M20 overfueling?

Fri Mar 20, 2009 1:11 pm

A couple of months ago I noticed my 320i started to drink more fuel than normal also failed emission test

it's regulary maintained every 10.000km, last month I changed air filter, fuel filter, valves adjusted, new oil and filter, blue temp sensor is fine, double checked...car itself goes like hell, idling perfect, shows some smoke behind when pushed to the limit but nothing major to worry...also when throttle pedal is released some popping from exhaust is showing, and exhaust pipes get black in a month...
what should I check first?

Fri Mar 20, 2009 1:27 pm

CO mixture?

If it failed emissions test, did the tester not try to adjust it, or would it not adjust?

Fri Mar 20, 2009 1:32 pm

toby wrote:CO mixture?

If it failed emissions test, did the tester not try to adjust it, or would it not adjust?

idling CO fine, at revs bad.

Fri Mar 20, 2009 1:38 pm

How did it fail the emissions?
So did it fail on high HC?
If that's the case, you may have an air leak.

Fri Mar 20, 2009 5:09 pm

high HC idle and high rev
high CO rev

how to check for air leak? Intake rubber is new

Sat Mar 21, 2009 9:13 am

Is your throttle switch working correctly giving on idle and WOT signals when it should do?

Sun May 31, 2009 6:36 pm

still trying to sort this out myself before going to specialist...

I was thinking of changing blue temp sensor and O2 sensor...

engine runs smooth on first start but after minute or two starts sound like ''wooom wooom wooom'', and whole body moves left-right...when warm, idles perfect and smooth but still makes tailpipes black after while, runs rich...but I need to be sure is this only bad mixture or some engine components needs to be changed

Mon Jun 01, 2009 9:25 am

Check for air leaks by spraying some brake cleaner or something similar over the rubber pipes. If the pipe is new unlikely to be leaking.

Sounds like over fuelling...

Mon Jun 01, 2009 11:31 am

toby wrote:Check for air leaks by spraying some brake cleaner or something similar over the rubber pipes. If the pipe is new unlikely to be leaking.

Sounds like over fuelling...

no air leaks, that's for sure....
also new O2 sensor is about 100 quid, manufacturer BERU...universal from NGK is 50 quid

Mon Jun 01, 2009 11:38 am

have you had a look at the wiring for the injectors at the main plug under the inlet manifold on the injector side of the loom for damaged wires because thats where the wiring is for the blue sencor and if thats damaged the sencor will be usless

Tue Jun 02, 2009 12:52 pm

I had this issue in my M20B27 recently. You could smell the mixture was rich, and the plugs were darker than normal.

The local "all things BMW" expert in my area advised me to lean off the mixture using the adjustment allen screw in the AFM. After a few trial adjustments I backed it off about 720 degrees. Spark plugs are now a nice grey colour, no more over-fuelling smell and fuel economy has improved greatly!

Tue Jun 02, 2009 10:47 pm

jermyns wrote:The local "all things BMW" expert in my area advised me to lean off the mixture using the adjustment allen screw in the AFM. After a few trial adjustments I backed it off about 720 degrees. Spark plugs are now a nice grey colour, no more over-fuelling smell and fuel economy has improved greatly!

Not good practice at all! The adjustment won't have moved itself, so you are masking another fault, and the car won't be running at its best

Wed Jun 03, 2009 9:01 am

Brianmoooore wrote:
jermyns wrote:The local "all things BMW" expert in my area advised me to lean off the mixture using the adjustment allen screw in the AFM. After a few trial adjustments I backed it off about 720 degrees. Spark plugs are now a nice grey colour, no more over-fuelling smell and fuel economy has improved greatly!
Not good practice at all! The adjustment won't have moved itself, so you are masking another fault, and the car won't be running at its best

Sorry Brian, the car runs perfectly and passes all emission tests since the adjustment. It has had a lot of mods done over the years, so I would expect that things have changed somewhat over that period.

Tue Jun 09, 2009 11:52 pm

A couple of days ago i was showing my friends some problems with my motor and he came to the conclusion that it was running rich. As i turned my back to grab something he proceeded to adjust the air flow meter. As i saw him doing it, remembering what Brianmoooore said about adjusting this and the screw on the throttle body so i told him to stop but now its been tampered with. I suspect the previous owner had tinkered with this in the past also. My question is, how do i know where this should be set? Is there any easy way to set this up correctly?

Wed Jun 10, 2009 12:29 am

kman82 wrote: Is there any easy way to set this up correctly?

Easy, but not DIY.
Needs a CO meter up the chuff, then just adjust for correct reading.
MOT due any time soon? Ask the tester nicely, and they may do it at the same time, either as a favour, or for a small charge.

Wed Jun 10, 2009 1:37 pm

Yeah its due in a couple of months so i'll ask them to have a look. Im trying to sort out lots of little niggles at the mo in preperation for the mot and you'll see from my other post today that fast idle is one of them. I just hope i can get it down otherwise i'm worried it wil fail on emmisions!

Wed Jun 10, 2009 10:48 pm

cro320 wrote:also when throttle pedal is released some popping from exhaust is showing

The M20 uses a fuel overrun cutoff, triggered by the idle signal from the tps, popping in the exhausts indicate fuel is present. Is your tps working as it should?

Wed Jun 10, 2009 11:39 pm

e301988325i wrote:The M20 uses a fuel overrun cutoff, triggered by the idle signal from the tps, popping in the exhausts indicate fuel is present

Switches back on below 1800(IIRC)RPM though.

Fri Jun 12, 2009 6:37 pm

that's worth noting, mine's never popped when it does cut back in though. . . when my tps wasn't working it popped and even backfired! Although this was on the drive home from buying the car and was quickly rectified!!!

Fri Jun 12, 2009 10:27 pm

My LPG system has a similar over run fuel cut off, and a while ago the ECU had a glitch and turned this function off when I was towing a heavy trailer in Europe somewhere. The car would pop away on the overrun, and on downhill stretches, where the trailer was pushing, it would give the occasional fully fledged backfire, which lit the trailer quite spectacularly in the dark!

Sat Jun 13, 2009 1:08 am

which lit the trailer quite spectacularly in the dark!

Sat Jun 13, 2009 9:07 am

My R19 16v started to backfire on the overun when my lambda stuck on to a lean reading. First it blew my decat pipe clean in half. Then it would spit 2 foot flames which would light up the whole road behind me like a lightning bolt!!! I was racing an MX-5 and he knew the road better than me, caught up right behind my bumper. I lifted off, and BANG, the road lit up, he pulled back about 5 car lengths!!!