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Old 02-01-2003, 06:29 AM
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Join Date: Feb 2000
Location: Santa Clarita, CA, USA
Posts: 133
86 190E 2.3 - No signal pin 3 of diagnostic port

Hello Everyone,

Car: 86 190E 2.3L 8V, 78,000 miles:

I felt like cleaning under the air filter housing and thought I'd check if everything was in place. I cleaned everything up a bit and noticed the protective cap on the Lambda tower was removed. I decided to check what the duty cycle was at pin #3 of the diagnostic port to see what the mixture was set at.

I turned the key on/engine off to see if I get an 85% reading (Ca car). The reading was 0%. I thought this was strange, but I started the car anyway. Still 0%, even when it reached operating temp. I measured the idle speed at pin #1 and it was working, between 770-780rpm.

I was beginning to suspect maybe there was no Lambda control. I shut the engine down and let it cool off a bit. I took out another multimeter that could read mA. I disconnected the harness at the EHA and hooked up the meter. At key on/engine off it showed 8 mA. I started the car and within a few seconds the mA started to drop. Shortly after the readings began to swing from 2-4 mA. Meanwhile with the other multimeter, still no signal from pin #3 at the diagnostic connector.

I wanted to make one more check at the O2 sensor. I piggy backed yet another multimeter to the sensor and got readings that fluctuated from 0.2-0.7v at idle. I assume the computer is functioning.

I looked at the schematic in the engine manual and saw that pin#3 of the diagnostic port goes to pin#23 of the ECU harness. There is continuity to that point so I assume there is something wrong internally with the ECU.

If there isn't a signal at pin #3, does it mean that the ECUs ability to manage the fuel system is compromised? In other words does the signal of 0% indicate anything? With the key off the reading goes to 100% (as if the meter is not hooked up). With the key on it drops to 0%. All the other tests seem to say the ECU is doing it's job.

Update: With my meter on duty cycle, 0% shows at pin #3, but when I switch to Volts, I get 3.2-3.6V. The Engine manual gives specs in Volts ranging from ~2v to 5v. Anything outside that range calls for a lambda adjustment. I guess the early model cars did not display duty cycle but rather voltage at the diagnostic port.

Any comments are appreciated...


Last edited by DieselGuy; 02-06-2003 at 12:27 AM.
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