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Code po171 06 Envoy, new throttle body. Mass air flow, tune…

Code po171 06 Envoy...
Code po171 06 Envoy , new throttle body . Mass air flow , tune up , checked for vacuum leaks
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Answered in 3 minutes by:
3/17/2018
Jerry Newton
Jerry Newton, Chevy Technician
Category: Chevy
Satisfied Customers: 5,694
Experience: ASE Master Technician, L1, Master GM Technician. Over 20 years of bumper to bumper GM experience.
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P0171 is lean exhaust. MAF may have been a candidate, but I would have eliminated a lot of other things first before replacing that. Tune up and throttle body won't cause a P0171.

P0171 is either an unmetered air leak.... not just vacuum, but any air entering the engine downstream from the MAF, so you have to look at the intake ducting, etc. and make sure there are NO LEAKS...... or it can be caused by a skewed oxygen sensor that it just reading lean all the time. Vacuum leaks can also come from devices like the brake booster, or even an oil fill cap that isn't screwed on all the way or is letting air enter the engine unchecked.

Do you have a scan tool that reads live data?

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Customer reply replied 4 months ago
the long term due is very high 18 and up
Customer reply replied 4 months ago
Fuel trim

What is the oxygen sensor voltage? Is it fixed at a low voltage, or is it varying rapidly between 0v and 1v?

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Customer reply replied 4 months ago
I am at work now but all the things I replaced was suggested by another mechanic on here

Understood. I don't know how he arrived at throttle body, but you can spray carb cleaner at the air ducting and other places, and watch the short term fuel trim to see if it suddenly spikes when you hit certain spots, and narrow down any air leaks that way.

If nothing else shows up, I would replace the oxygen sensor, and retest it. This may also be a fuel pressure issue, if the fuel pressure is low across the board, you'll have lean fuel trim. Can you put a fuel pressure tester on the engine?

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It's not common to find low fuel pressure causing a P0171 and no other symptoms, but it's not out of the question.

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Customer reply replied 4 months ago
I also replaced the fuel pump on my own opinion and I have used 4 cans trying to find a leak
Customer reply replied 4 months ago
I have also ordered new injectors and rail which should be here next week

I understand your frustration.

If you haven't replaced the oxygen sensor yet, I would. Did you get a new MAF from the dealer, or a rebuilt/aftermarket sensor?

I've never had 6 injectors fail at once and cause a P0171, either.

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Customer reply replied 4 months ago
All parts are ac delco and brand new
Customer reply replied 4 months ago
I don’t think they are all bad but maybe possibly a clog or gummed up ?
Customer reply replied 4 months ago
Bank 1 is driver side correct

Is this a V8 engine? I assumed you had the 6 cylinder, for some reason, but yes, if you have the V8, the driver's side is bank one.

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Customer reply replied 4 months ago
Lol no v6
Customer reply replied 4 months ago
My says it has 4 but it’s my “wife “

The 6 cylinder engine in an Envoy is a straight six, not a V6. That distinction is important because there is only one bank on an inline engine. A V engine would have P0171 and P0174 codes possible, for lean exhaust on bank one and bank two, but since you have an inline six, there is only one bank, and so only P0171 will set for lean exhaust.

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Customer reply replied 4 months ago
Ok thanks this has been a learning experience

So, the things that will cause lean exhaust:

  • Fuel pressure, it's worth testing with a gauge just so you "know" that it's not a fuel pressure issue. Pressure should be 50-57 psi at all times when the pump is running, and it should hold that pressure for a good bit after the pump shuts off.
  • Skewed MAF or oxygen sensor.
  • Air leaks anywhere downstream from the MAF: intake air ducting, oil dipstick tube, oil fill cap, vacuum hoses that go to accessories like the brake booster, etc.

That's it in a nutshell. I don't think I'd spend the time and money to put new injectors and fuel rail in this, I just don't think that's going to pan out for you.

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That reading should move rapidly between 0.1v and 0.9 volts. I realize your scan tool doesn't sample that quickly, but is it at least moving consistently? It's not fixed at that voltage, is it?

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Customer reply replied 4 months ago
No it’s moving up and down

OK, that's good. At least it's not fixed in one place. That doesn't necessarily mean that it's good, but if it was fixed voltage, we'd definitely know that it's bad.

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OK, now you can sleep knowing the fuel pressure is what it should be.

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Customer reply replied 4 months ago
Lol ok
Customer reply replied 4 months ago
I changed both 02 sensors before I sent the readings

OK, good.

Long term fuel trim is.... still not good?

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Customer reply replied 4 months ago
Also why does 1 code throw the check engine light
Customer reply replied 4 months ago
How do I test 2nd ary air injection valve

Take the hose off the valve. You shouldn't be able to feel any air going into or out of the valve, it should be closed.

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Customer reply replied 4 months ago
It’s closed nothing

OK, that's not the reason it's lean. You don't have any exhaust leaks at the exhaust manifold, do you? Ticking noise when you first start it up or anything like that?

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Customer reply replied 4 months ago
No sir

I am looking through a historical database of repairs for this vehicle. P0171 happens to be the number one reported concern. Very many of those repairs have to do with intake manifold gaskets, many techs reporting that they are finding loose manifold bolts. In some cases, just tightening the bolts caused fuel trims to drop substantially, others replaced the gaskets or the entire intake manifold to repair it.

This is, of course, after fuel pressure, MAF sensors, conventional vacuum leaks like hoses off, PCV fresh air intake missing, etc. If you've covered all of these bases, I would be looking very closely at intake gaskets, perhaps just get some and reseal the intake.

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Did you get this worked out?

Please take a moment to rate my answers by clicking on the stars at the top of the page, that's how I get compensated. If you need more help, just let me know, I am happy to follow up.

Jerry Newton
Jerry Newton, Chevy Technician
Category: Chevy
Satisfied Customers: 5,694
Experience: ASE Master Technician, L1, Master GM Technician. Over 20 years of bumper to bumper GM experience.
Verified
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Customer reply replied 4 months ago
I tested the fuel pump again and it’s at 30 lbs after it runs and 1hr
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