Hey NCG,
I've been following your videos and posts, and I definitely feel your pain. My setup is almost identical to yours, and I'm seeing the same AFR behavior at idle. Vacuum doesn't seem to be an issue, I average around 18 -Hg at idle. The only major difference is that I'm running a Raptor S (K26/6) instead of the Raptor X.
The other thing we have in common is old fuel, and after reading what chrischrischris shared, I'm starting to wonder if I've been chasing my tail too.
First off, thanks for documenting all of your testing, it saved me a lot of time. I've gone through many of the same checks and haven't found anything obvious. I smoke-tested and pressure-tested the intake with no leaks. I did, however, track down a condensation issue. Every time I started the car, it would leave a small puddle of water underneath. It turned out the water was coming from the downpipe flange on the exhaust side. The flange bolts simply needed to be re-torqued. After fixing that, I noticed a slight improvement in my AFR readings. My wideband O2 sensor is located just downstream of that connection, so I'm assuming the small exhaust leak was affecting the readings. I also have the same two-piece Lindsey Racing crossover pipe and plan to smoke-test it as well, just to be safe.
The reason I'm leaning (no pun intended) toward old fuel being the culprit is that my car has barely been driven over the last three years while I've been restoring it (I'll share more about that in another thread). When I recently filled it up, the tank was about half full of fuel that was at least a year old; possibly older. Looking back, I should have drained the tank instead of adding fuel stabilizer and topping it off with fresh gas. Unfortunately, I now have a full tank of this lovely fuel cocktail...Grrr!
For some additional background, I had my injectors cleaned and flow-tested before the car sat. It ran great afterward, but then it sat for about 11 months. When I finally started it again, it felt like it wasn't firing on all cylinders. After checking everything over, I noticed it was running extremely lean (16-18 AFR). I pulled the injectors, had them checked and found they had all gone bad. Once I had them refurbished and reinstalled, the AFR came back to where it should be (around 14.7). The car still has a slightly rough idle, and the AFR oscillates between about 14.7 and 15.1 at idle, but it averages right around 14.7 while cruising.
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Based on the new information about the gas, I'm beginning to think my old fuel mixture is the remaining culprit, and it may very well be the same issue you're dealing with. The more I read through the GPT information, the more they seem to line up with what I'm seeing. In fact, every case describing the effects of old fuel closely matches the symptoms my car has been exhibiting, from the rough idle and fluctuating AFRs to the way it runs fine once cruising. At this point, old fuel seems like the most logical explanation.
I really don't want to drain a full tank of gas, so I think I'm just going to take it on a long drive and burn through it. I'll keep the boost under 5 psi just to be safe and see if the symptoms improve after adding fresh gas.
Looking forward to your next update. Fingers crossed we're both chasing the same simple problem.
On a related note, I also want to check the MAP plug that is supposed to be shorted on the F9 DME with OBD+. I wasn't aware of that requirement, and I'm wondering if it could also be contributing to my rough idle.
Can anyone explain exactly what needs to be done or point me to an existing thread that covers it? I'd really appreciate it. Thanks!