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Old 10-16-2019, 12:13 PM   #1
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Dizzy intermittent OBII readings and issues - 2004 Vue 3.5L V6

Hello, I have a 2004 Vue with the 3.5L V6 at 177,000 miles. This is our "spare" vehicle that I've been driving to work everyday as of recent, so I can closely pay attention to it and fix anything that needs fixing. Now...I've fixed most of the issues I've noticed and things I've been concerned about but something about this car is eluding me at the moment. Everyday I drive it I use my BlueDriver OBDII reader to monitor Engine Temp and Short Term & Long Term Fuel trims for both banks. Here's my current issues/concerns... for some reason my fuel trims are not consistent at idle, especially the STFT. My numbers aren't real bad but shouldn't my STFT readings at least be steady at idle? With the engine warmed up, at any given time my STFT readings will swing anywhere from +/- 0.8% to +/- 4%. What's weird is that sometimes when I drive it, (checking @ idle) it'll swing (in a matter of seconds) from -0.8% to -4% and other times it'll swing from +0.8% to +4%. It's like... some days it wants to stay in the positive and some days it'll stay in the negative range..I've never seen it swing all the way from -4% to +4% in a single sitting. now, I know + or - 4% isn't bad but it's the inconsistent swinging that has me confused and concerned and why some days it's in the negative range and other days it's in the positive.

Now, the "more important" Long Term Fuel Trim (LTFT) at idle has mostly been staying at -0.8% which is great but sometimes it'll get out of wack too and i've seen it climb to +8 to 11% at idle and another time it was in the same 8 to 11 % range at idle but it was in the negative. What gives?

The car always seems to idle smooth no matter what since I recently replaced my old PCV valve that was stuck open, so...i can't easily tell that anything is wrong in terms of driveability because in general it seems smooth in everyday cruising. However, my last tank of gas yielded 15.2mpg but the tank before that got me 19.7mpg. same driving habits and same route to work everyday. So, my symptoms are: fluctuating MPG and sometimes the car will have less power than it should. That latter symptom is harder to notice sometimes because these 3.5L VUE's already had lots of power so it's easy to not notice in daily driving just cruising around but the intermittent lack of power I'm describing has to do with higher RPM "lets floor it" type of driving when you need to pass someone quick. During those times I can kind of notice it's slightly less smooth during the hard acceleration and I'll notice a slight "hiccup" or minor RPM drop when it shifts, like a quick stumble when it grabs that next gear as if the engine had to recover from the sudden change in load. Other times the car is light on it's feet, instantly peppy and runs like a bat out of hell again. It's just never noticeable when it's running like it's supposed to because it never idles rough and cruises a symptom flying under the radar, trying to be difficult to diagnose...

There's some other weird things going on, but first let me explain the current known "problems" with my car:

one of my Cat Converters is completely gone, it's hollowed out. It melted long time ago and blew the fragments out the exhaust. There's no exhaust blockage, i just had a shop check that out. The other Cat is deteriorating and on it's way out. I live in a county where Emissions testing is not required so I'm just going to let the other Cat fall apart and carry on about my business (I just need a good running, reliable spare vehicle). So, those are codes P0420 & P0430 so I expect the check engine light to be on ALL the time because of the bad Cats. However, sometimes the check engine light turns off and stays off for several miles but will of course show those codes as "pending" and then the check engine light will eventually come back on. What's strange though is that sometimes the check engine light will turn off for a few days and when I read it to check for codes it says there No codes and Zero pending codes. How could there be no pending codes when both my Cats are shot? Also, recently when I was checking for codes it popped up with a new pending code that I've never had before...a P0404 "EGR A Control Circuit Range/Performance". I've only seem this pop up as "pending" but hasn't actually caused a Check Engine Light yet. In fact, when I scanned for codes a few days ago it showed the P0404 as pending, then the next day when I scanned again it wasn't there at all, then the next day I scanned again and it showed it as pending again. So, the P0404 just comes and goes as a pending code... Here's another thing that I *think* is weird...sometimes while I'm driving around I'll tell my OBII reader to check for codes and the car has actually died on me a handful of times during the reading process just before it finishes at 100%. A few of those times the engine just stumbled real quick and almost died. The engine has only died on me like that when reading for codes but doesn't do it all of the time. I've also had an instance where the P0420/430 codes are present with the check engine light on and I decide to re-scan for codes which caused the engine to stumble and then the Check Engine Light magically disappears right after it stumbles and the car reports Zero codes and Zero pending. ..seems very strange to me.

kinda seems like the PCM/ECM is acting wacky but then again maybe the P0404 EGR issue is causing my swinging fuel trim readings and intermittent poor MPG and high RPM power loss?

Here's some things that's been repaired/replaced my car very recently:
Intake & throttle body was professionally cleaned of carbon buildup.
Fuel injectors were cleaned
New Spark Plugs
New PCV valve
New Air filter
New Honda DW1 Transmission Fluid
Flushed cooling system with EvapoRust ThermoCure
New engine coolant and new pressurized "radiator" cap
Fresh Oil change
Cleaned MAP sensor
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