DTC 41 on a stock 1985 231

[Regalindisimo1985]

So far, I have checked continuity between the ecm pins to the 4 wire distributor connector and checks out okay.

Engine code 41 is this: No distributor reference pulses to ECM with engine running.

I located information on GM ignition modules and found out that pin R on the module is the one that sends a reference pulse to the ecm. It also happens to be the PPl/white wire.

My question is how can I make sure that the ecm is receiving a pulse?
---> can I do this with a voltmeter and getting a read out on that wire?
---> What is that wire suppose to read with key on engine off?
---> What is that wire suppose to read with the engine running?

Appreciate the help...

 

[DoubleV]

I don't know the answer and if I were a betting man I would say that nobody else here would know either as it's a pretty specialized question. This is why everyone REALLY needs to get a GM service manual.

 

[Jshock]

CODE 41, NO DISTRIBUTOR REFERENCE SIGNAL

CIRCUIT DESCRIPTION
Code 41 says that there are no distributor references pulses to the ECM at a specified engine vacuum. This code could set with the key "ON", engine "Not Running" if the MAP or VAC sensor was defective by indicating "Engine Running" voltage with just the key "ON". With a constant open or ground in the reference signal circuit, Code 12 would be set along with a 41. Use Chart 12 if 12 and 41 are set. Code 41 alone indicates the problem is intermittent. When the distributor reference line signal is lost, the engine runs full rich and with retarded (base) spark timing. The result is poor performance, poor fuel economy, and possibly rotten egg odor from exhaust.

CHART DESCRIPTION
Step numbers refer to step numbers on diagnostic chart.
Checks to see if MAP or VAC sensor voltage changes with loss of vacuum supply. A good sensor will change voltage at Terms. 'A' to 'B' or ECM Terms. "20" to "22" by 1 volt or more.
Checks for cause of an intermittent open or ground in the distributor circuit. Fault could also be an intermittent stuck MAP or Vacuum sensor that has the same voltage output as an engine "running" with only the key "ON", thus, no reference signal. Terminals must be removed from connectors to properly check them. The distributor pick-up coil should also be checked.
Since the voltage change was less than 1 volt, the problem is in the MAP/VAC system. The ECM has "seen" engine running vacuum equivalent with no distributor reference signal, with the key "ON" and engine not running.
If Code 12 is present, with engine running, a distributor reference fault is indicated. See Code 12 CHART first.

 

[Jshock]

Hope this helps man! Good luck.

 

[Regalindisimo1985]

I solved that problem. Code 41 showed up because of this:

"The ECM interpreted MY engine as a running engine when I applied vacuum to the map sensor during Key On Engine Off, ( I was testing the sensor for awkward ohm readings). The equivalence of having no distributor reference signal.


Very informative diagram. Thank you for that