Random electrical/ignition/engine issues

[mason10198]

Hey guys, unfortunately I'm about to share an essay with all of you...
So the past few months I have been getting some strange and random problems. I'm just gonna go down the list chronologically...

Ever since I bought the truck (summer 2-3 years ago) I would get a P0302 code (cyl 2 misfire) about once a month. Tried chasing it down for a while (replaced sparkplugs, wires, coilpacks) but couldn't ever get it to fully go away. It's had a bit of an idle sputter too (see video here), but never caused any real problems though so I have just been clearing it off with the scangauge when it comes up ever since.

Now, my low beams went out. Well, not exactly the lights themselves, but the circuit. Tried to turn them on one day, and got nothing on either side. Tested all the fuses, relays, circuits, wires, entire HID system, everything was good. Couldn't trace it back farther than the HDM relay in the front fuse box, which is apparently not receiving power at all. I assumed that since it was in that whole low beam control circuit that it was computer related (BCM) and I just needed a new controller, so for the time being I just took the wires in my HIDs and flipped 'em backwards so I can use the high beam circuit to turn on my low beam bulbs by flipping the stick on the wheel forward, and just deal with not have working high beams (fine with me since I got the 50" LED bar).

Next up would be the forever-running engine. Around 8-10 times within the last month or two, I literally could not get my engine to turn off. The first time, I parked, turned the key off, and for 5-10 seconds nothing happened. Everything was still on, including engine. I turned the key back on and then off again and it worked. Shrugged it off, went home. Second time, same thing happened except after I had turned the key off and it kept running for 10-15 seconds, all my dash lights started going haywire. I watched in horror for a couple seconds, then it shut itself off. This happened around 2 more times before I replaced the ignition switch. It worked fine for 2 days, then started the same thing again. The last time it happened, I had parked and turned the key off, engine kept running, and I just waited for it to turn off. Nothing happened. 5 minutes of key on/key off and nothing would work. The ONLY way I got it to shut off was pulling the fuel pump relay. 2 hours later, I got in to go home and trans starts acting weird. I feel like I don't have any power and I realize it's stuck in 2nd or 3rd. I try forcing it to downshift with the stick and it works once, and after that I'm stuck driving 20 miles home in 3rd. I decided this was another load of computer BS so I pulled both my batteries and waited an hour. Hooked the power back up, and no problems for a couple weeks.

Now, within the last month, I've had 4-5 cases of my engine just shutting off. Not dying out or stalling, just shutting off. No weird sounds or anything, just sounds like I turned the key off. It happened once right after (2 minutes or so) I parked in a parking lot, then a couple days later while stopped in gear behind an unloading school bus. Then again a few days later while I was out on the trails rolling down a big hill with the gearshift in D1 to make it easier on my brakes, I got to the bottom of the hill and noticed the engine wasn't running. Considering there are never any weird sounds and it just acts like a normal engine shutoff with no codes or anything, AND remember I just replaced my ignition switch, I just assumed it was another computer problem that I couldn't really do anything about at the time.

3 days ago I went driving around at the local offroad park. No problems, had a great time. The next day, I drive to school and it feels kinda rough.. Didn't have time to think about it so shrugged it off for the time being. 3 hours later I have to drive 10 miles to go to class on another campus. I get half a mile down the road and notice the engine light is on. I figured it was just that P0302 coming up for this month, but the scangauge says its P0304 for cyl 4... Huh, weird... Oh well, don't have time to deal with it. 5 miles farther and I get on the freeway, and the engine light starts FLASHING. I immediately shut off my AC and radio and slowed down so I could hear, and I was definitely running on less than all 6 cylinders... Class was only 2 miles away so I went ahead and drove there and just had my dad come pick me up on a trailer later. Again, I thought this was some computer crap, so I went to the the local U-Pull and got a PCM, BCM, and 2 brand new-looking coilpacks. Went home and swapped the 2 computers in, did the CASE relearn, and swapped out coilpacks on cyls 2 and 4 (only codes I've ever got were for cyls 2 and 4). I found cyl 4 full of water, with the sparkplug submerged. I blew out the water with an air compressor and made sure the rest were dry as well. Started it up and it runs smooth for a few minutes, so it was just the water in there, right? So I put my tuned PCM back in and tried it again. Runs smooth down the road for 5 miles or so, so it MUST have been the water. SIKE. Drove to school fine today, but completely lost a cylinder on the way home again, flashing engine light and all... until about 5 minutes later when everything starts working fine again the rest of the way. I unhooked the batteries for an hour, plugged them back up and started the engine, and missing a cylinder right from the start. Except this time, engine code is P0301 for cyl 1... WTH!?!?!?

As of now I have concluded that the computer has NO idea what is actually going on in the engine... And I have NO idea what to do next. I'm about to leave for a 2 week long trip and I don't have just a ton of time to figure this crap out. My current best idea is just to post this, and also show it to my dealer mechanic buddy and see what info I come up with. If anyone has come across these wacko problems before and has any insight, it would be MUCH appreciated.

