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BMW N3 - GDI/NA misfire when cold
BMW N3 - GDI/NA misfire when cold
This is a really interesting one, N53 Engine, misfires on 3+5 when cold, sometimes 1 as well.
When it misfires all the ECU signals are there, spark primary on 2(good) vs 3 (bad) are normal and identical, current signature of (piezo) injectors is same on both.
Cam/Crank timing is good. Borescope in the cyl 2+3 shows some intake carbon build up but not (apparently) a huge amount. Some oil that looks like a valve stem leak seen in 3 but don't think that is the problem, plugs are not oily.
In-cylinder crank on 2 vs 3 identical. 6.7bar and 7.4bar respectively
In-cylinder idle on 2 vs 3 10.8bar and 10.6bar respectively - only difference is Cyl 2 (good) EVO is -35 BBDC and Cyl 3 is -28 BBDC
As there are what appears to be a lot of new parts - and a lot of fakes on the market, I swapped 2<>3 Coils, plugs and injectors - no change.
Went into the intake with a pulse sensor (pulled the MAP sensor out - N/A engine). Found an anomaly - huge pressure spike on the intake.... But it is bigger/smaller/none existent and even when it is not there the misfire is the same.
Along with the in-cylinder pressure waveform of Cyl 3 I put 2 overlays on it one synced to cyl 1 (on left) and one synced to the compression humps in Cyl 3 (on right)
Intake spikes in green - again note no difference when it is not there.. except about 1 bar compression drop on the cyl 3 pressure waveform.
On the overlay on the RHS you can see the intake pressure rises just about when Cyl 5's (also dead) intake valve opens - thinking maybe if it's exhaust valve didn't open then there would be exhaust gas pressure blown into the intake and then cyl 3 would be breathing the unburnt fuel - note the pressure intake pressure decay when cyl 3 intake opens .. however also note no difference in the pressure waveform for 3 when that spike is not there..
The misfire "goes" when the engine is warm - my theory on that is at idle when warm it is in stratified mode so the intake is open to the atmosphere.
Also when revving the engine the misfire is not noticeable but is there, also in-cyl 3 goes over 16 bar in compression.
Attached idle, rev, idle
Think I'm justified in getting the lid taken off for look, but I'm also trying to figure out what is going on !
When it misfires all the ECU signals are there, spark primary on 2(good) vs 3 (bad) are normal and identical, current signature of (piezo) injectors is same on both.
Cam/Crank timing is good. Borescope in the cyl 2+3 shows some intake carbon build up but not (apparently) a huge amount. Some oil that looks like a valve stem leak seen in 3 but don't think that is the problem, plugs are not oily.
In-cylinder crank on 2 vs 3 identical. 6.7bar and 7.4bar respectively
In-cylinder idle on 2 vs 3 10.8bar and 10.6bar respectively - only difference is Cyl 2 (good) EVO is -35 BBDC and Cyl 3 is -28 BBDC
As there are what appears to be a lot of new parts - and a lot of fakes on the market, I swapped 2<>3 Coils, plugs and injectors - no change.
Went into the intake with a pulse sensor (pulled the MAP sensor out - N/A engine). Found an anomaly - huge pressure spike on the intake.... But it is bigger/smaller/none existent and even when it is not there the misfire is the same.
On the overlay on the RHS you can see the intake pressure rises just about when Cyl 5's (also dead) intake valve opens - thinking maybe if it's exhaust valve didn't open then there would be exhaust gas pressure blown into the intake and then cyl 3 would be breathing the unburnt fuel - note the pressure intake pressure decay when cyl 3 intake opens .. however also note no difference in the pressure waveform for 3 when that spike is not there..
The misfire "goes" when the engine is warm - my theory on that is at idle when warm it is in stratified mode so the intake is open to the atmosphere.
Also when revving the engine the misfire is not noticeable but is there, also in-cyl 3 goes over 16 bar in compression.
