Chasing a CEL + misfire, please help
Update
Well...the misfire never came back, but the p1145 came back right on schedule after 3 days. I was watching the ST fuel trim on both banks with my new PLX gauges and I noticed that bank 0 would sometimes just stop moving and hold at 0 while bank 1 was always moving slightly up and down as it should. The CEL would occur soon after bank 0 fuel trim stopped moving.
Last week I replaced both 02 sensors...again since they were only a few months old. Voila! No more CEL's after hundreds of miles of driving in the last week
ST fuel trims on both banks look great and AFRs are almost identical on both banks (also watching with new PLX gauges) The takeaway here is...swapping the sensors isn't always good enough because when I swapped them the CEL didn't go away. I'm not sure why it didn't change to a p1155 when I swapped them but for now I am going to enjoy the CEL free and misfire free driving! Happy new year!
Last week I replaced both 02 sensors...again since they were only a few months old. Voila! No more CEL's after hundreds of miles of driving in the last week

ST fuel trims on both banks look great and AFRs are almost identical on both banks (also watching with new PLX gauges) The takeaway here is...swapping the sensors isn't always good enough because when I swapped them the CEL didn't go away. I'm not sure why it didn't change to a p1155 when I swapped them but for now I am going to enjoy the CEL free and misfire free driving! Happy new year!
Anyway...the whole point of the last post was that the CEL is gone now so no need to recheck for exhaust leaks.
And it continues...
Since my last post, I got another misfire and the P1145 returned. It turns out the misfire was on cylinder 3, where I moved the injector that was misfiring on cylinder 1. I'm not sure why it took so long to reappear but it did. I got another injector from EPL and that fixed the misfire, hopefully for good.
Logging showed a new boost spike also. It hits 1.5 with the 91 octane tune and 1.7 with the 100 octane tune at fairly early revs. I checked the wastegates and replace the N75 but still no improvement. For now I'm running the 91 tune with 100 fuel to avoid damage.
I finally broke down and took the car to the local shop to perform the "small valve lift" test that is called for. They tested it in the shop and it was fine and the final part of the procedure calls for a WOT pull while a passenger operates the Porsche system tester. The mechanic was freaked out by the acceleration and said it wasn't safe to perform (he has no dyno).
The shop also said they did a smoke test help fix the boost spike and they found no leaks. After picking it up from the shop, it runs perfectly but 5 minutes later, CEL light comes on. This time it's P0171 an P0174...probably a vacuum leak.
If I never see another CEL it will be too soon. I guess I will do my own pressure test again and maybe put some electric tape over the CEL. I just want it to be right again.
Now I have the old P1145 and a new P0171 and P0174 and I'm no closer to resolving anything.
Logging showed a new boost spike also. It hits 1.5 with the 91 octane tune and 1.7 with the 100 octane tune at fairly early revs. I checked the wastegates and replace the N75 but still no improvement. For now I'm running the 91 tune with 100 fuel to avoid damage.
I finally broke down and took the car to the local shop to perform the "small valve lift" test that is called for. They tested it in the shop and it was fine and the final part of the procedure calls for a WOT pull while a passenger operates the Porsche system tester. The mechanic was freaked out by the acceleration and said it wasn't safe to perform (he has no dyno).
The shop also said they did a smoke test help fix the boost spike and they found no leaks. After picking it up from the shop, it runs perfectly but 5 minutes later, CEL light comes on. This time it's P0171 an P0174...probably a vacuum leak.
If I never see another CEL it will be too soon. I guess I will do my own pressure test again and maybe put some electric tape over the CEL. I just want it to be right again.
Now I have the old P1145 and a new P0171 and P0174 and I'm no closer to resolving anything.
Since my last post, I got another misfire and the P1145 returned. It turns out the misfire was on cylinder 3, where I moved the injector that was misfiring on cylinder 1. I'm not sure why it took so long to reappear but it did. I got another injector from EPL and that fixed the misfire, hopefully for good.
Logging showed a new boost spike also. It hits 1.5 with the 91 octane tune and 1.7 with the 100 octane tune at fairly early revs. I checked the wastegates and replace the N75 but still no improvement. For now I'm running the 91 tune with 100 fuel to avoid damage.
I finally broke down and took the car to the local shop to perform the "small valve lift" test that is called for. They tested it in the shop and it was fine and the final part of the procedure calls for a WOT pull while a passenger operates the Porsche system tester. The mechanic was freaked out by the acceleration and said it wasn't safe to perform (he has no dyno).
The shop also said they did a smoke test help fix the boost spike and they found no leaks. After picking it up from the shop, it runs perfectly but 5 minutes later, CEL light comes on. This time it's P0171 an P0174...probably a vacuum leak.
If I never see another CEL it will be too soon. I guess I will do my own pressure test again and maybe put some electric tape over the CEL. I just want it to be right again.
Now I have the old P1145 and a new P0171 and P0174 and I'm no closer to resolving anything.
Logging showed a new boost spike also. It hits 1.5 with the 91 octane tune and 1.7 with the 100 octane tune at fairly early revs. I checked the wastegates and replace the N75 but still no improvement. For now I'm running the 91 tune with 100 fuel to avoid damage.
I finally broke down and took the car to the local shop to perform the "small valve lift" test that is called for. They tested it in the shop and it was fine and the final part of the procedure calls for a WOT pull while a passenger operates the Porsche system tester. The mechanic was freaked out by the acceleration and said it wasn't safe to perform (he has no dyno).
The shop also said they did a smoke test help fix the boost spike and they found no leaks. After picking it up from the shop, it runs perfectly but 5 minutes later, CEL light comes on. This time it's P0171 an P0174...probably a vacuum leak.
If I never see another CEL it will be too soon. I guess I will do my own pressure test again and maybe put some electric tape over the CEL. I just want it to be right again.
Now I have the old P1145 and a new P0171 and P0174 and I'm no closer to resolving anything.
__________________

