Rolls-Royce Phantom 2006 N73 Misfires
Well, it’s rolled back in the door.
Got a BMW-era Rolls-Royce Phantom, with permanent misfires on both banks.
Vehicle details as follows:
Make/Model: Rolls Royce/Phantom
Engine: 6.8 L
Engine Code: N73 B68A
Thought this job would have been a breeze too :S
Stuff checked to date:
- sparks plugs renewed
- coil packs renewed
- cylinder compressions okay
- confirmed power/ground to all coil packs
- checked intake for leaks (none)
- reset engine adaptations
- reset valve tronic limits
- capped off tank ventilation at manifold
- checked gdi injector coil resistances (all same)
- checked current of all injectors (all same - via scope)
- swapped injector modules from bank to bank (doesn‘t follow)
Only DTCs that continue to set on ECM 1&2 relate to misfires on multiple cylinders (6 and 12 reoccur over short term; 123 occur over longer term).
I’m thinking maybe GDI injectors themselves but want a firm diagnosis in place before digging them out (plus need special tool). I am also suspicious of the valvetronic system. I’ve been trying to set valvetronic to max lift while running to rule out, but can’t see where to do this in ISTA - maybe someone can help here. Also no faults stored relating to the variable valve adjustment system.
It should be noted that this vehicle had both low and terrible oil quality when we first saw it for servicing a while ago (service history unknown but suspected to be very poor).
If someone with experience of this N73 BMW engine can help out and chime in here. I’m tearing my hair out.
Many thanks guys and look forward to your replies.
Have you checked intake valves for carbon build up?? This is direct injection engine and they build up bad and cause random multiple misfires
I forgot to mention, I did some in-cylinder WPSing and didn’t see much of note (I’m new to pressure analysis though and may have missed something. I shall be sure to revisit...get a bore scope in or something?
Try and pull and throttle body off and throw a borescope in and check out the valves
Also how did the plugs look coming out? Any wet with fuel?
I’m trying to recall...initial checks on HT were complete months ago at a service before it came back in last week. I think they were wet - will double check tomorrow. Also, are cylinders 1&7 on banks 1&2 closest to the driver/rear or the engine? I‘m sure this is how BMW designate...?
Bank 1 is the left side when looking into engine bay from crank pulley side. Cyl 1 is front cyl of bank 1 and cyl 7 is front of right bank. Bank 1 is cyls 1-6 front to back and bank 2 7-12
You can see any leaking injectors in the coil primary voltage burn times or in the secondary burn times. If you have a 4 channel scope, scope 4 spark plugs at the same time. If the misfires occur only under load, do a steady 1500 rpm brake torque.
The scope will be coming back out. Thanks.
Check fuel quality....water.
As in, possibility of water in fuel? That’s okay, but can’t imagine customer is using premium fuel...which won’t be ideal long term...
Injectors is a possiblitiy, but may want to pull the vent tubes off the hpfp and look for fuel seepage. There should be 0 fuel in that hose. fuel seepage is indication of failing pump. You can also start let run shortly for misfire, pull plugs and check for signs of failing injectors (fouling plugs, wet plugs) As someone mentioned, looking at ignition primary voltage (pin 1 of coils) may show…
I would definitely say injector leak test is a good plan. You can watch your rail pressure after engine shutdown. Or you can backprobe the rail sensor. It should rise due to heat soak somewhat after shutting off the engine. Then, the pressure should decrease slowly. Alternatively, you could disconnect all the injectors, crank the engine for a bit, then pull the plugs to see if there's any fuel…
This totally a different vehicle but the same trouble was misfire on 4,6,7,and8 4 is on bank 1 and 6,7,and8 on bank 2. Changed plugs, coils even ran new driver wires. Turned out to be the pcm drivers were corrupted and the pcm needed replaced on 2005 Ford F150 5.4L to find the coils going all over the place on lab scope only while driving down the road is when it showed up the worst. Hope this…
Preparing for some in-cylinder analysis - in cylinders 1/6/7/12 (1 & 7 are my known-goods). With valvetronic & vanos...do these need to be disabled before capturing cranking cylinder pressures (with intake capped)?
If your in cylinder testing is going to be at idle, just disable Vanos. Actually I would leave everything alone at first to baseline your captures. Then if anything, you could disable Vanos.
When performing in cylinder captures on these bmw's just leave all connected and "active" , you want to try and catch anything abnormal while in its regular operating state. But before going in cylinder , I would strongly suggest performing crank no start capture of the intake pulses and exhaust pulses, and sync it to and ignition. This will give you great insight of the engines "breathing" and…
This is gold. Thanks very much. Updates to follow once I’ve done both banks.
Hi again, Now completed "crank no start" captures of: BANK 1 & 2 - ChA: Cylinder1 pressure (sync) - ChB: Intake pulse - ChC: Exhaust pulse *See attached. Obvious difference: Unevenness between each cylinder on the intake pulse on BANK1. Is this enough to confirm the carbon-contaminated intake vale theory, or at the very least stripping to check visually? Perhaps we are dealing with a…
In the first Bank 1 PSD file, the WPS in cyl 1 shows pressure drops at the EVC/IVO, but in the second Bank 2 PSD file, the pressure drops are not there?
Yes , id say right there is definitely enough actual physical visual "evidence" that the breathing ability is not the same from bank to bank , and being the fact that the plenum is split bank to bank its like having two engine breathing captures and knowing they should look the same but pulling up two different waveforms. The amount of "pull" doesn't reach as deep and not consistent, in…