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P1071 Code: System mixture to lean (Bank 1)

04-20-2008, 01:45 PM
For as long as I owned my Regal, I have always used 93 octane gas. But a few days ago I filled the tank up with 89 octane. Since the change in gas, the car was idling abnormal. Not rough, But when I'm at at full stop, the idle will lower and the car seems to bog or shudder and then it would idle normally. Sometimes it would stall too. I do notice a sort of lag in acceleration also. Next morning upon starting the car, the dreaded Service Engine Soon light came on. I had Auto Zone run a diagnostic and their scanner pulled a P1071 code. Is it possible that the change in fuel octane is causing these symptoms. Should I wait till the next fill up, and go back to premium gas. The car has 119k miles, just 2 weeks ago I changed the air filter and pcv valve. Fuel filter was changed last year. Would a tune-up
(plugs and wires) solve this issue. Thank you

04-20-2008, 06:46 PM
Recheck for both o rings being in place in the pcv valve/ map, common area for problems, 1 ring misseated or missing can cause all your symptoms. Not a fuel issue.

04-20-2008, 07:57 PM
Thanks for the response Maxwedge. Funny you mentioned the o rings. After I posted this thread, I went out to check if both air filter and pcv valve were properly installed. Both o rings for the pcv valve are present. Also checked around the engine to see if there were any hoses that were loose, but found nothing. still the problem persists.

04-20-2008, 08:06 PM
Switch back to the recommended 91 octane or better and then see what it does. Combustion chamber and exhaust temperatures are higher with lower grade octane. It may have affected the pre-CAT 02 sensor. The Bank 1 02 sensor is used to control the fuel injection system in closed loop mode of operation. DTC P0171 indicates you are getting a short term or long term fuel trim either due to a lean or rich condition.

Also, disconnect the MAF sensor and see what it does?

04-20-2008, 09:07 PM
Thanks BNaylor for your response as well. Yes I do intend to switch back to premium octane as soon as I use up the remaining fuel (89 octane) thats left. I will disconnect the MAF sensor to see what happens. Will reply back with those symptoms. Is it my understanding that I should have the pre-cat O2 sensor replaced and the bank 1 O2 as well. Or are both one in the same. I also intend to change the fuel filter, just to be on the safe side. I also threw in some fuel injector cleaner today just as a precaution. But the symptoms still remain. Again as always thanks for the feedback.

04-20-2008, 09:44 PM
You're welcome. Sound like a good plan to me and good luck!. :thumbsup:

The pre-CAT and bank, 1 sensor 1 one are the same. The second 02 sensor bank 1, sensor 2 is after the CAT and just monitors CAT converter efficiency so I don't think it is your issue.

The pre-CAT 02 sensor is now suspect since it will cause the P0171 DTC. Especially if the idle after sufficient engine warmup or driveability like cruising is abnormal in closed loop mode which is when the PCM uses that respective sensor to control the ideal 14.7:1 air/ fuel ratio.

04-20-2008, 11:12 PM
That code has been known to drive people crazy.:runaround: :banghead:

While the O2 sensor seems likely it doesn't seem to be the cause very often. You may have better luck - go with a Delco sensor.

The Maf sensor is another possibility. Unplugging it was already mentioned. You should also make sure there is no debris on the screen in front of the Maf.

Vacuum leaks are another possibility. Try visually checking all the vacuum lines & fittings. Try spraying throttle body cleaner or propane around all the vacuum lines, intake gaskets, throttle body gasket & fuel injector O rings. If the idle RPMs increase then you found a leak. You can also disconnect & plug the vacuum line to the brake booster. Might want to do that on a lonely country road & see how much pedal force is required before you get up to speed.

Fuel pressure & volume also need to be checked. Some people have used a fuel pressure gauge with extension & taped the gauge to the windshield to check pressure at wide open throttle.

That covers most of it, the EGR might also come into play with p0171.

You have to reset the code to see if anything helped.

04-21-2008, 11:12 PM
there ias a service bulitan out these.
If goes like this.

if you use 5% methanol you should use a conditioner too.
the reason is the methonal screws up the seals.
on all the componants(fuel pump to injectors)
91 octane is 5% or less so you have less trouble.

I had a case where I got bad gas and after that I researched it.

either use the premiem fuel or use injector cleaner at every other fill-up.


04-22-2008, 07:50 AM
Just to clarify is this a Regal LS or GS? You only need to run premium unleaded 91 octane or better in a GS/GSE model with the L67 supercharged SII 3800 engine.

LS models with the L36 normally aspirated SII 3800 engine should run fine on regular unleaded.

