997.2 issue with air flow fault codes
12-01-2016, 02:21 PM
#16
Upon cold start, and it doesn't have to be near 30F for this to occur in my experience, after a moment the exhaust will emit water vapor. There might be a bit of smoke mixed with this for as we all know these engines will emit a bit of oil smoke upon cold start once in a while.
Smoke hangs together even if it is carried away by a light breeze. Water vapor dissipates even in still air.
Even with a healthy/properly runnng engine, upon a cold start the exhaust will certainly contain "notes" of fuel. Everything is cold and this includes the converters. The DME supplies extra fuel which along with the air provided by the secondary air injection system is intended to burn in the converters to warm them up quicker. There will be a time after cold start that some unburned fuel will make it through the converter and this is what you smell.
As an aside, concurrently with the cold engine RPMs dropping to near normal hot idle level the DME switches from open loop mode to closed loop mode. It can do this because the sensors are working properly and the ones after the converters are signaling the converters are working.
Anyhow, with me handicapped by not being at the car all I can offer is unless the cloud is indeed smoke, exceptionally heavy, and white -- these would suggest an overly rich mixture at start up perhaps due to leaking injector(s) -- what you are seeing is probably normal cold start smoke/vapor.
As for the codes "7910" and "9410" I have nothing in my references.
All I have to go on then is the description that accompanies the error codes in the pics you posted.
7910: Air mass ahead of throttle valve, idle. No communication.
9410: Implausible mass air flow ahead of throttle valve. Value below lower limit value.
Not much to go on -- a tech would have his training and possibly a list of diagnostic steps to follow when encountering the above error codes but I have, we have nothing of the sort available to us -- but there's a common thread. "No communication." "Value below lower limit valve."
You have installed a new MAF. I trust it is one in which you have a high confidence that it is the right one and how to put this? Not some super cheap/questionable quality MAF?
I'm probably stating the obvious but no communication and a value below lower limit valve suggests a wiring/connection problem. (This assumes the new MAF is not defective and just "dying" a short time after engine start.)
I don't know the history of the car. I don't know what might have been done to the car -- servicing, repairs, modifications; prior to the error codes appearing.
With suspected wiring/connection problems, a couple of things come to mind. One is apparently the car received some rather extensive attention a while back. One must always then be concerned about a connection being marginal that in some way say has allowed moisture to enter the connection and corrode the connector pins and affect the signal. Or a portion of the wiring harness got damaged/pinched.
There is the concern about moisture getting into the car. In this case not necessarily the cabin but where the DME is located. Or the fuse box. Or into a relay box.
And of course if the car has sat any length of time infrequently or not used at all there is the possiblity of mice having been at the car, its wiring.
Smoke hangs together even if it is carried away by a light breeze. Water vapor dissipates even in still air.
Even with a healthy/properly runnng engine, upon a cold start the exhaust will certainly contain "notes" of fuel. Everything is cold and this includes the converters. The DME supplies extra fuel which along with the air provided by the secondary air injection system is intended to burn in the converters to warm them up quicker. There will be a time after cold start that some unburned fuel will make it through the converter and this is what you smell.
As an aside, concurrently with the cold engine RPMs dropping to near normal hot idle level the DME switches from open loop mode to closed loop mode. It can do this because the sensors are working properly and the ones after the converters are signaling the converters are working.
Anyhow, with me handicapped by not being at the car all I can offer is unless the cloud is indeed smoke, exceptionally heavy, and white -- these would suggest an overly rich mixture at start up perhaps due to leaking injector(s) -- what you are seeing is probably normal cold start smoke/vapor.
As for the codes "7910" and "9410" I have nothing in my references.
All I have to go on then is the description that accompanies the error codes in the pics you posted.
7910: Air mass ahead of throttle valve, idle. No communication.
9410: Implausible mass air flow ahead of throttle valve. Value below lower limit value.
Not much to go on -- a tech would have his training and possibly a list of diagnostic steps to follow when encountering the above error codes but I have, we have nothing of the sort available to us -- but there's a common thread. "No communication." "Value below lower limit valve."
You have installed a new MAF. I trust it is one in which you have a high confidence that it is the right one and how to put this? Not some super cheap/questionable quality MAF?
I'm probably stating the obvious but no communication and a value below lower limit valve suggests a wiring/connection problem. (This assumes the new MAF is not defective and just "dying" a short time after engine start.)
I don't know the history of the car. I don't know what might have been done to the car -- servicing, repairs, modifications; prior to the error codes appearing.
With suspected wiring/connection problems, a couple of things come to mind. One is apparently the car received some rather extensive attention a while back. One must always then be concerned about a connection being marginal that in some way say has allowed moisture to enter the connection and corrode the connector pins and affect the signal. Or a portion of the wiring harness got damaged/pinched.
There is the concern about moisture getting into the car. In this case not necessarily the cabin but where the DME is located. Or the fuse box. Or into a relay box.
And of course if the car has sat any length of time infrequently or not used at all there is the possiblity of mice having been at the car, its wiring.
Thanks for replay.
Well i bought MAF directly from dealer.. So it is the same quality as it was before (the old one looked good but just in case i bought new one i just swapped).
Well the only thing what that day i have done differently was that i was sitting in the car for about 40min with running engine and max heat air condition temperature as there was cold outside... And later after ~30min of drive CEL appeared..
I had durametric in the trunk so i just hooked it up to look what caused the CEL.. And there was those error. So i cleared it and after few min of running engine i felt some rpms drops, (instantly done refresh to check DME and there was same errors i just cleared anyway) rps back to normal instantly after error show up. All that happens in 1-3 seconds.
Anyway because i had installed BMS filters (drove car every day with them for 3-4 months) i thought maybe MAF burned due oiled filters.. So i ordered OEM papers filters and MAF and replaced. Performed errors clear, ECU reset and removed battery negative for 15mins but still error came up again.. Checked all vacuum lines.. Still no luck.. Tomorrow driving car to porsche..
