Need some help with weird aft/lambda

Hello again....

You guys are my final chance at any hope other then going to the dealer and letting them flash my car back to OE tune. Going to be honest. I don't have hptuners. But I know a lot about cars. I have a 2008 Pontiac Solstice GXP with the 2.0L LNF turbo motor and 82k miles. I've been here poking around and asking some questions before. However, I have an issue and nobody on the Solstice forum (as of yet) can answer some simple questions for me and point me in a direction to look for my issue. This could get long, but please bare with me....

I have a vibration around the 1k rpm range...it comes and goes. I have a ZZP dyno tune in my car for the last 4 years. 2 years ago I replaced the HPFP and the car ran great for about 6 months. Then last summer I got this vibration. So I didn't drive it much thinking it was the balancer...until the vibration went away one day for just the day.

Flash forward to this spring...I logged my car with my torque app. And we all know torque isn't the best unless you try to decipher it yourself. I now know that I'm not supposed to be looking at AFR, however, I've come to the following conclusions. My Commanded AFR (CAFR) was always, always, always 14.7 up until I got this vibration and a DFCO of CAFR at 29.4. It always had Commanded Lamba (CL) of 1 at that AFR. Now suddenly, once the car is up to temp, I still have the CL of 1, but my CAFR is 13.79 and a DFCO of CAFR of 27.58. Fuel in Detroit has not changed formulation...so they aren't adding more ethenol to our fuel....the news would have been all over it here. I have replaced both O2 sensors with no better result. However, my Wideband O2 (WBO2) does now go as low as .79 instead of the .84 that it was doing. My downstream O2 still seems a bit lazy, but it is working. My LTFT is around -8.5 continuously.

There's a bit more here....after replacing my O2 sensors, I started a log before I started the car. When the car is cold, it's CL is 1.03 @ CAFR of 14.23....then once up to operating temp it falls to CL of 1 @ CAFR of 13.79. So it's really weird. Also, I have a Fujita CAI and it used to sound like a rock tumbler from the turbulent air at cold start...this no longer happens. Is there a sensor that calculates ethanol percentage on the LNF? If not, what else can I look at? I have an appt at the dealer next Monday...So I'm hoping someone here can help me or point me in a direction to look at something. MAF readings seem to be okay, but I'm not an expert. I do know when I let off the gas abruptly, MAF does jump to 1800cfm...but it's only for a split second. Could it be my by-pass valve??? Please help!!

no e content sensor in the e69

vibration and performance issues together. i wonder if your loosing a timing chain tensioner and/or have stretched the chain out. this causes phasing performance issues and it shifts the balance shaft position causing erratic vibration in the lower rpm ranges when the shaft goes in and out of phase.

Thank you for your response! I thought it might be that, but wasnt 100% and didnt want to tear apart the engine and be wrong. My main concern is the CAFR. I know I should be looking at lambda, but I was learned on using AFR. So the fact that its consistently commanding 13.79 is a bit unnerving to me. Would this chain issue cause this? Also the vibration is always worse at cold start. My next issue using AFR is why would it command leaner on a cold start and then move to more rich? It's never done this!! Again...thanks for your help!!

chains can be worse at cold since the block and head havent expanded yet. its always possible the motor thinks its in a different operating condition due to sensor error caused by chain issues and thus you land in a different zone.
im not saying you should tear it apart im just saying its time to start doing inspections. there is a gear alignment in the back of the hpfp under he inspection cover. you can also pull the valve cover and look for other head related issues while also inspecting the timing chain guides and gear alignment from above.
its also easy to do leak down tests which can tell you a lot of information without taking anything apart except for some coils and plugs.
when was the last time you replaced the fuel injector o-rings?

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Originally Posted by cobaltssoverbooster

chains can be worse at cold since the block and head havent expanded yet. its always possible the motor thinks its in a different operating condition due to sensor error caused by chain issues and thus you land in a different zone.
im not saying you should tear it apart im just saying its time to start doing inspections. there is a gear alignment in the back of the hpfp under he inspection cover. you can also pull the valve cover and look for other head related issues while also inspecting the timing chain guides and gear alignment from above.
its also easy to do leak down tests which can tell you a lot of information without taking anything apart except for some coils and plugs.
when was the last time you replaced the fuel injector o-rings?

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They have never been replaced. I guess I should look at those too seeing as how my MAF o-rings were all coming apart and they've only been in the car for 4 years.... Hmmmm....cheaper and less time comsuming to buy a new motor maybe??? LOL... The guides looked good when I had the valve cover off about 3 months ago (issue has been around for over a year). How do I use this alignment mark on the back of the HPFP??? I appreciate all the help and suggestions.

hey Ghost, sent you a PM.