Code p0172 and p0175

[vertical99]

I have a 2003 tahoe z71 with a 5.3l motor not flex. I got these 2 codes (p0172 and p0175) so i figured it was the MAF sensor. I read a article that said if you unplug the sensor and the truck stalls the MAF sensor is ok, if the truck keeps running then your MAF sensor is bad. So i unplugged the sensor and the truck kept running so I bought a new MAF sensor and installed it . I started the truck and unplugged the sensor once again and the truck kept running with the new MAF sensor installed. should i replace the wiring harness to the sensor or is there a fuse that could be bad. i do not have any stalling issues and the truck starts great everyday I get a check engine light and fuel economy is bad. Thanks in advance AL

 

[HiHoeSilver]

I have a 2003 tahoe z71 with a 5.3l motor not flex. I got these 2 codes (p0172 and p0175) so i figured it was the MAF sensor. I read a article that said if you unplug the sensor and the truck stalls the MAF sensor is ok, if the truck keeps running then your MAF sensor is bad. So i unplugged the sensor and the truck kept running so I bought a new MAF sensor and installed it . I started the truck and unplugged the sensor once again and the truck kept running with the new MAF sensor installed. should i replace the wiring harness to the sensor or is there a fuse that could be bad. i do not have any stalling issues and the truck starts great everyday I get a check engine light and fuel economy is bad. Thanks in advance AL

Those are generic rich codes. There are any number of causes. The most effective way to diagnose is with a scanner.

It could be MAF, but you just replaced that. When's the last time you cleaned /changed your air filter? Plugs/wires? Could be O2 sensors or MAP sensor...

What kind of gas are you running?

 

[vertical99]

Those are generic rich codes. There are any number of causes. The most effective way to diagnose is with a scanner.

It could be MAF, but you just replaced that. When's the last time you cleaned /changed your air filter? Plugs/wires? Could be O2 sensors or MAP sensor...

What kind of gas are you running?

Just bought the truck a week ago. running 87 octane have not done the plugs and wires yet. i did change the air filter. what about when i unplug the MAf shouldn't it stall the motor. when i unplug this one the motor keeps running.

 

[01DenaliHiker]

My truck runs just fine with the MAF unplugged, I've tuned it out multiple times to the point it was negligent to even have plugged in when I was tuning. (IAT doesn't function if you're unplugged)

I've heard the MAF unplugged trick hundreds of times though, always seemed to be the way to go about it with Ford's. They can't live without it.

Sounds like another issue considering you've wandered that route. A good live data tuner would be the best way of targeting anything it could actually be. Beats throwing parts at guessing.

 

[HiHoeSilver]

Just bought the truck a week ago. running 87 octane have not done the plugs and wires yet. i did change the air filter. what about when i unplug the MAf shouldn't it stall the motor. when i unplug this one the motor keeps running.

The truck is designed to keep running if the sensor is disconnected or bad. The ECM uses TPS data to "estimate" load is the MAF is out of range or missing.

 

[vertical99]

The truck is designed to keep running if the sensor is disconnected or bad. The ECM uses TPS data to "estimate" load is the MAF is out of range or missing.

Do you think it could be the wire harness and the connector to the Maf sensor. I will be changing the plugs and wires this weekend

 

[HiHoeSilver]

Do you think it could be the wire harness and the connector to the Maf sensor. I will be changing the plugs and wires this weekend

I guess it could be. Does a good visual inspection give you reason to think that? What does your 02 sensor and MAP data look like?

 

[vertical99]

The truck is designed to keep running if the sensor is disconnected or bad. The ECM uses TPS data to "estimate" load is the MAF is out of range or missing.

So I changed the spark plugs and wires. Now the p0172 and p0175 are gone. The new code is p0300 random misfire. The plugs and wires that were on the truck had to be the original ones they looked really bad. Do you think one of the coils are bad . Thanks.

 

[vertical99]

So I changed the spark plugs and wires. Now the p0172 and p0175 are gone. The new code is p0300 random misfire. The plugs and wires that were on the truck had to be the original ones they looked really bad. Do you think one of the coils are bad . Thanks.

I put ac delco wires and NGK iridium plugs

 

[HiHoeSilver]

So I changed the spark plugs and wires. Now the p0172 and p0175 are gone. The new code is p0300 random misfire. The plugs and wires that were on the truck had to be the original ones they looked really bad. Do you think one of the coils are bad . Thanks.

