ECU Help

[malc_grn]

Hi

Anyone know why my ecu reads the battery voltage at 11.2V, when a multimeter shows the battery to be 12.4V?

I have checked readings either side of the 100 amp fuse in the passenger footwell and both show 12.4.

Will the ECU not fire if voltage drops below a certain level? could this cause my poor starting?

Any help gratefully recieved

Regards
Malc

[VPower]

Malc

Have you tried taking a reading of the ECU voltage at the power inputs?

Looking at the ECU drawings posted on here a few weeks ago.
There are 2 - PIN 6 and PIN 52 that should be battery voltage.
Check these against a test lead wire from the Earth NEG side of battery.

Could be an earth problem.
Earth connections at ECU are PINS 7 26 50 51.
Check these for resistance with that test wire from the NEG side of battery.

Yesterday my battery was low (one month sitting in garage) and it would not fire at all, not even a splutter, although it cranked for quite a while!

I suspect a new battery is required in my case.

[malc_grn]

Doing some more fettling today, and thanks VPOWER, I've looked at those pins its showing 12.2V on the positive pins, but still only showing 10.8V on ecu software??? just need to check the earth pins.

When I am cranking over the battery is spinning the engine over fine but not firing up as she should, only with an extra battery from another car will it start with any ease.
Anyhow I have noticed that lambda 1 is going up to and sticking at 1.85V, so am i right in thinking that the ecu thinks car is running rich, so is leaning out fuel mixture causing starting problems? obviously a new lambda is required i think.

Any thoughts?

[Steve_T]

How old is the battery? If it's a bit ancient and down on capacity then as you crank the voltage will drop more than a battery in good condition. This combined with the drop that you're measuring through the wiring loom, may stop the ECU from being able to function and fire the plugs during cranking. The extra battery is holding the voltage up during cranking, so I'd track down the cause of the voltage drop to the ECU and perhaps get the battery tested.

[VPower]

Just had a quick Google and confirmed that on cranking the voltage of a charged battery should not drop below 9 volts. Checked at the battery itself!

If it does, then you need to get the battery tested, but from my experience it will have a duff cell or two.

Bearing in mind how hot mine get on the engine side, I'm not surprised that go duff quickly.

[a1rak]

malc_grn said:

Doing some more fettling today, and thanks VPOWER, I've looked at those pins its showing 12.2V on the positive pins, but still only showing 10.8V on ecu software??? just need to check the earth pins.

When I am cranking over the battery is spinning the engine over fine but not firing up as she should, only with an extra battery from another car will it start with any ease.
Anyhow I have noticed that lambda 1 is going up to and sticking at 1.85V, so am i right in thinking that the ecu thinks car is running rich, so is leaning out fuel mixture causing starting problems? obviously a new lambda is required i think.

Any thoughts?

I would definatley ignore your LAMDA readings if the engine is not running as they need to get hot to work properly. If the engine is not firing they are most probably covered in unburnt fuel. Dont worry about the lamda readings for starting.
The cold starting system on the MBE i think is very basic I believe they just throw a load of extra fuel in based on engine temperature.

I would look on your the diagnostic sensor page and check that all the temp readings and throttle pots are where they should be. I would remove a spark plug check the intensity of the spark. if you have a 4.5 then remove the airboxes and check the injectors spray pattern. I would also put a temporary large main earth cable direct to the engine from the battery -ve battery terminal. anyway good luck I hope you get it sorted