Sensor grounding question

[rustybottoms88]

My engine is running now but my AFR is reading wacky,the battery voltage jumps from 12.7 to 15 and then back down to 9 and the engine will stall randomly and the fuel pump will continue to run. At the same time TunerStudio will say the MS2 is disconnected. Each sensor has it own individual ground wire going back to the MS2. This leaves only one ground wire from the pre-made wiring harness (from DIY Autotune) to ground the MS2. The diagram on page 14 of the Hardware manual has led me to believe that all the sensors ground go to one wire that goes back to the MS2 and there are atleast 4 wires from the wiring harness that are used to ground the MS2 to the battery.
The Engine is well grounded to the chassis and the battery is well grounded to the engine block. I refreshed all of these grounds to make sure I had good grounds to the chassis. Any help in clearing this up would be greatly appreciated.

[DaveEFI]

Have you looked at the inside of the DB37 connector? It is the (low) current capability of the pins in that which need multiple ground connections for an adequate power ground. Normal way would be to use multiple wires - but no reason not to use one adequate wire linked to four pins inside the DB37 connector.

But you don't need to run each sensor ground to a separate pin. I tend to use two, and link all the sensor grounds to those.

The important bit is to keep the power and sensor grounds separate, until they meet within MS.

[rustybottoms88]

Have you looked at the inside of the DB37 connector? It is the (low) current capability of the pins in that which need multiple ground connections for an adequate power ground. Normal way would be to use multiple wires - but no reason not to use one adequate wire linked to four pins inside the DB37 connector.

But you don't need to run each sensor ground to a separate pin. I tend to use two, and link all the sensor grounds to those.

The important bit is to keep the power and sensor grounds separate, until they meet within MS.

Thank you this is just the information I was looking for. I will do as you have said and see if that takes care of my problems and report back.

[kaeman]

You stated that you have the megasquirt grounded to the battery....... bad... the megasquirt should be grounded directly to the engine block, not the battery as voltage offsets will make sensor readings almost useless. Look at the grounding method in the manuals, they all tell you to ground the megasquirt to the engine block and then ground all the sensors to the megasquirt.
I fought the problems that grounding at the battery created until I wired it correctly to the engine block for the main ground. The system ran way smoother. Good luck.

[DonMaximo]

I'm having an irritating issue with my TPS and possibly MAP sensors.

I grounded my MS3 to the Battery because this is what the most recent documentation states:

(MS3-Pro User manual - July 2, 2015 - Page 51)

4.12 Grounding notes
The MS3-Pro uses multiple ground planes to reduce noise. It is important that you connect both the logic ground at pin 16 on the white connector and all the power grounds on the gray connector to the battery negative terminal. It is less than ideal, but still acceptable in most cases, to ground the MS3-Pro to the engine block or cylinder head. Avoid grounding the MS3-Pro to the frame rails or sheet metal; these points often have issues with rust and spot welds limiting how much current can flow through them.

Within the same documentation, there are several references to grounding to the engine as well. I will change to an engine ground in an effort to stifle the gremlins vexing my progress.

[kaeman]

I didn't look at the ms3 pro manual, my bad all I have been using was the info in the regular ms3 manuals. the hardware manual shows that wiring info that I switched to because of the gremlins I was fighting when grounded to the battery.
this is a clip from the manual I found that explained my issues at the time..... Good Luck.
MS3base/V3.0 Hardware Guide
3.2 Grounding (Earthing) Schemes
Implementing a correct grounding scheme is critical to a successful Megasquirt install.
Connecting sensors to the wrong ground, using corroded ground points or dubious original wiring are sure-fire
ways to give you a headache.
There are two key rules:
1. All sensors must ground at the Megasquirt
2. Ground the Megasquirt at the engine block/head using both available ground wires.
Reasoning:
When a current flows through a wire there is always a voltage drop, the bigger the current, the bigger the drop
(this is ohm's law.) During cranking there is a very large current flowing through the ground strap from battery to
engine and perhaps a few volts may be dropped across it. Even during running, a number of amps will flow
through the Megasquirt grounds to the engine.
The sensors (coolant, air temp, throttle position, wideband, tach input) all use low current, low voltage signals.
The Megasquirt measures the voltage from the sensor and converts it into a temperature, position etc. reading.
If that sensor is grounded to anything other than the Megasquirt itself, then that input voltage will be altered by
any external voltage drops. For a sensitive measurement such as AFR (lambda) this can be a real problem. All
good wideband controllers offer a high-current ground (connects to engine) and a sensor/signal ground
(connects to Megasquirt.)
Tach input (e.g. crank, cam sensors) will be even worse - they can show false or missed teeth and cause syncloss
due to the ground voltage difference.
The following two diagrams illustrate good and bad wiring schemes showing where the troublesome voltage
drops are created and how that would cause sensor readings to be garbage.
(