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hey there, Situation: I have an 86, the dash display looks good but avg/instant consumption reading is showing 0 most of the time. The curious fact is that sometimes it starts showing reasonably meaningful values after i turn the car (last time it happened i was turning left).I believe the issue might be cable or soldering related.
I found out by looking at the manual the dash cable carrying the serial data to the dash it's D10 orange, and should measure from 2.5 to 4.0 volts AC to ground with the engine running.
I would like to investigate myself the issue, but i'm not sure on how should i proceed so I would like to kindly ask you if you can help me with some doubts:
Speaking about dash connector, should i measure voltage on D10 (mpg serial input) by grounding it to D3 (signal ground), or should i use another ground pin?
Can i measure the same serial connection through the ALDL port? i read pin E should output the serial values as well, but i couldn't understand how should i inspect it (eg: should i enable diagnostics with paper clip method between A and B? which grounding point should i use?)
I read on the service manual the following line "SOLID STATE: DO NOT MEASURE RESISTANCE". Am i damaging the circuits if i try to measure it, or should i avoid this because i will get just meaningless readings since they are solid state relays? i'm not supposed to measure resistance for this specific mpg issue, but i would like to know its meaning for the future.
The ALCL pin E is the same serial that send MPG data to the dash. Wires are spliced together. If you "paper clip" pin A and B a different serial data package will be sent and MPG data on the dash freezes.
Using a 160 baud scanner ( https://winaldl.joby.se/ ) you can see the serial data. Both small 5 byte MPG-data and the full "10k ohm" or "paperclip" data.
Use pin A as ground. ( Any groud should work )
The ALCL pin E is the same serial that send MPG data to the dash. Wires are spliced together. If you "paper clip" pin A and B a different serial data package will be sent and MPG data on the dash freezes.
Using a 160 baud scanner ( https://winaldl.joby.se/ ) you can see the serial data. Both small 5 byte MPG-data and the full "10k ohm" or "paperclip" data.
Use pin A as ground. ( Any groud should work )
thank you very much JoBy, i followed your suggestions and used winaldl with a serial cable. unfortunately i got no output, and winaldl doesn't report any incoming data.
I supposed my home made cable was faulty so I tried to measure the voltage with a multimeter between E and A: it's 0V when the car is turned off, and goes to 5V when i switch to ignition or start the engine. No variations in voltage detected with the engine running it stays at 5V(car wasn't moving). I also tried to put a 10k ohm resistor between A and B, but i still got the same results, although i'm not 100% sure the resistor was well placed.
Range is shown and updated on the dash and from my understandings it's somewhat related to the same MPG serial signal.
May i kindly ask you how do you interpret this? Could it be the cable for serial is interrupted somewhere, or the fact i get 5V between A and E and Range is shown on the dash invalidates the broken cable hypotesis?
This is my old 1984 ECU on the bench transmitting data to WinALDL using 10k mode.
You also see the multimeter showing fluctuating voltages betwenn about 2 and 5 volts.
After checking cables voltage both at ALDL connector and ECU connectors i suspect the ECU is not functioning properly most of the time. During measurements i always got fixed values between 4.5V - 5V also with 10K ohm resistance between ALDL A and B pins, and cables doesn't seems to have any interruption between their endings.
I have a spare ECU but i prefer to leave the car as it is, i don't want to move the PROM chip with the risk of bending pins or similar.
MPG serial connection question
