[stickle1212]

I have a very strange problem. Lately while accelerating the car feels like It's placed in a lower gear (for about 1 second), even though I'm not in the act of shifting. It happens at random times. The last time I was in 6th speed doing 85 mph and suddenly the car felt like it was placed in second gear without me actually shifting.

Any ideas what's wrong?

[lowrydr310]

Originally Posted by stickle1212

I have a very strange problem. Lately while accelerating the car feels like It's placed in a lower gear (for about 1 second), even though I'm not in the act of shifting. It happens at random times. The last time I was in 6th speed doing 85 mph and suddenly the car felt like it was placed in second gear without me actually shifting.

Any ideas what's wrong?

This sounds like a slipping clutch. I drove a friend's Mustang where he had done one too many clutch drop burnouts and it felt just like this. As I was going up hills, it felt like an automatic downshifting with the engine revving out.

How many miles do you have on the car?

[whyzee125]

Only thing that can really be is a slipping clutch

[ctuna]

Is this and actual 3 pedal manual or are you talking about
manual mode on a automatic?

[marvinstockman]

If you have a manual, and the rpm's aren't flaring, you might have a fuel supply issue.

[stickle1212]

Sorry, I'm just responding.. Yes, it's a manual shift. When it happens the RPM drops sharply and if I don't come off the gas it just keeps bucking. I don't think it's a slipping clutch, because the RPM would increase not decrease. The jerking motions are really aggressive, it's as if something grabbing the vehicle from behind.

Short video of the rapid decrease in rpm. It sometimes cause the 4x4 light to come on

[e90yyc]

That’s some extreme shit. Not to kick a man while he’s down, but I think the way you described the issue in your original post caused some confusion. If I’m understanding correctly, you’re on the throttle when suddenly it feels like someone is stabbing the brakes, ya?

Scan for codes and let us know what you find. You’ll need a scanner or cable that can read BMW codes—not just your average AutoZone scanner.

My money is on a DSC system issue of some sort. I’m skeptical your tach is showing your actual engine speed during those brief moments when your car is taking a shit. So, that makes me think it relates to a sensor, and isn’t “mechanical failure.” That’s just a guess though; I could be very wrong.

It sounds a bit like I can hear the click of the ABS module engaging the brakes during the first conniption in that video. Any idea if that’s happening?

It would be useful to know whether your brakes are activating when the issue occurs.

BTW, I’m having a very similar albeit less extreme issue with my 328xi that started after I swapped in a manual transmission. Weird part is in my case there are no lights and no codes. Your use of the word “bucking” rang true for how what I’m experiencing feels. If I stay on the gas, it’ll often keep doing it until I tip off and then get back on, at which point all is well.

There’s a direct relationship between road surface and when it happens for me. If I drive over a bump that causes one axle’s wheels to spin at a slightly different rate than the other end, it’ll often feel like someone is jamming the brakes on, but I’m actually fairly certain in my case it’s just cutting throttle.

Anyway, report back with codes and hopefully we can figure it out.

[stickle1212]

Originally Posted by e90yyc

That’s some extreme shit. Not to kick a man while he’s down, but I think the way you described the issue in your original post caused some confusion. If I’m understanding correctly, you’re on the throttle when suddenly it feels like someone is stabbing the brakes, ya?

Scan for codes and let us know what you find. You’ll need a scanner or cable that can read BMW codes—not just your average AutoZone scanner.

My money is on a DSC system issue of some sort. I’m skeptical your tach is showing your actual engine speed during those brief moments when your car is taking a shit. So, that makes me think it relates to a sensor and isn’t “mechanical failure.” That’s just a guess though; I could be very wrong.

It sounds a bit like I can hear the click of the ABS module engaging the brakes during the first conniption in that video. Any idea if that’s happening?

It would be useful to know whether your brakes are activating when the issue occurs.

