MoTeC Global Forum

I know this should be simple but i think i have checked the obvious... I have had an M800 in my car for some time with no problem and just recently rewired the interior of the car (Honda S2000). I removed everything i didn't need from the wiring harness (was a street car) and now my "eng 0V" has 4.55V on it. The reference voltage is 4.99 volts and i have confirmed that they have continuity between the 0V and 5V pins respectively. The sensor do operate between 4.55V and 4.99V (ie when i press the throttle it slowly increases between 4.55 to 4.99). I have come across plenty of strange issues resulting from improper grounds or backfeeding aux outputs etc but none that have effected sensor values.

Raw inputs:

AT1 4.825 - AIT
AT2 4.828 - ETC
AT3-6 4.920 - empty

AV1 4.738 - MAP
AV2 4.641 - TPS
AV3-8 0.000 - empty

Lambda 1 1.563
Lambda 2 1.555 (empty)
Lambda 1 Vp 4.388
Lambda 1 Zp 80

Ref 4.25
Sync 4.23

Aux 3 3.6 (empty)
Aux 4 12.9 1kohm pull-up only not currently connector to tach (no difference in problem when removing pin)

Ign 5 12.9 lambda heater control (no difference when removing pin)
Ign 6 3.6 (empty)

I have a very poor set of wiring diagrams so diagnostics can take forever, i am using all data for reference and their diagrams are scattered tracing a single wire from a connector can take 5 different links and the loading time for those 5 pages so you can imagine the frustration. I'm pretty close to doing the same thing to my engine harness i know if i wire the whole car it will work fine but i would rather not have to do that at the moment.

Not really related but why can't you view the rest of the aux output voltages?

Any ideas?

well if my car is any indication. The first thing I definetly would point to would be a bad ground.

Reason is that they T off the ground through out the harness. Did you cut or did you trace and de-pin?:)

I depinned all the connectors at the firewall and looked up all the circut diagrams in all-data (granted they arent the best drawings) and pinned out what i thought was needed. I do not have all the wires connected that i think i need but i do have what i think i should need to be able to start the car. I do not think a bad power ground could cause a bad sensor ground unless it was a bad ground for the ecu (which i checked). Thinking that may have been the problem i grounded every wire that goes to any ground point (according to all data) to the battery negative, this changed nothing. I honestly think it would be easier for me to re-wire the engine harness than to trace all of the wires going though the firewall but i would like to avoid that. The only thing i can think of is somehow voltage is being backfed through an output to the sensor ground channel but without knowing the internal workings of the ecu i don't see how thats possible i would have thought it would be a separate circut.

One other thing i just noticed is "dig one" is "on" and there isn't anything in that pin but it is setup as a speed sensor input (its just not hooked up yet)...

Did you have the same problem or just another ground issue?

I forgot to mention that my "ENG 0V" has 4.55V on it (edited the original post to include it)

You have or had a short to 0V and blown a track inside the ECU Measure between the ground pin and the 0V pins on the ECU. You will need to return it to MoTeC for repair

It appears you are correct. However my wiring between the 0V, 5V and sensors has remained unchanged (all of them run through the firewall with no connector strait from the ecu and have not been altered since the car has run. What could cause this?

I assume i could just swap the eng 0V pin to the aux 0V pin and use that as a temp solution until i reach a point where my car will be down anyway?

As I said in my previous post somehow you have shorted 12V, 8V, 5V to the 0V pin or a incorrectly wired or connected sensor or problems in the wiring harness.

You can swap the 0V pin and it should get you out of trouble however check your wiring first so you don't blow the second 0V pin.