bronyaur

Thanks for the feedback, and glad I could help.

I don't think you'll see the reading change as you move the distributor. I turn the motor off, move the distributor, start the motor, raise the throttle above 1000rpm and that's when I see the CMP offset get updated. What I'm reading suggests a little different procedure (like raising the engine above 1500rpm), but the main thing is that the engine needs to drop below 1000rpm (or shut off), then raised above 1000rpm (or 1500rpm, depending on what you read) to update. I'm not sure I ever really paid attention to my actual engine rpms when updating the cmp offset. I typically start the engine and snap the throttle up and watch the numbers update.

Try to set the CMP offset with the engine running at 1000-1200 rpm. You really need to get it set at zero (or dang close to it). You will experience hesitations at highway speeds and they will gradually worsen.

Sorry, but I should have mentioned that the DashCommand app will not read the CMP offset unless and until you add the PID and pay an additional $10 for that feature. Go to the Data Grid and select "Add PID" at the bottom right of the screen. On the ensuing screen, make sure "Supported PIDs" is selected at the top, then select "General". At the top of the list you will see "CMP Retard (CKP/CMP Correlation)". That's the one you want. That's probably the only additional feature you'd ever have to add. Make sure you raise the engine RPMs over 1000 to accurately read the CMP offset. Watch the reading change after you reach 1000rpm and you'll understand why this is important. The other thing to mention is that the original distributor came with a slotted hold-down that allows you to turn the distributor a half inch or so either direction. Every aftermarket hold-down I've seen does not have this slot which makes it impossible to properly set the CMP offset. Hopefully you have the original.

You need to set the CMP offset. It needs to be 0, but at least +/-2. This involves moving the distributor slightly either direction until you get the CMP offset to 0. I've seen it cause a hesitation without setting a code, and I haven't seen the code come on until its around +/-14. You'll need a scan tool that can read the CMP offset. I use the DashCommand app on my phone with a wireless scanner that plugs into the OBD port. Ditch that distributor and get a new one. The best I've found is a billet aluminum from Summit Racing (after having nightmare issues with a couple plastic ones from NAPA). The one from the salvage yard might have a worn gear, even if it doesn't look like it. And, with the cap not being securely attached, that cap might just be floating on there. These engines are really picky about the distributor. Also, you didn't mention changing the fuel filter, but that's a good place to start if you haven't yet. You can get a can of MAF cleaner and take care of that (assuming it's otherwise in working condition), and you can pull the plugs to see if they're fouled. Try running the engine at night in the dark and you may be able to see arcing around the distributor or wires.

I have had this problem on both my GMT400 vehicles and both times it was the wheel bearings. The first time I went through all the same stuff looking at TSBs, cleaning the wheel speed sensor mounting surfaces, checking voltage, etc. Then I saw a post from a senior GM tech on this forum telling everyone to stop wasting time and check their wheel bearings. Pull the hub, grab the bearing and see if it's sloppy. Sure enough. The second time I went straight to the hubs and found the same thing. Any solution to this problem should include an inspection of the wheel bearings, especially for those of us on the west coast where corrosion isn't such an issue.

The biggest clue here is the brake pedal sticking down, which leads me to suspect something mechanical related to the pedal. Either the brake booster itself is binding it up or there's something in the connector rod or pedal fulcrum that's catching. Check the rod connected at the top of the pedal. The clip that holds it on there is a pain in the ass. It typically gets removed/installed by feel as it's almost impossible to get your hands up there and see what you're doing at the same time. Perhaps the clip is not on straight or the top may be pointed in an unfavorable direction and it's catching on something. I don't recall how that rod attaches to the brake booster but that's another thing to check. The final thing is the pedal fulcrum. Make sure it's not binding in some manner.

I had to buy an 18mm open-end wrench just for this. I never found an 18mm flare-nut wrench, but I've not had any issues using the regular open-end. I don't know why GM did this.

I have a second battery and use it to run a winch. A winch can drain your battery in nothing flat. I can combine the two batteries for extra power, or reverse their role. It's also nice to switch to the auxiliary battery when you get in your truck to go to work at o-dark-thirty and find that your main battery has given up the ghost because it's old, or your son left the map light on two days ago, or.... A battery separator/combiner from Hellroaring Technologies can be invaluable if you're running off-road or frequent the middle of BFE. And, it helps to upgrade to (at least) a 150A alternator.