BTW, I’m having a very similar albeit less extreme issue with my 328xi that started after I swapped in a manual transmission. Weird part is in my case there are no lights and no codes. Your use of the word “bucking” rang true for how what I’m experiencing feels. If I stay on the gas, it’ll often keep doing it until I tip off and then get back on, at which point all is well.

There’s a direct relationship between road surface and when it happens for me. If I drive over a bump that causes one axle’s wheels to spin at a slightly different rate than the other end, it’ll often feel like someone is jamming the brakes on, but I’m actually fairly certain in my case it’s just cutting throttle.

Anyway, report back with codes and hopefully we can figure it out.

I have no cel, brake light doesn't come on, however, I'm getting this code "54c6" which has to do with the transfer case. I changed the fluid a week ago as part of a preventative maintenance. I can drive the car perfectly fine but if I try to floor the throttle that's when the issue occurs. It happens exactly as you stated: "If I stay on the gas, it’ll often keep doing it until I tip-off and then get back on, at which point all is well. " Also the decrease in speed is drastic, if you suffer from back problems you'd be in a world of trouble.

Now I'm wondering if the transfer case fluid was the wrong type, all the problems occurred after the change. This is what I used: https://www.amazon.com/dp/B0057UJY7I...roduct_details

[e90yyc]

Haha man you gotta provide these crucial details upfront . When a problem like this starts happening after you’ve done work on your car, you first need to ask whether whatever you did could have caused the problem you’re experiencing. Sure, sometimes the timing is just a coincidence, but it’s usually not.

This is not the correct fluid for the transfer case. These units are notoriously picky when it comes to fluid, and I’ve never heard anyone recommend anything other than Genuine BMW or the Shell OE equivalent (TF0870 I believe). There are friction modifiers and other shit in these fluids that are essential for the T-case to function correctly.

So, drain and refill the t-case with the correct fluid. Once that’s done, see if the problem resolves. It probably will.

Now that’s got me wondering whether my issue could be related to the transfer case, but while there seem to be many similarities between what you and I are experiencing, what’s happening in my case feels more like a power cut, and the throttle seems to surge when I activate cruise control, making it unusable. Do me a favour if you don’t mind and try engaging cruise. Let me know if it behaves normally.

Good luck!

[stickle1212]

When I shift it in cruise it operates normally, no issues there. However, when I use the cruise to do a rapid acceleration I have the same issue. Long story short, I brought it to the dealer to do a diagnosis. My mechanic suggests the fuel pump is the issue, but I don't agree. I've driven vehicle before where the fuel pump cut out and it doesn't pull back as violently. Long story short, I dropped it off at the dealer for them to do a diagnosis, so stay tuned.

[Dave92N54]

Originally Posted by stickle1212

When I shift it in cruise it operates normally, no issues there. However, when I use the cruise to do a rapid acceleration I have the same issue. Long story short, I brought it to the dealer to do a diagnosis. My mechanic suggests the fuel pump is the issue, but I don't agree. I've driven vehicle before where the fuel pump cut out and it doesn't pull back as violently. Long story short, I dropped it off at the dealer for them to do a diagnosis, so stay tuned.

I'd find the fuel pump highly unlikely as well.

Out of curiosity, which dealer? A few dealers here in MD have been quite shit for me.

[e90yyc]

Why not start by draining the wrong fluid from your TC and put the right fluid in? Then go from there?

You’ll want to do that regardless of whether it’s actually the TC causing your issue.

That’s where my money is right now. Absolutely TC issues could cause what you’re experiencing. Hard for me to understand why someone posting on a DIY forum wouldn’t want to rule that out before giving money to a dealer , but if you insist on doing that, at least tell them what you did so they can focus their time in the right areas

[nsjames]

that is not the correct fluid as noted, but since the tach drops out I would suspect a cam/crank sync issue that causes the DME to cut.

There's no way that your engine RPM can drop that fast with the drivetrain spinning it, and the transfer case having the wrong fluid doesn't disconnect the rear axle, it's a solid shaft straight through the transfer case.

