89 350 TBI Code 42 Assistance

[neergX]

I am experiencing an intermittent code 42 on my 89 k5 350 TBI. In an attempt to correct the problem, I have replaced the cap, rotor, plugs, and wires. I also set the timing (with the ECM disabled) to 0%. However, I will occasionally feel what seems to be a miss, and then the Service Engine Light comes on. Once that happens, the idle is rough and the engine feels like it is going to stall out at traffic lights.

I don’t want to throw parts at it in a guessing game now, so I look to you all for help. My next *guess* is either the EGR or Knock Sensor, but that is only an uneducated speculation. The reality is that I am unsure what to do next, and any help is appreciated. Thank you.

[quaddriver]

Originally Posted by neergX

I am experiencing an intermittent code 42 on my 89 k5 350 TBI. In an attempt to correct the problem, I have replaced the cap, rotor, plugs, and wires. I also set the timing (with the ECM disabled) to 0%. However, I will occasionally feel what seems to be a miss, and then the Service Engine Light comes on. Once that happens, the idle is rough and the engine feels like it is going to stall out at traffic lights.

I don’t want to throw parts at it in a guessing game now, so I look to you all for help. My next *guess* is either the EGR or Knock Sensor, but that is only an uneducated speculation. The reality is that I am unsure what to do next, and any help is appreciated. Thank you.

Nope, its a stupid little module in the distributor in 99% of the cases...

The test is fairly easy, you pull the ECM connectors and with the EST hooked up (meaning the 4 wire plug to the dist is still on) you first test for proper resistance. On the D4 or D5 line - I forget without my book in front of me. Then you test the EST wire (tan w/black) by touching a hot test light and the resistance should flop high. There are other conditions based on a test light going on or off or resistance found here and there, but suffice to say that involves pinched (shorted) or cut (open) circuit wires in that harness.

to change the est, remove the cap and both harness connectors and 2 tiny screws that hold the module to the base, once done, gently pry it up to break the sticktion of the 'grease' and remove the internal 2 pin connector to the pickup coil. clean the dist base plate (as this serves as ground) and apply a lot of the supplied grease for the new one and connect everything back up. you wont even have to retime.

typically these just fail flat out and you lose all advance over 20*, but I have seen cases there they are intermittent.