HELP!!:Im really stumped here...LEAN AFR SPIKE.
 

**Update near the bottom since this first experience/what i've tried**

Ok fuel delivery technical question;

I've put about 200 miles on the car since pulling it out of storage. New build has 1200 total miles on it. I did new fuel filter, oil/filter to prep for this season. I have some fresh plugs but the ones in it obviously still look good.

Driving home from Warren last night on the highway cruising at 75 i noticed car felt odd and then AFR's went super lean. I was just cruising, in vacuum, not in boost. Pulled over on the highway and engine was idling rough. Limped the car a few miles to the next exit. Car wanted to die when i wasn't on throttle. I was down to about 1/8 tank of fuel (original full tank of premium that was stabilized for winter storage).

When i pulled into the station, before even coming to a stop, the idle stabilized and AFR's were right on the money. Let it idle for 5 mins, no change. I filled the car, added some injector cleaner, and proceeded to drive 45 minutes home monitoring AFR's. Car ran like a top. I even beat the piss out of it in boost on several pulls once I was back home. ZERO issues.

Today, for about 15 seconds after some spirited driving when cruising back into town, she did it again. Was right near my house. I limped it home, and it corrected itself again in the driveway.

Fuel pump on its way out? Bad gas still working itself out?

It's a Walbro 190...was in the car when i bought it on the old setup. Pressures at the rail have always looked very strong though (although i haven't been able to monitor the pressure gauge yet once it starts acting up). Injectors are Fuel Injector Clinic 650's with 1200 miles on them. Car is protuned. Running sequential injection from a megasquirt 2 board built by Braineack.

Can you monitor fuel pump voltage pull in Tuner Studio? Do you guys have any other ideas where i should start looking/monitoring?https://cimg7.ibsrv.net/gimg/www.mia...78986af9d1.png

Fuel system might be a false flag. An issue with a single spark plug wire or plug will mean that you're not burning any of the oxygen being sucked through that cylinder. The O2 sensor measured oxygen content, and if there's lots of oxygen, it will run lean. I would do plugs and wires and re-evaluate. Depending on how rough the idle was, it may have a coil going intermittently bad.

My car did this with both faulty CAS plug (loose and wagging around, just needed to be clipped back in) and also with a bad Innovate wideband. It would send false signals to the ecu and things would go to shit.

Both plugs and wires have less than 1200 miles on them, but I'll check it out. Thanks for the good information!

As a data point, I've had two fuel pumps fail and it was not intermittent either time. It started to get lean, and then just kept getting more lean until it wouldn't run. In at least one case I was able to get it to run by adding a bunch of fuel via tuning adjustment, but that only lasted about a day before it ran out of fuel again. This was just driving on the street, during my commute. So in my experience the failure mode did not match your symptoms.

Thanks for the info, yeah it doesn't seem like this matches what I'm seeing. Initially I totally suspected bad gas. The fact it did it again the next day and the information posted in here leads me to inspect/change:
1. Plugs (even though they're new)
2. Wires (even though they're new)
3. Coil packs
4. AEM Uego sensor - this is the 4.2 sensor model, so it's gotta be like 4+ years old and saw boost on the old 1.6 setup for like 3 years.

Appreciate the input guys.

So, update 4-19-2017:

Changed the plugs and wires (again) on Sunday. Didn't drive or start it after that. NGK BKR7E's gapped at .031 with NGK blue wires. Stock 1.6 coils.

Last night (Tues) I drove the car from my house to my buddies shop (about 5 miles). Car warmed up and idled fine in the garage for about 5 mins at near stoich. Once I started driving, the car kept slipping into super lean (~17+) and was sluggish/no power. Every once in a while, it would catch itself, run smooth for a few seconds and read better on my AFR gauge, then slip back into lean.

I limped the car to the shop in 4th gear obviously staying out of any sort of positive boost. Once at the shop, i changed my wideband sensor with a new bosch. No change...car idles super lean on the gauge.....every once in a while catching itself and returning near stoich and normal idle for a few seconds before slipping back. I had an extra set of OEM coils, so i tested those as well, and same exact results. I blipped the throttle repeatedly in the last log, and the wideband is reading because it would fluctuate richer but returned right back to lean upon letting off. Sometimes even stalling out.

I'm seeing:
1. Steady 50 psi FP at the rail (Walbro 190) - monitoring with fp gauge under hood
2. Unplugging the OEM mitsubishi MAP while idling killed the car
3. Unplugging GM IAT while idling showed no change to idle to be honest
4. Coolant temp sensor apears to be reading properly while monitoring in tuner studio

Car is on MS2 built by braineack, running seq injection mod with Fuel Injector Clinic 650's. Only 1200 miles on injectors. Car was protuned last year and NOTHING has been modified in the tune since I put it in storage last November.

You wizards wiser than me, can you look at the attached idle logs from last night? I'm extremely stumped here.....car ran perfectly fine up until that night cruising home on the highway when the lean slip started completely at random.

PLEASE and THANK YOU!

Attachment 179500Attachment 179501Attachment 179502