Is My DME DOA?

[bcrdukes]

Hey guys,

I'm in a bit of a stumper here.

1989 325i. Stock M20 motor. No mods. Canadian/US Spec.

The ECU in my car now throws no codes on the stomp test - 1444. It's a Motronic 173. Swap in a second 173, I first got 1223 (Coolant Temperature Sensor) but that got cleared and throws the dreaded 1222 - Lambda Control code.

Using the first ECU, it's hard to start, I'd have to crank it forever (15 seconds or so) idle is choppy and runs rich (I think). Second ECU, starts up simple with a quick crank, idles a lot smoother and drives well. No signs of lean/rich exhaust but throws the code and CEL. Tried to "reset" the ECU by pulling the battery. It still throws the code.

I'm at a loss as I've:

1. Swapped multiple AFMs and intake boots
2. Swapped ECUs
3. Checked for vacuum leaks (none AFAIK)
4. Fuel pressure regulator
5. Checked evap system
6. Changed coolant temp and engine temp sensor
7. Spark plugs (new and properly gapped to spec)

What I have yet to do:

1. Swap fuel filter
2. Change oxygen sensor
3. Check injectors (this is the last thing I want to do)

Any leads before I kick the bucket? Is my DME a POS? Thanks.

[jlevie]

In this case I'd really want to believe the faults from the second DME. A bad CTS and/or an upset to the A/F ratio would explain the hard starting and poor idle. Since I can't explain why one DME throws faults and the other doesn't, I'd really want to see what a thrid DME does.

A Lambda fault is most commonly caused be an aged O2 sensor or an intake leak. though there are other possible causes. The best way to check for intake leaks is to have a smoke test run.

[RedTRex]

I would agree - use #2 DME and replace the 02 sensor.....

[bcrdukes]

This is what throws me off:

DME #1 = Hard starting (long cranks) and when the motor starts, the exhaust smells very rich. Bad / fluctuating idle and mediocre throttle response. No DME codes (1444) O2 sensor when measured, voltage jumps all over the place.

DME #2 = Starts right away. Good idle and good throttle response. Throws code 1222 with CEL. O2 sensor voltage reading a lot more stable.

Ideally, I'd like the DME output of #1 where no fault codes or CEL but the performence of DME #2. :D

[bcrdukes]

Swapped a *used* O2 sensor - made no difference. Of course, it isn't new. Not sure what to do at this point.