Had codes P0171 and P0174

Tiny
THOMASSTUCKEY
  • 2001 CHEVROLET SUBURBAN
  • 136,000 MILES

I also had codes p0171 and p0174 so I looked at the intake gaskets and replaced them, also a few vacuum line elbows that I found cracked that went from the fuel pressure regulator to the air intake. And those codes have not come back.

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Tuesday, October 2nd, 2012 AT 5:58 PM

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Tiny
ASEMASTER6371
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102 is a mass air flow code. The 400 series are evap codes.

How does it run?

Are all connections good at the mass air flow? Is the big hose to the air filter tight and secure?

Roy

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Tuesday, October 2nd, 2012 AT 6:20 PM
Tiny
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With the MAF connected it would start fine then about 10 to 15 seconds the RPM's would decrease and it sounded like it was ready to stall but really just run rough. The air filter intake hose is secure the connection look good, i've got good PWR in 14VDC and a solid ground, from the signal side with the truck running I get about 5.04VDC. I didn't get the 400 series codes until I changed the MAF. When I disconnect the MAF it runs perfect with no issues.

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Tuesday, October 2nd, 2012 AT 6:34 PM
Tiny
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Most likely the sensor is bad.

Roy

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Tuesday, October 2nd, 2012 AT 6:38 PM
Tiny
THOMASSTUCKEY
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So you think that the new sensor I put was just bad?

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Tuesday, October 2nd, 2012 AT 7:13 PM
Tiny
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Possible. Why did you replace it

Roy

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Tuesday, October 2nd, 2012 AT 7:29 PM
Tiny
THOMASSTUCKEY
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Because I got the 102 code after replacing the intake gaskets for codes 171 and 174.

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Tuesday, October 2nd, 2012 AT 7:51 PM
Tiny
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Did you try the old mass air flow? Since you replaced the gaskets, the sensor may not have been bad, just unable to overcome the vacuum leak

Roy

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Tuesday, October 2nd, 2012 AT 8:41 PM
Tiny
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I changed the MAF after taking care of the other elbows and gasket

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Tuesday, October 2nd, 2012 AT 9:09 PM
Tiny
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Ok, did you put the old one back on?

Roy

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Wednesday, October 3rd, 2012 AT 12:16 AM
Tiny
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Nope I did a one for one so no $65 core charge

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Wednesday, October 3rd, 2012 AT 12:20 AM
Tiny
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I hear you. It sounds like the one you have is no good. Do you have acess to a real scan tool?

Roy

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Wednesday, October 3rd, 2012 AT 2:48 AM
Tiny
THOMASSTUCKEY
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I have a CanOBD2 Diagnostic tool (INNOVA 3100). I just replaced the MAF sensor one more time with brand new one. I still get the 102, 443, 449 codes. I took apart the whole wiring harness checking for damaged wires and found nothing, but I can tell you this I wrapped that harness back better than it was before. LOL

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Wednesday, October 3rd, 2012 AT 4:54 AM
Tiny
THOMASSTUCKEY
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Funny thing when I checked all of the fuses today everything was good I put that MAF sensor in and I still got the codes as stated before, so I got to looking at the schematic and read so more stuff on line and I found that the #1 Eng fuse had blown, after replacing that the truck wanted to idle iritic so I read for codes and got nothing twice. So then I drove it when I got back I read the codes and now I have a P0171 and P0174.

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Wednesday, October 3rd, 2012 AT 5:59 AM
Tiny
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You have either a vacuum leak, low fuel pressure, bad pcv valve.

It sounds like you need to start from scratch.

What are the long term trims?

Roy

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Wednesday, October 3rd, 2012 AT 10:00 AM
Tiny
CADIEMAN
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First get a vacuum gauge to ck. The vacuum. Use carb. Spray to help u find this leak spray down all the hoses and intake. When u find the leak the engine will surge when u spray to find the leak.

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Wednesday, October 3rd, 2012 AT 10:31 AM
Tiny
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Roy, I'll recheck the fuel pressure! I already replaced the fuel pump about a month ago with a new one and replaced the fuel pressure regulator twice. I haven't replaced the PVC valve and I'll try the vacuum trick and see if that works. What about the O2 sensors?

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Wednesday, October 3rd, 2012 AT 3:01 PM
Tiny
THOMASSTUCKEY
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Ok here's and update. I m getting codes P0171, P0174, P0300 and P1574. After going back through the whole system and not finding anything, the replaced all o-ring on the intake housing, reseated the new intake gaskets with no vacuum leak at all, I tested them and then I had a pro check them and no leaks. My fuel pressure is at about 54 psi with keys on (Eng not running) with Engine running it drops to about 50 psi, so good fuel pressure for my truck (VIN T ). I ve replaced upstream O2 sensors, MAF, TPS, PVC valve, Fuel pressure regulator (twice), Fuel pump, and Fuel filter and cleaned the fuel injectors. The truck wants to just take off it has a high idle and runs rough and seem like it wants to just die, but it doesn t and it only does this at idle or when your stopped for a period of time such as a red light. Truck runs great at speeds with not issues. When I disconnect the MAF everything run great. Still need help!
Or the fuel trim sets at 25 for both sides.

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Tuesday, October 9th, 2012 AT 4:26 PM
Tiny
THOMASSTUCKEY
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Alright the final update to the problems listed above and man it seem like I was chasing my tail most of the time. After looking back at the p0300 code I noticed that the O2 sensors I put in were different than the originals that were installed (pretty much aftermarket parts), because the originals O2 sensors has 6 slots and the aftermarket only has 3 and with the scanner that I use also has Fix assist with it, it showed me that the O2 sensor wasn t communicating right with the PCM, so I cleaned up the old sensor and installed them back in and the P0300 code disappeared. So I took it for a drive and got back two coeds still a P0171 and P0174 so back to square one right. Not this time I took those codes and goggled it and I came up with this video that helped (www. Youtube. Com/watch?V=kZsqEfP-5zM ). It turned out that I did have a vacuum leak and I found it by smoking the leak out as shown in the video. The leak ended up being at 5 of the 8 fuel injectors where they go into the intake so I replaced all the lower o-rings and the truck run great now problem solved finally. I hope this helps everyone.

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Monday, October 15th, 2012 AT 4:48 PM

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