Four Codes, One suspect: Crank Position Sensor?

[Tuffguy610]

Yea, its smoother, but the check engine light is still on (no more crank code, but P0171). I ran it through 50 miles of mixed driving (city/highway), with WOT runs, and smooth granny runs too at all speeds and it still didnt go out. I think somebody upstairs is trying to tell me its time for a new car

[93RedSled-SSE]

Yea, its smoother, but the check engine light is still on (no more crank code, but P0171). I ran it through 50 miles of mixed driving (city/highway), with WOT runs, and smooth granny runs too at all speeds and it still didnt go out. I think somebody upstairs is trying to tell me its time for a new car

Perhaps it just needs reset with a scanner. (?)

[bill buttermore]

If P0171 does not go away or re-sets once you clear it, the PCM is telling you: system too lean, bank 1.

Some possible causes: Vacuum leak, possibly a leaking o-ring on a fuel injector seal at the LIM bore. Spray these with brake cleaner or carb cleaner while the engine is running and listen for a change in idle speed. Check all of your vacuum hoses and fittings for possible leaks. Spray a volatile cleaner around any seal leading to intake manifold vacuum including the throttle body gasket, the UIM gasket, and the PCV chamber. Check to make sure you have a lower o-ring on the PCV valve and an upper big o-ring on the PCV chamber cap.

How long since you changed your oxygen sensor? If >60K miles, install a new AC/Delco or Denso sensor - do not use Bosch.

[Mechanical Mike]

P0171 can be a tough one to solve but more often than not seems to be caused by a good sized vacuum leak. If you have access to a scanner then check MAF frequency, LTFT (long term fuel trim) & STFT (short term fuel trim) at both idle & again at 2,500 rpms. If the fuel trims are richer at idle that'll pretty much confirm a vacuum leak. If the trims are richer at 2,500 rpm then you may have a fuel delivery problem (clogged fuel filter, bad pump).

[Archon]

Another place to check is the battery cables. IIRC, Bill Boost chased that problem around for some time before finding corrosion along the length of the positive cable. Replacing both cables solved his problem.

[Tuffguy610]

I don't have a scanner, I keep going to Autozone. It was never predicted for me have an issue with the SES light like this. The injector O-rings were replaced, my uncle told me they were when he rebuilt the engine. I did the vacuum leak brake cleaner/carb cleaner check, and no raise in idle. I find that brake cleaner test a little hard to believe because I took a vacuum hose off while the engine was running and sprayed around the open area and the engine speed didn't change. The entire upper/lower intake manifold assembly is new, gaskets and all, so that's ruled out. I inspected all of the lines in the front, a few fittings were cracked but i sealed them up for experimental purposes and its still on. Oh, and the 02 sensor is 10,000 miles old, its a denso unit from rock auto. I don't know what would cause that to go out again.

[harofreak00]

If you took off a vacuum line and the engine speed didn't change at all, that means you already have a vacuum leak. What is it idling at right now?

[Tuffguy610]

The factory tach (referred to as inaccurate) says about 850 rpms when idling at warm temp. I didnt really notice a change in idle speed when I took that line off. It was a line that comes out of the TB and goes to what appears to be something on the fuel rail.

[willwren]

That's the vacuum line to control your fuel pressure (fuel pressure regulator).

If the vacuum leak is small enough, the PCM can adjust the IAC to compensate for it over time.

[Tuffguy610]

Does the L36 also have a bank 2 when referring to the PCM? I say this because it only has one upstream oxygen sensor and one downstream. If there were two oxygen sensors it would be able to throw a P0174 code, correct? I am trying to rule things out here. My Camaro has two upstream sensors, and I received both a P0171 and P0174 code when my MAF was bad. I have been ruling out my MAF (and my brand new Denso O2 sensor from Rock Auto that is 9,000 miles old now) because it didnt throw both banks, but now I am thinking that there is only one bank due to the way the factory exhaust manifold is setup and that there is one oxygen sensor that determines the A/F ratio in my Olds. I don't have a scan tool, so I can't look at the cross counts and the LTFT/STFT as well as MAF frequency. I am almost certain that I don't have a vacuum leak, the car idles at 850 rpm and idles normal when cold started as well (1200 RPMS). When doing a full throttle run the car tends to hickup for a half a mile or so, its kinda hard to tell because I am moving so fast after the WOT run. Would something as dumb as an oil dipstick not sealing properly cause the P0171 code to pop up? I have checked for corrosion on the battery cables and have come up with nothing.

[Mechanical Mike]

You are correct. There is just one O2 sensor for determining the air fuel mixture on both banks.
Oil dipstick will not cause the code but a bad PCV valve or missing PCV O ring will.

You can try unplugging the MAF & see if the code goes away. Debris on the throttlle body screen or removing the screen can also cause the code.

Here's a few other things from the FSM that can cause the code:

Poor PCM to engine block grounds
Low fuel pressure (already mentioned)
Fuel injectors - you can connect an ohm meter to each injector & compare all six readings.
Exhaust leaks.

Can you tell if you're getting the code at idle or at higher rpm's?

[Tuffguy610]

I can't tell whether its at idle or at higher revs. I did remove my MAF screen unfortunately, and that was about the time that I got the code. The problem is that the new oxygen sensor was installed at the same time. The code originally came on intermittently and then stayed on, while that was going on the crank sensor decided to crap out as well. I have had a bad MAF in several cars, and they ran terribly (stumbling and lacking power, bucking at highway speeds), this car does not do that. I have tried cleaning my MAF, and the code is still on. I know that the MAF screen is supposed to smooth out the air before going into the TB. I guess I should go to a junk yard and grab one? I think the only way to get one out of a car is to destroy it, so I am probably screwed. I threw my old one out because it was destroyed when i removed it. That happened at the time gas went to $4.00/gal, I was looking to squeeze some MPGs and instead got into a big heap of trouble.

[bonnevillain]

remove the clip first, and use a toothpick or something very thin to pry it out. had mine off 4 or 5 times, and it still looks great.

[swampthing]

http://www.pontiacbonnevilleclub.com/fo ... =44&t=1681


#4 tells you how to remove one without damaging it

[Tuffguy610]

I just went to the yard and got a MAF screen. Got it out of a Grand Prix. I messed up a little piece of it, but I put it in so that the messed up piece wasn't near the MAF. I drove it around for about 15 mins to see if the light would go off, but it didn't. I guess it needs some more drive cycles. There are absolutely no idle issues with the car, and I used a half a can of carb cleaner on the vacuum lines again to see if there was a change in idle speed (no change). I wanted to grab a MAF out of the junker, but somebody already got to it. The yard was lined with L27 cars, but no L36's. I guess I'll cross my fingers for a day or two.

[harofreak00]

I have an MAF that will work for you. Let me know if you are interested.

[Tuffguy610]

Yea, I might need that eventually. I just drove from Philadelphia to Washington DC tonight (2.5 hour trip) for business and the light is still on. I basically got it pinpointed to a faulty replacement Denso oxygen sensor or the MAF. I might borrow my friend's MAF out of his L36 firebird to see if anything changes. If I do deem the MAF to be bad, I'll probably buy yours off of you. Thanks for all of the advice thus far. The car runs extremely well, it might be sluggish every once in a while but nothing that indicates anything major. Vacuum leaks are 99.9% ruled out at this point.