its contacts to feel the wire's conductivity to the ECU. I found both my 12v and the ground and one of the trigger point wire's not even touching the gauge where the rest had good contact with the gauge. I had an intermintent miss.

Posted by: pbanders Dec 14 2004, 09:52 AM

I suggest on my web page that you do your testing at the ECU plug, disconnected from the ECU. Many 914 wiring harnesses are in terrible shape and are the cause of many intermittant problems with the FI system. Procedures and expected values for this testing are at:

http://members.rennlist.com/pbanders/djetparts.htm