Car Mechanics (UK)

SE­LEC­TIVE CAT­ALYTIC RE­DUC­TION – ADBLUE

- Cars · Tonga · Iceland

Re­spond­ing to leg­is­la­tion to re­duce NOX emis­sions from diesel ex­hausts, some cars are fit­ted with NOX traps be­tween the ex­haust man­i­fold and the DPF. These are main­te­nance-free and have no mov­ing parts, but the down­side is in­creased CO2 emis­sions and re­duced en­gine ef­fi­ciency. An al­ter­na­tive is se­lec­tive cat­alytic re­duc­tion (SCR), which in­cor­po­rates an elec­tronic in­jec­tor (as shown) that doses a dis­tilled water/urea solution (Adblue) over a spe­cial catalyst ma­te­rial within the ex­haust sys­tem. This chem­i­cal re­ac­tion takes place, once the ex­haust gas tem­per­a­ture reaches around 170°C, or very soon after a cold en­gine start. By law, should the Adblue level be ex­hausted, or the SCR sys­tem mal­func­tion, the en­gine will stop run­ning, although the driver will re­ceive plenty of dash­board warn­ings be­fore­hand. From a DIY per­spec­tive, you may have to re­new the in­jec­tor if it de­vel­ops a fault. Should you have to re­place a DPF that in­cor­po­rates SCR, pay at­ten­tion par­tic­u­larly to the qual­ity of the cat­a­lysts, be­cause the car will not run, should a sub-stan­dard ex­haust be fit­ted.

 ??  ?? With the front pipe in po­si­tion, re­fit any brack­ets and mount­ings, so that ex­ces­sive stress is not placed on the front pipe as you as­sem­ble the rest of the sys­tem. Check for cor­rect align­ment as you do so.
With the front pipe in po­si­tion, re­fit any brack­ets and mount­ings, so that ex­ces­sive stress is not placed on the front pipe as you as­sem­ble the rest of the sys­tem. Check for cor­rect align­ment as you do so.
 ??  ?? Lo­cate the next sec­tion of ex­haust on/into the front pipe, not­ing that you do not need to coat the mat­ing sur­faces with as­sem­bly paste at this point. Do not let the ex­haust hang un­sup­ported.
Lo­cate the next sec­tion of ex­haust on/into the front pipe, not­ing that you do not need to coat the mat­ing sur­faces with as­sem­bly paste at this point. Do not let the ex­haust hang un­sup­ported.
 ??  ?? Unite the back-box and mid-sec­tion pipes. If you had to cut off the orig­i­nal back­box, dou­ble check the ex­haust’s align­ment, in case you have to dis­as­sem­ble and re­move any more ma­te­rial.
Unite the back-box and mid-sec­tion pipes. If you had to cut off the orig­i­nal back­box, dou­ble check the ex­haust’s align­ment, in case you have to dis­as­sem­ble and re­move any more ma­te­rial.
 ??  ?? Back-boxes tend to be a little awk­ward to fit, be­cause the pipe has to clear a beam axle, or sus­pen­sion parts, so you may need as­sis­tance. On some cars, you might have to re­move a road wheel to gain ac­cess.
Back-boxes tend to be a little awk­ward to fit, be­cause the pipe has to clear a beam axle, or sus­pen­sion parts, so you may need as­sis­tance. On some cars, you might have to re­move a road wheel to gain ac­cess.
 ??  ?? When you are cer­tain that the cen­tre sec­tion is aligned cor­rectly, lo­cate the U-clamp into po­si­tion and tighten both nuts evenly. Al­ter­na­tively, you can leave the fi­nal tight­en­ing, un­til the en­tire sys­tem is fit­ted and aligned.
When you are cer­tain that the cen­tre sec­tion is aligned cor­rectly, lo­cate the U-clamp into po­si­tion and tighten both nuts evenly. Al­ter­na­tively, you can leave the fi­nal tight­en­ing, un­til the en­tire sys­tem is fit­ted and aligned.
 ??  ?? Unite the ex­haust with the body mount­ings, if you are sure that this will not im­pede fitting the back box. Ap­ply ex­haust as­sem­bly paste to the outer slots only, smear­ing the paste using a gloved fin­ger.
Unite the ex­haust with the body mount­ings, if you are sure that this will not im­pede fitting the back box. Ap­ply ex­haust as­sem­bly paste to the outer slots only, smear­ing the paste using a gloved fin­ger.
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