Lumpy Idle, Possible Misfire? - Not Solved :'(

[LiftedMuffin]

Hi folks, just an update on this: I managed to get a better scanner on the Z3 tonight - seems my one is pretty bad at reading live data from the engine. Ill attach the graphs, as @colb suggested, of the fuel trims and o2 sensor voltage with RPM below. 3 codes popped up when checking:

- Random/Multiple Cylinder misfire detected
- Cylinder 4 misfire detected
- Cylinder 2 misfire detected

From the plots of short term FT, RPM and mass air flow: the short term trim bounces between about 10-15% at idle, and then drops to between 0% and -6% @3000 RPM. From what @Murray Wall was saying this would indicate a vacuum leak in the intake system? (there were 2 STFT variables in the scanner so I plotted both - they seem to follow each other quite closely, not sure what the difference is). Long term fuel trim was sitting at 0.8%

On the second plot I thought I'd check the o2 sensor voltage - seems to be cycling between ~0.8V and 0V which is within the expected range. It gave a consistently lean reading just after holding at 3k RPM, until the STFT rose above 10% and then you see the expected oscillating voltage waveform again. I'm guessing the scanner is taking instantaneous samples of the voltage rather than a time average. Seems like the o2 sensor is functioning okay and trying to adjust for the vacuum leak? Is a vacuum leak likely to caluse the misfires as well? Just wanted to get a sense check that I'm reading this correctly from the wizened heads on here . Cheerss all!

 

[NZ00Z3]

Yes you have a vacuum leak, time for a full inspection or a smoke test.

Nice graphs

 

[Oddly Godly]

I recently had an engine management light come on and my code reader suggested the fuel trims. I found I had a leak in one of the air hoses between the maf and the engine. I replaced both hoses and the light has stayed off. Before I replaced the hoses the engine idled at about 600 rpm on warm up and every 20 seconds or so the revs would drop for a split second and then recover. Since replacing the hoses it now warms up at a steady 900rpm and drops down to 600 after a couple of mins. Mine is a 2.8. I am sure the hose must have been leaking since I have had the car. It only seemed to correct its self after I had driven it for a short while. My hose nearest the engine was leaking on the offshoot about an inch diameter with the concertina bend. At first glance the hose seemed fine.

 

[colb]

Yes looks like an air leak from the graph readings you are seeing, best is a smoke test if you cant pinpoint where the leak is, may be more than one leak as well. Need to watch for leaks along the entire system from Maf to exhaust and that includes the cam/rocker cover if its a plastic one. Smoke is the best way of spotting leaks. As I have reported before a 2.2 I worked on had a leak on the throttle body side and as soon as that was fixed a further leak showed itself up through a crack in the cam cover around No2 plug well that had to be solved with a replacement cover. As soon as it was all airtight the fiel trims returned to normal, previosly it was adding 20% more fuel as the exhaust sensor was seeing all the unmetered air telling it that it was running lean.

 

[LiftedMuffin]

Well, had a smoke test done which showed a couple of interesting leaks: Turns out the seal was missing from the bottom of the oil dip-stick pipe which was blowing air out the sump/crank case and rattling around - end of the pipe and where it sits in the sump case are worn to hell! All the little rocker cover gaskets around the spark plugs were mis-seated and leaking as well, and slowly filling up with oil... Also showed a smaller leak from around the CCV valve. Somewhat surprisingly all the rubber hoses were fine though

Left it in the shop whilst they wait for a new tube to arrive from Germany... at least they gave me a tidy loaner over the weekend whilst I'm waiting! For anyone in Woking/SW London area, Graham at Star-tec Mercedes in Chessington is an ex-BMW master tech and a top bloke - had really good service there the couple of times I've taken the Z3 in, would recommend them!

 

[colb]

Sounds like you traced all the leaks, smoke test is so useful in finding these leaks on these BMW engines. Sure beats being sent off in the wrong direction by sensor codes that are caused by the air leaks and throwing parts at the car that it dosn't need. Once it is all buttoned up check the fuel trims in live data and see the difference, it will no longer be giving it 15% more fuel at the injectors as it will now see the correct exhaust measurement for the metered air entering the engine. Unmetered air will make the car think its running lean and demand more fuel to compensate. You will notice the difference in the amount of visits to the petrol pump at the garage as well. Post up the final results when you get it back.

