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E46 M3 (2001-2006) Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006.


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Old Sun, Jan-13-2019, 04:45:20 PM   #1
jtt777
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Default Major engine issue - misfire / compression issues - Advice please...

My mechanic and I are now in the midst of diagnosis of an issue with my motor. Here are the details...

+ 2004 E46 M3 with approx 55 kmiles
+ Stock engine wise, excellent maintenance history, no prior mechanical issue
+ Car has been tracked 3-5 events per year for the last 6+ years. Oil analysis has always been done, never indicated any issues. Car is only occassional driven on the street outside of this.

During my last track event, while powering out of a turn (no over rev likely), i noticed a reduction in power and an SES light come on (yellow one). I brought the car back in and it was idling very rough. Checked the codes and I had misfires on all cylinders. I cleared codes and restarted and it had a tough time starting but also still getting misfires. It starts as a misfire on a cylinder or two and then propagates. There are no other codes thrown.

Tried looking at all the coil packs and they are all fine.

Next started doing a compression test and see cylinders 1,3,4,5 are very close to each other. Cylinder 6 has ZERO compression. Cylinder 2 has 30% of the compression of the good ones.

Boroscoped Cyl 6 and it appears the piston is moving up and down just fine. From the boroscope you could not see any suggestion that something really bad happened inside the combustion area. Looks pretty normal, some rough areas might be seenon Cyl 2 edges but it could also just be carbon. Quick, leakdown test on Cyl 6 showed air going out the exhaust side we think.

We are now going to pull the head and see what is going on, seems the best step for further diagnosis. We are thinking somehow we have a bent valve. Is there anyway this could be a timing issue making it appear to have no compression? I am just puzzled it is only 2 cyl. I did notice the engine ticking a bit louder prior to the issue but just thought I needed a valve adjustment soon.

There is nothing abnormal looking at the valve deck. It appears all rockers, cams, keepers, springs, retaining clips, etc are in tact. I also didn't get any smoke or mixed fluids to suggest a head gasket issue.

Does anyone have any experience with such a situation? Appreciate any comments that might be helpful for diagnosis and fixing.
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Old Sun, Jan-13-2019, 05:47:41 PM   #2
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Default Re: Major engine issue - misfire / compression issues - Advice please...

Piston ring issues are rare on factory motors. Bent valves are not uncommon. A broken valve spring is a possibility but that’s a common S65 issue.

A faulty crankshaft sensor can cause weird issues but that wouldn’t explain no compression on 6 and low compression on 2.


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Old Sun, Jan-13-2019, 06:11:10 PM   #3
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Default Re: Major engine issue - misfire / compression issues - Advice please...

And seems unlikely to have two broken springs that I can't notice from the top end....

Can a weird Vanos Failure make these symptoms by throwing off timing so that you see compression issues?
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Old Sun, Jan-13-2019, 06:14:45 PM   #4
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Default Re: Major engine issue - misfire / compression issues - Advice please...

I can think of a couple of things...

1. Both of your exhaust hub tabs are broken

2. Chain sprocket bolts sheared

3. Bad cam position sensor(s). No camshaft sensor faults? Cam sensors can create issues.


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Old Sun, Jan-13-2019, 06:26:15 PM   #5
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Default Re: Major engine issue - misfire / compression issues - Advice please...

Can you retest 6 by itself on a rested battery and a cooled off starter?

Cyls fire in pairs and are on same strokes 15 36 24.

Could be a burnt valve. I wonder if you rev the engine if it smoothes out, when vanos goes, cams get stuck in one timing position which is more optimal for low rpm vs high or vice versa. Check your solenoid or tabs.

Any other codes outside of misfires? Cam sensors?

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All DIY: VANOS, WPC rod bearings, full SS (SS stepped V1 headers, catted S1, stock S2, SS sport), AFD E85 Proflex kit, Ohlins R&T/Hyperco 375f Swift 672r/GC street tops and camber plates, 330 ZHP steering rack, diffsonline 4.1 diff with rem polish, E60 short shifter lever, AKG black diff bushings/subframe bushings, Rogue rtab, Sachs clutch/flywheel, rear main, Beyer driveshaft, valve adjustment, cooling refresh.

Happy to help with VANOS or any other DIY job around NorCal. Have various specialty tools (VANOS, RTAB, engine bar, valve adjustment, tranny jack, ball joint separator, pilot bearing puller, tap&die kit, etc).
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Old Sun, Jan-13-2019, 08:19:33 PM   #6
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Default Re: Major engine issue - misfire / compression issues - Advice please...

Thanks for the input. Looking at the tabs, It doesn't seem that they are broken. I would have thought it would be obvious based on other pics I have seen.

For #3 .... no cam sensor faults detected.

I guess I can only check 2 after things start to get disassembled.

Quote:
Originally Posted by bigjae1976 View Post
I can think of a couple of things...

1. Both of your exhaust hub tabs are broken

2. Chain sprocket bolts sheared

3. Bad cam position sensor(s). No camshaft sensor faults? Cam sensors can create issues.


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Old Sun, Jan-13-2019, 08:22:57 PM   #7
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Default Re: Major engine issue - misfire / compression issues - Advice please...

Thanks for the ideas. Def 6 was tested with the starter cool and the battery nicely charged up. The car has actually been sitting for a while.

What could cause burnt valves? It doesn't get totally better when reved. It just sounded ugly enough I wasnot going to push it.

I can check tabs but how do I check solenoids without dissassmbly?

Any one ever seen vanos isssues give these compression concerns?

Quote:
Originally Posted by mrgizmo04 View Post
Can you retest 6 by itself on a rested battery and a cooled off starter?

Cyls fire in pairs and are on same strokes 15 36 24.

Could be a burnt valve. I wonder if you rev the engine if it smoothes out, when vanos goes, cams get stuck in one timing position which is more optimal for low rpm vs high or vice versa. Check your solenoid or tabs.

Any other codes outside of misfires? Cam sensors?

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Old Sun, Jan-13-2019, 09:45:13 PM   #8
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Default Re: Major engine issue - misfire / compression issues - Advice please...

If you're confident in the compression test, it sounds like she needs to come apart.
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Old Sun, Jan-13-2019, 11:51:10 PM   #9
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Default Re: Major engine issue - misfire / compression issues - Advice please...

The valve could be burnt. Mainly a issue on FI engines but I saw it a lot when I use to build NASCAR motors which are NA motors


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Old Mon, Jan-14-2019, 01:09:21 AM   #10
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Default Re: Major engine issue - misfire / compression issues - Advice please...

Do a leak down test. It will tell you where you are leaking from. I had a similar issue on my e36 and it was ultimately a brokenintake valve spring. I ended pulling the head and spending lots on a head refurb. If I would have know before pulling the head I would have replaced the spring from the top without pulling everything apart.
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Discussing Major engine issue - misfire / compression issues - Advice please... in the E46 M3 (2001-2006) Forum - Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006. at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)