[torrque]

I have the same problem, no error codes. I am suspecting the throttle body, and will swap soon and report back... Subscribing to thread also.

[BMWM.D.]

Originally Posted by torrque

I have the same problem, no error codes. I am suspecting the throttle body, and will swap soon and report back... Subscribing to thread also.

Did you ever swap the throttle body? I’m chasing a similar issue on a customer’s car, and am thinking throttle issue. The engine loses power for a split second, then goes back to normal. No fault codes, and it’s really hard to reproduce. It’s like nothing I’ve ever felt on an N54 before, and I’ve been working on these things since they came out in 2006.

[torrque]

Originally Posted by BMWM.D.

Did you ever swap the throttle body? I’m chasing a similar issue on a customer’s car, and am thinking throttle issue. The engine loses power for a split second, then goes back to normal. No fault codes, and it’s really hard to reproduce. It’s like nothing I’ve ever felt on an N54 before, and I’ve been working on these things since they came out in 2006.

Yes, I did, no change.... bought a new one from Rockauto.com, and didn't make a difference... sent it back. Mine is happening all the time, every few seconds I have the bucking, surging.
I logged some data with my Carly adapter, and it seems that the bucking happens when there is a PWM request from the low pressure pump, followed by a high drop in battery voltage.

EDIT: I suspect my EKPS module, low pressure sensor and/or pump, but I gave up on chasing it as cold hit New England, I don't have a garage and I need the car; took her in to a BMW specialist. Would have taken me another 2 weeks to buy stuff and replace.

Will report back as soon as I hear anything, they should have some results Monday or so...

[BMWM.D.]

Originally Posted by torrque

Yes, I did, no change.... bought a new one from Rockauto.com, and didn't make a difference... sent it back. Mine is happening all the time, every few seconds I have the bucking, surging.
I logged some data with my Carly adapter, and it seems that the bucking happens when there is a PWM request from the low pressure pump, followed by a high drop in battery voltage.

EDIT: I suspect my EKPS module, low pressure sensor and/or pump, but I gave up on chasing it as cold hit New England, I don't have a garage and I need the car; took her in to a BMW specialist. Would have taken me another 2 weeks to buy stuff and replace.

Will report back as soon as I hear anything, they should have some results Monday or so...

Interestingly, this car did have a bad low pressure sensor. I thought maybe that would fix it, but it didn’t. It only seems to happen at light load (below 2500 rpm), but it’s really intermittent on this car. If it was happening all the time like yours, I think I’d be able to track it down.

One thing that crossed my mind was a possible connection issue at the junction box. Most of these cars got the battery cable recall done, but that doesn’t mean there couldn’t be an issue back there. The voltage drop you’re seeing makes me think that’s a possibility. I’ll probably check that next if I’m given the okay to move forward.

[torrque]

Originally Posted by BMWM.D.

Interestingly, this car did have a bad low pressure sensor. I thought maybe that would fix it, but it didn’t. It only seems to happen at light load (below 2500 rpm), but it’s really intermittent on this car. If it was happening all the time like yours, I think I’d be able to track it down.

One thing that crossed my mind was a possible connection issue at the junction box. Most of these cars got the battery cable recall done, but that doesn’t mean there couldn’t be an issue back there. The voltage drop you’re seeing makes me think that’s a possibility. I’ll probably check that next if I’m given the okay to move forward.

I thought about that too, and opened up the junction box completely, took it out. All connectors were clean, no sign of spark or heating of any components or fuses. Junction box electronics with connectors was very clean. Somebody has been there before though, as there was a screw missing from the JB....

It doesn't mean yours does not have the problem, worth checking.

[BMWM.D.]

Originally Posted by torrque

I thought about that too, and opened up the junction box completely, took it out. All connectors were clean, no sign of spark or heating of any components or fuses. Junction box electronics with connectors was very clean. Somebody has been there before though, as there was a screw missing from the JB....

It doesn't mean yours does not have the problem, worth checking.

So the big B+ connection on the back was secure? Did you take the black plastic cover off and look at the actual terminal? There’s a 2.5 mm hex screw that secures the cable to the JB.

There’s also the actual crimp joint that’s tucked behind the carpet (where the repair cable is spliced onto the factory battery cable). I’ve seen some botched crimp jobs down there, but unfortunately it’s not possible to see anything unless you remove the heavy duty heat shrink that covers it.

Usually these cars have major issues if there’s a problem with that cable connection, so your EKPS or fuel pump theory could be a good guess. I wouldn’t think the high pressure pump could cause it without setting any faults, but this is a first for me.

[torrque]

Originally Posted by BMWM.D.

So the big B+ connection on the back was secure? Did you take the black plastic cover off and look at the actual terminal? There’s a 2.5 mm hex screw that secures the cable to the JB.

There’s also the actual crimp joint that’s tucked behind the carpet (where the repair cable is spliced onto the factory battery cable). I’ve seen some botched crimp jobs down there, but unfortunately it’s not possible to see anything unless you remove the heavy duty heat shrink that covers it.

