2012 Tahoe won't start

[Billeickmann]

My Tahoe has 55,000 miles and has been very reliable. Last week, I got the check engine light, but it continued to run properly on my way home. Just a few miles. Next start, it ran very rough and stalled. Check engine light was still on. I tried cleaning the MAF, as it had never been done and put in a new air filter. Now, she cranks just fine, but does not even kick. No hint of firing. I pulled a spark plug boot and it sparked a plug when cranked. Not a big spark, but it jumped the gap. I then tried some starting fluid and nothing. Three tries and just a little cough. Could it be a weak spark?

I next bought a code reader off Amazon. It shows the vehicle VIN, but no codes. I tried cranking with the code reader on and still no code. The check engine light is still on. Repeated several times.

I bought the truck new Jan. 2013 and it has had no engine work, so maybe I am overdue. Any suggestions please?

 

[Doubeleive]

My Tahoe has 55,000 miles and has been very reliable. Last week, I got the check engine light, but it continued to run properly on my way home. Just a few miles. Next start, it ran very rough and stalled. Check engine light was still on. I tried cleaning the MAF, as it had never been done and put in a new air filter. Now, she cranks just fine, but does not even kick. No hint of firing. I pulled a spark plug boot and it sparked a plug when cranked. Not a big spark, but it jumped the gap. I then tried some starting fluid and nothing. Three tries and just a little cough. Could it be a weak spark?

I next bought a code reader off Amazon. It shows the vehicle VIN, but no codes. I tried cranking with the code reader on and still no code. The check engine light is still on. Repeated several times.

I bought the truck new Jan. 2013 and it has had no engine work, so maybe I am overdue. Any suggestions please?

check to be sure you have fuel pressure

 

[wsteele]

My Tahoe has 55,000 miles and has been very reliable. Last week, I got the check engine light, but it continued to run properly on my way home. Just a few miles. Next start, it ran very rough and stalled. Check engine light was still on. I tried cleaning the MAF, as it had never been done and put in a new air filter. Now, she cranks just fine, but does not even kick. No hint of firing. I pulled a spark plug boot and it sparked a plug when cranked. Not a big spark, but it jumped the gap. I then tried some starting fluid and nothing. Three tries and just a little cough. Could it be a weak spark?

I next bought a code reader off Amazon. It shows the vehicle VIN, but no codes. I tried cranking with the code reader on and still no code. The check engine light is still on. Repeated several times.

I bought the truck new Jan. 2013 and it has had no engine work, so maybe I am overdue. Any suggestions please?

If you have a CEL and your scanner isn't displaying a code, I would maybe consider a problem with the code scanner first.

 

[OR VietVet]

Code scanner or operator problem. What color was the "weak" spark you saw? Orange or blue? Need fuel pressure reading. Age of tune related components? Original? At 55k miles I would assume they are.

 

[swathdiver]

My Tahoe has 55,000 miles and has been very reliable. Last week, I got the check engine light, but it continued to run properly on my way home. Just a few miles. Next start, it ran very rough and stalled. Check engine light was still on. I tried cleaning the MAF, as it had never been done and put in a new air filter. Now, she cranks just fine, but does not even kick. No hint of firing. I pulled a spark plug boot and it sparked a plug when cranked. Not a big spark, but it jumped the gap. I then tried some starting fluid and nothing. Three tries and just a little cough. Could it be a weak spark?

I next bought a code reader off Amazon. It shows the vehicle VIN, but no codes. I tried cranking with the code reader on and still no code. The check engine light is still on. Repeated several times.

I bought the truck new Jan. 2013 and it has had no engine work, so maybe I am overdue. Any suggestions please?

Bill, you have to get those codes, otherwise you're just guessing and wasting time and maybe money. Seems like a fuel problem to me but I haven't seen the codes!

 

[Billeickmann]

OK. I went out to my truck to try the code reader again and she started. There was no check engine light, but she did run rough. It slowly became normal after a minute. I tried the code reader and I got P0172, system too rich bank 1 and P0175 system too rich bank 2.

 

[Billeickmann]

Shut her off and let her cool. Started again and got the same two codes again. Yes, all of the engine is original. I have only done tires, brakes, oil, battery, and filters.

 

[wsteele]

OK. I went out to my truck to try the code reader again and she started. There was no check engine light, but she did run rough. It slowly became normal after a minute. I tried the code reader and I got P0172, system too rich bank 1 and P0175 system too rich bank 2.

Is your truck a flex fuel version?

 

[wsteele]

Also, if you could determine if your scan tool can do live data display, that is probably going to be helpful down the road (most do).

 

[Billeickmann]

Yes my truck has the 5.3 flex fuel engine and the code reader does do live data.

 

[Billeickmann]

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.

 

[wsteele]

Yes my truck has the 5.3 flex fuel engine and the code reader does do live data.

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.

 

[Doubeleive]

again check the fuel pressure

 

[Billeickmann]

getting fuel pressure tester tomorrow

 

[Billeickmann]

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.

 

[Fless]

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?

 

[wsteele]

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.

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.