Noise and Grounding, Your part of the MS install

[rickb794]

I do a lot of preaching about grounding and noise. I rediscovered this 10 year old PDF.
This PDF backs up my preaching and takes it a step farther. (adds pictures!)

http://www.bgsoflex.com/megameet2008/me ... gnding.pdf

I hope cross linking to B&G stuff is not politically incorrect.
Much of this has been incorporated into the new manual, but this doc goes into greater detail and does not contradict any Extra dogma

It explains why pins 15-19 should be connected directly to the motor, pictures of the board traces for visual confirmation.

This should help some folks with noise issues and give others some guidance for their installs.

Also Some good stuff there for the VR inputs, you can see what twisting the knobs does.

O2 sensors
Not spoken about in that doc is O2 sensor controller grounding, O2 sensor controllers can be very noisy devices.
Some O2 sensors don't have a separate signal return, separate from the Heater ground, so besides the power path the ground path can be a noise source as well.
O2 systems that do not have a separate heater ground should be grounded to the motor to sink any noise there.
Power for the O2 controller should be pulled off the fuel pump so any noise present on the power side will be absorbed by the pump.
This has the secondary benefit of turning off the O2 when the motor is not running (most all? MFGRs recommend not running the O2 with the motor off).
This is reflected in the current Extra wiring docs.

PLUGS and PLUG WIRES
Wires
The scurvy scoundrels in the marketing department have latched onto the idea that plug wires should have low resistance. This is not good for your electronics.
Google "spiral wound plug wire problems". The jury is still out on these wires and it is best to just avoid them. Easier on your wallet too!
Standard carbon core wires although having a shorter life will not interfere with your electronics and provide excellent spark.
Plugs
The scurvy scoundrels in marketing have also messed with your mind regarding spark plug choice always a new gimmick and a higher price.
Standard copper core resistor plugs are the only thing that should be on your menu here, V grooves, U grooves, split electrodes, are ok. But they wear faster.
And don't out-trick yourself by messing with heat ranges until the need arrises, use the plug your motor MFGR uses OEM for best results.
My only variation on this is platinum plugs, I would also avoid these as their only benefit is extended service life while they can cause issues in some situations.
Boosted motors will need some considerations but start with the cheap OEM resistor plug, your motor will tell you what you need when you turn it up.

Noise filtering
For me the software noise filtering is a bandaid for a poor install. It is always better to eliminate the cause rather than treat the symptoms.
This is not a situation like a HAM radio where you can only put up so much antenna, you will create noise antennas if you don't follow recommended practices.
Software guys always think it is easier to write some code to fix a hardware problem, I'm obviously a hardware guy....
For best results take the time to test and correct install problems rather than employ bandaids.
I have to date, never needed to employ noise filtering.
You can always use it as a fall back or emergency tool.

USB
Even though they are sold as such, do not use the internal USB to serial adapters.
ANY USB cable is susceptible to noise because of the operating voltage of the protocol.
The noise from the automotive environment is too much for USB.
Use a DB9 serial cable and the shortest possible USB cable (none is better).

Relay boards, Just say no!
The relay boards were designed to be used with a MS1 v2.2 main board.
The v2.2 main board did not support low impedance injectors and has no ignition output or VR support.
The interconnect cable provided for the relay board has very thin wires and no shielding.
All of the conductors are right next to each other in a very small space.
The thin wires are not good high current conductors and the close proximity over the distance of the cord do nothing to eliminate inductive or capacitive coupling of the circuits.
The relay board also introduces additional unneeded multiple points of failure.
The relay board also does not honor the newer grounding recommendations by separating the sensor ground from the high current ground.
I will NOT use one on ANY new install, and lobby for hard wiring whenever asked to repair an existing install that uses one.

[nathaninwa]

Where is the Like button! I too find many installs to have ground type issues. Nice post and great link

[kjones6039]

Relay boards, Just say no!
The relay boards were designed to be used with a MS1 v2.2 main board.
The v2.2 main board did not support low impedance injectors and has no ignition output or VR support.
The interconnect cable provided for the relay board has very thin wires and no shielding.
All of the conductors are right next to each other in a very small space.
The thin wires are not good high current conductors and the close proximity over the distance of the cord do nothing to eliminate inductive or capacitive coupling of the circuits.
The relay board also introduces additional unneeded multiple points of failure.
The relay board also does not honor the newer grounding recommendations by separating the sensor ground from the high current ground.
I will NOT use one on ANY new install, and lobby for hard wiring whenever asked to repair an existing install that uses one.

