Prob­lem­atic behaviour

Car Mechanics (UK) - - Diagnostics Doctor -

I’m hav­ing prob­lems with a 2007 BMW 325i M-line with 80,000 miles. The car was bought a few years ago in ex­cel­lent con­di­tion, but has been prob­lem­atic since then.

When start­ing from cold in the morn­ing, and also when the en­gine is warm af­ter 100 miles or so, it starts driv­ing very roughly, as if it’s not run­ning on all cylin­ders or the mix­ture is very rich or poor. When this hap­pens in the morn­ing af­ter start­ing, the EOBD light il­lu­mi­nates and you can’t drive faster than 30-35mph. The trick I de­vel­oped is to stop the en­gine and restart it. In 80% of cases it then drives fine, but in the other 20% the EOBD light still il­lu­mi­nates and the en­gine does not run as it should, al­though power is re­stored.

When the en­gine is warm af­ter a long run and you stop, say for a traf­fic light, the EOBD light turns on within 15 sec­onds. The en­gine runs roughly, but not as badly as when it’s cold. The rev counter dances on the scale, but when you con­tinue driv­ing, all is nor­mal again. Some­times the EOBD light re­mains lit for three days at a stretch, but the car runs fine.

The prob­lem may not man­i­fest it­self for two to three weeks, petrol con­sump­tion seems nor­mal and it’s us­ing half-a-litre of oil ev­ery 1300 miles. I’ve also no­ticed that the ex­haust pipe is very black. On the mo­tor­way, when I over­take an­other car and have to make power, there is a lot black smoke from the ex­haust.

I had the car di­ag­nosed lo­cally and found that the in­jec­tors on cylin­ders 1 and 2 were not work­ing prop­erly. All six were sent to an out­side firm for cleaning, but when the prob­lem re­turned, the in­jec­tors on cylin­ders 5 and 6 were to blame. Six new in­jec­tors were fit­ted, but it has made no dif­fer­ence. I also re­placed the fuel pres­sure sen­sor and all of the coils and plugs. In spite of the new in­jec­tors, the di­ag­nos­tics reader still says the in­jec­tors for cylin­ders 5 and 6 are not good, but re­plac­ing them with the good ones from cylin­ders 1 and 2 makes no dif­fer­ence. The car was then sent for three days to a Ger­man Bmw-dealer/garage to be re­paired there. They said that the in­jec­tors on cylin­ders 1 and 2 – which were new – were at fault, not 5 and 6!

I have es­tab­lished that other peo­ple with same car/en­gine have the same prob­lem. Do you think there is a so­lu­tion? Rolf Kni­jff My first com­ment is that the in­jec­tors should be coded to the cylin­der – hope­fully, this should have been done by the dealer, but will have been up­set by swap­ping the in­jec­tors around. The cod­ing data is printed as a six-digit num­ber on the in­jec­tor body.

how­ever, be re­lated to the ABS pump/ mod­ule unit or one of the other sen­sors in the sys­tem. For this rea­son, the only way to nar­row down the prob­lem is to list any fault codes in the sys­tem. If no

I am also as­sum­ing that the dealer checked the fuel pres­sure reg­u­la­tor and that this is cor­rect for the ve­hi­cle. This is very im­por­tant with the in­jec­tion sys­tem on your BMW and of­fi­cial lit­er­a­ture says, with re­gards to such prob­lems, to al­ways to con­firm the fuel pres­sure. This is a check that the dealer should have car­ried out to en­sure the fuel line pres­sure is suf­fi­cient. It should al­ways be main­tained at a higher pres­sure than the reg­u­la­tor is set. Also, If you have not al­ready done so, I would re­place the fuel fil­ter.

When the in­jec­tors fail they over-fuel. The ECU then de­tects the rich mix­ture from the read­ing given by the 02 sen­sor. As the 02 sen­sor does not spec­ify which cylin­der is over-fu­elling, only which bank, the fuel to all three in­jec­tors in the bank is re­duced. The re­sult of this is that the two good in­jec­tors are not putting suf­fi­cient fuel into the cylin­der. This fault codes are present, Au­to­data ad­vises you to “Re-pro­gram ABS/ESP con­trol mod­ule with up­graded soft­ware. To carry out an ef­fec­tive re­pair a soft­ware up­grade will be re­quired – re­fer to man­u­fac­turer.” can re­sult in a mis­fire de­tected in the two cylin­ders with good in­jec­tors. The sim­plest test to dis­cover which cylin­der is over-fu­elling is to re­move the spark plugs. The over-fu­elling cylin­der will have a black, sooty spark plug.

The in­jec­tors in the di­rect in­jec­tion sys­tem are prone to car­bon buildup. As you have had all six in­jec­tors re­placed, as well as the plugs and coil packs, I would check the con­ti­nu­ity and in­tegrity of the in­jec­tor plugs and loom, as well as the coil pack plugs and loom. An­other point to pon­der is the fuel qual­ity – you should cer­tainly con­sider only us­ing a pre­mium fuel, if pos­si­ble.

A set of BMW in­jec­tors.

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