Jerky acceleration when pushed

[Harper55987]

Been noticing the harder I push my 135i I am starting to get a sort of...jerky acceleration or like the car is holding back when I hit about 3500, 4000 RPM's.

I don't feel a lack of power and it still pulls hard but it seems hesitant almost.
I would say it happens more going uphill then downhill/flat.

I have a JB4 in my car as my only mod.
Only other checks/concerns in my car are:
Low Pressure Fuel Pump has been thrown. BMW dealership said not to worry since they could still hear it being turned on when my comfort access got close.

Is this a symptom related that it is not getting enough fuel or lacking in the LPFP?

[IGoFast1589]

Originally Posted by Harper55987

Been noticing the harder I push my 135i I am starting to get a sort of...jerky acceleration or like the car is holding back when I hit about 3500, 4000 RPM's.

I don't feel a lack of power and it still pulls hard but it seems hesitant almost.
I would say it happens more going uphill then downhill/flat.

I have a JB4 in my car as my only mod.
Only other checks/concerns in my car are:
Low Pressure Fuel Pump has been thrown. BMW dealership said not to worry since they could still hear it being turned on when my comfort access got close.

Is this a symptom related that it is not getting enough fuel or lacking in the LPFP?

Sounds to me like your ignition system. As the spark plugs and coil packs get tired and need to be replaced the spark can no longer keep up with the rotation of the crank. So when you're full throttle running through the gears those mini hesitations are tiny misfires. Eventually the ECM will throw a code once it gets dramatic enough. How many miles are on your car? When was the last time your spark plugs were changed?

[Harper55987]

I have 25,000 miles or so on my car. Not sure when they were last changed as it was bought around...21,000 miles.

[IGoFast1589]

Originally Posted by Harper55987

I have 25,000 miles or so on my car. Not sure when they were last changed as it was bought around...21,000 miles.

Could be on the original spark plugs really. Especially if you're tuned the plugs will die faster. The gap at the end of the spark plug becomes too large over time making it difficult for the spark to jump. You can pull the plugs and check them, but you might as well replace them as they're not very costly and it makes the most sense while you have everything apart. My car ran butter smooth after swapping out the spark plugs.

[ErvGotti]

Had the same symptoms, mine turned out to be carbon build up. Replaced the plugs and a couple of injectors and still had hesitation problems especially up inclines. I only had 35000 miles on her and some of the build up was 2-3 cm thick. IMHO this needs to be done every 15-20 thousand miles.

Ran a couple of logs on virtual dyno before and after the carbon blasting and the WTQ speaks for itself. Blue is before the cleaning, red and green after.

[Mr Kleen]

I'm having similar issues. I have spark plugs on order, going to try that first...

[Harper55987]

Is walnut blasting something a dealership alone can do or do any indie shops do this? My dealership hasn't been happy I bought my car from another dealership so my old SA hasn't been to happy I feel.

[Harper55987]

Just an update to this...

I upgraded my JB4 firmware to the latest version and some of the jerkiness/boost control has been resolved but not entirely.

I am also throwing these 2 codes now:
2A7C No Description Found
3100 low boost mode engaged -- CEL displayed

2A7C I have found on some forums as being the VANOS solenoid. Do any of my symptoms have to deal with this? Car has gone in to limp mode once or twice randomly. However...seems to happen when I turn the car on. Not at WOT as many think it should.

[foghat]

2A7C is intake vanos solenoid, I believe. A bad vanos solenoid will cause limp mode, but usually at wot throttle. the 3100 code is just a by product of the 2a7c code and is normal/expected.

I am throwing vanos codes as well and have 2 new solenoids on the way. My car, however, is not jerky. I did have the jerkiness you describe when I first got my jb4. New plugs took care of that.

[NORAGRETS]

sparks or coils...have the same issue.

going in to the dealer today to get my sparks changed actually

last time it happened i was on the highway and raced a tuned up shelby mustang...changed down from 4th to 3rd and gunned it....limp mode...ignition coil went kaput

[Harper55987]

Won't I be getting engine misfires? I thought there were codes for all of the spark and coils which could be detected?

[foghat]

I didn't get any misfire codes. Probably depends on how 'bad' the misfire is.

[Dackelone]

Why not FIX what you know is wrong with your car FIRST and then retest? IF you know your LPFP is bad(or the sensor as in a lot of cars) and you are running old spark plugs - replace that stuff first.

Sounds to me this "Jerky acceleration" is more of a "lean surge" issue. I would be concerned about that(!) and not put the diagnosis off.

