Misfire question
Thread Starter
3rd Gear
Joined: Sep 2021
Posts: 3
Likes: 1
Misfire question
Hoping some of you mechanically knowledgeable folks could chime in. I recently picked up a 991.2 CS, drove it with a misfire for some time, kept it under 4,000 rpm. Check engine code did not alert until much later. About how many miles of driving would be considered a threshold for potential damage? 50? 100? 25,000?
Concerned about unburnt fuel stripping oils off the cylinder walls casing wear, or anything else anybody could think of?
Concerned about unburnt fuel stripping oils off the cylinder walls casing wear, or anything else anybody could think of?
RL Community Team
Rennlist Member
Rennlist Member
Joined: Apr 2018
Posts: 2,096
Likes: 729
From: Palm Harbor Florida
Well, it seems like @rnl said, you have to look forward.
What year is the car and how many miles? Was the misfire present at the time of purchase? What did the seller say? Or sometime after? And you had a check-engine light after how many miles? And it's on at the moment or no?
I'd deal with what symptoms the car is having right now. If you have a check-engine light, probably want to have that read out by a dealer or indy to see what the car is saying, then go from there.
If you aren't throwing a code at the minute, and it is still missing, it could be bad fuel (from sitting on a used car; from a bad / sketchy fuel station?). I don't normally like to put additives in fuel, but in this case might try one in a tank. It's also possible one or more of the plugs, or coil packs, is on it's way out, and needs replacement. Hard to say, really.
What year is the car and how many miles? Was the misfire present at the time of purchase? What did the seller say? Or sometime after? And you had a check-engine light after how many miles? And it's on at the moment or no?
I'd deal with what symptoms the car is having right now. If you have a check-engine light, probably want to have that read out by a dealer or indy to see what the car is saying, then go from there.
If you aren't throwing a code at the minute, and it is still missing, it could be bad fuel (from sitting on a used car; from a bad / sketchy fuel station?). I don't normally like to put additives in fuel, but in this case might try one in a tank. It's also possible one or more of the plugs, or coil packs, is on it's way out, and needs replacement. Hard to say, really.
Three Wheelin'
Joined: May 2012
Posts: 1,343
Likes: 545
From: Pennsylvania
Well, it seems like @rnl said, you have to look forward.
What year is the car and how many miles? Was the misfire present at the time of purchase? What did the seller say? Or sometime after? And you had a check-engine light after how many miles? And it's on at the moment or no?
I'd deal with what symptoms the car is having right now. If you have a check-engine light, probably want to have that read out by a dealer or indy to see what the car is saying, then go from there.
If you aren't throwing a code at the minute, and it is still missing, it could be bad fuel (from sitting on a used car; from a bad / sketchy fuel station?). I don't normally like to put additives in fuel, but in this case might try one in a tank. It's also possible one or more of the plugs, or coil packs, is on it's way out, and needs replacement. Hard to say, really.
What year is the car and how many miles? Was the misfire present at the time of purchase? What did the seller say? Or sometime after? And you had a check-engine light after how many miles? And it's on at the moment or no?
I'd deal with what symptoms the car is having right now. If you have a check-engine light, probably want to have that read out by a dealer or indy to see what the car is saying, then go from there.
If you aren't throwing a code at the minute, and it is still missing, it could be bad fuel (from sitting on a used car; from a bad / sketchy fuel station?). I don't normally like to put additives in fuel, but in this case might try one in a tank. It's also possible one or more of the plugs, or coil packs, is on it's way out, and needs replacement. Hard to say, really.
It's a first post, we're being trolled.
Last edited by rnl; Sep 1, 2021 at 08:59 AM.
Thread Starter
3rd Gear
Joined: Sep 2021
Posts: 3
Likes: 1
Well alright, my apologies for being too open ended. I was trying to stay more ambiguous in the hopes of more expansive responses. I'll provide more context.
Car is 3+ years old, 10,000 miles. Just serviced at dealership and they replaced plugs. Test drive was fine at idle and with some fast pulls. No PPI. Next AM cold start the thumps began, no code, gave it the benefit of the doubt that it may be a bad batch of fuel. Drove 25 miles to work with thumps/hesitations throughout engine speeds, kept it under 4,000. On the way back home violent shaking and stumble, check engine codes thrown, dropped car off at dealership. PIWIS showed single cylinder misfiring, assuming it was a bad plug that acted up later. Current concern if there could be any long term consequences to the 50 mile trip, whether I should bring something up with the dealership or perhaps request a third party bore scope.
thanks in advance
Car is 3+ years old, 10,000 miles. Just serviced at dealership and they replaced plugs. Test drive was fine at idle and with some fast pulls. No PPI. Next AM cold start the thumps began, no code, gave it the benefit of the doubt that it may be a bad batch of fuel. Drove 25 miles to work with thumps/hesitations throughout engine speeds, kept it under 4,000. On the way back home violent shaking and stumble, check engine codes thrown, dropped car off at dealership. PIWIS showed single cylinder misfiring, assuming it was a bad plug that acted up later. Current concern if there could be any long term consequences to the 50 mile trip, whether I should bring something up with the dealership or perhaps request a third party bore scope.
thanks in advance
Last edited by 991losangeles; Sep 1, 2021 at 01:21 PM.