Just my 2cents worth here. I wholeheartedly agree! Been there, done that! My first (~9 years ago) project was an 85 Corvette TPI running EDIS with an MS2 v.3.0 using the MS relay board. Did not work well at all. I eventually trashed the relay board and bought a 4 relay strip from Summit. All was well after that.

Just to reinforce Ricks point....... IMO the relay board merely adds another level of unneeded complexity. After all, you're going to have to run all of those wires to the various sensors, injectors, coils etc. Why put yet another box in between?

I would hate to squelch anyone's sales, but I recommend avoiding the relay board whenever possible.

Ken

[LAV1000]

Is it possible to put Rick's linked pdf in the manual section ?
Did see some of those pages a while back but not the whole set, like it

[Raymond_B]

I like this portion when grounding is mentioned. So many people (including myself) ask why are there so many ground wires coming out of the Megasquirt. Most of us simply want to stuff them all together in to one large wire and be done. But the below statement is interesting. I ended up following the recommendation to use a dedicated junction block for the MS grounds with a large gauge wire running to the block. But really didn't know why, the explanation below helps somewhat.

"Each wire acts as a series resistor/inductor.
Multiple wires act like resistors/inductors in parallel… ."

[DaveEFI]

The reason for multiple power ground wires is one pin on the DB37 may not be able to handle enough current. The same reason is why the injector outputs have two pins each. You could connect all those power ground wires to one larger one, but that just adds another joint.

With the low curent sensor grounds, it's best to use more than one ground pin to ensure a decent low impedance connection.

[Marek]

The v3.0 board is very long in the tooth in that it now accommodates a lot of expansion that the original v3.0 board did not anticipate. The most sensible way to avoid noise is to separate the low current "delicate" inputs from the high current "noisy" outputs.

Whilst most (all?) of the low current inputs come to the main board, there is no need for most of the high current usage grounding outputs to also dip through the v3.0 board:-
1/ ignition, if run via BIP373s, should have their own box and that way only a low current signal leaves the MS box - the high current pulses which need grounding can stay outside the MS box;
2/ The idle valve output, which is probably a pwm function can be treated as an open collector output to feed a chunky 2n3055 or somesuch and this can be mounted outside the MS enclosure. Once again, the high current pulses are kept well away from the MS box.
3/ injectors, if run via peak and hold, should have their own ignitor box and that way only a low current signal leaves the MS box - the high current pulses which need grounding can stay outside the MS box and go directly to the engine block;
4/ any other pwm function should be treated similarly.

The net effect is that the MS board only ever sees low current signals which thus can't swamp the low level inputs.

The other thing not touched upon is that any diy expansion of the v3.0 board is often done in the most unstructured and unprofessional way possible, leaving a rat's nest of untidy wiring which is hard to troubleshoot and prone to fatigue as layer upon layer of upgrades overwhelm to original design.

Below is a 24way peak and hold board for a dual fuel v12. Not only do the high current pulses stay away from the MS box, but there is little scope for anything to fail here - note the complete absence of wiring and the generous heatsinking. Only two out four transistors are used per board so the layout is optimised with heat dissipation in mind.

If you want your MS to perform like an oem ecu, then build it up like an oem ecu and don't skimp on the wiring loom. Use all of the ground wires, even when there is almost nothing left to ground.

kind regards
Marek

[Raymond_B]

The reason for multiple power ground wires is one pin on the DB37 may not be able to handle enough current. The same reason is why the injector outputs have two pins each. You could connect all those power ground wires to one larger one, but that just adds another joint.

With the low curent sensor grounds, it's best to use more than one ground pin to ensure a decent low impedance connection.

I'm not sure I understand your last statement. I thought there was only one ground pin? Do you mean use on of the spare ground pins?

[DaveEFI]

All of pins 1-19 (except 3-6, the spares) go to the same internal ground plane on the PCB.

[rickb794]

The reason for multiple power ground wires is one pin on the DB37 may not be able to handle enough current. The same reason is why the injector outputs have two pins each. You could connect all those power ground wires to one larger one, but that just adds another joint.