Usually these cars have major issues if there’s a problem with that cable connection, so your EKPS or fuel pump theory could be a good guess. I wouldn’t think the high pressure pump could cause it without setting any faults, but this is a first for me.

Yep, removed the plastic cover, it was nice and tight, and very clean... I would think for the amount of current flowing there, if anything is amiss, you will see plastic melt or at least darkening due to overheating.
My problem is definitely electrical, as voltage drops during the event, so something is causing the drop.

I was thinking of the low pressure pump, in the tank, which is the one driven by the EKPS via PWM signals... I see a high request (99%) sent to the pump also every time this jolt happens, but I am not sure if it is the cause or a symptom... The guys at BMW I took the car said when you replace the lpfp you should also replace the EKPS, and that has not been done either.

Also, I looked back to all documentation I was given, and I see battery and alternator replaced, but not the cable; is that also problematic, I understand it has an active component that monitors the battery ?

Many thanks!

[torrque]

I remembered I took some photos, here is the connection

[BMWM.D.]

Originally Posted by torrque

Yep, removed the plastic cover, it was nice and tight, and very clean... I would think for the amount of current flowing there, if anything is amiss, you will see plastic melt or at least darkening due to overheating.
My problem is definitely electrical, as voltage drops during the event, so something is causing the drop.

I was thinking of the low pressure pump, in the tank, which is the one driven by the EKPS via PWM signals... I see a high request (99%) sent to the pump also every time this jolt happens, but I am not sure if it is the cause or a symptom... The guys at BMW I took the car said when you replace the lpfp you should also replace the EKPS, and that has not been done either.

Also, I looked back to all documentation I was given, and I see battery and alternator replaced, but not the cable; is that also problematic, I understand it has an active component that monitors the battery ?

Many thanks!

I was referring to the “battery cable” recall that affected most E90s. We were cutting that B+ cable about 15 CM from the junction box, and splicing in a new repair cable. If you were to remove the kick panel trim cover and pull the carpet over, you’d see a big piece of black heat shrink that’s covering the splice.

I can tell that your car had the recall done, as it has the updated connection with the hex screw. The original cable just had a plastic clip that secured it to the JB. I’ve done probably several hundred of these recalls over the last ~5 years, and I always thought it was a little sketchy that the extra length of cable (the new section added is actually longer) just kind of gets stuffed behind the carpet and could rub/wear on the metal floor over time. I’ve never seen it be an issue myself, but I could see it being one.

That said, I believe there is a fuse built into the battery power distribution box (on top of the battery) that would blow if that cable shorted to ground. But still, I could see there being contact issues in the crimp area if it wasn’t done right.

As far as something that monitors the battery, you’re referring to the IBS. That’s part of the negative cable. And while they do fail a lot, they just tend to cause false battery discharge warnings. The IBS won’t cause the kind of issue you’re having.

What is your voltage dropping to when you catch it in the act?

[torrque]

I attached this pdf, which shows the bucking/surging happening when it's highlighted in red... I ran a separate clock and noted the time minute and second when it happened, and it matched perfectly with what I have in red.

Thanks a lot

[BMWM.D.]

Originally Posted by torrque

I attached this pdf, which shows the bucking/surging happening when it's highlighted in red... I ran a separate clock and noted the time minute and second when it happened, and it matched perfectly with what I have in red.

Thanks a lot

What’s the difference between “battery voltage” and “current battery voltage” ?

Either way, it looks like there is definitely a connection between the voltage drop and the commanded fuel pump %. I’d like the see this same data, but with high and low pressure values as well. It’s hard to say whether a voltage drop is causing the EKPS to bump up the fuel pump duty cycle, or whether a big load to the electrical system from the fuel pump is causing a temporary voltage drop. I think either is possible.

[torrque]

Originally Posted by BMWM.D.

What’s the difference between “battery voltage” and “current battery voltage” ?

Either way, it looks like there is definitely a connection between the voltage drop and the commanded fuel pump %. I’d like the see this same data, but with high and low pressure values as well. It’s hard to say whether a voltage drop is causing the EKPS to bump up the fuel pump duty cycle, or whether a big load to the electrical system from the fuel pump is causing a temporary voltage drop. I think either is possible.

Thanks; I am not really sure what the difference between the 2 voltages is; might be read from different sensors ? It was available in the parameters and I decided to log it just for kicks, but values kind of follows the same pattern.
Yes, from what I noticed it's a PWM request first, and then a voltage drop most of the times.... It's never voltage drop first, and then a PWM request, so I think something is up with the pump request or EKPS. I will try to monitor the high and low pressure.

[torrque]

I just called the shop, and they said they found the problem. It seems to have been the crank angle sensor.... I am really confused, because that was one of the items that was replaced not long ago. I need speak to them more when I get there. They also told me it kind of smokes so turbos can be gone, but car had absolutely no smoke and signs of oil consumption or leaks when I took it in.... I really don't want to be blown turbos.

