MBE ecu causing lambda fault
Discussion
Hi can any of you good people help me out?
My 4.2 has suddenly started throwing up a lambda 1 fault. Plugged the laptop in and it was showing 1.87V on the display, so unplugged lambda but the fault was still there. Tried another sensor and still the same. Tested the yellow wire to pin 21 for shorts etc and all was ok. When I backed out pin 21 and measured the voltage on the pin coming from the ecu it reads arond 4.5V! So it appears the ecu is causing its own fault, I have took it out the case and there is no corrosion, water ingress or obvious defects. If I short pin 21 to ground the fault dissapears and the display show 0V.
So any ideas? Is it new/recon ecu time?
My 4.2 has suddenly started throwing up a lambda 1 fault. Plugged the laptop in and it was showing 1.87V on the display, so unplugged lambda but the fault was still there. Tried another sensor and still the same. Tested the yellow wire to pin 21 for shorts etc and all was ok. When I backed out pin 21 and measured the voltage on the pin coming from the ecu it reads arond 4.5V! So it appears the ecu is causing its own fault, I have took it out the case and there is no corrosion, water ingress or obvious defects. If I short pin 21 to ground the fault dissapears and the display show 0V.
So any ideas? Is it new/recon ecu time?
If the fault disappears when you short pin 21 to ground then I'd say the ECU is ok.
I assume pin 21 is the pin the lambda sensor goes to?
It WILL have voltage on it when there's nothing plugged into it, its an open-collector output, so the voltage on it will drift up to its full amount if nothing is pulling it to ground.
I would still suspect a cable fault - water in somewhere perhaps?
I had faults like that in my previous car. Inside the loom there are crimp connectors where wires are junctioned; these are not insulated, so if you get some moisture in the loom you can get paths of low resistance where there be no conductivity.
What about if you temporarily swap the 'faulty' cable to the other lambda sensor?
Does the fault still show? If yes then its not the sensor.
Andy.
I assume pin 21 is the pin the lambda sensor goes to?
It WILL have voltage on it when there's nothing plugged into it, its an open-collector output, so the voltage on it will drift up to its full amount if nothing is pulling it to ground.
I would still suspect a cable fault - water in somewhere perhaps?
I had faults like that in my previous car. Inside the loom there are crimp connectors where wires are junctioned; these are not insulated, so if you get some moisture in the loom you can get paths of low resistance where there be no conductivity.
What about if you temporarily swap the 'faulty' cable to the other lambda sensor?
Does the fault still show? If yes then its not the sensor.
Andy.
That all makes sense, but if I unplug the other lambda sensor its reading doesn't shoot up to 1.8V, and if its unplugged the wire which goes from the ecu to the now unplugged sensor isn't pulled to ground so how can that read 0V.
Also after posting I realised I had a spare ecu (it came with the car and I had never tried it), when I plug that in the lambda fault goes away.
Only thing is I can get the car to run on it, it looks the same unit inside and I have even tried the original chip from mine in it. It will fire but runs awful, ive cleared the faults and reset the adaptives but it wont play. The only physical difference I can see is the case is silver not gold (is this right?)
I was wondering if it was of a 4.5 but I found some pictures of a 4.5 ecu and it looks totally different inside, unless that was a revised type.
How can you tell the difference between the 2?
Also after posting I realised I had a spare ecu (it came with the car and I had never tried it), when I plug that in the lambda fault goes away.
Only thing is I can get the car to run on it, it looks the same unit inside and I have even tried the original chip from mine in it. It will fire but runs awful, ive cleared the faults and reset the adaptives but it wont play. The only physical difference I can see is the case is silver not gold (is this right?)
I was wondering if it was of a 4.5 but I found some pictures of a 4.5 ecu and it looks totally different inside, unless that was a revised type.
How can you tell the difference between the 2?
pjenni12 said:
Hi can any of you good people help me out?
My 4.2 has suddenly started throwing up a lambda 1 fault. Plugged the laptop in and it was showing 1.87V on the display, so unplugged lambda but the fault was still there. Tried another sensor and still the same. Tested the yellow wire to pin 21 for shorts etc and all was ok. When I backed out pin 21 and measured the voltage on the pin coming from the ecu it reads arond 4.5V! So it appears the ecu is causing its own fault, I have took it out the case and there is no corrosion, water ingress or obvious defects. If I short pin 21 to ground the fault dissapears and the display show 0V.
So any ideas? Is it new/recon ecu time?
My 4.2 has suddenly started throwing up a lambda 1 fault. Plugged the laptop in and it was showing 1.87V on the display, so unplugged lambda but the fault was still there. Tried another sensor and still the same. Tested the yellow wire to pin 21 for shorts etc and all was ok. When I backed out pin 21 and measured the voltage on the pin coming from the ecu it reads arond 4.5V! So it appears the ecu is causing its own fault, I have took it out the case and there is no corrosion, water ingress or obvious defects. If I short pin 21 to ground the fault dissapears and the display show 0V.
So any ideas? Is it new/recon ecu time?
What are your throttle pots reading and what are the adaptives telling you?
MB
pjenni12 said:
Throttle pots are around 18ish, and i didn't look at the adaptives as it would start and run fine on the original ecu (bar the lambda fault)
Do you reckon it just wants setting up?
Do you reckon it just wants setting up?
Sounds as if it needs to be set up. There are many variables that can effect the running/lambdas/idle etc and I've had a right laugh (not) faffing around with mine recently. I found that if my pots were set too high I regularly had a show of 1.87 on the lambda readings - too much oxygen in the fumes I presume.
Plus also the parts get worn and slack and you have to compensate for this by making minor adjustments. Its not rocket science, but it is bloddy fiddly. I've learnt that near is usually as good as it gets and its usually good enough. I have however slowly started to replace bits and bobs along the line as this seems to improve things gradually eg new lambdas both sides, big fuse, spark plugs air filter etc etc.
Cheers
MB
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