This has a bit of a long back story, so bear with me, I did post about it a little bit earlier on the forum.

I have an 08 h2 with a Magnuson supercharger bolted on. It has been installed and tuned correctly as far as my knowledge goes and is a kit specifically designed for the 08 H2. It has the canned magnuson tune. I contacted them and they said there has only been one version of the tune, and no one has had issues. The transmission went out on us about a year ago, so we took it to a gm dealer who used to sell hummers to have it replaced as they had a fair price. When we got the truck back, on the way out of the lot, accelerating up the hill, the CEL came on with a p0030 drivers side precat o2 heater circuit code. They took it back, said it was the sensor and sent us on our way. I looked at the work they did and noticed they put a new sensor, BUT they also ran a new wire along the frame from the ecu to the o2 sensor. I know it definitely wasn't there before. A few days later the CEL comes on again for the same code intermittently. They said it was just a stored code and the CEL would go away on its own.

Fast forward a year, it still intermittently came on. Also during this time, I noticed a slight knocking(what sounds like detonation) when going up hills at 3200 rpm in 2nd and 3rd gear that would get really get very loud when pulling my 3500lb trailer up on moderate grades from Alpharetta to iron mountain park in Dahlonega Georgia. I took it back and just told them to fix the CEL as I figured this might be my issue as well as fix my exhaust manifold leaks. They said it was a bad sensor, replaced exhaust gaskets. Sent me on my way. Light comes back on, and I take it back again. This time I mentioned the knocking noise and told them to diagnose that as well and that the two could possibly be related. I also said i noticed a slow leak from the inter-cooler system and told them to fix it, and make sure it's working. They said they used a sensor from an 05, put the correct one in, tightened up inter-cooler hoses, said they couldn't reproduce the knocking and sent me on my way. I figured they must have put the sensor in, and it fixed it.

But yesterday, I loaded up my trailer and made it about a mile. Engine has fully warm for a good 10 minutes(so its not piston slap), I hear a little bit of knock in 2nd as I'm accelerating up a small hill. Then the CEL comes on with the same p0030 code. I go home, unhook the trailer, drive around, CEL goes away. That's where I'm at right now.

I would like to get a video of the knock. I have tried, however, in the cold temperatures it doesn't get loud enough to be picked up by the mic on my phone. The best I can describe it is that it sounds like spark knock or marbles in a tea can that gets shaken harder depending on the load.

I am completely at a loss right now. Do I keep taking it back to them or take it to another mechanic? They haven't charged me for any of the o2 sensor fixes, and the service rep is a really nice guy who we've known forever, so we keep taking it back. I don't want to point fingers, but I know that a portion of the exhaust has to be unbolted and removed to get the transmission out. My thought is maybe they dropped it and tore a wire somewhere or something happened. They said they inspected the wiring, and it was fine, but at this point I have my doubts. I have seen someone on this forum a long time ago with 120k with the same year and same supercharger kit who tows 6k lbs up mountains with no issues.

A few more questions I need answered.
Can an o2 sensor heater circuit fault be related to the knocking noise I'm hearing? ie: the air/fuel ratio being off.
Does a heater circuit malfunction or the code being stored affect how the ecu finds the correct air/fuel ratio?
Could the knocking be something else? If so what?
What would cause a very intermittent heater circuit code?
Does the o2 heater affect the engine when its warm?

Any help on any portion of this would be very much appreciated and I would be very thankful. I'm starting to think the mechanic thinks I'm crazy, and I assure you I'm not. I now have a mom and friend who have been with me on these drives who can vouch I'm not making it up.
I am 16 and have been lucky that my dad is helping me financially, but he is getting to the point where he's annoyed. I plan on keeping it forever, but I'd like it to be reliable. My parents won't be the ones paying for repairs forever. Currently sitting at 99,380 on the odometer. Keep in mind this is an 08 with the newer L92 aluminum block engine.

