contrabombarde

Just an update, I bought a one VIN subscription to sps2, installed the PCM from the 2007 donor vehicle and programmed it. It started right up, and seems to run more normally now (It doesn't die as soon as you start it, it just starts and runs every time, no more misfires too), however, the MAF is still showing the same strange readings.

I went through again with a test light and everything checked out. I suppose it could be the MAF itself but I've tried 3 different sensors, 2 of which were in running vehicles previously (the one in this truck, and the one in the donor truck), as well as a new one I picked up from NAPA. I would just be surprised if all 3 were bad. EDIT/UPDATE: I swapped in the MAP sensor that was originally with the 2010 PCM, that made the code for map sensor voltage high Go away, and the map sensor seems to read normal with key on engine off (14psi or so), but it still doesn't run and does the same thing as before.

Yes, I used my multimeter to probe all of the wires at the MAF, both with the sensor connected, sensor disconnected, key on engine off, key on engine running, etc etc etc. I probed all of the wires again at the PCM, at the connectors, etc. All voltages are what they should be according to the service manual/wiring diagrams. All grounds are good, less than 20 millivolts from the battery negative under load. Both at the connector of the MAF, at the PCM connector etc. I know this throws a pretty big wrench into things, but this truck was acting up before the swap. I don't have very much information, if any on what was causing it, but if you cleared all of the dtcs it would do the same thing where it would crank, fire, then die. And it would do the same thing a dozen or so times, and eventually it would start and run, but the difference is that it would run and actually be drivable. Whereas now if you can drive it at all, it goes into reduced power mode almost immediately, and even then it's not running correctly. When you come to a stop at a light it stumbles down to for 500 RPM before catching itself and returning to the smooth idle. And if you go more than about 50% throttle then it immediately goes back to doing the misfire thing. Like I said, I know that throws a wrench into things, and unfortunately I was not able to pull any data or anything like that before I did this work, so I don't have much to go on. I'm trying to not fixate on one particular thing as the cause of the problem, but it seems like all avenues are pointing me towards the PCM. Like I said I have tested the wiring extensively (see above), and during cranking the sensor does produce seemingly legitimate values at least according to my multimeter, but as soon as the engine fires those values quickly descend into gibberish. I've tried it with multiple different known working sensors, I have done literally every test I can think of multiple times on the wiring (probing the signals, probing the pins with the sensors unplugged, probing the pins at the PCM, voltage drop, voltage drop under load, continuity, ohms, and double-checking everything against the wiring diagrams/ proper values in the service data.) Another thing that pushes me towards a possible PCM failure is, I have noticed in troubleshooting a little bit taking a break and coming back, that when I leave the truck to sit for a while and cool off, it starts and runs smoothly when I first start it up. However once it warms up. It starts having problems. For example, when I went out to the truck this morning after it had been sitting overnight, I was actually able to drive it down the block. And then once I got on the throttle a Little bit after going about a thousand ft, it started misfiring again. I pulled it back into the driveway, shut it down, and started it back up. It idled smoothly. As soon as I touched the throttle it did the misfire thing again. From then on as soon as I started it it would misfire. I shut the truck off and went to go get a coffee and do a bit more research. When I came back out I started the truck up and it immediately went into the smooth idle. After a couple of minutes of playing around with it, it would not idle smoothly anymore. Let it sit a couple of hours, rinse and repeat. This makes me think with temperature change something is going wrong inside the PCM. I have the PCM out of the 2007 donor vehicle and I'm thinking of getting a one-day subscription to the ACDelco programming service to try and program that and see if it helps. Like I said, I'm really trying to not fixate myself on one potential cause, but it seems everything is pointing me towards PCM failure. I would really like to try to confirm that, but unfortunately I don't have an oscilloscope or a signal generator to do the GM service procedure where you feed 5 khz into the signal pin.

No, I did not tune out vvt. From what I read it should still be able to run without it, it'll just lose some torque/power. I can see how that would make it not run correctly, but why would that cause the faulty MAF readings? EDIT: I just ran a quick test and checked, and as I expected, the computer sees that the VVT cam phaser solenoid is not present, and throws a code for it, and does not try to change the cam angle at all. Commanded position just remains at zero, 100% of the time. This makes me think that the VVT is most likely not the cause of the problem though if anyone has a different/better explanation, I'm all ears. UPDATE: I was able to find that my scan tool does indeed support reading the frequency (hz) off of the MAF (I thought it wasn't supported but turns out I just didn't know where to look for it). I noticed that regardless of engine state it always however this Is not what I observed with my multimeter. Like I said before, the MAF seems to put out a normal signal during cranking and then the signal drops to a very erratic reading once the engine is running. It seems from what my scan tool is telling me that the ECM is not recognizing this at all, and just reads 0 Hz 100% of the time. This pushes me towards the the PCM itself is faulty. I I have the PCM out of the 2007 donor vehicle, which I may try to connect and program (it's only ~50 bucks to get the software for a one-time programming)

These show the problem and symptoms, and I explain things too. to clarify again, I did not change over any computers or wiring (with the exception of the map sensor). All of the computers and wiring are original to the 2010 vehicle video 1 - background info/explanation and part of the problem video 2, idle misfire I think the reason that the MAP sensor is reading High is because the engine is misfiring so there is less vacuum... Additionally there's a p0102 for the MAF low frequency, and a p0108 for the map high voltage. Again, apologies for the somewhat long-winded explanation, it's a rather difficult problem to explain without going into the details.

I just did a little bit more research, and it seems that this Avalanche is not a Global-A vehicle, because the charts seem to list several models that were Global-A starting in 2010, but the Avalanche is not on there. And even similar models such as the Silverado are not on the Global -A platform until later in 2013. Please correct me if I'm wrong.

Yes, the 2007 is a GMT 900. Originally I had ruled out computers/compatibility as a problem because I did not change over any computers, only the engine. I know that the motors are different codes, but it seems like the lmg to lc9 is a fairly common swap, at least from what I can read online. I'm using all the wiring and sensors from the 2010 vehicle, as well as the computers (the only exception to that being the MAP sensor).

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.