This is a bit long-winded, so bare with me... The car has been running really well, so I decided to push the single Deatschwerks pump a little more by raising the voltage to keep the pressure up... which worked great: Deatschwerks DW300 High Flow In-Tank Fuel Pump Testing Post #115 After several days and another E85 fill up, I noticed the FT's going up and the car was starting to lean out a bit at WOT. So I took the Golan fuel filter apart, and found this (this is a new 40 micron element that I installed about 2 weeks ago): A few minutes in some clean gas, I ended up with this (notice how dirty the gas was afterwards ): I pulled the injectors and cleaned them as well. (They had some buildup, but I've seen much worse). After putting everything back together, FT's were back in line and the car ran good until... On my way to work yesterday (20 miles), I noticed fuel trims starting to go up again, and this time they were on a mission. As I pulled into the parking lot, AFR's were spiking to 18:1 during open-loop while shifting and during initial acceleration. At the end of the day, I adjusted global fuel to compensate somewhat and disconnected the boost-a-pump thinking maybe it was the culprit, even though the voltages looked fine. Long story short, it was a freakin' nightmare just to get the car home. The AFR error was rising faster than I could adjust global fuel to compensate, and by the time I got to my house I was coasting it into my driveway after chugging it up the street in low-load bursts at 19:1 AFR. I figured the fuel pump might have failed due to the constant 15v (which would be ridiculous but possible), so I disconnected the return line and timed the flow into a container. Sure enough, the volume of fuel was much lower than what it should have been flowing, so out came the pump. What I found was almost unbelievable; the sock, pump, and everything else was coated in the infamous E85 goo... nasty, sticky, tar-like crap. The sock was almost clogged completely, and it was even building up in the hanger hard lines. EDIT: I should also add that just a couple of days prior to the new tank of E85 that started this mess, I completely drained the tank to recalibrate my fuel gauge after reworking my instrument cluster and interior lights. As a matter of routine, I carefully inspected the fuel that I drained out (about 6 gallons of the same E85), and it was crystal clear with no sign of any debris at all. I poured it back in, and then filled up again a couple of days later. So I tossed the pump in some clean gas, and after a few moments of sloshing it around and pouring gas through it, it looked good as new. The jar of gas on the other hand, was so black that a light wouldn't shine through it. I cleaned the hanger, put everything back together, and drained the remaining E85 from the tank. I then put a couple gallons of gas in, and just ran the pump for a while to let the fuel circulate through the system and clean out any remaining buildup. After filling up with gas and driving around a while, the car seemed much better, but then it started leaning out bad at idle again. Thinking the pump may have been permanently damaged, I swapped to a Walbro 255 I had laying around...but I still had the same issue. The car seemed to run fine for a while, but after about 20 minutes it started leaning out like crazy again at idle. I pulled the fuel rail and injectors, but they were now clean after running a couple of gallons of pure gas through the system. This morning I drove the car to work again, and it seems fine except for a slight stumble as it goes lean on initial throttle input. I'm hoping any remaining glitches are due to residual crap in the system that will work itself out. It's also possible that I have some minor ignition issues now, although the plugs didn't look all that bad. (I'm hoping I didn't stress the ignition or anything else during the last few miles of trying to get the thing home). This is by far the worst case of an E85 goo attack I've ever seen or even heard of. This happened over the course of one or two tanks of E85, from the same station. I was also adding Stabil (marine or ethanol variant) to each tank, which may have actually added to the problem instead of preventing it. Once I get the thing cleaned out and back to normal, I'm going to do some testing to figure out what will actually prevent this, if possible. What I do know about the goo so far, is that gasoline dissolves it almost instantly but oddly enough acetone barely has any effect on it. Generic fuel injector cleaner seems to have no effect on it, and neither did the Stabil. But, Sea Foam dissolves it almost as fast as gasoline... so I'll probably add some Sea Foam to the next tank of E85 and see what happens.