 

when you supercharge an engine you need to also change your fuel octane levels to keep the engine from knocking since the supercharger is loading the chamber and causing a leaner then stock condition. usually fuel injectors need to be also sized to accommodate for the supercharger boost pressures

 

Usually yes. The Magnuson kit is designed for factory injectors. It makes less than 6psi of boost. Also I have never run anything lower than 93 octane.

 

 

How old were you driving the '03?

 

let a local tuner look at it with HP Tuners and see what's going on.

I've never looked into a Magnuson tune to see what they do so I can't help there but it takes that type of software to see everything need to diagnose.

The dealers are good at what they do but are not trained for this type of issue, it could be as easy as the MAP sensor but without knowing what to look for and the software to see it it will be hard to identify the issue.

Depending on the dealership and the knowledge of the service department they may have someone that knows and has the software to look at it.

My 2 cents,

Neal

 

Dang man you got me. I have all my accounts as feb 10 2000 for simplicity sake because I’ve always been too young. Also I said “my” because I’m lazy. Our 03 we had was used. We actually traded it to the guy that put in our hot tub. He still has it.

can assure you I am 16 now tho lol.

 

thanks. I guess it makes sense a dealer wouldn’t have that equipment. As of right now I’m going keep taking it in for the engine light until they figure that out since they’ve pretty much admitted it’s their fault.
If that doesn’t fix it, I know a local tuner, but he’s very expensive and constantly booked. I can tell the dealer is tired of seeing me back there and I’m tired of going, so we’ll se who outlasts who.

 

OK, So the code for the heater circuit likely has nothing to do with your knocking issue directly. The o2 sensor has a power and ground wire that heats the o2 sensor up when it is dead cold and the engine is in open loop (cold tune). That is the whole function of the circuit and does not fit your issues. The wire that has been run to the ECU is suspicious. If that wire was shorted to ground, it may have burned up the transistor in the PCM for that heater circuit. This could be why the code will not go away. The circuit will have to be scanned with a lab scope at the PCM to verify integrity.

The knock is very concerning and likely a more pressing and unrelated issue. What you describe (marbles in a can) sounds very much like rod knock. The LS is setup to priority oil the top of the engine and it has been known to have lower end oiling issues to mains and rods. You could drain the oil and examine for any metal particles. Another thing to check is the tightness of the torque converter to flexplate bolts. I have seen these come loose and make a knock like noise. You might also have a cracked flexplate, which would make noise under acceleration and load; I have seen this as well.

These are just my opinions, but I don't suspect the problem to be in the tune or anything to do with fuel/spark strategy. It could, but I feel the PCM would throw lean codes like P0171 or P0174. I feel it is mechanical.

If you have anymore symptoms, do any more tests, or have any more info related to the problem; please share! Id love to help you solve this!

 

Thanks. I appreciate the input. I usually examine the oil every oil change and never noticed any metal flakes or anything out of the ordinary. The oil pressure has always been good too. I know what rod knock sounds like. This is definitely not rod knock.

As for the flex plate, that might be something worth looking at. My issues here with the o2 sensor and the knock all started when they replaced the transmission back in January. I would think that they’d have said something if they saw the flex plate was cracked.

I could see it being loose bolts but I don’t think it sounds quite like that, but it might be worth looking at.

another thing I’ll note is the first time I heard the noise, I found the intercooler leaked it’s coolant out. After refilling, bleeding and fixing leaks, it helped, but the knock was still there. As we’ve approached cooler weather, it seems to improve I guess from lower intake temps. That’s what makes me think it’s spark knock.

I do think it’s odd that it throws the code while the engine is fully up to operating temperature. Specifically accelerating past the rpm where the knocking is. If I do light driving and never exceed 3200rpm, the code goes away after a while, but when I drive it harder, it comes on. I read somewhere that it throws the check engine light within 60 seconds of determining a fault.

It is definitely a weird gremlin. I suspect they damaged or pinched wires whether it just happened because of age, or it was negligence. It’s going back next week to be looked at again.


Edit: I just looked at a couple of videos showing what a damaged flex plate sounds like. It seems like that only happens at low rpm rather than the midrange.