Hey Hey,

I believe I have a voltage problem.

The ECU reads 13.1v and when in WOT it drops to 12.7 and moves between the two.

Alternator voltage reads 14.7. The battery also reads the same.

I've checked all grounds and made sure they are all good.

I also notice now and again my temperature gauge floats about. Almost like a bad ground. But other times it's stable as anything. (maybe nothing but thought I mention it)

I've attached my tune & Log. If you don't mind having a look and let me know what you think that would be perfect. I've done a full WOT from 2nd gear to 6th gear.


The car produced 364hp on the dyno. But another problem.. Well.. Possible problem is my VE table I've had to add over 10 points to make my target of 11.0 AFR. It started to go lean a couple of months after the tune. around 118 in WOT but I'm now up to 145 :S

I've re-calibrated my MTX-L and it's given me the same readings. Could it be in relation to voltage?

If it worth me checking at the fuse boxes the voltage? and see where it's failing. Or am I fussing over nothing and that's perfectly normal voltage.

I've been reading if the injectors match the ECU voltage then I'm fine. What's the best way to check injector feed voltage? Just poke in the connector hole? Sorry if that's a stupid question. When it comes to electric I'm still learning alot.

Any advise would be great.

Thanks.

 

If your sensor readings are affected it does sound like a grounding issue. A fluctuation on the 12 volt main power shouldn't affect the sensors as they run off the 5 volt VCC which is behind a regulator and filter circuit.

 

WIll have a look at the gauge cluster later on.


Where does the ECU take it's feed from? Or a wiring diagram to show route. As I would like to trace wire back and check and multiply points the voltage. As I'm losing pretty much 1.5v somewhere along the lines.

 

Not familiar with mk1 cars but I think the power for the entire engine management system comes from the main fuel injection relay.

There are wiring diagrams out there, just google.

Something to think about: if you did have a grounding issue this would also affect the voltage reported by the Megasquirt, because a high resistance ground would cause the ground at the MS to rise to a higher voltage than the true ground, and MS only measures the voltage relative to its own ground.

Let's say your ground connection is 1 ohm - high, but not impossible - and you're pulling 1 amp through it (again, a figure I pulled out of the air, but the megasquirt is likely to draw more current at higher RPMs, so the theory holds). V = I * R, so 1 amp through a 1 ohm resistor is 1 volt - ergo, your MS sees a full volt less than the real battery voltage. This would also cause your sensor readings to be offset by a full volt. Double-check those grounds... all of them... especially the ones at the head!

 

Thank you for the advise.

The ground I have checked. More than once.

Battery GND
PPF GND
White Block GND Bulkhead.
bulkhead to head GND
Camcover GND (I also added a wire from the back bulkhead to this also)
Little black tab not sure if this is a GND. sits near fusebox.


Is worth running a fresh wire GND from the ECU. possible cable breakdown causing problems.

 

I would say yes, run a nice fat ground wire from the head to the ECU ground, make sure everything's nice and clean and tight, and see if it solves your issue.

 

I shall give that ago.

When I had the car tuned. The guy bridged all the grounds together in the ECU itself and installed a bigger CAP to stablise the voltage.

I've been reading that the power GNDs 2C & 2D & Sensor GNDs 2A & 2B shouldn't have the same location? Is this correct.

This is going off FM ECU guide. running a thinker cable from 2C & 2D to the HEAD/BODY ground on the bulkhead.

 

this is a POS 1.6L issue, not a MS issue.


I'd also highly recommend, based on his replies, you cease from following any of TBJ's "advice"

 

good old 1.6. lol.

Braineack. Do you have any suggestions. **** 1.6 wiring? Run new wires?

What made the 1.6 a POS in regards to this.

Just want to workout what the problem is. Is it fixable. Or have I got to live with it.

 

first: measure the battery voltage at the injectors, then calibrate the battery voltage in the Tuner Studio to match what youre seeing at the injectors. It's pretty common so see between 13.5 and 14v.

 

Why was it wrong? It would explain the symptoms (fluctuating battery voltage measurement, fluctuating sensor values) from where I'm standing, unless I misread the original post.

 

Thank you.

Sorry for being stupid.

What's the best way to measure the injector voltage. Straight off the injector plug.


Once completed this and I have it matching if it isn't already. Should I be worried that I'm seeing as low as 12.7.



Calbrating the Voltage.

I'm guessing.. to raise the voltage adjust the min to a higher value. and to lower the voltage adjust the max to a lower value.

Any best practice? Run the car until fully warm. Measure injectors voltage and make tunerstudio match @ idle.

 

the 1.6L alternator is a piece of **** and your battery voltages always drop down at WOT.

But you always need to make sure the MS is reporting back the actual voltages as measured at the injectors. They should probably good about a 0.5-1.0v lower that alt and battery due to voltage drops across the shitty wiring.

 

This is a huge no-no, I think I've told you this before.

 

Sorry, my bad. I interpreted the the post as "The megasquirt is reading 12.7-13.1 and the alternator is outputting 14.7 *at the same time*"

 

I mentioned it on facebook when we did it. But you never said it was a huge no no.

He also added a bigger cap inside.. Should I remove this also.

 

You can leave the cap, but do remove the bridges on the grounds.

 

Thanks.

If it worth me running a new ground at all.

AS the 1.6 wiring is ****. What aspect is ****.

 

I've attached image of CAPs.

i have removed joined up grounds.

 

I've done the ground mod as per FM ecu manual.

Ive calibrated the ECU to match the injectors at idle.

min ADC 0
max ADC 31.5

this has returned me 14.0 give or take 14.1 etc

which matches the injectors voltage feed of 14.0