[maxxis]

Couple of things. From what I know the. I6 is notorious for valve issues. I've seen quite a few heads sent out to the machine shop. Let's hope it not that, second a lot of the electrical issues you have sound all linked to the fuse block under the rear bench seat. The flat ribbon cable connector is know to cause a lot of issues, in fact that section of your truck should be hermetically sealed to avoid complications i.m.o. That cable gets brittle over time and tears/cracks/rips/w.e I'd thorowly inspect that. When you say water do you mean coolant or water H2O? Also just trying to ring my memory but these trucks were one of the first few to get the gm star communicatons networks. And for some stupid reason a lot of the communications go through the rear tail gate module check that out if you can get your hands on a tec 2 see if you can set coms with that module. If not check there!

[maxxis]

Also do you know what your o2s reading? Because in many cases the o2s won't actually set a code of but will play with the fuel trim and cause a miss fire. If you can get a snap shot of what they are reading if the numbers are over the top or seam fishy check with them. I know I have v8 but I kept on getting a miss code and couldn't figure out why till I got pointed in the o2 direction.

[mason10198]

Wow, thanks for the quick reply!

I sure hope it's not valve issues... and I have checked out everything in both of the electrical "centers" and can't find anything wrong. Ribbon cable looks fine to me.

When I say water I mean H20. I read that since Cyl 4 is directly under the gap between the hood and the windshield, all that runoff water gets dumped right on top of it.

I ripped out all that OnStar stuff right when I bought the truck if that's what you're talking about, so that shouldn't be related... not fond of GM having GPS and mics in my truck, lol.

I don't actually know anything about my O2's, but I had considered it for the once-a-month P0302. But my current problem is it just dropping a cylinder altogether, not just missing occasionally. It just decides randomly when it wants one to completely die. And to make it worse, I seem so be getting a code for a different cylinder every time it happens. Would O2's cause that too? I can get my mechanic buddy to hook all his fancy gizmos up and take some readings.

[maxxis]

Naw the on-star should have nothing to do with it, I'm talking bout the class 2 communications between modules, i.e bcm to pcm to tcm etc. Let me do some digging and get on the pc and of the blackberry lol

[mason10198]

Oh! I read that completely wrong.. Saw comms and immediately thought onstar lol.

I can't remember.. Isn't the TCM included in the PCM in the ~'05 I6's?

[KingBird]

I'd check and make sure all grounds to the frame are good.

I had some issues with a couple of mine and it caused all kinds of jicky haywire crap.

As for your low/hi beam relay, I have the same issue, I just tap mine with my pocketknife and it works again. I actually refrain from using my high beams and use the roof lights instead.

[mason10198]

I'd check and make sure all grounds to the frame are good.

I had some issues with a couple of mine and it caused all kinds of jicky haywire crap.

As for your low/hi beam relay, I have the same issue, I just tap mine with my pocketknife and it works again. I actually refrain from using my high beams and use the roof lights instead.

Thanks! I've checked most of the grounds I can find, but I'm still digging.

The HDM relay I'm talking about is solid state so tapping it wouldn't do anything, and the relay itself works fine, but the pin that is supposed to supply power to it, well, doesn't.

Sent from my SAMSUNG-SM-G870A using Tapatalk

[KingBird]

See, mine has power, but I guess the pins don't make a good connection. Tapping it seems to get it back in contact.

I've been thinking of getting another box from a donor TB to see if that would fix it or if the problem lies with the actual connection to the wire on the plug. I'd assume my problem would be the former while yours is the latter.

[mason10198]

Alright! I got a couple things figured out and taken care of!

First things first, the complete loss of random cylinders... When I first got the code for cylinder 4 I took it apart and found a bunch of water under the coilpack, shorting out the spark before it made it into the cylinder. When I cleaned it out, the problem moved to cylinder 1. I took the coilpack off, and found a bunch of mud in there. I cleaned it out by spraying it with a good household sprayer filled with water, and then sucking it out with a shopvac and drying it out with an air compressor. Hair dryer would work good too. I repeated this 5-8 times on ALL cylinders. It ran a little better, but the problem was still there. I got to thinking more and finally it clicked. Water=rust. I pulled off the coilpacks again, pulled the rubber boot off of each one, and found 4 out of 6 of them with contacts looking like this (some of them worse).

The springs in the boots looked about the same way, so I squirted in some WD-40 and let it sit for a few minutes before wiping out the corrosion with a paper towel. I cleaned everything off and put the coilpacks back together with dielectric grease. Low and behold, IT WORKED!! Now I'm back to my slightly irregular idle.

I also fixed my low beam HDM circuit. Somehow, even after thoroughly searching at least 10 times, I missed a fuse. I found schematics and diagrams of the whole thing and started studying them before finally realizing I had missed the blasted (literally) fuse #53 for HDM. I'll go ahead and post this diagram and label it since I already have it open in my image editor, lol.

[navigator]

Glad you got them figured out man.