Carpokes Porsche Forum

chrischrischris wrote: Mon Jul 13, 2026 4:40 am Since you are out of ideas, getting some fresh gas seems like a good plan. I really think you may get some more clues by going for a gentle drive vs just testing in the garage.

I'm going to try a good fuel stabilizer first. I would just drain the tank, but I am 3/4 full and that's a LOT to try and dispose of. I agree on the gentle drive - I'm just extremely scared to do damage if I'm not burning all the fuel in the cylinders and washing them down with gas.

I think my next step is to put back the factory injectors, AFM and LR Maxx chip to see if that makes any difference.

I would guess that you missed your chance with the stabilizer; I don't think it can fix gas once it has destabilized. To test how the car runs on fresh gas you will need to fill with fresh gas.

Do you have the MAP plug shorted out with the pig tail that came with your F9 DME. I was having some issues with my 951(not quite what your having) and @Tom figured out my F9 DME had the quirk that required the MAP plug to be shorted out. Don’t know if that’s part of your problem but just trying to think of anything it could be.

Bad fuel isn't reacting with the oxygen and burning, so the wideband is seeing extra oxygen and reading "lean." Since it's not burning you would probably smell gasoline, as you described experiencing after one of your recent tests.

June 28 you wrote "Can feel misfires at idle and hear small "pops" from exhaust and it smells VERY rich, like unburnt fuel"

June 30 you wrote that chat GPT says "A system-wide combustion problem (likely ignition or engine management related) is causing incomplete combustion."

You had suspected incomplete combustion and were thinking that the ignition system was too weak, but the poor combustion could be a result of your old fuel being less combustible due to old age.

Mscromer wrote: Mon Jul 13, 2026 7:07 am Do you have the MAP plug shorted out with the pig tail that came with your F9 DME. I was having some issues with my 951(not quite what your having) and @Tom figured out my F9 DME had the quirk that required the MAP plug to be shorted out. Don’t know if that’s part of your problem but just trying to think of anything it could be.

I have never heard of this issue before. My F9 DME is going on 3-4 years old. I'll have to do some searching to see if I should give this a try!

chrischrischris wrote: Mon Jul 13, 2026 7:12 am Bad fuel isn't reacting with the oxygen and burning, so the wideband is seeing extra oxygen and reading "lean." Since it's not burning you would probably smell gasoline, as you described experiencing after one of your recent tests.

June 28 you wrote "Can feel misfires at idle and hear small "pops" from exhaust and it smells VERY rich, like unburnt fuel"

June 30 you wrote that chat GPT says "A system-wide combustion problem (likely ignition or engine management related) is causing incomplete combustion."

You had suspected incomplete combustion and were thinking that the ignition system was too weak, but the poor combustion could be a result of your old fuel being less combustible due to old age.

That could be the case - especially with the varnish like substance that's accumulating on the pistons. I still have around 15 gallons in the tank. Luckily, I have (2) 5 gallon containers in my shed. Unfortunately, the closest disposal location is about 25 minutes away.

I would find a new home for all that gas in your tank before you tear apart your engine again. The old gas hypothesis describes your simultaneous measured lean condition and un-burned fuel a.k.a. "rich" condition. It is also the "hiding in plain sight" solution you were seeking.

From ChatGPT:

If your gasoline is 9 months old, it is old enough that it can affect engine operation, but whether it causes a lean wideband reading depends on what has happened to the fuel and how the engine is running.

What happens to 9-month-old gasoline

Over that time, gasoline can:

Lose volatile components (the easiest-to-evaporate compounds leave first)
Become less effective at atomizing
Oxidize and form gums/varnish
Absorb water if it contains ethanol (common in pump gasoline)
Separate into an ethanol/water layer in some cases

The fuel may still burn, but it may not behave like fresh gasoline.

How it can affect your wideband reading
Case 1: Fuel is degraded but still burning

You could see:

Slightly lean AFR readings
Less power
More throttle needed
Poor cold starts

The injector may still deliver the correct volume, but the fuel's combustion characteristics are worse.

Case 2: Fuel causes misfire or incomplete combustion

This is the more confusing case:

The cylinder gets air and fuel
The mixture does not burn completely
Oxygen passes into the exhaust
The wideband reads lean

Your plugs might actually look dark or fuel-stained, despite the wideband saying lean.

Case 3: Actual fuel delivery problem caused by sitting

Nine-month-old fuel can contribute indirectly:

Injector deposits → reduced flow → real lean condition
Fuel pump/filter issues → low fuel pressure → lean under load

chrischrischris wrote: Mon Jul 13, 2026 7:27 am I would find a new home for all that gas in your tank before you tear apart your engine again. The old gas hypothesis describes your simultaneous measured lean condition and un-burned fuel a.k.a. "rich" condition. It is also the "hiding in plain sight" solution you were seeking.

Well.....looks like I'm draining gas this week...... Now to determine if it's easier to siphon from the sender hole on top or get the quickjacks out again and pull the line to the pump.