Try swapping them around and see if the misfire follows.

 

[SnowDrifter]

How did you gap the plugs, and what did you gap them to?

Verified wires are seated all the way? Sometimes they can feel like they are but they aren't

 

[vertical99]

Try swapping them around and see if the misfire follows.

Sorry to bother you but I am lost. Ok I changed the plugs and wires and now I changed all the coils. The p0300 still comes up. The motor idles fine and runs with no hesitation. One thing is now my fuel gauge is not working right. It has gone past full and is down at the bottom. I will be checking the fuel pressure next. I dont know if that is connected. Is there anyway to check the injectors or should I just replace them. Again thanks for the help.

 

[vertical99]

Sorry to bother you but I am lost. Ok I changed the plugs and wires and now I changed all the coils. The p0300 still comes up. The motor idles fine and runs with no hesitation. One thing is now my fuel gauge is not working right. It has gone past full and is down at the bottom. I will be checking the fuel pressure next. I dont know if that is connected. Is there anyway to check the injectors or should I just replace them. Again thanks for the help.

Also made sure all the new wires were on correct.

 

[HiHoeSilver]

Sorry to bother you but I am lost. Ok I changed the plugs and wires and now I changed all the coils. The p0300 still comes up. The motor idles fine and runs with no hesitation. One thing is now my fuel gauge is not working right. It has gone past full and is down at the bottom. I will be checking the fuel pressure next. I dont know if that is connected. Is there anyway to check the injectors or should I just replace them. Again thanks for the help.

I thought you had a specific misfire code, sorry I misread. Like @SnowDrifter asked, Doug you check/gap the plugs at all? You gotta be really careful with the little iridium nodes. You could check the fuel pressure easy enough at the Schrader valve on the rail.

 

[HiHoeSilver]

Remember we started this whole thing because of rich codes. I'm still interested in your fuel trim and O2 data. Computer could be pulling enough fuel to set the po300, I think.

 

[vertical99]

Remember we started this whole thing because of rich codes. I'm still interested in your fuel trim and O2 data. Computer could be pulling enough fuel to set the po300, I think.

I will take a pic of the fuel trim data. Yes it started with p172 and p0175 but once I change the plugs and wires those codes went away and I got the p0300 code which is multiple random misfire. I did look at the fuel trim the short fuel trim was hovering around 0 and the long fuel trim was hovering around -10 at idle.

 

[HiHoeSilver]

I will take a pic of the fuel trim data. Yes it started with p172 and p0175 but once I change the plugs and wires those codes went away and I got the p0300 code which is multiple random misfire. I did look at the fuel trim the short fuel trim was hovering around 0 and the long fuel trim was hovering around -10 at idle.

Your LTFT being -10 means it's pulling fuel. Not enough to set the same original rich codes, but maybe enough for the misfire. Look at your #1 o2 data and make sure they're cycling correctly.

 

[vertical99]

Your LTFT being -10 means it's pulling fuel. Not enough to set the same original rich codes, but maybe enough for the misfire. Look at your #1 o2 data and make sure they're cycling correctly.

Ok here is the obd data at idle. Also the p0172 and p0175 came back along with p0300. Also if you think it is the fuel injector what make do you think I should put in and since i am replacing stuff should i also replace the fuel regulator. Motor has a 157000 on it. Thanks

 

[HiHoeSilver]

Based on seeing the B2S2 o2 in both shots, it looks like it's cycling. Unless you say different, I'll assume B1 is, too. They should be switching from 0.1-0.7 ish every second or so. B1S2 looks like it may be lazy, but I don't think that's related. What are your LTFTs like? I'm betting they're - 25. Do the fuel pressure test. If I was doing injectors, I'd go OEM.

 

[vertical99]

Based on seeing the B2S2 o2 in both shots, it looks like it's cycling. Unless you say different, I'll assume B1 is, too. They should be switching from 0.1-0.7 ish every second or so. B1S2 looks like it may be lazy, but I don't think that's related. What are your LTFTs like? I'm betting they're - 25. Do the fuel pressure test. If I was doing injectors, I'd go OEM.

I am going to do a pressure test this weekend. The guy I bought it from said he changed the fuel pump but that doesnt mean it couldn't go. Also my fuel gauge is messed up. It went way pass full and is at the bottom. Thank you for all the help.