How many things can cause a "lean" condition

G

GRWeldon

6th Gear Poster
Joined
Oct 5, 2023
Messages
500
Location
Alabama
Country flag
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
 
Last edited:
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.
 
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 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...
 
Last edited:
1997ThunderbirdLXV6 said:
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.
Click to expand...
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...
 
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.
 
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.
 
GRWeldon said:
So it appears that what I thought was a rich condition is actually a lean condition. I wonder what is going on...
Click to expand...

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.
 
You must log in or register to reply here.

Similar threads

Back
Top