What could cause one side of the motor to be richer than the other?

04GTMustang

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Feb 28, 2006
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Stafford
I just got a DL32 Datalogger from innovate and dual lc1s. part throttle driving the air fuels seem to stay right with each other on both banks but under WOT in 3rd gear channel 1 lc1 shows an Air fuel of 10.7:1 and channel 2 is showing 11.8:1. that is the ratio my dyno operator tuned the car to be at.

I do not know which bank channel 1 and channel 2 are monitoring but i am curious as to why one side would be running richer than the other....

Any help stangnet?
 
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Could be your Mass Air sensor, make sure its functioning properly; like know obstructions that would cause a false reading.

alright i will check that. could there be a wiring issue?? I had my methanol hooked up to the MAF and disconnected the wire going to the methanol that was tapped into the MAF voltage so i wonder if that could be the culprit. I will have to check to see what the deal is.
 
You need to find out which bank corresponds to which sensor. An operating theory:

Fuel is delivered to the bank 1 (passenger-side) fuel rail. It must run across a thin tube to reach the driver's side (bank 2). Given the pressure drops occurring in the fuel rails (caused by the injectors opening), perhaps the driver's side is seeing reduced fuel pressure under load.

Are the two sensors properly calibrated? Not fouled by anything (e.g. octane booster, race gas etc)?
 
You need to find out which bank corresponds to which sensor. An operating theory:

Fuel is delivered to the bank 1 (passenger-side) fuel rail. It must run across a thin tube to reach the driver's side (bank 2). Given the pressure drops occurring in the fuel rails (caused by the injectors opening), perhaps the driver's side is seeing reduced fuel pressure under load.

Are the two sensors properly calibrated? Not fouled by anything (e.g. octane booster, race gas etc)?

sensor 1 is bank 2 and sensor 2 is bank 1. My car has always been a pain regarding the FRPS ever since i got it tuned. I did another pull today and both air fuel channels went down to 10.4 and 10.6 and the drivability is starting to smooth out. I am wondering if when they unplugged my battery if it lost all its "run strategies" and then it is making an attempt to relearn everything again. when i first got it back it was doing its usual bucking under light load until it goes anywhere near boost. (hahaha)

no octane booster and no race gas was added the 02s are calibrated for gasoline so its set for 14.7 AFR=1v lambada.

The car was even tuned on 9psi and i currently have the 11psi pulley on it and its making 12.5psi hahahaha my vac at idle is right around 21InHg and holds steady.
 
We had problems with fuel pressure with the stock rails. You might want to change the plumbing and Y the two rails together. The way they are fed now in series doesn't work as the power goes up. If that doesn't work, get larger rails.
 
Could be a vacuum leak on the lean side. Or more likely an injector not firing on the lean side or stuck open on the rich side. Could be a BIG exhaust leak ahead of the sensor letting in atmospheric 02. Could be an ignition problem on one bank. Bottom line, could be almost anything. Swap injectors bank to bank and see if the problem follows. Doubt it is the MAF as it affects both banks equally. One thing for sure, don't ignore it!
 
Don, I agree with most of what you say except for a single FI causing the bank to be lean. I will say that under higher power, my fuel pressure consistently dropped under full throttle. I went to a return-system after 2 of my cylinders went out similiar to the Terminator problem. At the end of the rail on the drivers side, the pressure is definitely lower, even if you are running higher power pumps.

For budget reasons and because this is what we did with the return system successfully, I would take the feed that goes into the passenger side rail and put a Y in it. then Y the output from both rails to send back. If that doesn't normalize your pressure, look for something else but you can make that change for $30 to see what happens.
 
Of course that would help... but I have seen multiple individual injector failures on the dyno. It does happen. I run two widebands all the time, and have tuned tons of returnless vehicles - some really high HP and usually only see this problem when there are issues with the things I have listed. But I'm sure it could be anything else - tough to diagnose those things sometime. Just trying to give him more to look at.

Could also be the wideband sensor on the lean side going bad. When Bosch sensors go bad, they read lean. For $60, I'd replace that sensor first. That's the first thing we do when we see that issue.
 
In this case, it's easy - he has two widebands and one is saying lean, one rich. In the case of the PCM and fuel trims, it uses data from the two front 02 sensors. The rear 02 sensors are not in the equation, they are there to monitor catalytic converter performance. To put it in really basic terms, the front 02 sensors switch around the stoich point of the fuel used and the PCM makes corrections based on the variance from stoich - at idle and part throttle in closed loop when it's at operating temp. At WOT it uses data mainly from the MAF and base fuel table to apply a global fueling to the engine. From the factory it can apply certain long term corrections to OL fueling, so in essence it does use 02 sensor data, but not directly - and in most cases, this is not a good thing and is usually changed when a car is tuned.

As far as one injector is concerned - it does not, it takes data from the gas coming down the pipe to the 02 sensor. If one injector is bad, it may or may not be enough to get the system so far out of whack it throws a CE light. If it is just happening at WOT, they it doe not know at all. A good check is to datalog 02 sensor volts and see what is happening - or use a Snap On Scanner to look at individual injectors performance.

That all applies until 2011. 2011 and up Mustangs run in closed loop all the time because they have factory wideband sensors in each bank that keep the system stable.

Bottom line - first thing I'd do is replace the lean wideband 02 sensor.... Then start looking at the motor.
 
i replaced all the spark plugs yesterday and cleaned the MAF. problem seems to have went away now. Air Fuels are much closer than they were. Still insanely rich though hahaha. I wonder how much power I am losing from running in the 10s on air fuel...on the 3in pulley it is making 12.5psi.

I will be switching over to a return style here in a couple years as well. would be sooner but I am getting married next year so the wife would kill me if i spent a couple grand on the car right now lol:D Not a good way to start off a marriage lol. :rlaugh:


oh and i am almost positive its not the sensor. I just put the system in less than a week ago lol.