Ever since getting this truck it hasn't ran right. it's a 1987 Chev Truck with factory installed 454 and TBI (very clean & well cared for truck).
When going down the road there is a slight surging and after doing several things to it, it has gotten better but not yet cured.

What I have done:
Used WinALDL to Log Data
Checked for vacuum leaks & EGR
Fuel Pressure @15 PSI
Set TPS to .54 Volts (smooth voltage changes)
Set timing @ 4 degrees BTDC (unpluged by-pass)
Coil replaced recently
MSD Plug Wires
New Spark plugs
New distributor Cap & Rotor (Brass)
New Pick-up Coil in Distributor
Tested ICM-Ignition Control Module at parts store until hot - No Failure

Very recently the SES light came on and it ran much worse. It was showing code 42 and code 13. After sitting with the engine off for a while and then restarting the light goes out and runs as good as it did prior but after warming up the SES comes back on and the engine runs bad again... same code 42 & 13. My guess was ICM but it tested good.

This lead me to do a voltage check pin by pin at the ECM (1227747). Someone made a Spread sheet for checking the pins and recording the readings. I will attach it here if I can.

I did the Ohm checks with the ECM and Sensors unpluged.

Cells in Yellow are ones of concern to me.

Cells in Orange show my wire colors in parentheses, if that matters.

My next action is to test the MAP just to rule it out.

Worst case I'll pull the complete harness to check each wire (last resort

 

Code 13 is an inactive O2 sensor.

Code 42 is a EST (distributor) handshaking issue.

The O2 error may be caused by a dead sensor, or a wiring issue. There is also a ground reference wire between the ECM and engine block for the O2 sensor.

The EST error on a running engine is caused by a mismatch in DRPs and EST pulses. A loose EST/BYPASS connector will cause this. A bad pickup coil or ICM will also cause this error.

Be sure to check all of the EFI harness to engine block grounds. They can be troublesome.

RBob.

 

Does the ignition timing advance when you rev it?
Check the ecm grounds.

 

I have cleaned and checked all the engine grounds that I know of. I did an ohm check from the ECM connector pins A11, A12, D1, D2, D6 to the engine block and 0 ohms.

I replaced the ICM today with a USA made unit and the code 42 hasn't come back but, I still have a slight and subtle surge or maybe a miss fire under light load. If I stand on the throttle, no issue detected.

With the by-pass connector plugged, the timing will advance. With it unplugged it doesn't seem to move.

I have MSD plug wires, I will looking at these and maybe change them to some known good wires to rule them out.

Is there a machine or a type of scope used to find issues like this?

Thanks