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I have a megasquirted car with itb's and nothing but fuel, ignition, radiator fan and brake lights in the car. Altenator is 100+ Subaru alt, battery is standard size car battery.
Everything but the fan and fuel pump(using chassis ground) are grounded directly though the battery. Currently I'm suspecting the chassis ground. Battery has a chassis ground and distributes power though a bus bar direct to battery and a distribution stud that's goest to the starter/battery, altenator and powers the fan.
My problem is when I hit the brakes sometimes the car stalls. Likewise when the fan kicks on the car wants to stall.
Voltage is typically 14.2-14.5 brakes or fan drop it 1v
When either event happens I can hear the fuel pump significantly change pitch so im attributing this to an electrical issues(note to self. I need to watch the fuel pressure). I have timing ramp up behind idle to combat this, 10 in idle cells 1k-1.3k and 18 at 800 rpm. Sometimes it's enough to keep it running but not always.
Running very rich in the past seemed to cover up the issue but I'm trying to idle 13 afr instead of the low 12's to combat exhaust smell.
I'm no tuning expert and am out of ideas.
Does this seem like a tuning or electrical issue? I'm not sure at this point.
Electrical issue: You have a loose or otherwise bad connection at the battery. The alternator cannot/will not be able to handle momentary load spikes. Stalling when you apply the brakes is a VERY common symptom of a bad battery connection,
It can also be a symptom of a bad battery. You definitely want to address this quickly since without a good battery in the system, everything electronic is subjected to a lot more noise. With a Midtronics style charging system tester, I have seen an alternator with over 100mv of ripple suddenly be "cured" with a new battery and ripple went down to 14mv.
Incidentally, I switched from MS1 on a 1.01 board to MS2 on a 3.57 board because of this. My battery is mounted in the cabin, and an emergency braking maneuver knocked something down in the back of the car and it pulled the positive cable out of the terminal. The car still ran but the next time I applied the brakes, the car stalled. The v1.01 fried due to a voltage spike from the alternator trying to regulate voltage with no battery in the system.
I was thinking ground issue. I really should run something from the battery to the engine.
Now that I think about it I used to ground the battery at the seat belt regulator bolt and I changed that recently. I bet the new spot just isn't as good and thats about when the problem started.
Its interesting, if you look at the logs everything just crashes then comes back.
frustrating as hell as I automatically assume i did something to the tune anytime something starts acting weird.
When you say 'everything' is grounded to the battery negative, does that include your ECU? You *really* want everything grounded directly to the engine, not to the battery.
Usually the biggest source of electrical noise isn’t RFI or other radio noise - it’s poor grounding or having noise injected into the power wires by another device. The MS3Pro works best when grounded to the battery negative terminal for maximum noise resistance. We do not recommend grounding the MS3Pro to the chassis or sheet metal under any circumstances. You may either crimp all ground wires to a single lug, or crimp the ground wires on the gray connector to one lug and the single ground on the white one to a separate lug. The sensors need to be grounded to the sensor return wire, which grounds them to the MS3Pro. Grounding sensors to the engine or body will create jitter from ground offsets.
Interesting, Here is the quote from the Microsquirt Manual (My only experience is with the uSquirt, I'm no expert!):
Make sure the grounds are correct. When running the grounds on MicroSquirt® EFI controller, it is important to remember that there are different "types" of grounds. These are:
High power grounds (Ampseal pin 22, & 23) - these are the returns for the fuel injector and ignition drivers, and the fuel pump/fast idle/spare output drivers. There are two wires on the connectors for these, going to pins 22 and 23 on the AMPSEAL - these are for the high power ground path. Both of these wires need to ground direct to the engine block. It is important to run both wires because it will reduce both the resistance and the overall inductance of the ground return path. Each wire has a resistance, and using three of them in parallel reduces the overall resistance. Equally important, each wire has an inductance, and inductances do not "like" fast-changing signals (like a pulse from a spark) and can cause very brief voltage offsets in the ground path. By having multiple wires it is the same as having multiple inductors in parallel, resulting in an overall lower inductance. At the point on the engine block where the grounds hook together, it is a good idea to run a separate wire from this junction back to the battery as well. This is redundant, however it often cleans up noise from sources like the starter motor. And, if it does help then you should take another look at your big positive and negative wire on the battery. Since we are talking battery - the point where you pick up the +12V to power the MicroSquirt® controller is very important. This will go through a relay in order to turn on and off the MicroSquirt® EFI controller, and the power source for the +12V on the relay needs to go back to the battery, or a path that leads direct to the battery without a long run of wiring. Just like for the grounds, run a separate wire from the relay direct back to the battery just to be sure.
Sensor grounds (Ampseal pin 20 and 18, if populated) - the coolant sensor, intake air temperature sensor, throttle position sensor, and external MAP sensor needs to be grounded back to pin 20 on the AMPSEAL. This is the low-current sensor return path and it needs to be kept away from the high power ground. This wire hooks directly to the sensors only and not to the engine block - it is its own return path.
Serial return (Ampseal pin 19) - the serial cable on the MicroSquirt® has a separate ground return path thru the AMPSEAL connector. This return goes direct to the RS-232 transceiver (and not thru the ground plane, keeping the noise off...).
Best practice for any ECU is to follow the star-earthing principle. In essence this means you pick a single earthing point for the ECU and all components connected to it. You connect them either to the engine or the battery negative, but never both. This eliminates the potential for ground offsets.
You use a single engine point as your ground point which then feeds out multiple ground connections to the ECU and all 12V grounds for devices actuated by the ECU. The engine block is then connected directly to battery negative, or to the chassis (with the battery negative being connected to the chassis at a different point), but not both. All sensor grounds are connected directly to the ECU, which has a regulated 5V or 8V output. If you have sensors whose body provides the ground to the engine block, then this provides a good reason why the star earthing point is best found on the engine block. This way the sensor shares a common ground with all other ECU components.
