How many things can cause a "lean" condition

[GRWeldon]

Recently repaired 95 4.6. New timing components, new lash adjusters, 4 new valves. Should have purchased new injectors but I really didn't want to spend another $200+ as I'm trying to keep this to a minimum cost-wise. The injectors were pretty dirty from carbon. Replaced the filters, caps and seals on the old injectors. No CEL...but...I replaced the CEL bulb with a new one and tested it with a battery, but it may not be working still. I also did the same thing on one of the turn signal bulbs but one of them doesn't work still. Going to see if there is a code in a few minutes. Car hasn't run much since engine has been repaired...less than two hours I'd say. I put some Berryman's in the fuel to see if it clears any internal carbon. Car starts well. When cold it has a high idle for a bit, then it will gradually come down to where it's supposed to be but sounds like it's loading up on fuel an starts to miss. Will continue running sounding really bad but will rarely die. Checked for vacuum leaks by supplying propane around vacuum lines, brake booster and intake/head joint. Pulled plugs on 4,3,2,7 and 5. All were clean except #4 seemed to be wet (normal maybe?)

What can cause lean (or rich) conditions? Please help me fill out the list...
Bad O2 sensors
Bad MAF
Bad Injectors

I expect there are more things that might cause a rich condition. That is why I'm asking y'all...the experts!

Thanks...
Glen

 

[1997ThunderbirdLXV6]

I don't think this will help you, but in the interest of sharing:

The MAF shroud has a little metal plate aft of the sensor. Once, in the name of science, I removed that metal plate. I got a rich code almost immediately. I imagine the sensor measured more air, even though air flow amount didn't actually change.

What I take from that is that, even if your MAF sensor is functional, air flow disturbances/changes around the sensor can lead to a code.

 

[GRWeldon]

So here is something I noticed just now when looking at Live Data on the code reader. I turn the key and the car starts right up. Short Term Fuel trim is around 20 for a few seconds. Then the STFT starts to come down to between 9.2 and 11.7 and stays there for a few more seconds. Then the fuel trim starts to comes down over about 10 seconds and the car starts to run crappy until the STFT goes negative and the car starts to die. Around -12 STFT the car dies. This is the same for bank 1 and bank 2.

I think the code was P0156 (edit...P0135) before I started the car...O2 heater bank 1 sensor 1.

I have two new O2 sensors sensors and I'm almost certain the sensors in the car are at least 10 years old. For some reason I covet O2 sensors and hate to use them. If the consensus is that I should replace them, I will.

So it appears that what I thought was a rich condition is actually a lean condition. I wonder what is going on...

 

[GRWeldon]

I don't think this will help you, but in the interest of sharing:

The MAF shroud has a little metal plate aft of the sensor. Once, in the name of science, I removed that metal plate. I got a rich code almost immediately. I imagine the sensor measured more air, even though air flow amount didn't actually change.

What I take from that is that, even if your MAF sensor is functional, air flow disturbances/changes around the sensor can lead to a code.

I started to think about changing the MAF when I saw the condition of all the other aluminum castings on the car. When I removed it, it was really crappy dirty and corroded. When I found out that my NEW MAF had the wrong connector, I removed the sensor and put my old sensor on the new casting and put it back in. I wanted to look behind the metal plate but I didn't have the correct size torx safety bit. But, as it turned out it didn't seem to make any difference (see above post). I have a new one in the cart that I intend to buy shortly...

 

[Grog6]

exhaust leaks play hell on the readings too. When you suspect the sensors, replace the front ones, and move the old fronts to the rear. the valve stem and ring leakage drizzles them with burnt oil.
Oh, ntk sensors only; bosch suck ih our cars.

 

[1997ThunderbirdLXV6]

. I wanted to look behind the metal plate but I didn't have the correct size torx safety bit. ..

Don't. They come from the factory with red loctite. The bolts easily break.

 

[Kidd-7]

Correct me if I’m wrong, but I thought the O2 sensors only regulate air fuel in closed loop once they are hot. Prior to that it’s the MAF.
If fuel trims are low that means less air than expected or more fuel. Maybe a leaky injector. I’ve bought rebuilt ones off flea bay with success.

 

[theterminator93]

STFT as reported by the PCM will be fuel lambda until the car switches to closed loop.

 

[dDUBb]

So it appears that what I thought was a rich condition is actually a lean condition. I wonder what is going on...

Measured against MAF sensor / if the sensor is off; reading more incoming air than actual / the PCM commands more fuel and the o2 sensors react .. subtracting from the fuel trims. Possible False lean condion.

 

[GRWeldon]

STFT as reported by the PCM will be fuel lambda until the car switches to closed loop.

I could have sworn that somebody on this forum told me that our cars don't actually go in to closed loop. I thought the info was suspect but others seemed to reinforce the idea. What is the REAL deal?

Maybe a leaky injector. I’ve bought rebuilt ones off flea bay with success.

I've seen those and really cheap chineesium injectors. If I remove the fuel rail I'm replacing all of them, not just one. I don't have equipment to test injectors.

exhaust leaks play hell on the readings too. When you suspect the sensors, replace the front ones, and move the old fronts to the rear. the valve stem and ring leakage drizzles them with burnt oil.
Oh, ntk sensors only; bosch suck ih our cars.

OK, I forgot to mention, I'm only running half of the exhaust, cats to resonator. The entire system isn't installed because the front piece is all bent to hell. It's on the punchlist to try to fix.

