backfiring.... bad gas?

[kbeefy]

My car started hesitating and bacfiring yesterday about the same time I filled up with fuel (90 chevron, the best we have available). It does it at 1/2-3/4 throttle around 5-6#. I'm pretty sure I can hear it popping back through the intake.

Car was running fine in the morning, filled up on the way home and that's about when the trouble started. I'll try some iso-heat today, any other suggestions? No CEL yet.

It's been around 0F for the past couple weeks BTW.

[Legacy777]

Yeah I'd probably start with the gas, since your problem coincides with filling up.

Do you have a wideband you can check AFR's? You may want to change your fuel filter after running the bad gas out(assuming it's the gas).

[kbeefy]

I do have a wideband, an lc1. I thought about that this morning, I can probably get it hooked up tommorow, also run in diagnostic mode for troubleshooting.

[Legacy777]

I'm not sure the stock ECU's diagnostic mode will tell you much unless there's a problem with a particular sensor, but it can't hurt to check it.

[Bheinen74]

sounds like what happened to me when i got a bad tank of bad gas. car never did run the same after that. go siphon out the gas and go to a different station and fill up before you detonate your valves.

[kbeefy]

some iso-heet didn't help, turned boost down to 5-7psi, no significant change. Gonna try siphoning the tank tommorow.

[kbeefy]

found it... loose plug wire. Doh!

[kleinkid]

I've had backfiring from bad gas before.