[m1bjr]

Hello guys,

I have a persistant issue with the N54 I cannot diagnose (so far).

After a hard drive I park up and leave the car, say overnight in the garage.

In the morning I fire her up and the idle RPM rises above the expected for a cold engine on an enrichment cycle - maybe 2k rpm or more.
After about three seconds the engine rpm drops as it runs rough and sputters badly.
There is noticable black smoke from the exhausts and a smell of unburned fuel.
This lasts a few seconds at most, eventually clears itself without any intervention on my part and then idles and runs absolutely without issue for the rest of the day.
There are no error codes at all logged. I get no limp modes or emissions errors on the dash - possibly as its cold and not on the lambda yet.

If I baby the car, and THEN park her up for the night, even nice and hot from a freeway cruise, it starts totally normally next day.
No long cranks ever, even with a cold engine.

So something is upset by a hard drive followed by shutdown.

Datalogging the HPFP rail pressure reveals a healthy pump with quick pressure rises on shifts and stable, and good, pressure.

Initial thoughts have to be a leaky fuel injector.
But WHY does the probelm only present in this way, and not during WOT or cruise?

Any ideas of the underlying cause guys, or best diagnosis route before shipping the injectors to a specialist?

I run a JB4 with latest firmware, a cooler and exhaust otherwise now stock.

[xbox_fan]

Have the exact same issue, though for me it seems related to running meth, I thought it might be meth puddling up in the fmic causing this after shut down...

Havent had this issue so far when off meth.

[m1bjr]

Hi and thanks for the info.

Perhaps its fuel building in the cylinder(s) in my case too.

Keep us posted.

[xbox_fan]

Originally Posted by m1bjr

Hi and thanks for the info.

Perhaps its fuel building in the cylinder(s) in my case too.

Keep us posted.

Maybe if you have a leaking injector, but that seems unlikely, are you running meth?

If not then maybe this is a injector dying issue or because of carbon build up.

I am not certain it is due to meth i see this issue, but it seems related so far.

[m1bjr]

I dont have meth injection, just JB4 now.

[Vorsprung_CJB]

Might not be possible if you park outside, but after a hard drive trying opening the hood for a bit after you stop to allow for better cool down. Reminds me of an issue I had with my old P928 where fuel would vaporize in the lines when it was parked and too hot under the hood.

[Chad McCan]

I have this same problem, right now. My dealer is replacing the low pressure fuel sensor, out of warranty, $400. They replaced injectors last year, I just put new plugs in. I got a new fuel pump two months ago.

One SA has a theory of waste gate trouble, but my SA has discounted that completely. I'll keep updating this thread as I get more info.

[m1bjr]

Originally Posted by Chad McCan

I have this same problem, right now. My dealer is replacing the low pressure fuel sensor, out of warranty, $400. They replaced injectors last year, I just put new plugs in. I got a new fuel pump two months ago.

One SA has a theory of waste gate trouble, but my SA has discounted that completely. I'll keep updating this thread as I get more info.

Thanks this is great intel.

I am confused by the way the car starts clean and easily, then turns rich.
If the injectors had leaked fuel I would expect it to be rough immediately.

It's only apparent after a hard drive, every time..... strange.
Please call back to the thread, I found a couple others with this problem too.

Have you tried disabling any tunes you might have, and then seeing what happens?

[Chad McCan]

My JB4 hasn't been in my car for 6 months. I got worried it was causing problems and removed it.

Before I took it in this time, I pulled the codes with INPA. I got a 29F3 and a 29CF, which is why they are replacing the sensor.

My misfires happened all the time, between 2-3k rpm, warm or cold. Way worse when the car was cold.

I'll be super shocked if this solves the problem. My car does have 92k miles on it and has had several fuel pumps.

