[bishopts]

Once you install your bosch plugs you should have a few days of the engine running pretty much like it does now. Then you should start seeing random misfires developing under a load. That will be the bosch plugs. They really only work in engines from Europe. So before you start pulling your hair out on why is it worse. Just order plugs that actually work with American GM engines. AC delco that have "japan" printed in the collar are ngk plugs. They work pretty good. Or just buy ngk plugs. I think you need to change the heat range for e85 but I'm not sure on that one. Factory gap isnt as critical as you think. You can easily gap plugs to the spec you need, just make sure all of them are the same gap.

[Taco-Giz]

Originally Posted by bishopts

Once you install your bosch plugs you should have a few days of the engine running pretty much like it does now. Then you should start seeing random misfires developing under a load. That will be the bosch plugs. They really only work in engines from Europe. So before you start pulling your hair out on why is it worse. Just order plugs that actually work with American GM engines. AC delco that have "japan" printed in the collar are ngk plugs. They work pretty good. Or just buy ngk plugs. I think you need to change the heat range for e85 but I'm not sure on that one. Factory gap isnt as critical as you think. You can easily gap plugs to the spec you need, just make sure all of them are the same gap.

Do you have a recommendation for a good spark plug part number? I've seen the NGK 4344 Iridium IX, but its gap is 0.044", and I'm not comfortable adjusting it. That's why I chose Bosch. I've also seen a few forum posts where people are running them without issues.

Do you really think plugs could cause sputters tho..? I mean I changed them cause it says to change them at 60k mile and I'm at 58K..

[bishopts]

The max tolerance is .043, if your running .044 then it's close enough you can't notice. .001 difference is less than the thickness of hair. The difference in gap between each plug will be greater than that. So just run them. Spark plug gap isn't so critical that .001 changes anything.

[Taco-Giz]

Originally Posted by bishopts

The max tolerance is .043, if your running .044 then it's close enough you can't notice. .001 difference is less than the thickness of hair. The difference in gap between each plug will be greater than that. So just run them. Spark plug gap isn't so critical that .001 changes anything.

Ok thanks, I guess I'll order them then.

AI suggests that if my spark plugs are black and wet, it could indicate issues with the piston rings or valve seals, which is concerning because, in the EU, I don’t have access to resources to fix this car, and it’s my daily driver. I know AI can sometimes provide inaccurate information, and I hope this is one of those cases.

[bishopts]

Yea AI is dumb.
Sooty black is kinda rich. Wet black is really really rich. White deposits is oil consumption. Clean wet is coolant.
Obviously each of those could be slightly different depending on the situation.
For instance, you could have a clean wet from a failed coil. Looking at spark plug condition helps in diagnostics but you can't get the entire story there.

[Taco-Giz]

Originally Posted by bishopts

Yea AI is dumb.
Sooty black is kinda rich. Wet black is really really rich. White deposits is oil consumption. Clean wet is coolant.
Obviously each of those could be slightly different depending on the situation.
For instance, you could have a clean wet from a failed coil. Looking at spark plug condition helps in diagnostics but you can't get the entire story there.

I guess I run really really rich then lol. I'm starting to wonder if I should order some injectors as well..

[Taco-Giz]

Hey everyone,

I recently changed my car's spark plugs, and the performance has definitely improved. However, I've noticed an odd issue since the change:

• If the car sits outside overnight, it sputters in the morning. (outside driveway has a slight slope)

• If it stays in the garage overnight (flat ground), it runs fine with little to no sputtering, even after 3 consecutive mornings. -> https://youtube.com/shorts/ktciLBIaaNM

A thought just crossed my mind. could this be related to the PCV valve or the vapor canister purge valve..?

I saw somewhere that the PCV Valve needed to be replaced every 30k miles but I'm not sure it could cause the sputters on cold start..

[ctrlz]

Anything bad in the evap system will likely give you a code.
Doubt the PCV valve is bad. If you can remove it without breaking it, you could always spray some gumout to clean it a bit.

[bishopts]

How is the overnight fuel pressure loss doing?

[Taco-Giz]

Originally Posted by bishopts

How is the overnight fuel pressure loss doing?

Still the same. I just noticed that when it rains overnight and it's a bit cold, with the car parked outside, I can be sure to have engine sputters. But if I put it in my garage, I get very tiny ones or close to none.


I wonder why the weather affects the engine bay to make it run like that.

[bishopts]

Only thing i could think is ambient air temp reading is affecting cold start fueling amount.
Still that loss of rail pressure overnight isn't normal. Its leaking down somewhere.

[Taco-Giz]

Originally Posted by bishopts

Only thing i could think is ambient air temp reading is affecting cold start fueling amount.
Still that loss of rail pressure overnight isn't normal. Its leaking down somewhere.

Agree but I don't have that issue in my closed garage tho.. it's weird..

[Taco-Giz]

Side note: I've noticed that it doesn't sputter when the gas tank is full and it's parked in the garage. However, when the tank isn't full, I experience a very slight sputter, similar to what I showed in the second video. ( https://www.youtube.com/shorts/ktciLBIaaNM )


It seems that this issue mainly occurs when I let it parked outside overnight, also I don't know if it's me but rain seems to worsen it when park outside.