00 Regal intermittent P0171
 

Hi,
I have no-super charger 3800 series II engine with check engine light will come on
once in 200 miles and then turn off after few on/off engine cycles. This started
after changed spark plugs, wires, front O2 (all AC Delco) and Carmax changed
upper and lower intake gasket and MAF replaced.

Attached fuel pressure gauge, instead of 48-55psi, I got 44 with ignition on only.
Waited 10 minutes, instead of 5 psi drop, I have 12 psi drop to 32 psi.

After starting engine and idling at fully hot temperatur, its 40 psi, spec said
drop from 3 to 10 psi, which is 38 - 52 psi so I am in spec when running.

Disconnected hose at regulator while engine idling, reading jumped from 40 to 48
and when applied vacuum at port, it went back to 40 psi. No fuel in the hose,
or hose crack. And 22""Hg vacuum at the hose.

So my question is that these symtoms related to bad pump or regulator or something
else. Car always starts immediately hot or cold and no stumbling or rogh idling.

Thanks.

the pressure doesnt sound that bad, the regulator and pump are just getting old. whens the last time you replaced the fuel filter and whats the code?

Forgot to mention fuel filter was changed about 2k miles earlier. Regal has now 112k miles.
When MAF and upper and lower gaskets plus upper manifold changed, code was P0102
which was MAF related. Thanks.

So is it running fine now? the light stayed off after you replaced the maf?

Yes car is running very good now. After changing MAF, light turned off (previous code was P0102) automatically and then after 200 miles it turned on, this time code was P0171. Then turned off after 3 engine turned off cycles. Then after 200 miles, it turned on again. Both time engine was hot and running and continued from stop and acceralation in the parking lot, so speed was less than 15mph. Thanks

there are alot of things that can cause lean codes, on the 3800 more common areas are vacuum leaks, vacuum leak through the upper intake, the others are possible but less common

from code descriptions;
Causes
A code P0171 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 may cause the MAF to become dirty if the filter is over-oiled. There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry.

There could be a vacuum leak downstream of the MAF sensor

Possible cracked vacuum or PCV line/connection Faulty or stuck open PCV valve

Failed or faulty oxygen sensor (bank 1, sensor 1)

Sticking/plugged or failed fuel injector

Low fuel pressure (possible plugged/dirty fuel filter!)

Exhaust leak between engine and first oxygen sensor

Since upper and lower gaskets replaced, and car is not stalling or rough idling, your
suggestion about failed injector. Thanks for your help.

i said check for vacuum leaks first the gaskets are not the only source of vacuum leaks, there are a ton on 3800s. the upper intake can be cracked, tb gasket, egr, vacuum lines that go to fpr and evap purge solenoid, anything after the maf

Got it. I will check for vacuum leaks. Since I do not have a smoker, I will start checking each line at a time- fpr/evap, brake booser/a/c and at PVC. Then start engine and use carburetor cleaner spray method. I will post results. Thanks

rpm m/h tempFmaf map shortf1 longf1 load netvac
723 0 212 4.27 9.7 -7.8 10.9 2.4 20.18
2109 23.6 215.6 35.73 18.6 -7 9.4 19.2 11.32
1601 53.4 206.6 32.64 26.6 6.3 11.7 18 3.34
1815 64.6 201.2 42.93 27.8 1.6 13.3 23.5 2.16
1985 70.2 199.4 38.3 20.4 6.3 13.3 24.7 9.54
2003 70.2 197.6 10.61 10 0.8 6.3 11 19.88
1666 66.4 194 4.98 6.2 3.1 10.9 3.1 23.72
1222 54.6 195.8 3.94 6.5 3.9 10.9 2 23.42
1098 46 195.8 4.04 7.1 -2.3 11.7 2.4 22.83
875 26.7 194 4.09 8.3 3.9 13.3 2 21.65
844 12.4 194 4.34 9.2 9.4 11.7 2.4 20.77
771 4.3 192.2 4.27 8.9 10.2 13.3 2.4 21.06
764 4.3 194 3.93 9.2 10.9 14.8 2 20.77