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      05-05-2015, 10:27 PM   #1
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Surging during acceleration

Background
On the Thursday before Easter while completing a 3,500km road trip from Brisbane to the BMW Nationals in Sydney, out of the blue, my car developed a surging problem along with a lack of power during hard acceleration. There were no problems with the idle or during normal driving with light acceleration. Initially, I thought I may have got a tank of crap fuel from one of the independent service stations that I had to use during the journey. That night, I plugged in the Cobb Accessport to see if there were any diagnostic trouble codes (DTC) displayed but there were none. I did a visual inspection of the engine bay to see if any vacuum hoses had come loose or cracked or leaks in the diverter valves or charge pipe but nothing was apparent. I covered another 1,500km using light acceleration before getting home to Brisbane. the average fuel consumption for the 5,000km was 8.3L/100km.
Progress to Date with Issue
Once home, I jacked the front of the car up, removed the belly cover and had a better look around. I checked the intercooler and connections, the hoses to the turbo wastegate actuators to ensure they were OK and removed the DCI intake and diverter valves and checked them. I found that one of the diverter valves was loose where the two halves screw together but tightening this made no difference. I changed the spark plugs only because I had a set there and they were almost due for changing. The plugs that I removed looked perfect. I put everything back together and took the car to James at Bayside Performance Services (BPS) who did the custom tune. He run the car on the dyno for a couple of hours to check what he could. He identified there was an over boost occurring for unknown reason which when detected by the ECU (DME) would partly close the throttle valve thus causing the surging. He checked everything he could and said the ECU was doing everything it should. He hadn't seen anything like it before and was of the opinion that it would be something stupid causing the problem. He suggest removing the exhaust system from the downpipes and giving it a run on the basis of there being a restriction in the system. From a practical point of view, this is said than done. Driving around the streets to do a datalog with no exhaust may draw unwanted attention.
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The problem can easily be seen on the dyno graphs. The 3 graphs include the original graph (297.7kW) done during the custom tuning, the current graph (277kW) and a graph after the tune was changed to the Cobb Stage 2+ generic tune (261kW). the change of tunes proved that it wasn't a software issue as the same problem was evident in both graphs. as can be seen by the dyno graphs, at the higher rev range, it comes good and takes off. I get the same experience on the road.
Since leaving BPS, I have conducted several datalogs using both the custom tune and the Cobb Stage 2+ tune.
Cobb Stg 2+with OEM Turbos.zip
Cobb Stage 2+ with OEM turbos (June 2014)
Cobb Stg 2+ with RB Turbos.zip
Cobb Stage 2+ with RB turbos (April 2015)
BPS Custom Tune with RB Turbos.zip
Cobb Custom Tune with RB turbos (April 2015)
Datalog 1.030515.zip
Cobb Custom Tune with RB turbos (April 2015)
Datalog 2.030515.zip
Cobb Custom Tune with RB turbos (April 2015)
The data indicates a couple of things. Fuel pressure from both the LPFP and HPFP appear OK. When the Boost Means ABs exceeds the Required Boost the throttle partly closes as it should thus causing the surging and power loss. The boost appears to increase and decrease in a linear fashion up to 18-19psi. The Lambda AFRs for both banks appear to lean out to extremely dangerous levels(21) prior to the over boost occurring. Whether the sudden change from an AFR of 21 to 12 is causing the over boost, I am not sure. My understanding of the AFR process is that the oxygen sensors in the downpipes measure the exhausting gases and as soon as a lean situation is detected by the ECU, it will immediately have more fuel injected into the engine to make the mixture rich and drop the AFR readings down to the 11-12 range and visa versa for a rich situation. This does not appear to be happening as quick as it should be. Although I have checked the vacuum system to the turbo actuators and replaced a couple, my thinking is that the turbos, intercooler, charge pipe and diverters must be operating as expected because of the way the boost is shown on the data. another observation is the Required Load for the Cobb Stage 2+ generic tune with the OEM turbos was higher than it is now with the RB turbos and that the Actual Load is now exceeding the Required Load during the partial throttle closures. What is causing all of this is the issue. I am out of ideas and reluctantly at the point of taking the car to BMW with all of the information to get them to see if their diagnostic tools can detect something wrong but do nothing else.
I know this is a lengthy story but if I can resolve the issue, it may help someone in the future. I will keep you informed on progress.
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      05-07-2015, 03:59 AM   #2
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Did you sort this out yet Coupes?? I'm guessing No
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      05-07-2015, 04:24 AM   #3
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Sounds complicated... I would have thought you should be able to identify it by looking at air, fuel, ignition... It should be one?

And you're sure the spark plugs were all fine?

