'85 Chevy Celebrity 2.8L mpfi AT.
Help! My engine gradually begins racing shortly after startup, or immediately races if engine is already warm. The 'Check Engine' light also flashes codes 12 and 52 when engine is running. If I clear the ECM memory (disconnect battery) only code 12 is flashed until, after the engine has run a few minutes, it slightly coughs or misses and the acceleration begins kicking in. I get the same trouble codes with engine Off, when jumping A-B on the diagnostic connector.
This began very suddenly: one day the car ran normally, the next it was a little hard starting and initially rough idling (or rougher than usual). About a half mile from home, after the car began wanting to do at least 50 on the rocky dirt road, I had to turn around come back home.
Not knowing what the codes meant, my first impulse was to visually check the Idle Speed Control assembly connections (the 3-lead speed sensor connector, and the 4-lead motor power and control connector). Turning the ignition key to On, but without engine running, I could hear the idle control motor, and it seemed a little loud, making something like grinding noises. Later, under the same circumstances, I could neither hear the motor from inches away, nor could I feel any vibration: it seemed to be not running at all.
After going online and getting a code list, I focused on the HEI module in the distributor which, as I interpreted it, is responsible for sending the 'distributor reference pulses, ' without which Code 12 will flash with the engine running. Maybe my interpretation was wrong; at any rate, I replaced the HEI module with a known good one, and nothing changed.
As far as the question of whether the ECM is working beyond just flashing codes 12 and 52, I settled my curiosity by disconnecting the MAP sensor leads for a few seconds while the engine was running. Subsequently, the appropriate code 34 was flashed along with 12 and 52.
According to the code list I got, Code 52 indicates trouble with the CALPAK. However, it also says " 3.2 liter engine, " which is not the engine I have. Whether I have a CALPAC or not remains unresolved. I believe it is just a calibration chip. Since I wanted to check the ECM connections for corrosion, I removed the unit, opened a small panel on one side of the box, and discovered beneath it three chips, two if which are large and have plastic casings possibly meant to ease removal. But, unsure whether they are removable, I have left the chips undisturbed for fear of breaking something.
Is one of them the CALPAK?
Should/can I remove it/them and clean their connectors?
Should I open the ECM box and check any other interior details?
After brushing off and applying some conductive grease to the box's exterior connector pins, I plugged it back into the car, but the problem remained unchanged. Should I open the box and check/clean any interior contact, too?
If any of you wizards get any clear ideas of what all this adds up to, please shoot me a reply soon. Living way out in the sticks, I'm in a bad way for transportation.
Friday, January 13th, 2006 AT 9:25 AM