Short Term Fuel Trims

Alright, so I have been working with a tuner from SCT troubleshooting my car running rich. I've been data logging and running new programs for weeks with out really figuring anything.

Before we go any further, the engine I have in my car was a used one I used to replace my broken one in April. Before it was installed it had compression tests and leak down tests done to it and it was fine. Also done again in the beginning of August when I brought my car to a shop to see if there was anything mechanically wrong with it causing these issues, which was me having p2196 and p2198, o2 sensors stuck rich. I've replaced my MAF and replaced my spark plugs (multiple times, all with the same results)

I've analyzed my last data logs, and you can see the short term fuel trims pretty far off from one another, to the point where at some instances one side is reading .60 and the other is 1.40 when there is no load on it. But when I go to accelerate the values align up. My o2 sensor voltages are also off from one another until I accelerate as well.

So to sum that up, my short term fuel trims and o2 sensor voltages only align with one another while accelerating. When I am just cruising (not putting any load on) the values vary greatly.

I know my o2 sensors are connected correctly (not swapped) and when i did try to swap them, to see what happened and provide a data log for SCT, I didn't feel comfortable driving it around like that.

Anyone know what I could possibly be missing? This is driving me crazy, killing my gas mileage, and my car is not as responsive as it used to be.

Mods: BBK shorty headers, Ford Racing Cold air intake, Ford Racing 0-degree spark plugs (for my nitrous kit), walbro 400lph fuel pump, catless exhaust.

Are you still using the stock injectors. I would flow test them. A ford dealer can hook up the ids and do a flow test.

sounds like a vacuum leak, or exhaust leak on one bank. How are the injector o rings, intake manifold?

eighty6gt said:

sounds like a vacuum leak, or exhaust leak on one bank. How are the injector o rings, intake manifold?

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Yes. Find a shop with a smoke machine and stop pulling your hair out.

^^^^ Agree. Vacuum leak check is next. Vacuum gauge tells a lot. The old propane torch bottle test or TB cleaner test can help isolate. An old racing guru around here turned me on to using a propane torch with the valve cracked lightly open (not lit obviously) as the means to isolate vacuum leaks. Works the same way as TB cleaner without all of the wetness.

It really sounds like the o2 sensor connectors are swapped. I'd start there.

^^^ That's what I thought and started to suggest but reread his post and he says he already verified that.

seems a lot of guys been connecting 02's upside down lately.

no they're not swapped.

JonT said:

no they're not swapped.

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What happened to the trims when you swapped them? I'm talking about the forward sensors, not the ones in the cats. I'm sure you are too, just making sure.

Right now you have one trim stuck rich and one lean. It's almost always the result of the computer giving fuel corrections to the wrong side resulting in correction runaway and stuck rich and lean conditions.

The only other scenarios I can think of are bad injectors on both sides or an issue with the ecu although I'm not sure how the ecu would cause both banks to be off rich and lean.

I'm guessing the long term trims are also maxed out, have you looked at them? Also, when you swapped o2 sensors did you reset the kam? If a kam reset wasn't done it will take awhile for the long term trims to come back to normal. Since the short term trims are an instant correction to the long term trims they would be whacked until the ltft came back.

I didn't end up data logging the car when I swapped the o2 sensors connectors because the car didn't run well enough to the point where I felt comfortable driving it around doing tests. But I guess I should see what happens.

In all my of my data logs, my LTFTs have been steady at 1.00. The interesting part is my short term fuel trims end up averaging out around 1.00 (give or take .05).

I've reset the KAM on several occasions when I swap the o2 sensor connects because I need to remove the battery to make it easier to get to the o2 sensor wires. By the time I end up putting the battery back in and connected its like 20 or so minutes.

It is so frustrating because I feel like it is something small I overlooked. I've replaced the MAF sensor, replaced PCV hose, the fuel injectors and spark plugs have all been replaced in August, I checked for vacuum leaks, did leak down and compression tests, I've been data logging with SCT, i've been checking the resistances and voltages sent to the spark plugs, o2 sensors, fuel injectors, FPS, and MAF sensor. I even replaced the o2 sensor connectors on the wire harness side. I've had people and shops look at it. They all said its poor tuning and the Tuner said there's something wrong with the car. Where I started data logging and testing tunes since Sept 1.

The latest thing someone told me check was the base oil pressure to ensure there is enough pressure to run the VCT system and try to rule out the variable timing. But i have not gotten around to it.

The whole reason I am going through all of this is because I plan on turboing my car for Christmas and I want to ensure there won't be catastrophic failure while doing it. But it sounds like some extra air would be beneficial.

Any chance the problem or part or the problem resides in the colder plugs? Tried putting the standard heat range plugs back in to see what happens?

When you swapped the motor, did anything else change? Did you check the base timing? Are you tuned for the cai?

what o2 sensors you running? how old are they?

maybe, they don't wanna act right until you get some heat in them.

Bosch are garbage but I dont see the 02 sensors themselves acting up after a motor swap. It sounds like its the motor itself if thats all that changed before he had all these issues.

Are the vvct working properly? prob messing with timing?

wait you're running the walbro 400 lph pump?
Now is that the drop in one? or did you replace the pump from the stock hat?

I now you need to specifical tune that pump or you will end up running rich! in which will cause the car to loose a lot of power.


Also those 0 degree plugs don't play nice in the cold, my car acts really weird during the cold weather and want to misfire as lot, as soon the engine and temp get warm (y) issues goes away!

It's the full fuel pump assembly. And yeah, my car runs like poop when I first start it.

The extra ground that comes with some walbro hats have been removed?

If you want to send the logs over, PM me.