P0171 and P0174 error codes

**initechpeter** · 09-15-2013, 10:31 AM

My friend has a 2002 Firehawk completely stock. We were getting the follow errors P0171 and P0174. We have replaced all 4 o2 sensor and the passenger side catalytic. We only change the passenger side cause we stripped the o2 sensor holes in the pipe. We are still getting errors from the p0171 and p0174 code. The car is all original and the owner has only changed parts when need. It's a 2002 Firehawk with 64000 miles auto. Can you guy point in the right direction to getting this fix. A list down below will show what has been done so far.

Items change/replace.

4 - o2 sensors
1 - passenger side catalytic

Cleaned the following:

MAF Sensor
Throttle body.

**35th-ANV-SS** · 09-15-2013, 10:43 AM

Being those are lean codes for both banks, I would check for both vacuum leaks and fuel pressure. Running lean means too much unmetered air is entering (vacuum leak) or insufficient fuel to the motor (fuel filter or fuel pump related possibly). Fuel pressure at the rail should be around 58psi.

**pajeff02** · 09-15-2013, 05:10 PM

^^ This. Take a good look at the PCV hose close to the throttle body and at the back of the passenger side rocker cover. Is the bellows secure between the MAF and the throttle body?

**initechpeter** · 09-16-2013, 10:00 AM

Yes everything is tight at the bellow. I never look at the pvc valve. I will have to look at that. It got fuel pressure.

**theorangeguy** · 09-16-2013, 03:02 PM

Originally Posted by initechpeter

Yes everything is tight at the bellow. I never look at the pvc valve. I will have to look at that. It got fuel pressure.

does it idle high when you are in neutral or when the clutch is in...? Anything over 1000rpm's imo should be considered high and is usually a dead give away for a vacuum leak.

**35th-ANV-SS** · 09-17-2013, 09:39 PM

What was the fuel pressure reading?

**Too Fast** · 09-18-2013, 02:25 AM

Can't believe nobody has suggested a dirty MAF as a potential cause. If it's dirty that will cause lean running, like the ones that get dirty from over-oiled K&N air filters.

**pajeff02** · 09-18-2013, 02:40 AM

Good point. A real dirty MAF will report less air flow as the built up crud actually insulates the MAF wires.

**35th-ANV-SS** · 09-18-2013, 10:51 AM

It wasn't suggested because if you read his post he says they already cleaned the MAF.

**cpop98ws6** · 09-18-2013, 03:15 PM

Still could be a bad MAF, cleaning them doesn't always cure the problem.

**cpop98ws6** · 09-18-2013, 03:16 PM

I would spray come carb cleaner around the intake and pcv hose and see if there is a change in idle, if not I would get a new MAF.

**theorangeguy** · 09-18-2013, 03:58 PM

Originally Posted by cpop98ws6

Still could be a bad MAF, cleaning them doesn't always cure the problem.

or if he cleaned it and plugged it back up wet...or touched the stuff inside the MAF when he cleaned it...

**35th-ANV-SS** · 09-18-2013, 04:06 PM

I know the MAF can go bad, but that is less likely then a vacuum leak in my opinion. You don't hear of a MAF going bad very often. Certainly it could be suspect though. I was just saying he said they cleaned it already lol. OP - did you use an electrical MAF cleaner spray or something else?

I wouldn't suggest throwing a $150 part at it without doing some investigative work first.

As Chris mentioned, check for vacuum leaks first. That's free.

You can also unplug the MAF and see if the car runs any different. There is also a way to check the MAF using an ohm meter. Both of these are free too.

**cpop98ws6** · 09-18-2013, 04:20 PM

1. Disconnect the MAF sensor and reset the fuel trims on the scan tool.
2. Start the engine and run until it goes into closed loop. Note the fuel trims, if they are still going high check fuel pressure and injector flow.
3. If they are going slightly negative, check for air getting in the engine other than through the MAF or a MAF not reading properly. Check the Air straightening grid for debris or damage.

**pajeff02** · 09-18-2013, 04:47 PM

Originally Posted by 35th-ANV-SS

It wasn't suggested because if you read his post he says they already cleaned the MAF.

Ooops. I just responded to the post without checking the details of the original question.

**initechpeter** · 09-18-2013, 06:18 PM

Well I have had a chance to get ahold of the car to check for a leak, but tonight he called and said the the check engine like it comes and goes off. It not mechanically inclined so he is very short about stuff like this. The car is running fine. RPM's are right on. There is not hesitation when driving. I will look at the car tomorrow night as he is coming over.

**cpop98ws6** · 09-18-2013, 06:26 PM

I had those codes poping up last year when my intake was cracked, they wouldn't come on all the time. That ia what is making me think its a vacuum leak. My car still ran fine and went 11.6 at the track with a that crack.

**35th-ANV-SS** · 09-18-2013, 08:31 PM

Originally Posted by initechpeter

Well I have had a chance to get ahold of the car to check for a leak, but tonight he called and said the the check engine like it comes and goes off. It not mechanically inclined so he is very short about stuff like this. The car is running fine. RPM's are right on. There is not hesitation when driving. I will look at the car tomorrow night as he is coming over.

Let us know what you find.

**Too Fast** · 09-19-2013, 02:48 AM

I feel stupid now. Officially! I missed that on post number 1.

After cleaning the MAF, if I still had the lean codes I'd be checking fuel pressure next also, then look for vacuum leaks. Our MAFs are pretty reliable.