Hi,

After standing in garage in winter, my '91 'Bird runs rich. There's pretty bad gas smell from exhaust and the fuel consumption is too high. I used WinALDL to log the ECM data during the driving to work and the log show that the car runs rich (BLM average 115) and there's something weird happening with MAP reading. Engine warm and idling at about 600 RPM, shifter in D position - the reading is about 90 RAW/45 by sensor, accelerating to 2000 RPM its ca 175 RAW/75 by sensor.

I used multimeter and vacuum pump to test the sensor and found no anomalies - it fluctuates from 4.7 V open to 1 V applying vacuum and the process is smooth. So I reattached the MAP sensor and measured the voltage change with engine working - and then real anomaly occurred. Engine idling the voltage reads about 1V, raising slowly the RPM, the voltage raises to about 2.7V and then drops to 50-100 mV. The control voltage is exactly 5V all the time measured between the sensor ground or body ground and the control voltage pin. Weird seems to me the fact that after voltage dropping, there is about 100 mV potential difference between the body and the sensor ground. Looks like bad grounding somewhere. I did check the ground between the engine and body and it's good (about 100 mV of voltage drop with engine and all the accessories running, full lights on).

I think there is something wrong with sensor's electrical circuit, it seems like something grounds the sensor at about 2000 RPMs. It doesn't seem logical that the engine vacuum changes like that - the engine works fine and revs nicely after the voltage drops, there seems nothing wrong with air flow. And removing the vacuum pipe from the sensor and blocking it with thumb, it feels like the vacuum constantly drops when the engine runs faster as it should.

I would appreciate if someone could give some ideas to check. It really drives me nuts.

The datalog itself is downloadable from http://lepo.it.da.ut.ee/~rnahkur/Sta...083425_LOG.xls if someone wants to see it.

 

Well, I found the reason for incorrect MAP reading - one of the vacuum pipes leading to EGR solenoid was pinched and after replacing that one, the anomaly mentioned above haven't occured anymore...