 

[LiftedMuffin]

Well, disappointing news - sorting out the air leaks on the intake side (plus CCV and spark plug replacement) hasn't solved the problem - If anything it seems to be worse! The rough idle is much more noticable when the engine is up to temperature now, and it still seems to be using a lot of fuel - I reckon I've driven 40-45 miles since picking it up and used a quarter of a tank (~3 uk galons?) which means about 15 mpg . Fairly sure it wasn't that bad before!

Took it to work the day after I picked it up and for about 5 seconds after I started the engine it was super rough - really felt like it'd lost a cylinder completely! It's not done that since, but is still worse than it was.

Fault codes I pulled just now (was clean when it left the garage, they hadnt got any after sorting the air intake leaks):

• Misfire, sum, relevant to exhaust
• Misfire cyl 4, relevant to exhaust gas
• Misfire cyl 3, relevant to exhaust gas,
• Oxygen sensor upstream of catalytic convertor

I did realize that I've been a bit af an idiot and not properly locked the fuel filler cap off, so it's basically been sitting open for quite some time. I'd been wondering where the occaional strong smell of fuel was coming from when I had the window cracked... I guess that one should be solved at least! Don't know if this could have affected anything with fueling or spark/exhaust?

Other stuff wot I noticed:

• Stil a noticable metallic rattle from under the car at approx 1.1k revs and 1.9k - 2k revs when moving (doesn't seem to do it when the car's stationary)
  
• It sounds a bit 'blowy' to me underneath the front of the car, but the guys at the garage said they couldn't find anything wrong with the exhaust...and maybe I just wasn't paying as much attention before, it could be normal I guess.
  
• Theres a fast clicking noise coming from the coil pack when the engine is running. Anyone know if that's normal?

Will hopefully get my mates scanner on it this week so I can graph the fuel trim and o2 sensor again & see if anythings changed. Will post the results up!

Obviously, intake vacuum should be good after that rather expensive trip to the garage! I'm inclined to look into spark and fuel (maybe MAF?) next - what would be the most sensible things to test/clean/repair next? Any other stuff I should check? Maybe the o2 sensor is on the way out?

Thanks in advance!

 

[colb]

Still inclined to think there are air leaks somewhere before the exhaust sensor, so we are looking for leaks between the Maf and the exhaust sensor(s) post Cat. High fuel trims together with the high mpg would indicate its being told it is running lean and to compensate its increasing the fuel at the injectors. If they are very high then the misfires are probably due to the excess fuel being fired into the cylinders. Bet the garage didn't smoke test it, if they did they didn't find all the leaks. Dont rule out a bad fitting rocker / cam cover or even splits in the plastic if its got a plastic cam cover, seen one on a 2.2 that had cracks in it which was only found after fixing leaks found on the throttle body side of the engine. Only managed to find that after the inlet side had been fixed, having done so the engine filled better with the smoke and it found the cracks further along the system. Once you are positive all lweaks are sealed then turn attention to the Maf, use Maf cleaner on the sensor then see if its fixed. Live data on your scanner should be able to show how its performing. Bad Maf's do not always set codes. I had a bad Maf but no codes, putting a replacement oem spec Maf on cleared my problem in an instant.

 

[NZ00Z3]

There should be no sounds coming from the coil pack. The clicking sound is most likely a discharge occurring somewhere. Start by changing the HT leads between the coil pack and the plugs. If the noise remains, then its the coil pack that needs to be changed.

 

[LiftedMuffin]

Yeah I'm pretty sure they said they'd done another smoke test after replaceing the rocker cover gaskets, dipstick tube and CCV valve (which was where the leaks were coming from first off) - came out fine the second time. I'll give the guy a call and check just in case I'm mis-remembering.

I could do with getting the car up on a ramp to have a good look over the exhaust, but they did apparently check that too and didn't find anything. Right now I'm eyeing up:

• MAF
• Lambda sensor
• Coil pack & plug leads
  
• Fuel filter/fuel pump?
  
• Injectors

Hopefully the fuel trims & o2 sensor readings will give some clues!

 

[handsomejackuk]

the anndroid torque app and a bluetooth OBD reader is great for live monitoring. i use an old android phone running the torque app and keep it running in the car it tells me when car is up to temperature and warns me of engine overheating, fault codes and When @GZed was driving it told me that he was using more that 50% throttle pedal travel....:-(

honestly its a must have tool to have in the car... i just stick the mobile to my windscreen or place it in the little tray by the handbrake..


