2003 Chevrolet Suburban • 98,000 miles

Hi 2carpros

I have a 2003 Chevrolet Suburban Z71, V-8 5.3L.

I have the P0171 and P0172 codes popping up. This is what I have done and what I have experimented with.
1. Changed the PCV/ Orfice
2. Replaced the MAF sensor
3. Replaced the Air Filter and Fuel Filter

My friend has a Gynesis pro scanner. So we scanned it and replaced the MAF. Now the MAF works fine. When I put the new MAF in the Check engine codes appeared again. I reset the codes with the scanner. The following week we took the car out again. In the morning it has a rough start with a very rough idle, once the car warms up it still idles a lil weird but much better than cold. We reset the car again with the scanner. We turned it off and on a few times and nothing all the codes disappeared we drove it for about 30 minutes, took it on the freeway and nothing. The next morning I turned the car back on and the check engine light went back on. Now I am at the point I do not know what to do.
Should I do a vacuum leak test?
How or who can perform one? How much do they run for?
Anything else I should be looking for?
I read worst case scenario the intake manifold gaskets are shot, however I do not mind getting them replaced but I do not want someone to replace them and I still have problems.
If you have nay other advice I will greatly appreciate it.


Marijan Rudela

Check your fuelpressure low pressure will set those codes. Should be 55-62 psi

Mar 5, 2013.
Thank you.

Anything else you can think of?

Sorry I gave teh rong info for fuel pressure it should be 48-52 psi. I'm sure you will find it low otherwise it could be bad injectors causing this as well. When the intake gaskets go you usually see coolant loss. Auto parts stores rent the gauge to check fuel pressure you may need to disconnect the line to put an adapter in.

Mar 6, 2013.
Okay thank you for the advice.

Since I live in California, I have to get my car smog tested, I took it in today. I passed everything but under the Emission Control System (ECS) I Failed the Air Injection test. What does that mean? As well three codes popped up P0101 MAF sensor but I replaced it 3 weeks ago. The other two are P0171 and P0174 (System Too Lean Bank 1 and Bank 2), Any ideas? The internet said something about secondary air injection check valves could be faulty, what do you think I should do?

Thank you!

Do what I suggested in first email for lean condition. Your secondary solenoid is at right rear of engine it'snot a valve. Check for vacuum leaks with choke spray with engine running andmake sure all engine grommets like to valve cover are good with no holes in them that effects maf as well. If you are unable to do this stuff suggested then taek it to a pro

Mar 7, 2013.