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Billeickmann
TYF Newbie
Yesterday I tried starting it again and it would not run. I just went back out and unplugged the MAF sensor and it started right up.
2012 Tahoe won't start
- Thread starter Billeickmann
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- 2012 tahoe will not start
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One quick thing to check is if you get it to run with everything connected, take a look at a couple of things.
See what the ethanol content of the fuel your PCM thinks it is burning. It will be in percentage terms.
Mine has been fooled to think it was like 60%, when the most I had put in the tank in quite a while had been like 10%. I reset the value and my ST fuel trims cleaned up fairly quickly and it ran better when cold (before it had gotten to closed loop.
On the open/closed loop thing, if you can get it running, after it warms up a little, see in the scanner if it is going into closed loop. If it stays in open loop (like it is when it is cold), the fuel trims can be off for what the conditions are for the engine.
I would check that stuff before spending money on parts (like a new MAF).
Also, if you get it running, check what the MAF says is flowing. If it is way off, you might have your reason why the engine is running rich.
again check the fuel pressure
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Billeickmann
TYF Newbie
getting fuel pressure tester tomorrow
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Billeickmann
TYF Newbie
OK. New MAF sensor is in. Fuel pressure tester is hooked up. Showed 20 with ign. on, but not running. Showed 60 when started, running rough. Then settled down to a nice idle and fuel pressure is steady at 42.
Shut it off for a few minutes, then tried again. Erased codes. Fuel pressure at ign. on, but not running was 60. When started , 42 steady. Code reader showed fuel pressure as 42/43. MAF at .8 increasing to 2+ with RPM. Nice smooth idle and easy RPMs. BUT codes P0172 and P0175 came back.
Shut it off for a few minutes, then tried again. Erased codes. Fuel pressure at ign. on, but not running was 60. When started , 42 steady. Code reader showed fuel pressure as 42/43. MAF at .8 increasing to 2+ with RPM. Nice smooth idle and easy RPMs. BUT codes P0172 and P0175 came back.
When you test fuel pressure with the KOEO (key on, engine off), you're getting a very low pressure and an acceptable one. Without starting the truck (KOEO), if you continue to watch the fuel pressure, how long does it take to leak down and to what psi, or does it hold relatively steady over 10 or 15 minutes?
I would also take a look in the live data at the O2 sensor data, specifically that they all look normal (voltages are jumping up and down and none are just sit-in there with very little voltage variation).
Things I would also check are the ethanol content the PCM thinks is in the tank, versus what you know you pumped in. If the PCM thinks it has more ethanol content in the fuel than you actually have, it will try and run rich (what the codes are about), at least until you get to closed loop.
Also, make sure after it has warmed up it is going into closed loop. Also look at the coolant temp and IAT temps and assure they all reflect expected values.
