Occasional misfire on cold start. P codes...

**Mike WW** · 01-13-2018, 12:11 AM

02 525it, 134K. Vanos, VC gasket, plugs, CCV and related hoses all done in the past 20K or so. Occasionally on a cold start it will have a miss. If driven right off at a minimum of a moderate pace, it goes away immediately. It coded yesterday for the second time, last time was just over a year ago. Both times it went to fuel cutoff it was on a very slow takeoff. Otherwise it's running very well with no codes, although occasionally a brief pause on hard acceleration from a stop, almost like my foot wasn't even connected to a throttle cable.

(yes, I know it's drive by wire)

Last year was P1351 Misfire Cylinder 5 with Fuel Cut-Off. Shut off for 30 seconds, restart and all was fine.
Yesterday, P1350 Misfire during Start Cylinder 5, P1343 Misfire Cylinder 1 with Fuel Cut-Off. Restart several hours later and all was fine, CEL was even off.

Last year I swapped #5 coil to either 4 or 6, I can't recall, but not 1, so that suggests it's not a coil. Yesterdays research seemed to suggest an exhaust camshaft position sensor, which I'm leaning towards in lieu of anything more likely.

So, does that sound like a likely cause and if so is the current school of thought to use BMW CPS only or are better aftermarket such as Meyle or Hella or Febi reasonable alternatives.

**nikh23** · 01-13-2018, 01:12 AM

Same issue as well. I’ve replaced coils with some extra ones. New plugs. New gaskets. Occurs only on cold starts if I let it sit. Have yet to check my injectors though which may be the cause after 180k miles

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**Mike WW** · 01-13-2018, 01:39 AM

Well it's nice to see I've got company. I don't have any cam sensor codes either, but whatever search terms I was using yesterday pointed strongly to the ex cam sensor with a number of forum posts from all over, not just here, saying it solved their problem. Occasionally intake or both, but usually exhaust. Usually without codes. I didn't dig too hard today and was using different search terms, but I wasn't seeing it. However going off yesterdays results I'm buying an exhaust can sensor unless I get different, logical, info here.

**wagons ho** · 01-13-2018, 03:31 AM

I guess my only comment about this is, if something is wrong, why would restarting it clear the issue?
Unless the dme is super sensitive and trips the check engine light over nothing. And why on cold run when it is in open loop programming with no feedback from o2 sensors?

**geargrinder** · 01-13-2018, 11:07 AM

Originally Posted by wagons ho

I guess my only comment about this is, if something is wrong, why would restarting it clear the issue?

well. electronic components can fail in weird ways intermittently. likely it gets 'stuck' at a cold start but removing and restoring voltage once its had even a few seconds of 'warm up' lets the component work again.

this is a slow and fairly dorky video, but pretty much assplains it. https://www.youtube.com/watch?v=wVl6CgKuT18

the trick they show of monitoring starter amps to try to confirm ballpark timing is interesting incidentally.

**Mike WW** · 01-13-2018, 03:33 PM

GG, I hoped you'd chime in. What's your take these days on BMW vs respectable aftermarket cam position sensors? I know it used to be BMW only, but it's hard to believe it's that complicated a switch so making a quality knock off is impossible.

**geargrinder** · 01-13-2018, 07:43 PM

Yeah those aren't exactly switches. They are hall sensors, meaning they are really a semi-conductor type device, therefore actually yeah you can prob make em real cheap if you shortcut on materials and line speed and QC and stuff like that and indeed it's prob something that unless proven otherwise is best OE.

**Mike WW** · 01-13-2018, 10:51 PM

Originally Posted by geargrinder

...and indeed it's prob something that unless proven otherwise is best OE.

I was afraid you were going to say that and relieved at the same time. Thanks for your input.

I'll allow they're fancy switches, but with where switches, semiconductors, and parts in general today, it's probably a $3 part. Or should be. Oh well, what's the price of not being stranded by the side of the road.

**geargrinder** · 01-14-2018, 08:49 AM

Originally Posted by Mike WW

I'll allow they're fancy switches, but with where switches, semiconductors, and parts in general today, it's probably a $3 part. Or should be. Oh well, what's the price of not being stranded by the side of the road.

Yeah maybe. For a truly good one, I'm sure the cost comes in three areas:
- least significant but not non-existent probably is materials - cheaper plastic, cheaper PCB inside, etc.
- internal design and details to make them robust and highly ruggedized (vs a pure light-duty hall-sensor component which costs about $1.50 retail)
- volume vs the specific unique part application

The last one is what keeps the good ones from being ripped out by the OE for $10. The big Tier 1's make millions of these all of which are probably nearly identical electrically inside, but each has to have a unique housing and connector or pigtail on it.

