Car Mechanics (UK)

Emis­sion prob­lems

- Alan Bid­mead

I hope you can shed some light on a prob­lem with my three-door 2001 Toy­ota RAV4 NRG VVTI. I’ve owned the ve­hi­cle for two years and have been im­pressed with how it drives. After the 2018 MOT, where it ini­tially failed on emis­sions, my garage changed a Lambda sen­sor and the car passed.

Since then, I have only used Shell V-power or BP Ultimate fuel and, on the last fill be­fore the 2019 MOT, I put a bot­tle of Forte fuel emis­sion sys­tem cleaner into the tank. The car sub­se­quently re­ceived a fail cer­tifi­cate, which de­tailed the fol­low­ing: Ex­haust hy­dro­car­bon con­tent after 2nd fast idle ex­ceeds de­fault limits (8.2.1.2(b)) Ex­haust Lambda read­ing after 2nd fast idle out­side spec­i­fied limits (8.2.1.2 (c)) Ex­haust car­bon monox­ide con­tent at idle ex­ceeds de­fault limits (8.2.1.2 (b)) The tester’s com­ment was that it is run­ning too rich. My me­chanic changed the sec­ond down­stream oxy­gen sen­sor (bank 2 sen­sor was changed at the last MOT). The en­gine did not reach the lev­els re­quired at an­other check.

Then the cat­alytic con­verter was changed and it passed the emis­sions test, but at the up­per end of the limits. The en­gine coolant sen­sor was also changed and, although the limits re­main within the pa­ram­e­ters for a pass, my me­chan­ics are con­cerned that the high level means the cat may be de­stroyed by next year’s MOT. The garage’s di­ag­nos­tic equip­ment picked up that the sen­sors were now all sig­nalling, but ob­vi­ously it is not a Toy­ota main dealer, although my me­chan­ics felt that the level of di­ag­nos­tics re­quired should be ad­e­quate using their equip­ment given the age of the car. Hav­ing said that, the high-level has not yet been ad­dressed so your thoughts would be ap­pre­ci­ated. Other in­for­ma­tion from the V5: Vari­ant ACA20(Z), Ver­sion ACA20R – AZMNKW(2B) 1998cc CO2 211g/km VIN and en­gine num­ber supplied. Ex­haust Emis­sions CO (g/km or g/kwh) 0.610 – HC (g/km or g/kwh) 0.070 – NOX (g/km or g/kwh) 0.040.

I would agree with the sim­ple ex­pla­na­tion given that your Toy­ota is run­ning rich. The prob­lems ad­dressed have so far all been at­tacked from an en­gine man­age­ment per­spec­tive. Chang­ing the 02 sen­sor and the tem­per­a­ture sen­sor are all ac­tions that would en­cour­age the ECU to lower the fuel con­tent. Re­plac­ing the cat­alytic con­verter would ini­tially com­pen­sate for the richer mix­ture, as it has done, but over time this will again fail, as you fear.

I would con­sider the pos­si­bil­ity that the in­jec­tors are worn and al­low­ing too much fuel into the man­i­fold. This would ac­count for the rich mix­ture and, at some point, no amount of elec­tronic con­trol will re­duce this. The in­jec­tors are eas­ily re­moved, so it may be ad­vis­able to have them checked.

One other com­po­nent which has not been men­tioned is the MAF sen­sor, which on your Toy­ota also in­cor­po­rates the air tem­per­a­ture sen­sor. Although the MAF sen­sor is dif­fi­cult to check using a scan­ner, the air tem­per­a­ture should be checked to en­sure that it is giv­ing ac­cu­rate in­for­ma­tion to the ECU.

 ??  ?? The is­sue may lie with one of the petrol in­jec­tors.
The is­sue may lie with one of the petrol in­jec­tors.
 ??  ??

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