Customer changed timing chain and then vehicle developed lack of power. Fault code PO170 stored (fuel trim). Emissions (4 Gas) excellent at normal and fast idle. Vacuum good at normal and fast idle. Ticks over ok. However customer went for MAF and swopped for S/H unit. Also changed cam, crank and 02 sensor.What I have found is MAF only goes up to 3V which I think is a consequence of the fault. When revving engine, butterfly is only partially open at about 5K revs. Accelerator pedal sensors read ok, but both TPS's are significantly under reading. When actuating throttle butterfly via acr 4, it snaps wide open. Vehicle will apparently reach 70mph after an age. Suspect throttle motor or ecu fault. Not done fuel pressure check - yet. Good these fly by wire cars! Any ideas? Many thanks

Hi Pete
What are maf sensor readings at idle and wot in 3rd gear. The maf sensors are very common faults on these vehicles. I had similar fault on a merc the throttle valve was only opening half way that was the maf sensor, i think that the reading at idle should be about 10 kgh. Hope this is of some help.

Regards Jamie

what is your vacuum reading at idle. ray

>>>>However customer went for MAF and swopped for S/H unit<<<<

Pete, tell customer unless he is prepared to fit a bosch or vauxhall NEW maf you are not going to waste anymore time with it.

>>>>Also changed cam, crank and 02 sensor.<<<<

were these all second hand parts too? and why were they changed?

Has cam timing been double checked?

It is likely that during repairs the block learn has been reset thereby showing up a previously hidden MAF fault.

Mike

Hi all. Many thanks for your interest and responses. The answers to your questions are as follows: Cam, Crank and 02 sensors are new and fitted on advice from another garage. The guy is a time served mechanic (no longer in the trade) and he double checked cam timing the day after he fitted timing chain. The vacuum at idle was 20"hg and the same at about 5000 revs in neutral gear. I think my gear only measures MAF in voltage terms ie: 1.3 volts at idle and low 3 volts at 5000 rpm in neutral. However will double check that when I go back and measure wot in 3rd gear. The emissions are 0% CO, 0ppm HC, 16.1% CO2, and 0.3% 02. and about the same at 5000 ppm. I have essentially ruled out cam timing at the mo due to good vac and emmission readings. Customer tells me tonight that 2nd hand MAF sensor made the vehicle drive worse than the original one, so there is a question mark there. Can't check part numbers on MAF because the original one strangely has last 3 digits rubbed off. Will let you know outcome on return visit. Many thanks Pete

Hiya Pete, 90% sure its MAF. Volts at idle are about right, volts under a sharp sudden type acceleration should be very near 4.0 volts. Wide open throttle while not under load will not give you the best reading. Not advisable either, maybe bugger up the new timing chain! Best would be live readings on the road. I have had that many problems with these MAFs that I now carry a brand new genuine bosch unit. Every time, I have sold the new unit!I must also warn you against any of the cheapies, they will come back to bite you!
If you do fit a new one, check the emissions, as they will probably go rich. ECU will have compensated for weak mixture and will continue to do so until reset, either by scanner or by driving the car for a few miles. If the car is due for MOT, say next day, it could possibly fail, Best Wishes, Gwyn

Carried out WOT test this evening in 3rd gear as suggested by Jamie. All measurements in volts only. Origninal MAF showing 3.2volts max. 2nd hand unit fluctuating wildly between 0.4 and 3.2 volts. Interestly I mentioned in an earlier thread that last 3 digits of original unit had been shaved off and no match with 2nd hand unit could be made. This was not so. Further investigation showed it was the s/h unit that had been tampered with. Draw your own conclusions. Customer politely advised to obtain a Bosch or Vauxhall unit. He will report back with results and will let you know. Many thanks for your interest and inputs. Pete

I had one of these recently that gave fuel trim fault codes with a new bosch MAF on it and it turned out to be the wrong MAF. It looked identical but had a different part number.

Hi All,

Customer fitted genuine MAF and now OK. He did promise to let me know the outcome but obviously couldn't be asked. Saw him yesterday about another car and got the result then. Thanks for your inputs.

Regards

Pete M