[chuckd05]

pull all your plugs, look for any that are black....


you could have a bad injector or a bad coil... if you throw any misfire codes , check that cylinder... if the plug is good, move the coil to another cylinder, if misfire follows it change that coil...

my guess is that you have a bad injector... look for a fouled plug that is very black compared to the others


For the poster who just said they are changing the low pressure sensor, I just had my HPFP replaced and on the work order, they listed a series of tests they did before and after replacement which went over low and high fuel pressures and sensors... Those sensors are not that hard to change.. look around at DIY threads.. they are rather cheap too, If i changed all my plugs and pump and still had the problem I would def do the high and low pressure sensors next, but do them yourself... they are easily accessible.

[Chad McCan]

Too late. I couldn't find a DIY on the low pressure sensor. I do most of my own work, but with no clue on how easy the sensor was to get to, I had them do it.

I got my car back yesterday morning and this morning it's throwing codes already. I'll pull them when I get home. Low pressure sensor did not help.

The move the coil trick doesn't work if you have multiple cylinder misfires.

[m1bjr]

Okay, went and gave the car a beating and put it to bed for the night.
Before starting, pulled all the plugs this morning to see which injectors are leaking.

None. That is a surprise.

All plugs in first class condition, and no loose fuel in any chamber.
As far as I can see the tops of the pistons are in good shape to, no carbon at 80k miles.

Whilst the covers were off I pulled the manifold suction pressure sensor too.

WOW. This thing was caked in oil gunk and carbonised dirt.
It got a good clean with carb cleaner before refitting.
I should have checked the one on the charge pipe but didnt think about it.

However, the engine fired up perfectly - it would NEVER do this after a beating the previous day.
And the power delivery is much smoother, no slight surge/hiccup which was common at low rpm and big throttles.

I wonder If this is coincidence, or there is a real relationship beween these messy starts and a gunked up sensor(s)?
Of course the intake manifold was also pretty dirty inside, no doubt the valves are in a mess too.
It does stand to reason that after some hard running there is likely a lot more oil vapour about in the inlet.
Perhaps I have other issues with the PCV system to investigate too.

Let me know if cleaning the Pressure Sensors made any difference to you....

[A418t81]

My old 335 did the same thing you are describing. Only a cold starts, it would crank up fine and after 3 or 4 seconds the idle speed would drop and it would idle extremely roughly for a little bit until I rev'd it and "cleaned it out" a little. I had a weird map sensor code that wouldn't go away that the dealership thought was unrelated (wouldn't replace, I thought it was total BS.) It appears the map sensor was the issue after all based on your experiences.

[Chad McCan]

I just replaced the coil pack on cylinder 3. That didn't help my problem either. I'm still searching for a solution. I'm considering putting the JB4 back in and doing some data logging to see if that helps anyone diagnose this problem. I'm at the point where throwing parts at it is getting old.

[Chad McCan]

Originally Posted by A418t81

My old 335 did the same thing you are describing. Only a cold starts, it would crank up fine and after 3 or 4 seconds the idle speed would drop and it would idle extremely roughly for a little bit until I rev'd it and "cleaned it out" a little. I had a weird map sensor code that wouldn't go away that the dealership thought was unrelated (wouldn't replace, I thought it was total BS.) It appears the map sensor was the issue after all based on your experiences.

Any idea where the MAP sensor(s) is/are? Can I clean them? How?

[chuckd05]

Repost. Sorry.

[chuckd05]

One sensor on the charge pipe other is on the intake manifold I believe.

[Chad McCan]

I replaced my injector on cylinder 3 this morning. Problem solved. No more misfires. Acceleration doesn't feel buttery smooth yet, but I have a feeling I could clean that up with a carbon cleaning.

[mobilefitt]

How did you know to change injector 3? I have had this problem for a while, just figured I will have to live with it. Didn 't you say when you checked plugs that they were all clean( no fuel on them).

[Chad McCan]

Drive it like you stole it, the first 5 minutes in the morning. It will throw a code. Don't let it warm up, mine will only code when it's cold. Runs like CRAP.

[Chad McCan]

I wanted to update this post:

I got my carbon cleaning done yesterday. During the carbon cleaning, they found two bolts had backed out, in the back of the intake. The intake had actually pulled away from the head. I'm left wondering how much the carbon cleaning helped, but needless to say, I'm happier with the way my car is running.