If the AFR is extremely lean but the fuel pressures are good... have you checked sensors?
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      05-07-2015, 04:58 PM   #4
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Quote:
Originally Posted by Socket View Post
Did you sort this out yet Coupes?? I'm guessing No
No Socks. I haven't sorted it out yet. I need to get it checked with a diagnostic tool and see what that may discover.
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      05-07-2015, 05:07 PM   #5
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Quote:
Originally Posted by Scotty89 View Post
Sounds complicated... I would have thought you should be able to identify it by looking at air, fuel, ignition... It should be one?

And you're sure the spark plugs were all fine?

If the AFR is extremely lean but the fuel pressures are good... have you checked sensors?
Scotty, the plugs were fine and if it was a sensor, I would have thought a DTC would have highlighted that. My thoughts are that there is something a miss between the oxygen sensors, ECU and injectors. Initially, I thought it could be a fuel issue maybe with the fuel filter causing a restriction but found that our 335s have a life time filter. I don't know how that works if you get crap in the tank. If there was a restriction, I don't believe the HPFP pressure would remain between 2,000 and 3,000psi.
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      05-11-2015, 01:49 AM   #6
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Update on Progress
Today, I took the car to Superior Automotive Group who are BMW specialists at Albion, Brisbane. They carried out a diagnostic scan using a BMW ICOM. No faults were stored. They tested the module turbo operation and found both turbos tested ok. Tested both vacuum solenoids for turbo valves and the actuators and all tested ok. They couldn't find anything wrong or what is causing the surging issue. I will look further and keep you informed.
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      05-11-2015, 02:08 AM   #7
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Intake valves need a walnut blast? Also, check your coils yet? Obviously you took them out to change the plugs already, so you inherently checked those...

Just grasping.

My guess is a sensor, not giving a fault necessarily, but failing nonetheless. Computers nowadays, you can't always trust them!
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      05-11-2015, 02:48 AM   #8
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Very mysterious, looking forward to you working out what this is Coupes
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      05-11-2015, 05:40 AM   #9
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Quote:
Originally Posted by GB-335xiCoupe View Post
Intake valves need a walnut blast? Also, check your coils yet? Obviously you took them out to change the plugs already, so you inherently checked those...

Just grasping.

My guess is a sensor, not giving a fault necessarily, but failing nonetheless. Computers nowadays, you can't always trust them!
Intake ports were cleaned 10,000kms ago and if any of the coils were faulty a DTC should be showing up. The problem doesn't appear to be electrical in any way. From the datalogs, I still believe it is software related but not the tune as two different tunes have been installed and the problem is same with both. The Cobb Accesstuner manual states the "BMW's DME operates in a constant closed-loop state, constantly utilizing the A/F values in its tables and making adjustments via its equipped wide-band O2 sensors". This is not working correctly in my car as AFRs of 20-21 shouldn't be happening as the DME should be immediately reacting and making the mixture rich and this is not occurring. The manual also states for "Boost Control - The BMW DME does not target boost but rather engine load. Engine load is calculated based on pedal position, air flow/boost and rpm." Whether the inputs into the DME for calculating engine load are not correct could be another possibility. Who knows? I will just keep trying to eliminate possible causes.
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      05-11-2015, 05:43 AM   #10
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Quote:
Originally Posted by Socket View Post
Very mysterious, looking forward to you working out what this is Coupes
I hope I can or someone can work it out soon Socks as it is getting very frustrating and I am getting growing negative thoughts about BMWs.
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      05-11-2015, 07:09 AM   #11
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Hmm sounds weird!

I'm sorry I cant really help you, but obviously its something other than the usual plugs/coils!

Have you tried posting up in the 'worldwide' N54 tuning sub section?

http://www.e90post.com/forums/forumdisplay.php?f=58

My guess is perhaps its a DME related issue... (once again im no expert, but it seems fueling, turbo hardware diagnosis is all ok)
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      05-11-2015, 07:58 AM   #12
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Why would they test the turbos? That makes no sense to me. If turbos were bad, you'd be getting little boost - but turbos don't cause surging, they just make the acceleration feel weak. The RPM's wouldn't surge.

If the turbos were bad you would see the Waste gate activity doesn't match the boost level in the logging data.

It sounds like a fuel issue or sensors causing a fuel issue.
The low pressure fuel pump has a sock filter, that is lifetime with the pump. It wouldn't cause the problem.
If there was a restriction in the fuel system you would see a mismatch in fuel pressure levels.

I currently have a problem with O2 sensors in my car that are causing issues at high boost (but no issue at standard boost). They are causing codes though.

Does your flash tune disable any tuning codes??
What do the logs look like when it surges??
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      05-11-2015, 07:13 PM   #13
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Quote:
Originally Posted by Scotty89 View Post
Why would they test the turbos? That makes no sense to me. If turbos were bad, you'd be getting little boost - but turbos don't cause surging, they just make the acceleration feel weak. The RPM's wouldn't surge.

