taximan
New Member
- Posts
- 1
- Location
- Windermere, Cumbria
I have a 1998 P38 4.0 which has seriously failed its MOT emissions. The vehicle shows no sign of a performance problem apart from recently, when sooty black deposits have been evident on the garage floor and fuel consumption has worsened but it usually isnt good as my journey to work is only 2.5 miles per day. I have OBD software which has identified fault code PO102 and P0103 indicating the airflow circuit both high and low at some point? The live data monitor on the tester indicated a very low mass airflow reading of around 0.11 grams per second at idle and this rose to about 0.16 at 2500rpm. This was way off the spec which I believe should be 5.5g/s at idle and rising to 16.7g/s.
The MAF is a replacement as my original unit gave slightly lower MAF readings. This replacement unit is apparently in working order but is second hand of the internet so there is no guarantee.
I have tapped into the signal wire at the MAF and ECU and measured the output voltages with a DVM expecting to see a low voltage in line with g/s results on the OBD reader. However, the MAF sensor output seems to be good. I am reading 1.4VDC on idle and output rises gradually to about 2.5VDC at 3500rpm. This seems reasonable, although I haven't been able to find a detailed voltage spec for the MAF sensor. I am not sure what full scale output should be but hoping somebody can advise. The ECU voltages match those found at the MAF.
I was thinking initially that my OBD software might not be compliant in some way, but its reading the codes ok and the other live data like engine revs and temperatures are all sensible numbers, so have no reason to doubt it. I have also used other software and got the same readings.
Has anybody seen similar to this? I have searched at length but couldn't find anything directly related. There was a lambda sensor fault previously but this has been replaced and the fault cleared. My next thoughts are that it is an ECU fault. I have a spare ECU which again was purchased of the internet as a working unit, however I will need to buy a sync mate @ £150 to install it and I am reluctant to do this as there might be some other cause. My p38 is a rarity in this part of the world its either farmers Landys or Chelsea tractors so its difficult to find anyone interested, let alone capable of resolving the problem. Any help or advice would be appreciated.
The MAF is a replacement as my original unit gave slightly lower MAF readings. This replacement unit is apparently in working order but is second hand of the internet so there is no guarantee.
I have tapped into the signal wire at the MAF and ECU and measured the output voltages with a DVM expecting to see a low voltage in line with g/s results on the OBD reader. However, the MAF sensor output seems to be good. I am reading 1.4VDC on idle and output rises gradually to about 2.5VDC at 3500rpm. This seems reasonable, although I haven't been able to find a detailed voltage spec for the MAF sensor. I am not sure what full scale output should be but hoping somebody can advise. The ECU voltages match those found at the MAF.
I was thinking initially that my OBD software might not be compliant in some way, but its reading the codes ok and the other live data like engine revs and temperatures are all sensible numbers, so have no reason to doubt it. I have also used other software and got the same readings.
Has anybody seen similar to this? I have searched at length but couldn't find anything directly related. There was a lambda sensor fault previously but this has been replaced and the fault cleared. My next thoughts are that it is an ECU fault. I have a spare ECU which again was purchased of the internet as a working unit, however I will need to buy a sync mate @ £150 to install it and I am reluctant to do this as there might be some other cause. My p38 is a rarity in this part of the world its either farmers Landys or Chelsea tractors so its difficult to find anyone interested, let alone capable of resolving the problem. Any help or advice would be appreciated.