Attached idle, rev, idle
Think I'm justified in getting the lid taken off for look, but I'm also trying to figure out what is going on !
- Attachments
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- 20231110-0002 BMW synch 1 ckp incyl 3 puls intake revs long 50v web.psdata
- (18.3 MiB) Downloaded 75 times
Re: BMW N3 - GDI/NA misfire when cold
I always begin with disabling the fuel system or unplugging the COPs, except for COP cylinder 1
On one channel, connect your amp clamp on the starter feed, to compare each cylinder's compression strokes
On another channel, put a pulse sensor in the intake, to compare each cylinder's intake pulses while cranking.
On another channel, put a pulse sensor in the tailpipe, to compare each cylinder's pressure pulses while cranking.
On another channel, scope the COP cylinder 1 trigger to use as a sync.
On one channel, connect your amp clamp on the starter feed, to compare each cylinder's compression strokes
On another channel, put a pulse sensor in the intake, to compare each cylinder's intake pulses while cranking.
On another channel, put a pulse sensor in the tailpipe, to compare each cylinder's pressure pulses while cranking.
On another channel, scope the COP cylinder 1 trigger to use as a sync.
Re: BMW N3 - GDI/NA misfire when cold
Thanks, I like the plan for a one shot, think I'll use that next time I come to the it's mechanical conclusion.
I focused on the faulty cylinder(s), eliminated bad new/old parts, eliminated ECU control, and then went in for in-cylinder, though I did do an RC first (all even).
I actually now have an idea of what might be the issue- and it does not show up in cranking !
I focused on the faulty cylinder(s), eliminated bad new/old parts, eliminated ECU control, and then went in for in-cylinder, though I did do an RC first (all even).
I actually now have an idea of what might be the issue- and it does not show up in cranking !
Re: BMW N3 - GDI/NA misfire when cold
And what do you think the issues is?
Re: BMW N3 - GDI/NA misfire when cold
I think Cyl 2's intake valve is leaking on the power stroke spiking the intake with exhaust gas, right at the time Cyl 3 opens it's intake valve. See the overlay pic above.
When Cyl 3 misfires it has spark, fuel and compression and all at the right time. That leaves a) measuring error or b) bad air.
Cyl 5 is also on it's intake stroke though alternatively that may have an introduced issue (injector replacement) as that originally was a more intermittent issue. One problem at a time!
So next visit I will look at the intake spikes shown above and disable #2 and see if they go and if #3/#5 stop misfiring.
When Cyl 3 misfires it has spark, fuel and compression and all at the right time. That leaves a) measuring error or b) bad air.
Cyl 5 is also on it's intake stroke though alternatively that may have an introduced issue (injector replacement) as that originally was a more intermittent issue. One problem at a time!
So next visit I will look at the intake spikes shown above and disable #2 and see if they go and if #3/#5 stop misfiring.
Re: BMW N3 - GDI/NA misfire when cold
I had this 2014 Chevrolet Impala 3.6L, crank no start, and the low compression cylinders were caused by carbon on the intake valves. Unfortunately, I didn't have my pulse sensor in the intake.
After the shop removed the front valve cover and the intake manifold, I did the cylinder leakage test and the air was blowing thru the intake port.
After the shop cleaned the carbon off of the intake valves, the engine started and ran well.
After the shop removed the front valve cover and the intake manifold, I did the cylinder leakage test and the air was blowing thru the intake port.
After the shop cleaned the carbon off of the intake valves, the engine started and ran well.
- Attachments
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- CH A COP 4 secondary, CH B WPS in cyl 4, CH C even COP amps, inverted.psdata
- CH A COP 4 secondary, CH B WPS500 in cyl 4, CH C is the even COP fuse amps, CH D starter amps
- (11.82 MiB) Downloaded 69 times
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- CH A COP4 secondary, CH B WPS500 in cyl 4, CH C the even COP fuse amps, CH D starter amps