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By contrabombarde · Posted
Apologies in advance, this is a long post, there's a lot to explain. A friend had a 2010 Avalanche with a 5.3 (LMG) that blew the head gaskets (amount other problems). He gave me a donor motor out of a 2007 suburban (LC9). I got it all installed, and everything hooked up. Went to go start it, and it stumbled a bit at first and died a couple times, but after trying a few times it sounded like it was running very well. Went out to go get some coolant, and came back the next day. Upon trying to start it, the truck will crank and fire normally and the RPMs will raise to around 1,200 or 1,500, sounding great, and then the RPMs will decrease and it will just die. Repeat that a dozen or two dozen times, and eventually it will fire and idle beautifully. As soon as you touch the throttle, it will start misfiring and sound like absolute trash. When you let off the throttle it will come down and hunt around shaking and misfiring like crazy. A message will come up on the dash saying reduced engine power. It is throwing codes for a map sensor circuit voltage High, as well as MAF sensor low frequency. With key on engine off, the map sensor reads about 4.8 volts on the vout pin, which the PCM interprets as about 17.8 PSI, contrasted to the barometer which my scan tool tells me reads about 13.5 PSI. However, once the engine starts and is idling this reading drops to about 5-6 PSI at a stable idle, and varies significantly when the engine is misfiring/ hunting like I said before. I should note that I used the intake and MAP sensor from the LC9 engine. I changed the connector on the 2010 harness to The 2007 connector. The pinouts for the sensors were printed right on the top, and I triple-checked that I put the correct wire into the correct place. On the other hand, the MAF sensor reads consistently 0.0 g/s regardless of State. I have pulled my hair out trying to figure out this last detail. I have tried three different sensors, (all of which should be good, one of which was new), I have verified all the wiring from the sensor going back to the PCM, and have verified that the readings at the PCM are the same readings as at the sensor itself. The intake air temperature sensor is also functioning as normal. I verified all the voltages and grounds etc, and everything is as it should be. I don't have an oscilloscope to verify, but I probed with my multimeter (Klein mm720) on frequency Mode, and it reads that on initial cranking, the maf is producing between 3000 and 7000 HZ, and as soon as the engine fires that falls off to below, 1000, and if the engine continues to run, it will produce somewhat erratic readings between 5 and 100-200 HZ. It does increase notably when the engine is revved despite the misfirings. As I said before, I have verified all of the wires going to the PCM, and I have tried multiple known good sensors. I've tested all the pins and voltages from the sensor and verified them against the manual that they are what they should be. I tested all the wiring for both ohms and voltage drop, and everything tested fine. Like I said I tested at the sensor as well as right at the PCM, everything checked out. The only other thing of note at least I think is the fact that the engine originally in the truck had VVT, but the engine I put in, the lc9, does not have VVT. I modified the cam sensor plug to work. I reference the wiring diagrams and double-checked that I modified the harness correctly to adapt it. There is obviously a code for the VVT solenoid, but I don't think that's the cause of my problems, and this friend will probably have the PCM sent off to tune out the codes at some point. I'm writing this for my bed so I don't recall the exact codes, but I'll update the post tomorrow morning with the exact codes. And ideas or feedback much appreciated. -
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I forgot to answer the question as per what market mine is set to and yes I finally found that area on mine and yes its also set to America. So here's something I realized as I wasn't looking at that part in the Sierra section until now, your right that what I see here as choice 3 under Sierra which says 07/2023-06/2026 ( 433 MHz 13542523 ) it has no choice 5 for tire pressure selection. Where as it does under the Chev choice. However I kept going down the list within the Sierra and I am really wondering if choice 9 will work for your truck as it has the same model number and hertz sensor as my truck. I would say try that choice first, if that doesn't work then jump over to the Chev section and again choose that same model and hertz choice as for some reason the Chev section gives the choice 5 of tire type/pressure selection for going back a number of years. Could very well be an Autel thing that they just didn't get the updates all done properly under Sierra but anyway first try that selection 9 I suggested under Sierra and then go from there. -
Looking for this piece that holds the hose clamp in place. I have the hose clamp just not that other piece. Dealers and wrecking yards in my area will not sell just that piece. They want you to buy the whole air tube $100 +/- to get that $5 part. that piece isn't molded to the air tube as I looked at my friends truck. It's held on by a screw and nut. I'm trying to put the OEM parts on the truck as the previous owner butchered things up installing an aftermarket CAI. It really looked homemade. 🤣 Thanks -
Ok I missed that part that yours is a GM. The strange part is that the choice for year ranges and within the year of 2026 is different on the Sierra then on the Chev for some reason as I am looking at my tool at the Sierra choices. Now I am guessing you see as to your sensor part number as it may be different on your truck for some reason and a call to GM should get you the part model number of the sensors you should have as well as which MHz your sensors are. I know mine are the ones as per what I listed but there are other choices in the Autel and got me wondering if by some chance they put different ones in your truck. Having said that, did you try using each of the choices starting from No 1 and going on down the list, not sure if that would mean shutting off the engine each time and resetting the tool and going at it again each time. Also I thought of something else which may sound retarded but if there was some stupid chance that the chev choice would work. The reason I say that is that the Sierra is showing a range up to 06/2026 for the various choices of sensors it could be where as the Chev has one choice that has that 12/2026. By the way it is possible to not run the truck and you may know that as per not pressing the brake but pressing and holding the start button for a few seconds and it lights up the dash ( its called service mode ) but that sucks battery power and if it were me doing it that way I would be throwing on a decent sized battery charger before doing it that way as killing your battery won't make you happy at me at all !. Like I say, just a thought to try the Chev choices if you have already exhausted the Sierra choices but first it would be nice to know for sure what exact sensor model and hertz your truck uses as I assume only those choices that mention the sensor would work unless a choice that does not mention the sensor model would somehow work. Its frustrating when one is trying to use tools like this without the experience of the tool and the vehicle, as I am sure dealer techs themselves struggle with it when starting out or a new model year comes along that is slightly different.
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