NiklasFalk

iTrader: (1)

The MTX-L is grounded at exactly the same point as the ECU (on the intake next to the TB, not sharing an inch of cable with anything else), but when the ground for the whole engine/trans/PPF/diff fails, the voltage in the whole car can get a bit wonky (especially at load when coils and injectors start to pull some amps).

I have had similar problems before and then it was a glitch in the FIA master switch. At that time the OEM ECU rebooted during load and the problem was easily solved with a new switch (when I found the intermittent glitch). I'm getting used to analyzing electrical problems during races...

But I dropped a valve in the last race so there will be some time before I do some tuning again (April or so). Hopefully I have one (or two) working MTX-L's by then, and better grounding on the whole car (I don't want to have that problem again).

Braineack

iTrader: (62)

i still dont see how a bad grounding strap would kill the controller.

Joe Perez

iTrader: (8)

Just as a point of reference (it's probably unrelated to this issue) it is generally better to ground the controller of a wideband sensor to a point as near as possible to the ECU. In the case of a traditional megasquirt, I recommend actually connecting the wideband's ground directly to the DB-37 connector. In the case of a Plug-n-play, splicing into the ananlog ground wire of the harness (at a point near the ECU connector) is recommended.

You'd be correct in observing that this is not the "best" ground in the car with respect to establishing a low-resistance path to the engine. Obviously running a direct wire to the head would accomplish that.

However, you have to consider that during operation, there is a fair amount of current going down the the ECU's ground wiring, and thus there is likely to be some miniscule voltage developed across the ground wire. Thus, the ECU will perceive "ground" to be a few millivolts higher than it actually is.

Now, if the ECU is receiving an analog signal from another device which is grounded separately, then the difference in potential of those two grounds (from the point of view of the devices) will show up as an offset in the analog signal between them, causing an error in the reading of the signal.

By grounding the wideband sensor at the ECU, any change in ground potential from the ECU's point of view will also be "seen" by the wideband controller, and thus no imbalance will exist.


[/thread hijack]

NiklasFalk

iTrader: (1)

I don't have the full logic behind it either, but the first one went after I changed the engine (the ground strap in the engine bay was touched of course). The second one went just after a race where I got a lot of MS reboots (problems that went away after fixing the ground strap).

Could there be a problem if the MTX-L is used as part of a grounding circuit (MTX-L ground line to the O2 sensor to the header, that might have some access to chassis ground, it's not a perfect exhaust install)?
Just for clarity, this is not intended, just one thing that might happen if you loose driveline ground straps.

Strange things can happen when currents start to flow where they shouldn't.

Braineack

iTrader: (62)

Ken yelled at me for grounding my LC-1 in such a manner. Really doesn't like that this is recommended.

He urged me to run the lc-1 to the ECU ground point through a deciated wire ; now I dont have such a voltage drop during cranking at the LC-1 and can log cranking AFRs after it warms up.

MD323

Not sure how either but another example happened to my ecu at the track last year when my negative terminal decided to come off. It burned the 12v trace right off the ms board.

Joe Perez

iTrader: (8)

You can't trust foreigners.


If any particular piece of electronic equipment happens to be the least-resistive path between two points of differing potential, then as much current as possible is going to attempt to flow through it, backwards if necessary.

Ever hear of people melting steel clutch lines by cranking the starter without a ground strap hooked up? Same deal here.

gregaustex

The instructions say ideally ground to the negative terminal of the battery.

bahurd

iTrader: (8)

You get todays award...