04-22-2008, 02:36 PM
I just found the cause of my P0171. (

04-22-2008, 09:23 PM
Well first off, let me begin by saying,thanks for all the responses and feedback
I've been getting relating to my inquiry. Your all ACES. This forum has been so helpful since I've joined. Mainly because of all the ACES that you all are. Well let me describe whats been happening since my last post. Today after starting the car ( 00 Regal LS-119K mi.), I again checked for leaks and cracks
in vacuum lines. Found none. Checked air filter and pcv again...still normal. Inspected all connector plugs to fuel injectors and they seem to be fine. Looked at the plug connectors for the IAC, IAT and MAF and they are fine. Then I disconnected the plug wire to the MAF and there was no change to the motors idle. Then I, so I think? Located the O2 sensor behind and below the rear valve cover. Inspected the plug and wire and tapped the sensor a bit. Then the SES light went off. Weird huh. But the engine did bog-hesitate
once then after. Even when the SES light no longer appearing. Drive home
about 12mi. SES appears again. I'm close to 1/4 tank of gas (89 oct), till i go back to the premium 91 plus. I believe as mentioned by a few before, that this is the doing of just some bad gas.

04-23-2008, 04:46 AM
What are we classifying as bad gas? The lower octane level or was it really bad gas maybe with contaminants, poor quality or water, etc.? Just because it is lower octane level doesn't mean the gas is bad. Also, staying with GM recommended top tiers fuels reduces these type issues.

Your LS should run absolutely fine on 87 octane regular unleaded gas. Waste of money using anything higher especially with the high cost of gas these days. Our '99 Regal LS with 129K miles runs fine on 86 octane. In West Texas and the Rocky Mountain states regular unleaded is rated at 86 not 87 because of the higher altitudes.

Another issue is running premium unleaded gas when the engine is not designed for it is excess carbon buildup which will cause the 02 sensor to malfunction. I'd have it tested for a bad or lazy 02 sensor. Also, if you are DIY capable you can remove it and inspect the tip/vanes. Look for carbon buildup and abnormal discoloration. For a DIY operational check with a DMM you can check and monitor the output which is the purple wire. Look for changing voltage .1 to .9 volts (100mv - 900mv).

04-25-2008, 06:56 PM
Well today I finally took my car in for service. Gave my mechanic the history of whats been happening. He test drove the car and told me that it also bog-hesitated also. He then put the scanner to it and a few other codes appeared. P0102,P0107,P0171,P0463,P1107,P1811. Now some of these codes
might have been my doing, when I initially was checking the terminal plugs for such items like the MAF,IAT,IAC and others. Not knowing that you should not pull plugs while the motor is idling ( thats what mechanic told me ). Anyways he replaced the O2 sensor and cleared my car of all codes. Drove home (12mi.), and the car hesitated again and the SES light appeared again.
So what is the next course of action.

04-25-2008, 07:21 PM
Yeah, pulling the connectors to the various sensors is not recommended while the engine is running. Was the mechanic able to see the short and long term fuel trim values with his scan tool?

Best thing to do is get it scanned again and see what DTCs are really valid and go from there.

I see you have the P1811 DTC which is tranny related. The infamous PCS solenoid issue. :eek:

04-26-2008, 05:09 PM
Hi BNaylor and the rest of AF. Update on symptoms. First off went to AutoZone to rescan for codes. The following codes appeared. P0171 twice and P0102. Then those codes were cleared from my car. So I believe that so far these are the only valid codes. Now today I changed the plugs ( AC Delco Iridiums 41-101 and plugs Borg Warner 7mm ), not a very easy task but I conquered it. Started up fine and let run for awhile. Drove it a bit and the car hesitated and bogged again. But no SES light has appeared. So now am I wrong to suspect that the P0102 code is the culprit. This is getting to be frustrating, but with patience I know I'll succeed. BTW how do I post pics here. I have pics of the plugs that I removed and would like to show them. Just to determine what condition or category of the type of burn they show.

04-26-2008, 06:46 PM
I would would pursue the P0102 DTC which is the MAF sensor. It has a low output frequency of less than 1500 Hz. Also, FSM lists it as a possible cause of the P0171 DTC. A scan with a full function scanner which Autozone does not use would probably show the short and long term trim values out of spec and point to the MAF.

I mentioned earlier to disconnect the MAF and then check driveability. See if the hesitation and bog disappears. You can safely drive with the MAF disconnected. The PCM will switch over the default programming when it sees no MAF signal.

Switch back to the recommended 91 octane or better and then see what it does. Combustion chamber and exhaust temperatures are higher with lower grade octane. It may have affected the pre-CAT 02 sensor. The Bank 1 02 sensor is used to control the fuel injection system in closed loop mode of operation. DTC P0171 indicates you are getting a short term or long term fuel trim either due to a lean or rich condition.

Also, disconnect the MAF sensor and see what it does?

05-12-2008, 12:11 PM
Well I pursued the P0102 DTC. As suggested I unplugged the maf (with car off this time). Car idled much better with no hesitation or stalling at all. Purchased some CRC maf cleaner, removed maf, cleaned and re-installed.
But symptoms remained the same. Ordered a new maf sensor from AZ
(cardone). Installed as per directions supplied, and the car is performing beautifully. Prior to installing the new maf. I sprayed the throttle with CRC throttle body cleaner. BTW SES indication dissapeared on its own. So in closing this thread. I would like to thank the following for there help and input.
BNaylor, MaxWedge,Mikey#1 and Stripe. Thanks.

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