[Colt]

Originally Posted by Harper55987

Is walnut blasting something a dealership alone can do or do any indie shops do this? My dealership hasn't been happy I bought my car from another dealership so my old SA hasn't been to happy I feel.

Dealership can do it but you're going to pay more for it. Best I have seen is $375 for the walnut blasting and new gaskets (think it was Helixs' quote). Getting mine done soon for $440 near me (price is with new gaskets).

[Harper55987]

The LPFP I am debating on getting "fixed". I have a warranty still but they refuse to replace the issue.
The dealership is claiming it is just the LPFP sensor and not the pump itself. Apparently: Pump is under warranty. Sensor is not

As for the VANOS, I will ask to get these fixed next time it is in the shop.

What is a typical price for new plugs/coils on a 1 series? say dealership vs. indie shop.

[foghat]

Originally Posted by Harper55987

The LPFP I am debating on getting "fixed". I have a warranty still but they refuse to replace the issue.
The dealership is claiming it is just the LPFP sensor and not the pump itself. Apparently: Pump is under warranty. Sensor is not

As for the VANOS, I will ask to get these fixed next time it is in the shop.

What is a typical price for new plugs/coils on a 1 series? say dealership vs. indie shop.

The plugs and coils are dead simple to replace. Do it yourself. I would guess dealer/indie will charge an hour labor.

[Harper55987]

I'll take a look! All areas around me think it is impossible that it can be the spark plugs with my mileage (25k or so).

I'll give them a change and see if anything improves

[Swadeness]

To the OP I suggest running a data log and taking a look at it. Maybe share it with some knowledgeable folks on the forums and get their input too. I have developed a similar issue to what you described. Mine is especially prevelant after hard shifts at WOT (also going uphill). To me, the hesitation/stutter felt just like a misfire and I assumed I would be needing new plugs. But after taking a close look at the data log the DME is partially closing the throttle whenever actual boost exceeds the commanded boost (the DME reacts almost instantly to this). As the DME cycles the throttle valve (several times a second) to get the boost under control it feels like a misfire. I can't be 100% of the cause but I believe my issues are associated boost overshoot. It might be a good idea for you to explore some other possibilities before dropping the $ on the Walnut blasting. I'm no expert, these are just some observations I made, hope it helps and keep us informed.

BTW Do you get the same issue with traction control fully off? Are you N55 or N54?

[foghat]

Originally Posted by Harper55987

I'll take a look! All areas around me think it is impossible that it can be the spark plugs with my mileage (25k or so).

I'll give them a change and see if anything improves

It is pretty much considered a truth on this platform that if you are running a tune, plugs should be changed every 25,000 miles. That is about what mine had when it was acting up. Plugs fixed the hesitation.

[Harper55987]

Originally Posted by Swadeness

To the OP I suggest running a data log and taking a look at it. Maybe share it with some knowledgeable folks on the forums and get their input too. I have developed a similar issue to what you described. Mine is especially prevelant after hard shifts at WOT (also going uphill). To me, the hesitation/stutter felt just like a misfire and I assumed I would be needing new plugs. But after taking a close look at the data log the DME is partially closing the throttle whenever actual boost exceeds the commanded boost (the DME reacts almost instantly to this). As the DME cycles the throttle valve (several times a second) to get the boost under control it feels like a misfire. I can't be 100% of the cause but I believe my issues are associated boost overshoot. It might be a good idea for you to explore some other possibilities before dropping the $ on the Walnut blasting. I'm no expert, these are just some observations I made, hope it helps and keep us informed.

BTW Do you get the same issue with traction control fully off? Are you N55 or N54?

I had Terry take a look at my logs. He had me cut the diodes on my JB4 and then upgrade to the latest firmware. This did resolve a lot of the issues so I'm torn between deciding if it is a JB4 issue or not. I'll try running on Map 0 for a bit as well to see the difference!

[Vorsprung_CJB]

Lots of good suggestions, I would also suggest again cleaning the Vanos solenoids. I just cleaned both again and it definitely helped smooth out the Vanos crossovers around 2K and 4k RPM. Especially noticeable in 1st gear acceleration where the gearing made the effect more pronounced. Dialing in your wastegate and duty cycle settings for your particular car in the JB4 ISO settings can help a lot too. Good luck!

[jbarzelatto]

any updates?

im getting the same problem when i pass 3000-4000 rpm slowly, not wotting

n55 fbo meth vtt stage 2+ turbo