2001 996TT 3.6L and stock ECU
9.66 seconds @ 147.76 mph 1/4 mile click to view
160 mph @ 9.77 seconds in 1/4 mile click to view
50% OFF ON PORSCHE ECU TUNING BLACK FRIDAY SPECIAL

2001 996TT 3.6L and stock ECU
9.66 seconds @ 147.76 mph 1/4 mile click to view
160 mph @ 9.77 seconds in 1/4 mile click to view
50% OFF ON PORSCHE ECU TUNING BLACK FRIDAY SPECIAL
I'm not sure if you are being sarcastic or not, but if you're not - this setup was running perfectly for 4 months before any of these problems so I don't think the injectors and tune are the cause, and the stock injectors aren't up to the task of fueling my Alpha 28s at any decent power levels anyway.
I refuse to give up, the problem has a solution; I just need to find it.
I refuse to give up, the problem has a solution; I just need to find it.
For the record I've got a stock 3.8 bar FPR and you're right, I have tried just about everything to get rid of the CELs
My mods are in my signature and they occurred ~4K miles prior to these issues starting.
Well it's an easy thing to do just look at the filters and make sure there's no metal shavings in there just to be sure. You won't really see the slivers in oil you drain....
Good sign that they were clean tho. Reason I bring this up is a car came in with similar codes and sure enough... Those lifters do fail sadly. Wasn't driven enough to trigger more misfires in other cylinders.
We've certainly seen leaky injectors over the years (seimens ones that folks use for 700hp kits). Rare but happens. A 997tt also had one bad injector which caused a nasty issue too but factory ones seem immune. That can lead to misfires too yes.
On the sound if you have a loud enough exhaust it's pretty quiet as far as the sound. But hopefully that isn't an issue anyway.
Good sign that they were clean tho. Reason I bring this up is a car came in with similar codes and sure enough... Those lifters do fail sadly. Wasn't driven enough to trigger more misfires in other cylinders.
We've certainly seen leaky injectors over the years (seimens ones that folks use for 700hp kits). Rare but happens. A 997tt also had one bad injector which caused a nasty issue too but factory ones seem immune. That can lead to misfires too yes.
On the sound if you have a loud enough exhaust it's pretty quiet as far as the sound. But hopefully that isn't an issue anyway.
Both banks are identical and couldn't much better at +1%
It is so random...I watch my PLX gauge monitoring two standalone W/B O2 sensors and 90% of the time both banks are extremely close together. Sometimes, they are off by a noticeable margin. This happens when I've been driving it for a while and an example is bank 1 will show an AFR of 13.6 while bank 2 shows 15, or bank 1 will show 13 and bank 2 will show 11.5. This is always under light throttle inputs. As soon as I give it some both banks go right back to being close until I let off the throttle. Restarting the car fixes this and both banks will once again remain close at all throttle inputs.
The gauge really helps to see what is causing the P1145 CEL.
So strange!
It is so random...I watch my PLX gauge monitoring two standalone W/B O2 sensors and 90% of the time both banks are extremely close together. Sometimes, they are off by a noticeable margin. This happens when I've been driving it for a while and an example is bank 1 will show an AFR of 13.6 while bank 2 shows 15, or bank 1 will show 13 and bank 2 will show 11.5. This is always under light throttle inputs. As soon as I give it some both banks go right back to being close until I let off the throttle. Restarting the car fixes this and both banks will once again remain close at all throttle inputs.
The gauge really helps to see what is causing the P1145 CEL.
So strange!
Not likely - MAF is very recent and voltage readings are right on target. That was one of the first things I changed.
I had the exact same code(s) P1145/P1155 this past year, car ran great albeit light low throttle position hesistation, CEL would come on if car was driven a fair bit a lower throttle opening...I have no misfires
New O2's, MAF, plugs coils etc etc...did pressure test at end of year right before storage and found a large leak at wastegate seal, will replace wastegates this winter and see if fixed in Spring..
New O2's, MAF, plugs coils etc etc...did pressure test at end of year right before storage and found a large leak at wastegate seal, will replace wastegates this winter and see if fixed in Spring..
Last edited by 993GT; Feb 14, 2014 at 04:11 PM.






