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Discussion Starter #21
So another update today. I did both compression and leakage tests - car appears to be very healthy, mechanically. I tried to do it dead cold (when the misfiring occurs) - I could feel it when I pulled it into the shop but it wasn't dead missing like it does sometimes. It had sat in 29F outside for 4 hours before I did the test (was driven to operating temp before that - lunch run), but the needle was still on blue when I shut it off to do the tests.

CylinderCompresion (psi)Leakage (%)
11795
21807.5
31796
41786
51755
61736

I did not have the car hooked up to a battery charger - I believe the declining compression was the battery getting tired - even if it's not, they're all within 7psi of each other and leakage is near perfect.

When I said earlier I had ruled out plug or coil (switched them to different cylinders and fault for cyl 6 still came back) I had mentioned that I had all the fuel injectors cleaned, leak tested, and flow balanced - so I was ruling them out. To be on the safe side, tonight I switched cyl 6 fuel injector with cyl 2 and when I get a misfire code again I'll see if it follows. I also replaced my secondary air valve vacuum line to the solenoid - it was brittle, but had no effect on my rough cold start after I put everything back together tonight.

I drove home 40 minutes with no check engine light and the car ran buttery smooth besides the first 20 seconds on cold start. I checked for stored codes and bank 1+2 lean air mixture codes were pending, but not confirmed.

I've been watching both banks STFT live while I drive and Bank 1 definitely is way more out of whack than bank 2. Bank 1 will get up to the low 20's at idle, Bank 2 is usually between 6-12. I'm not sure the criteria to set the code for lean mixtures. I spent 20 minutes on the highway at 60mph steady throttle trying to get the catalyst and O2 readiness tests to set but they did not - not sure if that had something to do with the pending codes. I was hoping to get them to set before I get an actual code stored so I could get through emissions and renew my license plates (expired this month and requires testing).

I guess I'll go ahead and change the valve cover and both pre-cat O2 sensors next. Now that it looks like the motor is healthy, I don't mind spending money on the car. I have a backpressure gauge that I can thread into the precat O2 bung to test to see if the cats are clogged - I don't think that's it because I would imagine I'd have more symptoms than just cold start.

Any thoughts are appreciated. I suppose it's really all moot until I solve that smoke test failure of the valve cover. Still just erks me that it's leaking in that area but only cylinder 6 has a hard misfire at times.

If anyone knows the DME's criteria to set the lean air mixture faults for a bank, let me know - I'm curious if I can do the throttle dance and still get readiness tests to set to get my sticker if the next steps don't solve the problem.
 

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Discussion Starter #23
Quick update: replaced both pre-cat O2 sensors, no change in symptoms. I'll be changing the valve cover and gasket tomorrow and I'll report back with a new cold start OBD Fusion log afterward.

Food for thought - I've been googling my arse off for similar symptoms with little/no vacuum leaks (I still don't think the tiny bit of smoke from the spark plug well o-ring is causing this), I came across a gent who said it he had the same symptoms caused by a secondary air system issue. In his case, the electric vacuum valve was lazy and wouldn't close the secondary air valve right away like it's supposed to. With the valve slightly open (or closing slowly), air sucked in after the SAP was shut off caused lean mixtures and rough cold starts that would go away shortly after driving.

He ended up changing the vacuum valve and seafoaming through the SAP valve hose (cleans the SAP exhaust valve ports) and it fixed his rough cold starts.

If the valve cover doesn't resolve this, I'm going to look into this direction. The SAP works for 90 seconds or engine temp of 100F (whichever comes first) - that would explain why my rough cold starts have seemed much harsher/longer now, than they did in the summer..
 

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Discussion Starter #24
Changed the valve cover (with new gaskets and bolt grommets), no difference - in fact if felt worse but it's never consistent. I actually popped another cylinder 6 misfire code. Then it both banks went lean and it threw the lean air mixture codes. Then random cylinder misfires after that, and also had a purge control solenoid fault (which is brand new).

So I plugged up the air line from the fuel tank vent valve (purge control valve) that goes to the intake and no change - mixtures still going lean.

Tomorrow after work I'm going to smoke the intake for the millionth time. I'll also individually smoke the brake booster, SAP system, and purge control system. I'm at my wits end.

The cylinder 6 thing kills me - I've swapped coils, plugs, and injectors and it stays on 6. I've done compression and leakage tests and they turn out great. I've tested fuel pressure and it's perfect. I just can't figure out what would make JUST cylinder 6 chug so hard on start up to cause cylinder deactivation before any other cylinders do it.

My only other thought is timing - but I would assume that if I had a bad camshaft sensor, it would through a code, or if I had a timing chain tensioner that was slow to fill with oil, it would give me camshaft timing faults, or if I had a stretched timing chain, or one that was off even slightly, the car wouldn't run so damn good after it's warmed up.
 

