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Here's something I noticed in the latest log. The camshaft deviation on bank 2 increases steadily from 0 to 2998. At 2998, it immediately drops to 4 and the cylinder 6 misfire resets to 0. The camshaft deviation then continues to rise and cylinder 6 logs another misfire less than one second later. No clue what any of this means.
I just did another log session while idling/revving in neutral. The results appear to make a lot more sense this time in terms of the misfire counters. I also included more measurements, like MAF and MAF voltage. Take a look: https://drive.google.com/file/d/1tKp...ew?usp=sharing
Looks like there are misfires on virtually all cylinders, but I don't see any weird MAF behavior to account for that. When there are misfires on both banks you have to look at things shared by both banks, such as the MAF sensor itself or the crankshaft position sensor but if that was bad I don't think the car would run well at all - might not even start.
Fuel trims are now above 1, which means its lean and the DME is adding some fuel. This could happen from an intake leak upstream of the MAF, like at the plenum or throttle body.
Here's something I noticed in the latest log. The camshaft deviation on bank 2 increases steadily from 0 to 2998. At 2998, it immediately drops to 4 and the cylinder 6 misfire resets to 0. The camshaft deviation then continues to rise and cylinder 6 logs another misfire less than one second later. No clue what any of this means.
The camshaft deviation should not be 0, it should be something like the top number for both banks. When my camshaft position sensor failed and read 0, I got rough running and misfires. Replacing the sensor solved the problem. Doing actual values, see what the bank 1 and bank 2 camshaft deviation numbers show. If one is 0.00000 that sensor has failed. Not very exoe dive and easy to replace.
The camshaft deviation should not be 0, it should be something like the top number for both banks. When my camshaft position sensor failed and read 0, I got rough running and misfires. Replacing the sensor solved the problem. Doing actual values, see what the bank 1 and bank 2 camshaft deviation numbers show. If one is 0.00000 that sensor has failed. Not very exoe dive and easy to replace.
Gotcha. I did one more log, and this time I deleted all the meaningless rows at the top. I think this one should make sense, and you can see the camshaft deviation values clearly. Open the file with Google Sheets and you'll see color coding to point out spikes in the values.
Gotcha. I did one more log, and this time I deleted all the meaningless rows at the top. I think this one should make sense, and you can see the camshaft deviation values clearly. Open the file with Google Sheets and you'll see color coding to point out spikes in the values.
I think it's your MAF. You're getting random crazy spikes like from 22 to 143 from 1 line to the next.
First thing to try I'd get a can of that mag specific spray cleaner, remove the MAF (don't touch the wires) and spray it inside and out with a healthy dose of cleaner. Put it back in and reconnect it, disconnect the battery for 10 minutes to reset the fuel trims and try it again. Give it some driving time to readjust, then log MAF values vs throttle position values and see if you're still getting those same random spikes when the throttle plate angle isn't changing.
If not, then see if you're still logging misfires.
What kind of air intske are you running - stock airbox and stock paper filter or a CAI with dry or oiled filter. If the oiled filters are over oiled they can contaminate the MAF wire and ciser these kinds of issues.
I think it's your MAF. You're getting random crazy spikes like from 22 to 143 from 1 line to the next.
First thing to try I'd get a can of that mag specific spray cleaner, remove the MAF (don't touch the wires) and spray it inside and out with a healthy dose of cleaner. Put it back in and reconnect it, disconnect the battery for 10 minutes to reset the fuel trims and try it again. Give it some driving time to readjust, then log MAF values vs throttle position values and see if you're still getting those same random spikes when the throttle plate angle isn't changing.
If not, then see if you're still logging misfires.
What kind of air intske are you running - stock airbox and stock paper filter or a CAI with dry or oiled filter. If the oiled filters are over oiled they can contaminate the MAF wire and ciser these kinds of issues.
I forgot to mention - I blipped the throttle quite a few times and also tried holding the rpms at 2000-3000. Second column shows engine rpm. Whenever the rpm goes up, the MAF output and voltage go up.
I used MAF cleaner on the MAF and throttle body 2 days ago. Removed the MAF, sprayed it down, and sprayed the throttle body without removing it. Also disconnected the battery for about 1 hour and drove for about 30 min yesterday. All the data logging happened today.
