geophray

Hi all... I just adjusted the timing in my truck last night and I took it for a test drive afterward and it was driving beautifully, but then when I was stopped at a light and the light turned green it started stumbling and sputtered and died on me. I turned it off, then started it again, and it started ok but then the service engine soon light came on, so I drove it right home. I rechecked the timing and everything seemed to be alright. I disconnected the battery to reset the computer and then took it for another spin to see if it did the same thing. About 2 miles in, when I came to a stop at a stop sign, it did the exact same thing, except this time it was hard to start when I tried to restart it. (2nd or 3rd try it started up and I drove it home.) Today I took it for another spin and it is shifting funny and randomly giving me the same behavior. (I drove it about 5 miles with no problems other than the shifting being off a little. When I turned it off and started it again, the tachometer was jumping all over the place - which I forgot to mention that it did last night when I punched on the gas about a half mile before it sputtered and died on me.) After it died on me today, I couldn't get it to idle smoothly unless I disconnected the electronic idle control wire, which I had to do to drive it home.)

For the record, I set the timing to 4 degrees BTDC with the electronic idle control wire under the dash disconnected. (I know most of these trucks are supposed to be set to TDC at idle, but my manual and the label under the hood say to set it to 4 BTDC.)

Any ideas on what might be going on here? I had the guy at the auto part store check the engine trouble code and he said it was error code 12, but I don't think he did it right so I'm gonna go check it again now myself. (Didn't realize I didn't need a scanner to check it until I got home and started searching about the error code, which turns out is just the code for "Diagnostic Mode" according to http://www.troublecodes.net/GM/ )

Thanks in advance for your sage advice!

geophray

Ok, I just retested it and the error code I got back was 12, then 42. It says code 42 is the EST circuit. I have it reconnected and am going to try resetting the codes and letting it idle again, but once again, any help you can provide would be greatly appreciated!

geophray

So it looks like the problem is definitely with the EST circuit somewhere, but I don't know how to troubleshoot exactly where it is within the circuit. Is there a tutorial for dummies somewhere on how to do this?

EinST

You had the "the electronic idle control wire under the dash disconnected" but you either have had to disconnect the vacuum hose or ignition control wire (TAN/BLK) from the distributor before setting the base timing. If not, your timing will be off as soon as it goes to the closed fuel loop.

MDTAHOE

Why did you mess with the timing in the first place?

geophray

@EinST - for my year, make, and model the tan/blk ignition control wire is under the dash and not next to the distributor. That is what I was trying to refer to when I referred to the "electronic idle control wire"... sorry if I got the terminology wrong.

@MDTAHOE - I "messed" with the timing because it was not set correctly.

I followed the directions in my repair manual step for step, and I know the timing is set correctly. After I set the timing but before it started acting up it ran better than it has in a long time.

I'm taking it in this morning to have the computer tested and will update this thread later.