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GeeWiggles 04-19-2012 03:32 PM

Engine lean bank 1 o2 sensor code
Just checking, but an engine too lean code, loss of power around 3-4k rpm and carbon build up on the plugs would denote faulty code from the upstream o2 sensor, correct? If it were actually running lean, there wouldn't be carbon build up on the plugs after such a short while. Just want to make sure before I buy an o2 sensor if it could be something else.

OldNuc 04-19-2012 03:47 PM

Re: Engine lean bank 1 o2 sensor code
Check your fuel pressure and when was the fuel filter changed last? Use a WIX filter.

Idle pressure 31-36psi
Key on engine off 38-44psi
Idle pressure with vacuum line to regulator connected and plugged 38-44psi

An exhaust leak anywhere between the engine and the CAT inlet will indicate a lean condition and run rich. A seriously restricted CAT will cause a loss of power at higher RPM but usually shows up as running rich. Running excessively rich will result in a loss of power as well.

Look at the rear O2 sensor and see if it is indicating lean as well.

GeeWiggles 04-19-2012 04:36 PM

Re: Engine lean bank 1 o2 sensor code
Rear o2 isn't throwing any. Do upstreams usually throw incorrect codes when they fail or is it usually a circuit failure code? The filter is "suppose" to be recent but I don't really trust it after the work I've had to do. Exhaust does smell a little foul but not really sulfer like could just be the rich condition.

OldNuc 04-19-2012 05:20 PM

Re: Engine lean bank 1 o2 sensor code
You have to actually look at the rear O2 signal and see if it is lean. The O2 sensor is a primary sensor and if it actually fails it will set a code. The lean code may be caused by several things but O2 sensor failure is not one of them. Most likely the sensor is fine.

OldNuc 04-19-2012 05:25 PM

Re: Engine lean bank 1 o2 sensor code
You can not diagnose mixture strength by smell. If in doubt replace filter and pressurize exhaust and look for leaks carefully as a minute leak will cause this. Pressurize with a low pressure blower to 1-2 " H2O pressure only. Then go over every inch of the head pipe and manifold flanges. Soap/water solution works.

madpogue 04-20-2012 12:54 AM

Re: Engine lean bank 1 o2 sensor code
What's the actual code?

GeeWiggles 04-20-2012 10:15 AM

Re: Engine lean bank 1 o2 sensor code
Po171 system too lean (bank 1)

OldNuc 04-20-2012 11:02 AM

Re: Engine lean bank 1 o2 sensor code
That is what I thought it was.

GeeWiggles 04-20-2012 01:59 PM

Re: Engine lean bank 1 o2 sensor code
So I checked fuel filter and it indeed appeared to be new. As I don't have immediate access to a pressure gauge I decided to take everything apart again and inspect/clean. Is it possible for a miss-gapped spark plug to cause a lean condition? I noticed the #2 cylinder plug's gap looked a little narrow and I checked it and it was undergapped, I must have missed it when I was putting them in :/ Anyway after cleaning erg/map/everything I could and all their connectors the car runs smooth now. It was only a short test drive, but before it almost immediately started hesitating, now no hesitation at all and much less fuel smell from the exhaust.

I will be checking fuel pressure, probably this weekend, regardless. This could also be signs of a pressure regulator or fuel pump and I definitely don't want to get stranded somewhere.

OldNuc 04-20-2012 03:41 PM

Re: Engine lean bank 1 o2 sensor code
The regulator is a possible issue as well aged ones may not consistent in pressure. Failing fuel pump will have inconstant output before completely failing.

Closed up plug gap will potentially cause problems.

What brand of plugs are you using?

GeeWiggles 04-20-2012 03:46 PM

Re: Engine lean bank 1 o2 sensor code
I'm just using the autolite copper cores. None of the parts stores around here in rural west tn had any of the NGK coppers in stock, autolite were the only alternative as I needed them same day.

OldNuc 04-20-2012 04:33 PM

Re: Engine lean bank 1 o2 sensor code
That is fine, just wondering about the closed up gap. Fuel pressure is still of interest, as well as an exhaust leak.

GeeWiggles 04-20-2012 04:47 PM

Re: Engine lean bank 1 o2 sensor code
I thought I'd checked the gaps on all of them, but I must have let one slip by me. usually they're spot on, this one was not lol.

I'm about to take a moderate trip so we'll see how it reacts and I'll report back here once I get to where I'm going. Exhaust leak is a possibility too, the flex pipe area looks like it's seen better days.

OldNuc 04-20-2012 05:25 PM

Re: Engine lean bank 1 o2 sensor code
Pull the plugs and if they look like you are running rich then your problem is an exhaust leak as the leak causes the O2 sensor to think you are way lean and it dumps in gas like mad.

bluesl2 04-20-2012 06:15 PM

Re: Engine lean bank 1 o2 sensor code
Don't forget about the ever so popular ect/connector issues.

OldNuc 04-20-2012 10:18 PM

Re: Engine lean bank 1 o2 sensor code
That could very well be part of the problem also.

GeeWiggles 04-23-2012 12:45 AM

Re: Engine lean bank 1 o2 sensor code
I replaced the ects about two weeks ago and checked the connector, also replaced the iat and thermostat, and three days later the water pump lol.

Well on the way up to where I was going the car ran like a champ til I got about half way, then the ses came on so I raged and pulled into the nearest autozone for a code scan. This time it was circuit faults on BOTH O2 sensors, which I found very peculiar that they'd both fail at the same time so I started going back over what I had done the other day and noticed that I had put the battery ground at the transmission back on the wrong post, the rear one under the EGR and not the front one behind the coil. In my efforts to fix my problem I tore about most of the intake and emissions system and cleaned it all, and I noticed my map sensor and it's access hole were full of carbon/sludge. Anyway I figured I take off the grounds and clean any corrosion I found and I guess when I put them back on, being in the usual hurry I am, I put the battery ground on the wrong one.

Weather or not this had any bearing on the sensors I dunno, but I drove it 100+ miles home tonight and the ses never came on and it was smooth as butter the whole way.

OldNuc 04-23-2012 07:45 AM

Re: Engine lean bank 1 o2 sensor code
There are 2 ground wires that have to connect there and the actual sensor grounds and PCM sensing circuit grounds are the 4 wires bolted to the back of the block over the top of the starter. They must be clean and tight as well. You can reach them from above as they are just on the back side under #4 intake runner.

Replaced sensors and cleaned connectors helps but there is a possibility of a poor connection on either sensor. The actual performance should be checked with a scanner.

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