Bench testing Lambda ECU

[Bitsyncmaster]

I've got two working spare Lambda ECUs and had two dead Lambda ECUs so I decided to set up a bench test.

Current draw by the ECUs is low around 40 ma. That's not counting the current draw of the frequency valve.

The two dead ECUs would not drive the frequency valve with any power (FV has 12 volts one side the ECU clocks the other side to ground). So I traced the fault back to the one IC in both units (LM2901). Replacing the IC got both "dead" ECUs driving FV power.

The two good units drive the FV at 68 Hz with a duty cycle of 50% with the O2 input floating and the thermal throttle enrichment signal floating. One of the "bad" ECUs is running 49 Hz and 68% duty cycle. The other bad ECU is 0 Hz (not oscillating). So it looks like my new IC may need some of the calibration resistors adjusted. I'm guessing there are 5 trim resistor values looking at the units. Probably the duty cycle when the thermal throttle enrichment signal is grounded which is also the wide open throttle switch. Then I'm guessing there is a trim to set the O2 sensor threshold voltage (should be around 0.50 volts).

Which I had a schematic. But this brings up a point I've always been thinking of. That plastic ICs are only guaranteed to work for 10 years. In reality they work a lot longer since the idle ECU has a lot of plastic ICs.

[DMCVegas]

Do you think that if we wrote to BOSCH, they would be willing to share the schematics for the various ECUs, as well as calibration procedures?

[Bitsyncmaster]

I would not think Bosch would help us out.

I found the one bad unit, I swapped the readings when I wrote them down so it seems to be working and calibrated the same as the good two units. So its looking like the new IC change did not upset those two calibrations. The other bad one that is not oscillating must have a bad capacitor.

[jamesvnz]

Do you think that if we wrote to BOSCH, they would be willing to share the schematics for the various ECUs, as well as calibration procedures?

with this sort of thing I tend to follow it up as there is always no harm in asking :-) and it also depends who you get on the other line.

maybe they will help a delorean owner and if they did they may get business from other delorean owners. who knows

[Bitsyncmaster]

Got the second "bad" unit fixed. One of the small signal transistors was shorted. I replaced it with a general purpose PNP 2N2907 and it also is working the same as the others, 68 Hz and 50% duty.

I grounded the WOT signal and duty went to 40% (my meter reads backwards) it reads 60% in the car with my Snap-On meter.

So now I just have to setup a signal input I can vary above and below 0.50 volts DC. Below it should swing the duty to the minimum duty value and above to the maximum duty value

[FABombjoy]

Not sure if it's useful for what you're doing, but grounding terminal 11 will get you nearly 100% D/C

[Jonathan]

Dave,

Are there any in-car tests one could do to determine if they have a failed Lambda ECU as you've described? I mean with as little removed or altered in the car as possible. Like say just by disconnecting the frequency valve and taking readings on that connector only?

[Bitsyncmaster]

Dave,

Are there any in-car tests one could do to determine if they have a failed Lambda ECU as you've described? I mean with as little removed or altered in the car as possible. Like say just by disconnecting the frequency valve and taking readings on that connector only?

As long as the frequency valve is buzzing, your driver transistor is working and your oscillator is working. Then you can just take the readings off the orange monitor wire circuit. I used my multi-meter to read the frequency of 68 Hz. Also used it to read the duty cycle but you get the same reading dwell but dwell is 90% of the value of duty cycle. So yes you can do all the testing that I have done in the car. You can also do the battery test on the O2 signal. I plan to actually read the threshold voltage of the O2 on my bench test but really the battery test will tell you if it's working.

Now there are lots of filtering for noise in the circuits and those won't get tested. But those design values are done with caps and resistors which have very low failure rates.

[Bitsyncmaster]

Not sure if it's useful for what you're doing, but grounding terminal 11 will get you nearly 100% D/C

I will test that. Wonder why they wired that to and external pin.

[AirmanPika]

Semi related question.

I've been rebuilding the electronics in vintage audio gear for several years now. Would the ECUs in our cars benefit from rebuilds also? I'm thinking of the aging capacitors and any other component that may have been strained over 30 years. Certainly reflowing of the solder joints but anything else?

I'm aware we could simply create new equipment to replace the old stuff (hence why I bought a new DMCH fuel pump) but if the existing setups are still viable but aged I don't mind doing the work to refurbish what I have...same goes for any other electronic component in the cars on a circuit board.