RL Community Team
Rennlist Member
Rennlist Member
Joined: Apr 2018
Posts: 2,096
Likes: 729
From: Palm Harbor Florida
Well alright, my apologies for being too open ended. I was trying to stay more ambiguous in the hopes of more expansive responses. I'll provide more context.
Car is 3+ years old, 10,000 miles. Just serviced at dealership and they replaced plugs. Test drive was fine at idle and with some fast pulls. No PPI. Next AM cold start the thumps began, no code, gave it the benefit of the doubt that it may be a bad batch of fuel. Drove 25 miles to work with thumps/hesitations throughout engine speeds, kept it under 4,000. On the way back home violent shaking and stumble, check engine codes thrown, dropped car off at dealership. PIWIS showed single cylinder misfiring, assuming it was a bad plug that acted up later. Current concern if there could be any long term consequences to the 50 mile trip, whether I should bring something up with the dealership or perhaps request a third party bore scope.
thanks in advance
Car is 3+ years old, 10,000 miles. Just serviced at dealership and they replaced plugs. Test drive was fine at idle and with some fast pulls. No PPI. Next AM cold start the thumps began, no code, gave it the benefit of the doubt that it may be a bad batch of fuel. Drove 25 miles to work with thumps/hesitations throughout engine speeds, kept it under 4,000. On the way back home violent shaking and stumble, check engine codes thrown, dropped car off at dealership. PIWIS showed single cylinder misfiring, assuming it was a bad plug that acted up later. Current concern if there could be any long term consequences to the 50 mile trip, whether I should bring something up with the dealership or perhaps request a third party bore scope.
thanks in advance
Probably need to wait till the dealer fixes it; chances are probably better than average it's a bad coil pack on one or more cylinders that was cracked/damaged/inop when the plugs were serviced (or a plug went bad, which sounds weird.)
After that, I'd drive the car and enjoy it. These motors are pretty robust.
RL Community Team
Rennlist Member
Rennlist Member
Joined: Dec 2013
Posts: 7,591
Likes: 3,230
From: Minnesota
nuanced question in the OP, which I will answer here:
is one cylinder completely dead, or is it a sporadic misfire?
is it a failure to ignite, or a failure to inject?
if it's failing to ignite and it's a constant misfire, damage will occur much faster. I wouldn't drive it 50 miles, I'd limp it to wherever I need to go to work on it and that's that.
if it's failing to ignite and it's a sporadic misfire, such as under high load only, then you're fine limping it around for any reasonable amount of time. increased wear on your catalytic converter on that bank plus increased fuel content in your oil are the potential concerns here.
if it's failing to inject, there's little to no problem driving it here other than the engine will run rough. perhaps more wear to engine mounts if you wanna get pedantic about it. cat will be fine, you won't be washing out the cylinder with gas since it isn't injecting, etc..
now, most of that kinda goes out the window as a lot of modern cars will actually shut off a cylinder completely if it's consistently misfiring, then try to fire on it every now and then just in case it's a temporary fault. this is to prevent the washout, oil dilution, and emission problems you'd be worried about in the first place.
to answer the more specific question.. no. don't worry about it. if it's just a plug problem, you'll be fine. if it isn't a plug problem it'll be an injector problem, and SOP will be to change the oil after driving for a length with a stuck-open injector.
is one cylinder completely dead, or is it a sporadic misfire?
is it a failure to ignite, or a failure to inject?
if it's failing to ignite and it's a constant misfire, damage will occur much faster. I wouldn't drive it 50 miles, I'd limp it to wherever I need to go to work on it and that's that.
if it's failing to ignite and it's a sporadic misfire, such as under high load only, then you're fine limping it around for any reasonable amount of time. increased wear on your catalytic converter on that bank plus increased fuel content in your oil are the potential concerns here.
if it's failing to inject, there's little to no problem driving it here other than the engine will run rough. perhaps more wear to engine mounts if you wanna get pedantic about it. cat will be fine, you won't be washing out the cylinder with gas since it isn't injecting, etc..
now, most of that kinda goes out the window as a lot of modern cars will actually shut off a cylinder completely if it's consistently misfiring, then try to fire on it every now and then just in case it's a temporary fault. this is to prevent the washout, oil dilution, and emission problems you'd be worried about in the first place.
to answer the more specific question.. no. don't worry about it. if it's just a plug problem, you'll be fine. if it isn't a plug problem it'll be an injector problem, and SOP will be to change the oil after driving for a length with a stuck-open injector.
Trending Topics
Rennlist Stories
The Best Porsche Posts for Porsche Enthusiasts
Porsche Reveals Coupe Variant of the Electric Cayenne With a Fresh Look
Verdad Gallardo
10 Porsche Colors That Have More Personality Than Most People
Verdad Gallardo
Guntherwerks' Final Speedster Creation Is the Ultimate Porsche Restomod
Verdad Gallardo
10 Reasons I Hate Going to the Porsche Dealership (& the 1 Reason I Stay)
Joe Kucinski
Porsche Shakes Up The Nürburgring Lap Record Table Once Again
Verdad Gallardo
6 Ways the Porsche 911 GT3 S/C Redefines Performance
Joe Kucinski
10 Wildest Homologation Specials Porsche Ever Sold
Verdad Gallardo
Super Rare RUF BTR III Comes Out of Hibernation, Looking For a New Home
Verdad Gallardo