Utc connection to m84 problems

[extonson]

Hi - I have a m84 mounted in cab , and I can log on to ECU no problem when engine is not running , but when engine is running , I have a lot of issue with the connection.

I am using harness from Motec .

Any ideas would be great.

[David Ferguson]

If your laptop is connected to an A/C adapter, try disconnecting it and running on batteries.

Make sure your USB cable (from the USB to the laptop), meets the USB specs (i.e. does it have the certified USB logo?)

What happens if you hot-plug the USB after the engine is started and running?

Put an oscilloscope on your 12V power line to the ECU? How much noise is present? Do you see noise on the ground lines connecting the ECU to the chassis (or battery) ground?

Can you improve the quality with larger (smaller gauge number) wire for power and ground?

Hopefully that will help.

[Holmz]

Maxwell pointed out that the magnetic and electric fields are related.

A triangle with the floor of the vehicle as one leg, the ECU-Computer as the second and the Computer to 12V outlet would make up the third leg.
The area in between these makes a coil which produced voltage when a magnetic field changes within the coil.
If you make that area go to zero (like a twisted pair does), then the voltage will go to zero.
So you would want the 12V line to be twisted around the comms-cable and the back along the floor to the 12V plug.

But if it is purely electric, then you filters somewhere.

To start... Do you have a lot of engine noise on the AM radio?

[extonson]

Hi - I have separated the power from the rest of the loom, and tried to ensure as much distance as possible between them. I know it must be noise somewhere , as coms is ok with engine off , when you start the engine you get bumped off pretty much straight away , but if you disconnect , then reconnect the USB it will come back online. It will still bump you off if you give it a rev. I have a m400 in another car , wired the same , with no issues at all. I have made sure that engine has good grounds , and alternator feed is well away from main harness.

[extonson]

No change with laptop Ac adapter in or out. I am not running a radio , so can't say.

[SprinterTRD]

Are you using wire spark plug leads?
Are you using resistive spark plugs?

If you are using wire leads, replace them with supression ones
If you are not using resistive spark plugs the get a set.

[mstech]

If you test the coil outputs, do you get disconnected? if you do then that is a good place to start looking for the solution to your problem.

[Holmz]

And an AM radio in the garage would tell you if there is a lot of noise.
Just tune it to the far left side where no stations are at.
We did this in New Mexico on road trip once for a hour or so watching a very distance electrical storm.
The kids were very impressed.
One would think that the clouds are at DC and the sinking of the DC to ground would be DC, but the nature of the 'impulse' is that there are frequencies from DC to day light. (Which is evidenced by the flash of light).

If you are not getting any RF emission then that is a clue.
The idea of coil test is a similar clue.

If it is not an 'electrical', then it is magnetic... (Which assumes that the two are separable).
At some point one needs to use a scope to see what is on the wire and then work out the physics of why it there, which leads to working the engineering of how to mitigate it.

These things are generally tricky at first.
The general idea of twisted pair eliminates many issues... Particularly the magnetic field issues.

Along the lines of bizarre, a friend put some LED lights by his pool.
The FM radio reception was total shot because of the RF coming out of the LED lights... Who would imagine that?
Your coils are just about something out of Tesla's lab in comparison to what one would expect from a LED light...