Running lean -100 on bank 1? Possible causes?

[98whitexploda]

My check engine light came on a while ago and autozone told me it was running lean on bank one. I replaced my spark plugs and wires just cuz it had been over 3 years since that had been done and then my brother in law reset my check engine light and the light has stayed off but I noticed I was burning through gas faster then I used to so I hooked it up to a code scanner and it was telling me running -100 on bank one and bad o2 sensor. The machine couldn't complete some other test either because it said it couldn't find the exhaust? Basically wondering is the 02 sensor the only cause of my running lean -100? Or could it be my MAF or cat or something else? I also noticed I have to downshift to 3rd more now to go up hills or it loses power. (It's a 5-speed manual) What's my best bet, is there a way to test each part or just start replacing possible causes? Any help would be appreciated. I have about 153k miles on the engine if that helps with anything.

 

[jlsparky7]

Sounds like an O2 sensor or a bad vacuum leak.

 

[WhitEngineering]

Keep us updated on what you find out. I'm working on the same problem. All 3 O2 sensors show 0.000 volts and both short/long term fuel trims are at -100.6%. No check engine light, no stored codes. 10-12 mpg hwy.

 

[98whitexploda]

Will do. Prolly won't order the new sensor till next week sometime when I get paid again

 

[2000StreetRod]

Rich not lean

If I remember correctly fuel trim is the adjustment required to achieve optimum Air/Fuel ratio. If the fuel trim is negative that means the A/F ratio would be too rich without the adjustment. When the PCM is in closed loop the A/F ratio cycles between slightly rich and slightly lean as reported by the O2 sensors. The PCM continues to richen the mixture until slighty rich is detected or until the trim limits are reached. Once slightly rich is detected the PCM leans the mixture until slightly lean is detected or until the trim limits are reached.

If your trims are actually negative, I suggest that you search for sources of a rich condition. You may be able to confirm a rich condition by detecting black smoke in the exhaust or carbon deposits on the spark plugs. O2 sensors degrade with age, new: 0.95 to 0.07 volts, aged: 0.83 to 0.09 volts. An O2 voltage less than 0.1 volts indicates a lambda greater than 1.02 (lean). However, a reading of 0.0 volts is very unlikely for a functional O2 sensor.

 

[98whitexploda]

I don't blow any smoke and the spark plugs still look good thankfully seeing as I just replaced em last month along with the plugs

 

[2000StreetRod]

Correct trims?

According to the model year 1998 OBD System Operation Summary:

P0171 Bank 1 Lean
Lean malfunction: LTFT > 25%, STFT > 5%

I assume since you have a 1998 with a manual 5 speed that your engine is the OHV V6. Do you have 3 O2 sensors or 4? Are you sure that your scanner is reading the bank 1 fuel trims? There should be long term and short term fuel trims for bank 1 and bank 2. I suggest further investigation before replacing the pre-cat O2 sensor on the passenger side (B1S1).

 

[98whitexploda]

Ill have to check into that then. Not sure exactly what engine just know its 4L v6

 

[carboy400]

Ill have to check into that then. Not sure exactly what engine just know its 4L v6

It will say "SOHC" on the beauty cover over the intake.

I to am chasing a code P0171 and P0174 bank 1 and 2 lean and my scanner is reporting the O2 ST and LT trims at -100.0 and no voltages but if I look at freeze frame data I get readings but always the same. If I check my scan tool on a different car I get proper readings, so I'm a little confused if its a car issue or a scanner issue. On a side note and more confusing point I get no VSS signal but trans shifts just fine.
The code P0171 and P0174 bank 1 and 2 lean as I read it means the A/F ratio is lean and the PCM has enriched the A/F past the upper limit. Possible culprits are Unmetered air after the MAF, Bad injectors, base engine problem. I have pretty much traced all the primary vacuum lines on the engine and found nothing. I have checked injectors and base engine issues, none exist. I don't think its a timing chain issue but I haven't ruled it out. I am leaning more toward a cracked intake or bad injectors. I do have a question about injectors I measured mine cold and they all came in around 17.3 - 17.8 ohms, Heat increases resistance so could these injectors fail after warming up?

 

[Scout3]

Carboy,
Not sure about your car, but my 97 SOHC is not compatible with most readers. I have a Harbor Freight cheapo and it will not read Fuel trim or O2 values or speed data. Reads most other values though. I tried a friends Actron and it did the same thing. I found on the web that the 97 does have a compatibility issue with some scanners. Not sure about other years.You may want to make sure you dont have a software issue with your scanner befroe going to far. If your all your fuel trims are 100% and O2 are zero you have a scanner issue.

Ed

 

[WhitEngineering]

Carboy,
Not sure about your car, but my 97 SOHC is not compatible with most readers. I have a Harbor Freight cheapo and it will not read Fuel trim or O2 values or speed data. Reads most other values though. I tried a friends Actron and it did the same thing. I found on the web that the 97 does have a compatibility issue with some scanners. Not sure about other years.You may want to make sure you dont have a software issue with your scanner before going to far. If your all your fuel trims are 100% and O2 are zero you have a scanner issue.

Ed

Thanks for the info. Like yours, my Actron will not display live fuel trim, O2 values, or speed data on my '97 OHV. While testing that the scanner worked on another vehicle I noticed it had captured a freeze frame from the '97 the last time I drove with it plugged in and actually recorded the missing data.

Now to solve the horrible mpg and absent entrance ramp power.

 

[Scout3]

I noticed the same thing on my scanner. Freeze frame did display the missing data. I toyed with the idea of intentionally triggering a fault code just to check the data but have not tried that. It is frustrating that the live data does not see it.

 

[98whitexploda]

Fixed the issue. I had a few lol. Bad o2 sensor, I had 4 total but only one was really bad, replaced fuel pump assembly, and had a bad manifold gasket.

 

[kingkitty]

Intake seals leaking on plastic intaks

These vehicals are famous for intake leaks on seals, smoke test it.

Additional research only Ford sells manufactor upgraded seal kit to address problem. Also replace bolt gromets on lower intake must be green in color,
black ones break down.