[e90yyc]

Originally Posted by nsjames

that is not the correct fluid as noted, but since the tach drops out I would suspect a cam/crank sync issue that causes the DME to cut.

There's no way that your engine RPM can drop that fast with the drivetrain spinning it, and the transfer case having the wrong fluid doesn't disconnect the rear axle, it's a solid shaft straight through the transfer case.

Good point. Think the timing of fluid change and issue occurring is merely coincidence then?

Curious to see what this ends up being…

[nsjames]

Originally Posted by e90yyc

Good point. Think the timing of fluid change and issue occurring is merely coincidence then?

Curious to see what this ends up being…

possibly.
also possible that something got damaged along the way.
it may be worth checking on the main chassis ground since it's in the vicinity. maybe it got disturbed and is a problem when the engine lays over under hard acceleration.
edit:
i'd have a look at the o2 sensor wiring too, a shorted o2 sensor on the manifold would drop the DME. just a general gander looking for damaged wiring at all the known spots.

I wouldn't think it's a kombi issue since the economy gauge keeps working and it doesn't appear to reset itself.

OP, speedo acts normal when the tach drops out?

it's gonna take some data logging to figure out what drops what.
in my opinion anyway. I'm not a professional.

this guy had similar symptoms and it was the dme, but it's a turbo car which i assume the OP doesn't have since it's got an econ gauge.
https://www.e90post.com/forums/showt...1445102&page=8
so not the same.

I'd be curious to see if OP loses communication with the DME at corresponding times with the bucking.

[e90yyc]

nsjames Good point again on possibility of having accidentally mucked something up doing the job. Another reason IMO to re-do the TC job with the correct fluid and thoroughly check everything over.

I honestly find it hard to believe OP is getting no codes other than 54C6 - Oil Wear. I would think if DME was dropping out at any point there would be multiple lost communication codes stored?? Bit of a head-scratcher, but then again in my case with the mysterious DSC intervention, I have no codes related to it…

[stickle1212]

Here is the assessment from BMW of Silver Springs:

https://api.mykaarma.com/video-walka...mage_and_video


I must say that I have the MSV80_A951181_328i_to_330i mod with 330 manifold. I'm wondering If I should just stop at the diagnosis and reflash the DMI.

What is the best course of action should I take from here?

[e90yyc]

How long have you had the 3IM for? Unless this started after you installed it, I wouldn’t pay too much attention to that. Certainly doesn’t hurt to reflags (or maybe just flash default coding to start).

Don’t pay them to reflash the DME obviously, but I think you knew that.

I’m not surprised to see some of those codes. You had mentioned the only code you saw was VTG oil wear. What did you use to scan?

[stickle1212]

I had the 330 flash for a few months but I couldn't tell if it was actually doing anything so I reflashed it 2 weeks ago. I did see that ecu error but I thought it was one of those expected errors when you do a flash so I didn't share that. I use IMPA and Blue Driver which actually does give BMW codes. I doubt it's the fuel pump but I will get one from the junkyard just to test instead of spending $500 and that's not the issue.

Sorry, @nsjames, what exactly is the "OP"?

[marvinstockman]

What is your tach doing when this is happening.

If you can measure fuel pressure while your driving, that would be a big help. I had a car with a partially clogged internal fuel filter, and the pressure was normal during cruising but would drop like a rock when I accelerated.

[stickle1212]

marvinstockman If by tach you mean rpm gauge see the video I posted earlier in the thread. I'll try to capture a freeze frame. On my way to get it from the stealer.

[nsjames]

the no coding error is meaningless and causes no issue. I've had it for over two years because too lazy to do this:

2FA3 can either be ignored, or you can clear it by default coding 6BMOT in NCSexpert. It doesn't do anything except show up in INPA.

https://www.e90post.com/forums/showt...g#post27588028