Greetings fellow Bricksters, I'v been working on this '89 240 (235.00 miles) with a rich running problem.
The car is definitely running rich, the o2 sensor read .55v at cold start then climbs to approx. .9v and then stays there. After a short while it throws the CEL.
The coolant sensor checks out OK as does all the connections at the ECU (power, ground, voltage and resistances.
I tried swapping the fuel pressure regulator with one from an "88 240 (lower pressure) with no difference.
I have two codes that I think are false: #312, missing knock sensor signal and #213, throttle SW full-throttle contacts misadjusted or shorted to ground.
I swapped the knock sensor with a used one and measured the .7v at ECU pin #28 ;then same code, installed NEW knock sensor and no change.
Tested the throttle switch and wiring and all is good but still get the code #213
Still get random fuel codes #231, 113, 221
Tried swapping the AMM with an #007 from an "88 volvo, did not idle at first then ran rich.
So I'm down to leaky injectors, bad AMM or bad ECU. I have rarely seen a problem with injectors which makes me lean to the ECU.
Have I missed anything else ??
Thanks
peter

I would try a new air filter first. If not enough air gets through, then there's too much gasoline mist in the combustion chamber in relation to the air, and your engine will run rich. It happened on my 1987 740 turbo. New air filter and those problems disappeared.

I went through this about 3 years ago on my 1990. It was the ECU. There currently is a 951 ECU on Ebay for $105. Buy it now! Note the that the 951 may give you a bit lower MPG.

Mark

Me too, on a '89 245. The main symptom for me was intermittent engine fuel cut, which is the classic ground problem in the 561 where the fuel pump relay ground goes bad. In your case, it could be something else, but since it's a 561, I'd say replace it anyway.
After I got a used, white label 561, (later, upgraded one) I tried an ECU from a '94 940 n/a car, and the engine ran much better, more even running than with the 561, better on regular gas, and ran like a modern car should.
I still have a good 561 here that I don't need, but the money would be better spent on any 9XX ecu from a 940 n/a, as long as it's for the Bosch LH 2.4 systems.

The label on my 561 ECU is pink with a second smaller label that is white. Judging by the fact that this ECU had some mounting screws missing, I'm gonna guest that someone already changed it once before.
What does a "white label" 561 ECU look like??
I will try the junkyard for a 951 ECU or another 561.
thanks
peter

Hello
if you would need a ecu let me know.
i have a couple white label 951s volvos answer to the bad pink label 561
60.00$ shipped guarenteed. peopleguy999@yahoo.com
good luck
Mike