[BMWM.D.]

I’ve seen plenty of those crank sensors fail, but it’s usually really obvious. Super long crank, DSC warning light, etc. Not saying it’s not possible, but that’s what I’ve always seen.

[torrque]

Originally Posted by BMWM.D.

I’ve seen plenty of those crank sensors fail, but it’s usually really obvious. Super long crank, DSC warning light, etc. Not saying it’s not possible, but that’s what I’ve always seen.

Yes, I agree, I don't believe what I was told. The proof in the pudding is that the car is still not ready, so I am pretty confident it wasn't that and they are still digging or waiting for parts... I'll give them till Thursday then call. I kind of need the car for Xmas ?

EDIT: I just need to sit down when they give me the bill I suppose; hopefully it is fixed and no more running around to find the fault. Straight to the Android phone she goes for a MHD stage 1 map.

[BMWM.D.]

Originally Posted by torrque

Yes, I agree, I don't believe what I was told. The proof in the pudding is that the car is still not ready, so I am pretty confident it wasn't that and they are still digging or waiting for parts... I'll give them till Thursday then call. I kind of need the car for Xmas ?

EDIT: I just need to sit down when they give me the bill I suppose; hopefully it is fixed and no more running around to find the fault. Straight to the Android phone she goes for a MHD stage 1 map.

Hopefully they can figure it out. The owner of the car I was messing with didn’t want to spend any more money to have me keep chasing it, so I probably won’t have any updates for you. With as intermittent as it was on this car, it probably would have ended up as an expensive guessing game. It sounds like yours is pretty easy to reproduce, so here’s to hoping it’s a little easier to track down.

Be sure to update this thread when you know anything. I’m still really curious as to what’s causing it. Who knows, maybe I’ll be seeing the car again in the future.

[torrque]

ARGH, mistery was resolved. I am a fool. I replaced the DME relay in the fuse box, but not the one in the e-box.. My Bentley says the relay for 2008 is in the right hand side of the fuse box, the black one. Apparently, on these early 2008 models, it is still inside the e-box.
It was the relay in the e-box causing it, dropping power to the DME intermittently. Apparently it was a connector loose inside the socket. The crank angle sensor was also changed after the DME was rectified as it was pushing an error, car idles even better now.

Hope this helps someone someday. Check your DME relays for sure when you have surging and no codes.

[BMWM.D.]

That actually makes a lot of sense. Going into the E-box was going to be my next step, but I never got the chance. There’s a few replaceable relays in the junction box, but none are for the DME. You might have replaced a Terminal 30G relay.

And just for the record, was it actually a relay issue, or was it a loose pin in the harness that the relay plugs into? Glad it’s fixed.

[torrque]

It was a loose connection in the relay socket, relay is still the old one...

[MysticRob]

Originally Posted by torrque

It was a loose connection in the relay socket, relay is still the old one...

Good to hear. Just a thought, but you might want to update your original thread here, which I believe discusses the same issue, right?:
http://www.e90post.com/forums/showthread.php?t=1445102

I'd recommend not restarting 5yr old threads like this so others don't have to slog through all those old posts not related to your specific problem before finding your posts.

[torrque]

Originally Posted by MysticRob

Good to hear. Just a thought, but you might want to update your original thread here, which I believe discusses the same issue, right?:
http://www.e90post.com/forums/showthread.php?t=1445102

I'd recommend not restarting 5yr old threads like this so others don't have to slog through all those old posts not related to your specific problem before finding your posts.

Well, nobody replied there, and BMWM.D. replied to me here so...

[torrque]

Originally Posted by BMWM.D.

That actually makes a lot of sense. Going into the E-box was going to be my next step, but I never got the chance. There’s a few replaceable relays in the junction box, but none are for the DME. You might have replaced a Terminal 30G relay.

And just for the record, was it actually a relay issue, or was it a loose pin in the harness that the relay plugs into? Glad it’s fixed.

Problem I had is not fixed yet; believe it or not, car has been with German Performance since Dec 26 and they could not find the root cause. They just called me that they replaced the wiring to the Crank angle sensor, and problem is still there. They suspected the wiring due to the fact that the stutter got less frequent since the swap of the sensor... I told them it's not the issue, and we have an electrical problem timing out the DME and taking out the RPM's to zero also... Due to the fact that the crank sensor is powered by the same relay from the same fuse as the DME, it manifests as a crank sensor timing out, but it's more than that. Whole DME is being taken down.

At some point there were errors for Water pump voltage when problem occurred.

I am away next week, but I will take it from them when I come back, I am sure they are not able to do it... I will have at it again on my own.
Is it possible for the EKPM module to shut down car like that ? I am seeing PWM issues when the stutter occurs, and these modules are known to fail...

Thanks all for any input again!