E46 318 help

[sag]

im currently working on bmw 318 n42b20a(2003) ...on idle cars is miss-firing ..on accleration theres no missfire flatspots/hestation...ive checked the coils and plugs all seem to be fine... iv plugged on the diagnostic machine and no codes present
conducted a rough running test on idle and vechile in park(auto)-
cylinder 1....0.16
cylinder 2....-1.98
cylinder 3....-1.68
cylinder 4....3.99

car on idle with gear in drive
cylinder 1....-0.33
cylinder 2.....-1.28
cylinder 3....-0.98
cylinder 4 .....2.45

it looks to me that cylinder 4 is at fault any ideas or can shed a light
thnks in advance

[jimjim]

have you tried swapping coil 4 with another cylinder to see if the missfire moves?

[sag]

yes i have ive put new coils and plugs mate... done comp test all over 100 bar.... ive switched off the injectors and coils one by one through the diagnostic machine all seem to have equal miss fire when dissconnected..
ive been told cud possibley need DME software upgrade or vavles seats might need to be cut
but not sure
any idea what this smooth running thing is were its sitituated wat it deos ????

[jamesjohn318is]

what oil do you have in it. should be 0w30 ideally (according to castrol)

The N42's are very picky about oil and run really rough if not given the correct grade.

also could be the timing chain tensioner, allowing the chain to slaken at idle.

another weak spot is the MAF.

These engines show symptoms for ages without throwing out any codes.

[jamesjohn318is]

also the last N42 with lumpy idle I worked on the problem was a split vaccum hose right at the back under the pollen filter housing.

[johnt0709]

also the last N42 with lumpy idle I worked on the problem was a split vaccum hose right at the back under the pollen filter housing.

+1

Ive had an E46 and the lumpy idle is a split crank case breather hose - to get access to replace you remove the pollen filter - you should be able to feel the split without replacing it.

And the vaccum pipes at the fuel pressure regulator can perish as well.

My money is on the crank case hose - £25 from stealers iirc.

[sag]

what oil do you have in it. should be 0w30 ideally (according to castrol)

The N42's are very picky about oil and run really rough if not given the correct grade.

also could be the timing chain tensioner, allowing the chain to slaken at idle.

another weak spot is the MAF.

These engines show symptoms for ages without throwing out any codes.

recently done a oil change had put 5w/30 fully systh
if the chain slakend wouldnt it show codes for cam sensor timing out or vanos codes??

it diffently sounds like a miss fire rather than lumpy idle
i can not hear any hissing noises but i will check the pipe underheath the pollen filter.....

any ideas on this rough running test???wta the reading means and relates to.............,cylinder four reading is quite high

[jamesjohn318is]

Was the oil BMW LL01 Spec?

Not sure about the rough running test ..it could indicate poor injector performance. Have you done a fuel pressure test? Injector tests?

Another point is gasket failure. There is a gasket in the rocker that can fail and cause to oil start seeping into the plug sockets. However the contanmination should be visable on the plugs and the tip of the coil.

It doesn't necessarily throw a code when the chain slackens (at least it didn't on mine). It tries to adjust for the variation, which causes missfire symptoms. Eventually the chain will jump a cog and throw the timing out completely. If the chain is allowed to flap around for a long time, the guides can snap. BMW realised this to be an issue and replaced the tensioner in 2007 with a different more robust design.