Been looking around and apparently there's an "updated" version of the ECM on my blazer. These old ECM's had the ability to learn but from everything I've found they cannot adjust to the changes in the operation of an engine as the engine ages.

My engine has over 140K miles and is showing some wear..ie rings are starting to wear. I know this because last time I changed the spark plugs there was some oil on them.

First of all am I correct in assuming that the ECM controls spark advance? Is there a way to flash or program the ECM? Is it even worth messing with?

 

The ECM adapts to current conditions. I do not believe that any OBD1 ECM actually learns though. They just adapt to the current conditions.

Oil on the plugs is not a real good indication of engine wear. It could just mean that your valve seals have started to go and it is not affecting compression. You really should test compression and leak down to assess the condition of the valve seats and ring sealing.

 

Tomorrow the compression test will be done. I'll get back with the results.

Maybe it's just a vocabulary discrepancy.

Light Duty Truck Shop Manual
pg 6E-7 Driveability and Emissions

"ECM Learning Ability
The ECM has a "learning" ability. If the battery is disconnected to clear diagnostic codes, or for repair, the "learning" process has to begin all over again. A change may be noted in the vehicle's performance. To "teach" the vehicle......drive at part throttle...until normal performance returns."

Never fooled with an ECM.

 

"learning" for the OBD1 PCMs is centered solely around the AFR (air fuel ratio) and not much else. Learning for an OBD2 PCM is MUCH more.

 

If all it learns the AFR all it is really doing then is adjusting spark advance?? Or am I way outta line?

 

It adjusts injector pulse width to maintain AFR. It adjusts the advance to maintain proper timing for the conditions. The MAP, TPS, O2, and knock sensor(s) are used to modify these two parameters.

 

Were they "programmable"? Is this just a waste of time?

 

You can get different eProm modules to swap into your ECM to reprogram it.

 

Expect to pay around $300-$400 for a EEPROM programmer if you plan to do it yourself. I have scoured the internet to no avail and could not even find plans or a kit so I could do the PCM on my Bonneville.

Other option would be to scour the J/Y'ds for another PROM identical to yours, send it to a shop with your VIN, engine type, trans type and let them know what you want changed. Of course, they also may want the whole computer.

 

Ok. We'll mess with the ECm later.

Engine: 1986 305CID RPO-LE9-High Output.
Snap-On MT307KB Compression Test Gauge
Dry Test
Engine at operating temp.
All plugs removed
All plugs but cylinder #3 had oil on them. #5 had the most.
Cylinder # Rotation 1 Rot 2 Rot 4 Max Pressure (about 8 Rotations)
1 65 115 151 195
2 75 125 154 190
3 78 125 150 195
4 76 125 150 195
5 74 125 152 185
6 75 125 150 195
7 75 120 150 200
8 75 125 150 195
Difference hi/lo 13psi 10psi 4psi 15psi

What do we think?