With the low curent sensor grounds, it's best to use more than one ground pin to ensure a decent low impedance connection.

I'm not sure I understand your last statement. I thought there was only one ground pin? Do you mean use on of the spare ground pins?

Pins 15-19 at the minimum should be grounded with individual wires directly to the motor on any MS2.

[Raymond_B]

Sorry, I made a typo, I meant only one *sensor* ground.

[DaveEFI]

Sorry, I made a typo, I meant only one *sensor* ground.

My standard method for the sensor ground is to link pins 1&2 together. But then I always make my own looms from scratch. What I actually do is bring two wires from 1&2 just outside the DB37 shell, connect then together, and connect all the sensor grounds to those.

[rickb794]

There is little if any current flowing in the sensor return circuit.

0.1a is the most load that can be run off the VREF (from the manual).

Compared to 7A each for pins 32-36 for a total of 28A plus the relay drives and IAC for a grand total of 30~35A!
Those are constant current limits, but a MS2 can likely see higher instantaneous loads.

This may be why a Microsquirt seems to be more susceptible to noise having only 2 ground wires (2 less available pins) 22.5A total.

[gjestico]

.

USB
Even though they are sold as such, do not use the internal USB to serial adapters.
ANY USB cable is susceptible to noise because of the operating voltage of the protocol.
The noise from the automotive environment is too much for USB.
Use a DB9 serial cable and the shortest possible USB cable (none is better).

.

How well does the MS3 card work with its built in USB adapter ?

[rickb794]

It works excellent on the bench!

YMMV in the car, some cars are not as noisy as others.

I have had so many problems with USB I don't fool with it anymore.
My USB cable in the car is only long enough to keep me from ripping the USB port off my laptop AGAIN!
I recently had to tear down my EeePC and replace all three USB jacks due to abuse.

[Targa44]

Sorry, I made a typo, I meant only one *sensor* ground.

My standard method for the sensor ground is to link pins 1&2 together. But then I always make my own looms from scratch. What I actually do is bring two wires from 1&2 just outside the DB37 shell, connect then together, and connect all the sensor grounds to those.

I thought the hardware guide showed pin 1 = crank sensor, pin 2 = crank sensor shield (so that covers Dave's statement), but the guide also shows pin 7 as a sensor ground... page 18 of 222 "MS3base/v3.0", James Murray. Is it no longer current?

I just noticed as I picked this up while searching for things and see it's an MS2 topic. Any difference with pin assignments?


thanks,

kj

[rickb794]

All but 4 of the low number row on the DB37 are ground pins and the ground pins are interconnected inside the MS on a 3.0 or 3.57 board.

However their differences electrically are spacial in that the high current grounds 14-19 are physically closest to the high current path and devices.

Pins 1&2 are farthest from the high current (noisy) side of the board and thus are somewhat isolated from them by the internal ground plane of the circuit board resistance.
Electrons follow the path of least resistance and the traffic in the noisy (high current) side of the neighborhood is less likely to influence the quiet loving sensor side.

This is another reason NO externally powered device (like an O2 Sensor heater ground) should be connected to the MS end of the ground path.
Besides providing an alternate ground path (ground loop) which can cause noise, (O2 sensor controllers are inherently noisy and can even cause noise via the 12v line).
This is another reason to connect the O2 heater power to the fuel pump circuit as the fuel pump will shunt any noise emitted by the O2 controller.

[R100RT]

Helpful consideration, actually one of the key pitfalls on installs perhaps, and a good review for sure.
There are other ways of course to set oneself up for random operability, had one such adventure this summer. Low speed stall only when turning to the right - had to happen in front of the owner of the company I work at for me to get serious troubleshooting. As it turns out there were some stale "original" wiring in the bike headlight bucket that did allow an interruption of ignition feed power - which help launch me on a tangent repair.
Finally I realized pulling the clutch in was the actual offending occurrence on the right turn. In fact, I had trapped the crankshaft VR cable below the clutch cable with a zap strap and it must have semi broken the connection - and just before saying uncle towards a proper repair it further manifested in a harsh load state miss at mid rpm's. Last weekend I routed a new cable and its just like I've washed and polished her!
Needless to say, this winter the bike will see a slow, methodical revamp of its entire wiring harnesses, MS and stock BMW in its entirety.
Bloody bike never did let me down tho, riding every day of the summer again