Need some help folks. I've been dealing with a significant engine roughness and stumble. Over the weekend I replaced the NGK plugs with a new set. That wasn't the problem, and I also found a faulty wire at #8 and swapped it out with a relatively new AC-Delco wire which was previously removed. Started up ok last night ran to the store, there was a minor miss but not as significant.

This morning I start off to go to work and everything went down the toilet (ok I know that is not technical). Let me be more specific, on the way to work I stopped at the bank shut the engine off. When I restarted it was missing and running pretty rough. As I started to drive away the engine stumbled and threw an SES and ASR lamp. Also the SYS flashed three times. I stopped the engine and restarted. It wouldn't go away, I did this twice and was able to get it going. One thing that happens when it throws the SES is the AC switches from cold to full HOT. And you can only shut it off. I limped it back home. Pulled codes and got a C41 from mode page 1.1 (CCM). So following the troubleshooting, I probed the Ignition Coil Module connector with a DVM and on Terminal B to Ground I get less than .5 volts. So following the diagrams the next test is to switch the DVM to AC mode and crank engine with the B to ground probe. I got 1.47 volts which is within the diagnostic step (between 1 and 4 volts). So the next step was to put a test light between the B+ terminal and the C terminal. The test light did NOT light. The results say "Open Ignition Coil Module Ground Circuit."

So I then tested continuity between the two and found .43 ohms resistance. I verified it directly to the engine ground connection just under the water pump back to the C terminal (in other words I went directly to ground) same thing .43 ohms resistance.

It appears (can't tell for sure since the wires to the Ignition Coil Module connector are inside of black tape but appears like that black wire comes out of the connector and goes straight to that ground on the engine block.

Now the engine is not that dirty but on that bolt for the ground it does appear a little dirty there. Do you think removing that connection and cleaning it up would resolve this?

Has anyone else had experience with this situation?

HELP I'm DOA and need to get up and running again.

BTW, I did just recently replace the ignition coil but not the ignition coil module.

 

Well I answered my own question. That ground connection G155, when I put a wrech to the bolt is was already loose. Damn.... I went ahead and remove it cleaned all the surfaces and re-attached the ground connection. I couldn't find a torque value for this bolt so I just tighten it up until it felt good.

And presto... the mis-fire is gone. Well at least on the short test ride I took. Keeping my fingers crossed this was the culprit.

Oh on my test ride saw a perfect condition, looked to be early 50's Corvette Convertible. Red and sweet. Got a wave too.