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Discussion Starter #25
Here is a log of cold start this morning. It's actually my entire trip in to work (sorry, forgot to disconnect OBD Fusion to cut log off).


For some reason, cyl 6 did not misfire hard this morning - could still feel the car running roughly but not the rythmic chugging of cyl 6 like yesterday's cold start. In fact, I drove all the way to work without setting an SES but was watching STFT and LTFT and they were headed that way... both LTFT were at +8%+ after my 30 minute drive. As usual, car drove like an absolute dream with smooth idle, power, etc after driving about 1/2 mile from cold start.

My list of things to do after work today:

Smoke test intake (again - if only to verify the new valve cover and gasket do not leak)
Smoke test purge/fuel tank breather line towards intake, and then backwards towards fuel tank
Smoke test the FPR reference vacuum line back to the fuel filter
Smoke test SAP line from valve back to intake
Remove and inspect SAP valve
Possibly seafom the SAP system

I paid $1200 for this car with this problem, so I guess I got what I paid for. It's in EXTREMELY nice condition and being auto/awd, has some value in snowy Chicago where I live. I see these routinely sell for $3500-$5500 depending on mileage/condition so I'm willing to sink some money into it.
 

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Discussion Starter #26
Ok, I guess I'm writing this to go through my own thought processes - perhaps this helps someone else with these issues.

So Thursday night I stayed late at work went through the above tests (except I didn't Seafoam the SAP system).

Intake smoke test led me to a clamp on my CCV bypass kit that must have loosened up since the last smoke test - I tightened it - no more smoke. I also found my oil filler cap was leaking smoke (it wasn't leaking last time either). Perhaps changing the valve cover and gasket that were leaking before exposed the next weakest links. After these two were fixed, no more smoke from the intake.

Purge valve and fuel filter smoke tests passed - no smoke

SAP system smoke test - HOLY COW. So if I apply smoke directly to the SAP valve vacuum hose at the valve, I get a reasonably decent leak at the back of the intake manifold. I don't get ANY smoke there when I smoke test the intake. It's impossible to see back there but if I wiggle the SAP vacuum hose the smoke volume will change. I'm not messing around, so I ordered the electric valve, check valve, and new vacuum hoses and plastic vacuum tubes.

With these leaks remaining, my LTFT climb much slower now. I didn't have a check engine light for 2 days so I checked my readiness monitors and they were all set except EVAP! I rushed it over to emissions with LTFT's being both banks at 9.6 (right before SES will come on), and it passed! I have no doubt the light will come on soon, but at least I can drive it legally on the roads for the next 2 years.

I haven't had a serious cyl 6 misfire since the first start after the valve cover was replaced. I'm not sure if that's because it's about 5-10 degrees warmer here nor not. I'll be attacking the SAP system parts either Monday or Tuesday. I've heard it's a real nightmare to do it blind back there, but I'm not pulling the intake manifold unless I absolutely have to.

A funny side note - when I pulled my SAP valve to check function (it works fine) and carbon buildup (not terrible) I found two very large chunks of hose inside the valve... the hose between the SAP pump and valve is new - the old one must have broken pulling it off and pieces got inside the valve. Not sure what kind of blockage that did, or what symptoms I might have had from it, but WTF people, either do the job right, or don't do it at all :)
 

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Discussion Starter #27
Another minor update. SAP parts came in but I haven't had a chance after work to install them - the SES light came on a day after the car passed emissions, and it's still lean. I had one cold start recently where cyl 6 chugged but it didn't set a code.

There has been a new development! I drove down and back to my brother's place (about an hour each way). Car was feeling strong like it always does and he lives back by some nice curvy country roads so I put the shifter in DS and gave her a good romping. Car performed flawlessly (SES was off at that time, LTFT's were in the 8's). As I was nearing home, it sounded as if the engine tone had changed - deeper or throatier.

I pulled into my driveway, turned off the radio and opened the door while it was idling and gave it a rev - EXHAUST LEAK! It was flapping and grunting from the passenger side right behind the front wheel. I brought it to work the next day and lifted it and found the connection between the end of the header pipes (stock headers with cats) and the mid pipe was leaking. In fact, the studs and nuts were completely corroded and maybe 50% their original size.

I'm off today but either Thursday or Friday I'll bring it in to work and try to get the studs and nuts off without damaging the rear O2's - I have the new gaskets.

I'm really crossing my fingers that between the SAP stuff and this exhaust leak, this will be the end of my journey here. I even have hope that my cyl 6 cold start misfire is caused by the SAP stuff - it was a pretty significant leak, and those nipples are right on the cylinder 6 intake runner. I still have my doubts on this because I'm not 100% certain the air travel in the manifold, and that misifire often seems to be a dead miss, not typical of vacuum leak, but who knows.
 
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