For my '86 coupe, I've just purchased an EZlink scan tool. Most times, it says "vehicle not responding" BUT, when driving, occasionally the tool does connect and download data. At the same time, the dashboard mpg readout starts to work, and the TCC engages. This latter problem, i.e. intermittent operation of the mpg and TCC was why a bought the scan tool !. Data stored shows wierd values, e.g 1 mph(actually doing 50 mph), 1025 rpm (about right), -34 F Inlet manifold temp (very cold !), 0 gr/sec MAF (suprising its working at all), 127 coolant temp (dash shows 210 f, it really is warmed up) throttle sensor 4.15 v (but actually about 25% open) O2 sensor 4 mV, open loop, injector pulse 924 ms. The trouble codes are 41 ESC "error", 34 MAF too low (yep !, zero is probably too low), 32 egr failure (which is a shame, since its new)

What connects the mpg/TCC stuff to the adl link ? I've checked ecm earths at the engine, by disconnecting, cleaning, and reassembly. After all, the car actually works, performs O/K, is tricky to start when cold and has awful fuel consumption (13 mpg) but ...

For a start, consistent connection to the ecm would help !!!

 

The 1227165 ECM can transmit both 160 baud ALDL data and 8192 baud ALDL data. The 160 baud data normally send 5-byte (or 6?) data packages to the dash with MPG data.

With a 10k resistor (or less) between A and B on the ALDL connector the MPG readout will stop working and 25 byte 160 baud data will be transmitted instead.

On command the ECM can switch to 8192 baud instead. MPG will still not work.

ENGINE USAGE:
5.0L PFI CPC - (LB9) - (F) - 87,88 (160 & 8192 baud)
5.0L PFI CPC - (LB9) - (F) - 86 (160 baud only)
5.7L PFI CPC - (L98) - (8) - 87,88 (160 & 8192 baud)
5.7L PFI CPC - (L98) - (8) - 85,86 (160 baud only)

DATA PIN : READ DATA ON PIN "E" OF ALDL CONNECTOR

BAUD RATE : 8192

MODES : DATA STREAM ATTACHED FOR ALDL MODE 1

THESE ENGINES USE A 'HYBRID' ECM, AND THE 8192 DATA
COMMUNICATIONS OCCUR ON ALDL PIN 'E'
Serial data shall be unidirectional from the ECM to a connected
device at 160 baud when the ECM is not in the ALDL mode. When the
ECM is in the ALDL mode (10k), the ECM shall transmit the normal
25 parameter ALDL list at the 160 baud rate. The ECM shall then
be moded to listen for a period of 50 ms for an inbound message
from an ALDL test device at an 8192 baud rate. If a valid message
is received, communications shall continue at an 8192 baud rate
until a power down reset. Otherwise, the ECM shall be moded for
160 baud, transmit the 25 parameter ALDL list and then listen for
50 ms for an 8192 baud inbound message.

 

Thanks for the tips. I checked voltages at all th eECM connector pins, and they seem in range; the engine coolant temp voltage (0.3V at 190F indicated) and the MAT (3.5v) seem a bit wrong, but the passive resistance of both devices (8K ohm when cold), droppin when warm seems O/K ; everything else checks out, including solenoid resistances; although the "cansister purge" solenoid turns out to be "open". Still no clue as to why the ECM does not respond to the scane tool...... THEN I gently pressed the PROM onto the baord, and the engine stumbled. Sure enough, poking the PROM produces a stumble every time. I removed, and cleaned as best I could the connectors, but the thing is still not working correctly, i.e no scan connection UNLESS the mpg system has woken up by itself.

Maybe I need a new ECM and PROM. Where from (in the UK ?)