Would this influence the rich/lean condition much?

So in general, without proper test equipment, what i think im hearing is that I need to replace MAF, O2 sensors and injectors?

I'm going to try a different MAF first as I have several around. See if the behavior on startup is different. Doesn't have to be good, just different. Then I'll know at least that the MAF is suspect...

 

[theterminator93]

I could have sworn that somebody on this forum told me that our cars don't actually go in to closed loop. I thought the info was suspect but others seemed to reinforce the idea. What is the REAL deal?

The car will always start in open loop, but it should always switch to closed loop in less than a minute unless it's really cold out. The O2s cannot be used to adjust fueling until they have heated sufficiently. If the engine is close to or at operating temperature when started, the car will switch to closed loop within a few seconds of startup. If the engine is really cold it can stay in open loop for over a minute - this is partly to warm up the O2s but also because a super cold engine needs to run a little richer until it warms up; our O2s are narrowband O2s and the PCM can't maintain/monitor AFRs beyond a few points of stoich.

 

[Kidd-7]

This: https://a.co/d/0ON37Td
And a can of carb cleaner and you’ve got your fuel injector tester. I bought just the plastic adapters and wired up a 12v battery with a push button and some clips.

 

[GRWeldon]

This: https://a.co/d/0ON37Td
And a can of carb cleaner and you’ve got your fuel injector tester. I bought just the plastic adapters and wired up a 12v battery with a push button and some clips.

Have you actually used this? I would think that a steady pressurized source would be needed, not just a spray can.

But, as I said...at this point if I pull off the fuel rail, I'm replacing ALL the injectors...

 

[KevinVarnes]

I don't get the feeling that injectors are your issue here, but there are a lot of places that can clean and flow test your injectors for you. Might be a better alternative to purchasing new aftermarket injectors. I used Injector Rx down in Houston last year for some GM inkectors.

Have you checked fuel pressure running to see what is going on? You can also see an injector leaking down after you shut the engine off. I know you don't have a parts store close by to rent a pressure tester from, but I think it would be worth a look see. It seems strange that it is starting out way lean and then transitioning to rich. Is the engine ever able to get up to operating temperature or does it stall out before then? Will it start back up after it stalls?

 

[Kidd-7]

Have you actually used this? I would think that a steady pressurized source would be needed, not just a spray can.

But, as I said...at this point if I pull off the fuel rail, I'm replacing ALL the injectors...

So yes I have used this set up and the injectors I tested are currently in my Cougar as well as me explorer.

 

[GRWeldon]

Have you checked fuel pressure running to see what is going on?....

No, however its a new fuel pump. I know that probably is no assurance of proper fuel pressure...

It seems strange that it is starting out way lean and then transitioning to rich.

I thought positive numbers were rich and negative was lean, buy I really am new to this game...

Is the engine ever able to get up to operating temperature or does it stall out before then? Will it start back up after it stalls?

Sitting at idle it will die before getting to operating temp. I have test driven it several times, getting up to temp. Still idles like crap after driving. Generally it will still start up after it dies. Honestly I can't remember if runs well or for how long after restart. I'll make a note.

 

[theterminator93]

Given the presence of an O2 heater circuit code, there is either a bad sensor or bogus wiring. I myself had two front O2 heater circuit codes that ended up being the harness that goes down behind the intake and firewall (near the heater hoses) was melted with gobs of shorted out wires in the bundle.

Sounds like your engine runs until it switches to closed loop, which further reinforces a bad O2 sensor giving bogus fueling feedback to the PCM.

Swap the O2 sensor sides per Dan's suggestion, clear the code and report back when it returns with the code number. If it follows the sensor then it's a (relatively) easy sensor replacement fix. Otherwise there's some harness troubleshooting to do.

 

[dDUBb]

I thought positive numbers were rich and negative was lean, buy I really am new to this game...

Fuel trims are an indicator for adding or subtracting fuel. You would add fuel to correct a lean condition and subtract fuel when its too rich.

It's normal to have constant switching rich to lean on the short term .. that is adjusted over time in long term. When the threshold for fuel on the long term is over 30% it will throw a code.

 

[GRWeldon]

Given the presence of an O2 heater circuit code, there is either a bad sensor or bogus wiring. I myself had two front O2 heater circuit codes that ended up being the harness that goes down behind the intake and firewall (near the heater hoses) was melted with gobs of shorted out wires in the bundle.

Sounds like your engine runs until it switches to closed loop, which further reinforces a bad O2 sensor giving bogus fueling feedback to the PCM.

Swap the O2 sensor sides per Dan's suggestion, clear the code and report back when it returns with the code number. If it follows the sensor then it's a (relatively) easy sensor replacement fix. Otherwise there's some harness troubleshooting to do.

Put the car up on the lift in preparation to change bank 1 O2 sensor when I discovered that the connector had become disconnected. I reconnected and started the car. With the scanner connected I watched the STFT start at 32% and slowly work it's way down to -11.7. Then it started to come back up in the positive range. It bounced between 20 and -17 for a while, slowly narrowing the range, settling in about 4.7 to -7. After entering closed loop it bounced between 5 and -4.

BTW, what is a good value for MAF at idle. Mine is about .80 lbs per minute...

Video clip of fuel trims at the bottom...

 

[dDUBb]

Long term is more important in determining air / fuel ratio - running lean / rich; or if the engine computer is attempting to compensate for a bad sensor or other condition.