Observations:
1) The MAF value skyrockets (>100 kg/h) almost exactly whenever a new misfire is logged.
2) Misfiring only occurs at lower rpms, sometimes at light throttle but especially at heavy throttle. When I gave full throttle from 3000-6800 rpms a few times, there were no misfires logged.
I may try disconnecting the MAF and going for a drive again. Any other suggestions? Very confused why the engine feels so good and doesn't misfire at high rpms, even at WOT, but at low rpms it feels like a dog.
Interesting. Yet another possible cause to add to my list haha. I'll take a look at Lambda values during my next data log session.
I just disconnected the MAF and went for a short drive. Engine ran even worse. Here's something else I noticed: lots of oil residue where the intake plenum meets the throttle body. Mostly on the underside, directly above the oil filler tube. Could this be a sign of bad AOS? I do get a bit of white smoke on startup.
I had the same problem. You're starting out from a dead stop, and your 997 just hesitates. No throttle response. The problem is with one of the limit switches that signal when the brake or clutch pedal are not depressed. See https://rennlist.com/forums/997-foru...l#post16123311
I had the same problem. You're starting out from a dead stop, and your 997 just hesitates. No throttle response. The problem is with one of the limit switches that signal when the brake or clutch pedal are not depressed. See https://rennlist.com/forums/997-foru...l#post16123311
I think your issue was different. My engine is hesitating due to misfiring on multiple cylinders during low rpm load. For example, even at 30mph in 5th gear.
Interesting. Yet another possible cause to add to my list haha. I'll take a look at Lambda values during my next data log session.
I just disconnected the MAF and went for a short drive. Engine ran even worse. Here's something else I noticed: lots of oil residue where the intake plenum meets the throttle body. Mostly on the underside, directly above the oil filler tube. Could this be a sign of bad AOS? I do get a bit of white smoke on startup.
Yes, that can be a sign of a failing AOS. With the engine running, try to remove the oil filler cap and see if that's fairly easy or it if feels glued on by vacuum.
I have also seen the ground wire to the MAF have issues where it essentially is like disconnecting the maf for a second and maybe that could cause the type of spikes you're seeing in MAF readings from 1 second to the next. The fact that you've observed the abnormal MAF value at the exact same time as the misfire I think is a pretty big clue to something, just not sure what yet. The intake air temp sensor is integrated into the MAF. If the MAF is losing it's electrical connection due to an intermittent ground, then I would also assume it would lose it's temperature reference too. Maybe do another session where you track intake air temp next to the MAF values and see if when you create the misfire, we see anomalies in both those readings or if the temp stays consistent and it's only the MAF value that freaks out.
You might also want to take out the throttle body and clean it. Bad throttle bodies (since it's a drive by wire system) have also caused odd hesitation issues.
I just looked at the data again, and next to the column you've highlighted, the actual throttle plate angle does the same freak-out as the MAF readings. I think your throttle body may be bad. Take it out. clean it, and clean the electrical connections to it with Deoxit D5. If you have a friend with a 997, swap throttle bodies with him and see if that resolves the issue.
I just looked at the data again, and next to the column you've highlighted, the actual throttle plate angle does the same freak-out as the MAF readings. I think your throttle body may be bad. Take it out. clean it, and clean the electrical connections to it with Deoxit D5. If you have a friend with a 997, swap throttle bodies with him and see if that resolves the issue.
I cleaned the MAF again last night after getting poor results driving with it disconnected (rougher idle and still misfires at low rpm load). The intake air temp doesn't show any anomalies. It idles around 50C and drops steadily to 42C as I start driving. The misfires don't seem to affect it. See here.
The reason the throttle plate angle rises along with the MAF output is because I'm applying heavy throttle to trigger the misfiring. For example, I would roll from a stop, shift into 3rd gear at 1500rpm, and apply 70-80% throttle. This is why you see the Engine Speed go up at the same time. This seemed to trigger the misfire pretty easily.
I sprayed down the throttle body but didn't thoroughly clean it. Guess I need to do that. I may also replace the ignition coils again since they were last done by the previous owner in his garage 2 years ago. Maybe he didn't tighten them down.
By the way, thanks for all your help. I'm learning a lot from this process.
11-11-2020, 12:16 AM