If the turbos were bad you would see the Waste gate activity doesn't match the boost level in the logging data.

It sounds like a fuel issue or sensors causing a fuel issue.
The low pressure fuel pump has a sock filter, that is lifetime with the pump. It wouldn't cause the problem.
If there was a restriction in the fuel system you would see a mismatch in fuel pressure levels.

I currently have a problem with O2 sensors in my car that are causing issues at high boost (but no issue at standard boost). They are causing codes though.

Does your flash tune disable any tuning codes??
What do the logs look like when it surges??
No, the Cobb Custom Tune doesn't disable any tuning codes. The second and third datalogs that I attached at the start of the thread show what happens when it surges. The throttle valve partly closes causing the surging. The throttle valve closes because the Boost Means Abs is exceeding the Boost Req Abs. What is causing the over boost or low Boost Req Abs is one of the issues. The other is the Lambda AFR values rising to 20-21 (Super lean) when they are generally 11-12. As the hardware appears from all inspections and testing to be ok and two different tunes have the same issue, I believe it is something in the DME software that has gone haywire.
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      05-11-2015, 07:17 PM   #14
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Quote:
Originally Posted by DR-JEKL View Post
Hmm sounds weird!

I'm sorry I cant really help you, but obviously its something other than the usual plugs/coils!

Have you tried posting up in the 'worldwide' N54 tuning sub section?

http://www.e90post.com/forums/forumdisplay.php?f=58

My guess is perhaps its a DME related issue... (once again im no expert, but it seems fueling, turbo hardware diagnosis is all ok)
My thinking is along the same lines of yours Dr JEKL, that is, something in the DME software has gone haywire for some reason.
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      05-11-2015, 08:14 PM   #15
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WD40 on the sticky throttle bro. Just kidding! But would be hilarious if it worked
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      05-11-2015, 11:29 PM   #16
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Is the map sensor reading correct boost?

I had logs of 17afr the other day and fairly certain it is O2 sensors. Have they tried swapping them with known functioning sensors?
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      05-12-2015, 02:48 AM   #17
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Quote:
Originally Posted by Scotty89 View Post
Is the map sensor reading correct boost?

I had logs of 17afr the other day and fairly certain it is O2 sensors. Have they tried swapping them with known functioning sensors?
As both Banks 1 & 2 are showing similar AFRs, I discounted the oxygen sensors as all four would have to go faulty at the same time for that to occur. A faulty oxygen sensor should throw up a DTC, I would have thought. If you look up AFR sensor in Wikipedia, it tells you how to test the sensors in our cars. Of course, you require a scanner to do it. It states "the best way to test an AFR sensor's signal is by monitoring the voltage conversion circuitry which the DME sends out as an AFR-voltage PID." PID stands for Proportional-Integral-Derivative. Once again, Wikipedia explains it in detail. I have booked the car into BMW Motorline next week to see if they can detect anything.
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      05-17-2015, 03:56 AM   #18
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Coupes did you figure out whats causing the surge problem yet??
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      05-17-2015, 05:08 AM   #19
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Quote:
Originally Posted by Socket View Post
Coupes did you figure out whats causing the surge problem yet??
No Socks not yet. I have been reading another thread on E90 Post where fellows have had the same problem and had no DTCs indicated. Some of the responses are scary to read. Fellows have had HPFPs, injectors, wastegates & etc replaced by BMW without finding the cause. Some stated BMW have had quite a few of these surging issues and cannot find the cause. One fellow had his engine replaced and that fixed it. This option is a bit dramatic and expensive for me. However, another fellow who had the same problem mentioned about taking the car for a 30min run with it locked in 4th gear and revs set at 4k. This apparently fixed his problem. Another fellow tried the same thing and it fixed his also. I will try it tomorrow and see what happens. There is nothing to lose from doing it. Currently, I have the car booked in on Wednesday with BMW to see if they can diagnose something but am not very confident of getting a positive result just a big bill.
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      05-17-2015, 07:28 AM   #20
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GL buddy let us know the outcome.... hope they find something and that it turns out to be something simple like a faulty accelerator pedal switch
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      05-18-2015, 01:28 AM   #21
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Today, I tried the 40min in 4th gear which has worked for a couple of fellows in the US with the same surging issue but had no success. At 100kph, the engine was revving at 4,200rpm in 4th gear. Before commencing the drive, I poured a 350ml bottle of Caltex Techron 5000 into the tank. It is suppose to clean deposits from the fuel injectors and combustion chambers. In the US, they us a similar product called Sea Foam. With no success, I guess it is back to the drawing board.
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      05-18-2015, 02:15 AM   #22
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I think that Techron (and similar) product takes a while to work, if it does anything at all.
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