A quick google shop around turns up the cheapest ones for M62's at $10-15. Do the math... if they are selling them that cheap then retailer is buying them for $5, therefore wholesale cost is probably $3-4... meaning probably cost $1-2 to make... So how good do you think they can afford to make these things if there's only $1-2 they can spend per piece to cover materials and mfg overhead and packaging and the whole bit...? Maybe so great.

What always does make me nervous is when there's these vast discrepancies in parts, i.e. $100 dealer vs $10 knock off. Clearly there's some difference between the two. But what about the ones that turn up in the middle for $50? Are they the same $10 ones but they figure they can charge more based on the $100 dealer part? Sometimes there's really just one or two cheap knockoffs but they are being marketed & branded differently and so "the middle option" isn't really some "half way inbetween" option.

**Poolman** · 01-14-2018, 09:51 AM

Just noticed a post over on one of the other forums, questioning a problem with the shunt resistor that is located in the coil pack wiring harness. I dodn't have a clue if this can, or could cause a problem, but will be looking into the one on my car, when it warms up a bit. Here's the link,

http://forum.e46fanatics.com/showthread.php?t=1207497

**geargrinder** · 01-14-2018, 11:22 AM

Yeah the scan tools are notoriously too slow to catch stuff like this so don't bank on that.

The shunt resistor thing is interesting. I was unaware of that wiring.

Read the MS43 factory doc. Its good stuff.
https://www.slideshare.net/B33MER/e46-m54engs43

If you look at the page illustrating the shunt resistor though, if it failed, it would fail for all cylinders. Just hypothesizing failure modes...
1. either fails short or fails 'excessively low resistance' - engine should run perfect but DME won't 'see' cylinders firing and will be confused. could cause DME to act oddly.
2. fails 'excessively high resistance' - might cause weak sparks, DME may or may not notice 'huh something seems odd'.
3. fails open - car won't run at all, no cylinders will fire (since there's only one shunt resistor to ground all coils)

Easily a resistor like that could go intermittent however and cause random behavior, and as mentioned above for hall sensors, easily the intermittency could be driven by temperature and humidity, therefore stuff like "only on cold starts when its rained in the last 3 hours and there's a full moon and a black cat has crossed the street in the last hour". In electronics we often tap and poke old resistors like that with a stick (seriously) to try to get them to act up if we are suspicious - like the guy tapping the CPS in that video (am I the only one who watched the video?)

Interestingly its clearly not a common issue or replacement part because there's zero chatter about it. Would be interesting to find out its a secret hidden missed problem that's not been widely identified.

**Poolman** · 01-14-2018, 02:22 PM

Well, there are so many of us, that have about the same compliant with the i6 engine. Cold engine cranking and then a bit of rough idle, with a lope , followed by a misfire code. I have this happen often and I know I have everything checked off, no vac leaks and good parts for coils and plugs. I'll have this lope at idle and a code light come on, I'll stop the car, turn the ignition off, then crank the car again, and it's like nothing has happened, car is just as smooth as can be. I'm not sure about the resistor deal, but when warmer weather gets here in a week or two, I will be looking into the wiring harness to see if the one on the car is cracked.

**Mike WW** · 01-14-2018, 09:12 PM

Originally Posted by wagons ho

Ok,I'm back. Mike WW; in your first post, you mention that research indicated a camshaft position sensor. Have you had a code for it?

No, only codes have been misfire and misfire with fuel shutoff. And it's been an occasional problem for over a year. Maybe 2. It was a Google search that produced the cam position sensor diagnosis. Usually exhaust, occasionally intake or both. But I think the latter were more severe symptoms. I believe the fuel shutoff is do to the ECU sensing a severe misfire to save the cat, rather than a efficiency reading. It only codes if it's a slow takeoff, if moderate it clears right up.

**geargrinder** · 01-15-2018, 08:25 AM

Originally Posted by Mike WW

No, only codes have been misfire and misfire with fuel shutoff. And it's been an occasional problem for over a year. Maybe 2. It was a Google search that produced the cam position sensor diagnosis. Usually exhaust, occasionally intake or both. But I think the latter were more severe symptoms. I believe the fuel shutoff is do to the ECU sensing a severe misfire to save the cat, rather than a efficiency reading. It only codes if it's a slow takeoff, if moderate it clears right up.

Hmmm. I could see scenarios where either cam sensor or that ignition part could cause that type of behavior. Weak or missed spark under load, affected by temp/warm-up.

So Mike you haven't replaced a cam sensor yet? If you have to 'fire the parts cannon', this is a good application for a junkyard part maybe. Pull a cheapo from a yard, if it seems to work, throw that in the spares pile and invest in a proper new one, if not, you're out $5-10 or whatever vs the $100.

**Mike WW** · 01-15-2018, 01:50 PM

Originally Posted by geargrinder

Hmmm. I could see scenarios where either cam sensor or that ignition part could cause that type of behavior. Weak or missed spark under load, affected by temp/warm-up.

