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Bad running engine

2422 Views 9 Replies 7 Participants Last post by  rangeroverklaas
Hi there,

4.6 HSE 1999 with bosch motronic with engine problem.
Faultmate ODB P0172 and P0175 say both cilinder banks lean mixture.
Also misfire at specially at nr 7, have change HT lead and plugs, no result.
Engine hesitates during acceleration.
I guess the misfire is a result of the lean mixture.
On petrol less misfire then at LPG.
It's not every day very bad, cold weather and cold engine is worse.
Something to do with an airleak after MAF sensor? , broken inlet manifold ?



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I think this is probably all a result of a low Maf reading,if it was just inactive Oxy sensors the engine would end up running very rich,but if the Maf reads low the ecu wont allow a wide enough injector pulse width to get the sensors to switch rich.So have a look at airflow readings,22-25Kg at idle and approx 90-100kg at 3000rpm engine hot all loads off.So if the readings are low its either leaks or a failing Maf.After a short period of Oxy sensor inactivity the ecu will get fed up and go open loop making the situation worse.What you can try with the failing Maf - just at idle is to carefully tape off part of the Maf to increase the speed of the air going through the remaining open part. If you then watch live data you should be able to get the Maf to read right - then watch to see if it will trim the fuelling and make the Oxy sensors switch.Apart from being an interesting thing to play with it can also prove the state of the Oxy sensors.
1 - 1 of 10 Posts
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