21558953_358177424618677_6608485237815440445_n by handsomejackuk, on Flickr

21200872_353840258385727_7698799074940566206_o by handsomejackuk, on Flickr

 

[LiftedMuffin]

There should be no sounds coming from the coil pack. The clicking sound is most likely a discharge occurring somewhere. Start by changing the HT leads between the coil pack and the plugs. If the noise remains, then its the coil pack that needs to be changed.

Thanks mate - good to know! I'll look at getting it repalced.

@handsomejackuk - is that with a OBD2 port in the cabin? My '99 Z3 only has an old 20 pin port under the hood

 

[handsomejackuk]

no its connected to the 20 pin underbonnet you need the 20 pin to obd cable i just tuck the obd adaptor by the brake servo and it sends the data to the car no porblem

https://www.ebay.co.uk/itm/Fits-For-BMW-20-PIN-TO-16-PIN-OBDII-OBD2-DIAGNOSTIC-LEAD-CABLE-CONVERTER-ADAPTOR/333442576591?epid=0&_trkparms=ispr=1&hash=item4da2b9f0cf:g:uW4AAOSwihxdEeK2&enc=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&checksum=3334425765915c5883e7dba743d7a69687ac879fa9a4

 

[LiftedMuffin]

no its connected to the 20 pin underbonnet you need the 20 pin to obd cable i just tuck the obd adaptor by the brake servo and it sends the data to the car no porblem

okay nice, yeah I have an adapter already, wasn't sure it'd work outside the cabin though!

 

[LiftedMuffin]

Another update on this: just got my head down under the bonnet after a drive and there's a crunching-ticking sound coming from around the DISA valve - sounds like the one in this video but it isn't constant, or as loud:

View: https://youtu.be/uGWpa9OYiZc


This site here lists the symptoms of a dodgy DISA valve as:

• Lack of power
• Misfire
• Running rough
• Rattling, clicking or buzzing noise from the engine at idle and above

Which would fit pretty well, also says it can throw up lean condition, misfire and o2 sensor error codes so it kinda fits with what I'm seeing. I did notice a very faint clicking coming from the DISA when I first started digging into this but it was very quiet and occasional so didn't thinkmuch of it.

Now I'm just waiting for a quote from Soper's on a coil pack, set of plug leads.. and soon to be DISA valve. Good job I haven't got much else to be spending money on at the moment!

Will update this when I get some parts swapped out.... Coronavirus allowing...

Also wondering what statutory rights I have for a used car purchased from a dealer - I'm out of the 3 month warranty from them now, but this is getting expensive!

 

[colb]

A Bad Disa will make what is described as a clacking sound, had this on my 1.9 M43 a couple of years back, got a replacement oem one from BMW at great cost, popped that in and that sorted it.

 

[LiftedMuffin]

Did your DISA cause any issues with idle or running in general @colb?

I got a better scanner on the Z3 - STFT, RPM and MAF plot is below. Doesn;t seem to show the high fuel trim at idle now. Don't know if the dip in FT after letting off the revs is normal though, or the big spike in the MAF sensor flow on the 3rd ramp up of RPM... Anyone see any cause for concern there?

The lumpy idle remains.....haunting me....

 

[colb]

My clacking Disa was changed out for a new one whilst I was trying to find a running fault I had, poor performance was my main issue the car just felt like it was being held back, eventally put a oem Maf on it and that sorted it straight away. Diagnostics were not that helpful when tracking down the fault on mine led me all over the place fitting new sensors including exhaust sensors. Not had a problem since. Mafs dont always set codes which can lead you astray. I did have more success with the mates 2.2 with the diagnostics which pin pointed the air leaks by viewing the fuel trims, smoke test found them straight away.
Your fuel trims look ok on your live data bit of a cramped display, prefer to view them on my laptop which displays nice clear graphs using my Engine Check Pro software.

 

[g8jka]

Still looking for a dodgy idle cure for on mine. It's only when cold, started not long after rebuilding the vanos and DISA. Can't see any leaks or don't have error codes and have swapped both the MAF and DISA with my Dad's which made no difference. It feels like the power is being held back also. Recently I put new spark plugs in, no change apart from I'm now getting less MPG. I don't know whether to try a new camshaft sensor next as I've read a dodgy one could cause poor performance.

 

[spurs fan in a coupe]

Also in Woking, with piles of spare parts if you want to try solutions before coughing up at a garage.

PM me