So Mike you haven't replaced a cam sensor yet? If you have to 'fire the parts cannon', this is a good application for a junkyard part maybe. Pull a cheapo from a yard, if it seems to work, throw that in the spares pile and invest in a proper new one, if not, you're out $5-10 or whatever vs the $100.

No I haven't yet. I really don't like buying parts I don't need, but it is the wife's car and I'm more preemptive than if it was mine. But you know, a yard isn't a bad idea, not for sure they'd have one, but they might. Of course as regularly as it does it, or rather doesn't, it might be a while before I know for sure. Ah well, such is life.

**Poolman** · 01-21-2018, 07:40 PM

Just for giggles and noodles included, I have thought about this a bit, and the deal with the resistor in the ignition harness. If the resistor reads into the DME and then reports misfires because of readings from the ground wire, why not add some effect of ground wire readings. I installed wiring into the car today, to add 2 other ground spots, beside the one we already have. Just noodleing mind ya, but will see if this makes any diif in the problem with cold starts.

**Poolman** · 02-04-2018, 04:00 PM

Well after a week or more with the added wiring , which was noodled about, have found each start up when cold has been a pleasure with no notable rough starts. I'm running an M56 cover on my 525 so that is a different beast somewhat, but still the same for the wiring trick,,has worked great so far.

https://photos.google.com/share/AF1QipNoFs4eApgkLappkj0JpYqdlMeSLAjg2N93WqFvkAu6UN X7uUjXUptwLIwbyUCT7g?key=bTFtcUNoLWo3YTNhZ0wxRWdfV XVTNEVWSk5pNUxR

The white wire is grounded on the normal terminal and then leads off to 2 other, so the ground is located on 3 different areas now

**geargrinder** · 02-04-2018, 05:19 PM

Poolman, great findings, hope it lasts. If it holds up, the better fix would be to just properly rewire that ground to a single clean location... I'm betting you didn't need your 'extra locations' (unless there was contamination on that nut etc. preventing it from being as good as the others), but I understand your 'what the hell lets triple-down' impulse.

**Mike WW** · 02-04-2018, 09:27 PM

It would be great if it's just a bad ground. I haven't done anything to mine and it hasn't acted up since I started the thread. But I know it's lurking...

**Poolman** · 02-04-2018, 11:19 PM

Don't know if it will last as well as it seems, but there hasn't been a misfire t=since this was done, and every morning when she's cranked cold, just fires up nice and stable and takes on off. That resistor deal made me think more about what the DME is reading and checking for. May have just been a contaminated ground, but you wouldn't think of that, without knowing what the obc is looking for. Hope it stays stable. Liking this M56 valve cover and the added piece that I devised also. Oil usage is way down now.

**geargrinder** · 02-05-2018, 09:04 AM

Originally Posted by Poolman

That resistor deal made me think more about what the DME is reading and checking for. May have just been a contaminated ground, but you wouldn't think of that, without knowing what the obc is looking for.

Well said. A lot of the time reading the factory docs, if you're a seasoned/experienced wrench, doesn't learn you too much... But with the electronic related stuff ,sometimes there's a hidden nugget there.

Like you say, normally you'd think "car otherwise runs great, ground looks fine, ground tests fine w/ multi-meter"... but the DME is basically measuring oscilloscope-level signals off it, so, indeed it needs a really good consistent ground...

**Poolman** · 02-05-2018, 09:38 AM

- - - Updated - - -

Thought about a pic that I had seen about a year or so ago. This is from an M54 engine , thinking it's a 2005 model. Note the grounding on the ignition. Seems like BMW thought a little longer and harder about this problem also.

http://cdn4.pelicanparts.com/techart...mall/pic07.jpg

I would like to know if there is an shunt resistor inside the ignition wiring case, as is in the ones we use. How about all that.

**geargrinder** · 02-05-2018, 11:13 AM

From what I can tell from perusing WDS, for later motors they abandoned the shunt resistor, and those lines are directly grounded vs going through the resistor.

**Poolman** · 02-05-2018, 01:06 PM

Wonder if BMW knew there was a problem and the later was the fix, but hesitated to let anyone else know? They wouldn't do something like that would they?

**geargrinder** · 02-05-2018, 02:20 PM

Naw. I don't know if I'd say "there was a problem". Only about a billion of these cars running around and seems like its not that common an issue (yet... with age, very well may be...) I bet the change was more of a long term engineering simplification, they must have found they could adequately monitor the coils without the shunt. Hell maybe even was a cost containment move. Its still relatively obscure and unknown, I think it only happens to cars now that they are really old, so as far as BMW is concerned, wasn't a problem when the cars were in 'current model' status, the cars are just at "end of life" now. If it'd been a problem, they'd have had a TSB on it or at least we'd all know/have-heard of it way way more often.