ECU Replaced Recently - High LTFT and STFT Values
 

I recently replaced the ECU and the dealership programmed it. I have high fuel trims at idle (~20% LTFT and ~20-35% STFT). It's closed loop so it's using the O2 sensors. Prior to replacing the ECU the fuel trims were within ~5-10% for this engine on both LTFT and STFT. The reason the ECU was replaced is due to code P0354 (Ignition coil D, primary/secondary - circuit malfunction). This melted/cracked my coil pack in the middle of the boot.

I have very good fuel trim values on throttle but at idle those numbers concern me. I don't have any sort of a smell coming from the exhaust. It's pretty neutral. I experience a little bit of a dip in idle from time to time. There is a code that keeps pending periodically but never actually throws the check engine light. That code says the 02 sensor stuck in lean/rich. This happened pretty quickly after taking the car on its first drive after getting the ECU replaced. I haven't see that code pop up as pending on the last 3 or 4 trips. Those 02 sensors were perfectly fine before the ECU was replaced. I'm hesitant to throw parts at the vehicle. Although the 02 sensors have some miles on them. Vehicle at 139,500 miles.

Is the ECU still calibrating? I've driven for about 75 miles so far. It took a little while for the LTFT values to kick in and take over as the ECU was still learning. I just don't know what to expect here and wondering if anyone else has had similar experiences. Maybe I just need to be more patient? Or should I start looking into this as a problem?

All help is welcome.

I could be wrong about this ,but,,,,,,,,,,,,,,,,,,,,,,,,,,,

First,,,,, your engine has a vacuum leak.
Second,,,,,,,how was it determined the ECU caused the ign syst problem ?

It would be helpful if we knew the year and what engine was in your vehicle.

The code you mentioned involved the ign system and resulted with the overheated coil problem..
Before going any further need to get that answer regarding reason for ECU replacement, somebody thought the ECU was the cause for the coil to overheat.
My question is why ?

So far,,something doesn't add up.

I'm with you. Something doesn't add up.

Thanks for taking the time to respond.
2012 Ford Escape 3.0L Flex Fuel. V6.

I may do a vacuum test on this tomorrow but I'd like to just point out that the vehicle did not have a vacuum leak prior to turning it in. And with the fuel trims as high as they are I wouldn't expect a smooth idle consistently (especially if a vacuum leak were present) but it still dips randomly maybe every 5 or 10 minutes of idle and then it comes right back up. Never fluctuates enough to make me think the engine is going to cut off but it's a noticeable fluctuation. Scan tool was plugged in and actively monitored prior to turning in the vehicle to replace the ECU and this issue was not present. The dealership agreed after completing their diagnosis - ECU was replaced as a result. They didn't just put the part on there because I asked them to do that. They completed a diagnosis of the issue. This is apparently a fairly known issue on these models for the ECU to go bad and melt an ignition coil.

Here's a pretty good rundown of what I found just hunting around on the issue a bit. This person experienced an almost identical error code and issue. Coil D on mine instead of A.

https://www.justanswer.com/car/onoxh...v6-melted.html

I did post a follow up, but in the interest of keeping personal opinions out of the forum , deleted it

Maybe you might have better luck with a coil built by STANDARD or WELLS.

I probably used an inferior quality coil pack when I did an engine refresh/tune up this summer. So I switched brands and went with one I probably should've gone with the first time. I'll be looking the engine over here in a bit after it warms up some more. Hopefully it's an easy fix. Thanks for the response.

Maybe this will help,
When we have positive fuel trim, the oxygen sensors are reporting a lean mixture too much air, and the ECU increases injector on time to increase fuel to the mixture.
When we increase the air coming in , increase throttle, the computer gets that info from the MAF sensor and automatically increases fuel so the engine runs better and fuel trim comes closer to normal..
That is why I suggested a vacuum leak after the MAF sensor , and that extra air requires extra fuel, hence increased fuel trim.