99 Malibu DTC P0172

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#1
I have posted this a couple of time without getting any help. Even though I have been working on cars for a long, long time, this one is making me pull my hair out. I have even took it to my buddy's shop and he had it for a couple of weeks. Here's some information.
1999 Chevy Malibu LS, 3.1L, Auto Trans, Calif. emissions, with about 81,000 miles on and P0172 trouble code. It's my daughters' car and with the check engine light on I haven't been able to get it smogged. Sometimes the light goes out , but it was shows back up in a couple of days. It has had a tune-up and all the other maintance stuff done recently. I have research this problem for awhile now using friends, the internet, ALLDATA and Mitchell On-Demand. Everything I check, checks out fine. I could really use some bat auto brains on this one.
Thanks, Al
 

jay

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#2
Could be MAF. dirty air filter, high fuel pump pressure. What is freeze frame data such as MPH, and MAF readings when code sets. Does your buddy have a scan tool?
See below info.

P0172 OBD-II Trouble Code
Technical DescriptionSystem Too Rich (Bank 1)

What does that mean?Basically this means that an oxygen sensor in bank 1 detected a rich condition (too little oxygen in the exhaust). On V6/V8/V10 engines, Bank 1 is the side of the engine that has cylinder #1.

Note: This DTC is very similar to P0175, and in fact your vehicle may show both codes at the same time.

SymptomsYou will more than likely not notice any drivability problems, although there may be symptoms such as a misfire.

CausesA code P0172 may mean that one or more of the following has happened:

The MAF (Mass Air Flow) Sensor is dirty or faulty. Note: The use of "oiled" air filters (K&N, etc.) can cause the MAF to become dirty if the filter is over-oiled
There could be a vacuum leak.
There could be a fuel pressure or delivery problem
Possible SolutionsPossible solutions include:

Inspect all vacuum and PCV hoses, replace if necessary
Cleanthe MAF sensor. Consult your service manual for it's location if you need help. I find it's best to take it off and spray it with electronics cleaner or brake cleaner. Make sure you are careful not to damage the MAF sensor, and make sure it's dry before reinstalling
Inspect fuel lines for cracks, leaks, or pinches
Check the fuel pressure at the fuel rail
Check the fuel injectors, they may be dirty. Use fuel injector cleaner or get them professionally cleaned/replaced
 
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#3
Disconnect you MAF sensor and let idle in closed loop and tell what your long and short term fuel is reading.

The code is system running lean and PCM is turning your system rich to make up the difference.
All Data or Mitchell al have a repair flow chart for that code.
All you have to do is go threw that repair flow chart.
 

Gus

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#4
Crunch, that code means just the opposite.....

As Jay said, an over oiled K&N filter can cause MAF problems....make sure the inlet to the air box isn't plugged.....Pull the vac line off the fuel pressure regulator and check for fuel......check that the canister purge is not the problem.....A bad O2 sensor could be the problem....

Disconnect the MAF, and see if the problem is fixed.....

If none of that takes care of it, then a fuel pressure and an injector balance has to be done....if OK, we may be looking at a PCM....
 
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#5
Thanks for the help. It doesn't have an k&n filter and The maf has been cleaned. I pulled the vacuum off the fuel reg. and no fuel. I haven't checked the canisters yet or the fuel trim. Won't be able to take it back to my buddy until after the holiday. Thanks again for the help, have a nice 4th and God Bless America...
 
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#6
Gus said:
Crunch, that code means just the opposite.....

As Jay said, an over oiled K&N filter can cause MAF problems....make sure the inlet to the air box isn't plugged.....Pull the vac line off the fuel pressure regulator and check for fuel......check that the canister purge is not the problem.....A bad O2 sensor could be the problem....

Disconnect the MAF, and see if the problem is fixed.....

If none of that takes care of it, then a fuel pressure and an injector balance has to be done....if OK, we may be looking at a PCM....

Gus you should know by no that I always get that crossed so just reverse what I tell you and you will be shooting dead center on it. :)
 

Gus

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#7
Crunchy, I KNOW that! But the poster doesn't..... ;D
 
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#8
Okay I'm back working on this I didn't take it back to my friend, because believe or not I have a smog license and 35 years experience. I've been working on heavy equipment, (cranes. dozers, dumptrucks among other equipment) for the past 25. Things have changed a lot since the earlier 80's. I checked the fuel trim and with the MAF wire connected it's in a closed loop. When I unplug it it's still in a closed loop and the readings are about the same.
KOER;
ST TRIM (%) 0
LT TRIM (%) -21
MAF (gn/sec) 3.49
MAF (hz) 1994-2026
TPS (norm %) 0
TPS (v) .63
BARO 30.2
BARO (v) 4.86
MAP 1.46
MAP (hg) 11.3
IAC 21
O2 B1S1 MV between 65-920 moving a lot
O2 B1S2 MV
 
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#9
Okay I'm back working on this I didn't take it back to my friend, because believe or not I have a smog license and 35 years experience. I've been working on heavy equipment, (cranes. dozers, dumptrucks among other equipment) for the past 25. Things have changed a lot since the earlier 80's. I checked the fuel trim and with the MAF wire connected it's in a closed loop. When I unplug it it's still in a closed loop and the readings are about the same.
KOER;
ST TRIM (%) 0 --- LT TRIM (%) -21
MAF (gn/sec) 3.49 --- MAF (hz) 1994-2026
TPS (norm %) 0 --- TPS (v) .63
BARO 30.2 --- BARO (v) 4.86
MAP 1.46 --- MAP (hg) 11.3
IAC 21
O2 B1S1 MV between 65-920 moving a lot --- O2 B1S2 MV 772 moving little ---O2 ready yes
DES EGR (%) 0 --- EGR Pos 0 --- EGR FBK (v) .82 --- EGR Closed (v) .80
EVAP Purge (%) 17 --- EVAP Vent Sol off --- EAVP no fault
Also I checked the FPR vaccum line. I did a Fuel pressure test; KOEO 54lbs drops to 50lbs in 10 minutes. KOER 48 lbs drops to 30 lbs in 10 minutes. I think I might have a leaky injector, but which 1? I could use some help teaching this old dog some new tricks. Thanks, Al