Need your Expert Help to Trouble Shoot Lean AFR in Closed Loop

I started my daily driver up this morning and it immediately went lean and stopped after 5 seconds - very weird. It's an Evo VIII GSR, I've been running E85 for the past 2 years, mods are in my sig below. I'm running a single Walboro 255 in tank and stock FPR.

Normally it idles in open loop between 12-13 AFR while it warms up. After restarting, holding the throttle open enough to keep it running, and plenty of lean coughing and spluttering, I managed to warm it up past a coolant temp of 84 deg F. This is where I've set the open to closed loop transition. The idle AFR stabilized at 15.5 - 16.5. It's normally 14.7 - stoich.

Next I drove 6 miles, staying out of boost and in closed loop. The AFR showed 15-18 and it was lean misfiring under load. AFR is normally at 14.7 stoich.


Possible Causes & Troubleshooting Strategy
(Please comment, add your own, or suggest a better troubleshooting strategy)

1. Front NB O2 sensor is starting to go loco - check output voltage at sensor & O2 trim at ECU
2. Walboro GSS324 255LPH fuel pump is dying and fuel pressure drops - check fuel pressure at the rail is in spec
3. FPR is failing - run pressure test across FPR diaphragm
4. Obstruction in tank feed with reduction in fuel pressure - open tank and inspect sock and Walboro input.
5. Injectors somehow clogged up overnight - remove and inspect.

 

E85 black gunk? I would start at the injectors if that were a risk. I've seen that pop up a few times around evom. Appears to be a residue of using e85 in old diesel tanks.

 

/\/\ this. Pull the fuel pump and check for black crud in pump sock. If it is there you might as well get a new pump housing as the filter in the housing is for sure plugged too. And you cant clean that. Then figure out how to clean all the lines, tank, regulator and injectors. I would then replace the pump as it will have crap in it as well.

This is why i'll never run E85 a lot of threads about this.

 

Thanks Rats for the suggestion. I just pulled them. No black goo on the injectors. They were cleaned and flow balanced 2000 miles ago by FIC.

Next,on to the tank, sock, pump, filter, lines, rail and FPR.......

 

No problems here either. The tank is like new inside. There are no solids in the bottom or corrosion anywhere. No brown precipitates in the sock or filter. Free flow through filter and out the feed line, tested by blowing, with my lungs. Walboro sounds like - well, a Walboro, when spun up with a 12V battery. It's 8 years old and has lead a hard life so I guess it is possible that it is starting to fail. I've never had a turbine style fuel pump fail so I am not familiar with the failure modes. Return valve in the pump stops reverse flow. Voltage at the pump when cranking is battery voltage.

On to the lines, rail and FPR......

 

Sean Burgess at FFTEC very kindly let me use his fuel pressure gauge today. Pressure at the rail is 47 psi at idle so the Walboro is good....and the mystery gets stranger.

Then it hit me on the drive back from the shop. There is nothing wrong with the car....the problem is with the driver! I realized (too late) that I must have held the accelerator down too long and switched to my alt maps which are set for 91. This explains the leanness at idle and throughout the load range. Face palm of the year I stopped and switched back to the E85 map. Slow flashing lights - good - problem solved. At least I know the fuel system is in like new condition after three years of E85. There is no black goo anywhere. The grommet at the top of the Walboro looks like new. The siphon pipe connectors are not hardened or cracking.