Running Lean, Surging, Stalling after track day

[Hikari1]

Hey everyone,

Been running an Edelbrock supercharger for about 2 years, regular oil changes, build list here:
Edelbrock S/C
Tomei Header & Overpipe
HKS dual res Front Pipe
Full Blown Motorsports Oil Cooler
Tuned by Delicious
OEM fuel pump and injectors
OEM spark plugs and coil packs
85,000km

Car handled the track day fine, except for when the belt slipped and sheared off a rib. Swapped to a spare and drove 30min to cottage fine. 2 days later went to drive home and about 15min into the drive I noticed RPMs drop while cruising at about 80km/h in 5th gear. I could hear the belt chirp everytime the AC compressor kick on so I assumed the belt was stretched as it was an old I kept as spare. Seemed to run fine after turning off the AC for the remaining hour home.

Swapped to a brand new belt, car drove fine for about 30min to a meet, when trying to leave the meet the car would start up but then stall when going to idle. I thought it might be out of gas as it was very low and I planned to get more next to the meet before I left. I filled it with 20 litres and it still had an issue stalling at idle on startup. I was able to get it to idle by applying throttle at startup for a couple seconds and it would idle fine after that. Drove it home and AFRs seemed to be okay, thought it was the fuel being low.

Couple days later I drove 30min, car seemed completely fine on highway and city streets, when suddenly, going 60kmh the car started surging wildly, RPMs bouncing up and down and AFRs all over the place. I put the clutch in and the engine stalled immediately. When trying to restart it kept stalling on idle. I managed to get it to keep running by giving gas, it chugged a bit at low speed at first but after a minute it drove 5min to my dad’s place fine.

Been trying to diagnose the problem since. I tried swapping the throttle body and MAF sensor with spares I had, it at first started up completely fine after swapping, car seemed to run fine for about 15min on a test drive, but then it started running lean, stumbling, and feeling like there was a parachute behind the car when accelerating.

I did some data logging for Bill @ Delicious of its behaviour, but I’m at a lost for what it could be at this point. I’ve checked all the connections, all the vacuum lines, nothing was damaged from the sheared rib either.

From doing some reading I’m thinking coil packs perhaps. They are the original and I’m wondering if the best from the track is causing it to fail. Although I’m getting no CEL or codes after scanning with torque and ecutek

[54fighting]

Have you tried disconnecting the battery for a few minutes?

[Fred E]

If it was the coil packs, you'd see misfires on the log and a CEL for misfires. It's surprising that there's no CEL at all, or even a pending code.

Running lean suggests a fueling issue and considering this started when you were really low on fuel, it could be the in tank fuel pump. When you turn the key to ACC, the in-tank pump underneath the rear driver's side seat primes and pressurizes the line. You should be able to hear the pump priming even from the front seat; can you hear it at all? Has the fuel tank ever been opened before? If you still hear the pump, it's possible the feed line coming off the pump could have came off the pump itself. I had this issue before and it basically meant the low pressure in the line was essentially sucking fuel into the line rather than the pump pumping into the line.

Another thought is the SC's bypass valve? I think the bypass valve is only in use during idle and partial throttle, but should be closed at WOT. If this is the issue, WOT should feel perfectly fine while everything else would feel like shit. However, I don't recommend testing WOT if the car is already running lean in case this isn't issue the issue and you force the car into a high load situation under a lean condition.