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keyap keyap is offline
Posts: 1,674
Join Date: Jun 2012
Car: N55 135i
Default 10-29-2016, 05:47 AM

There's been some talk on here of N55 E misfires and errors in the COBB BEFs so I thought it was worth posting how I solved mine as it may support the MHD development.

I do use my own BEF so there are quite a few differences to the BMS and FuelIt versions and I also think, where possible, this means the errors in the COBB OTS maps were corrected. What I've listed below though is the parameter which I think impacts misfires:-

What I found was that with without a BEF the HPFP values under full load show considerably higher than with a high load BEF. This is from memory, so these figures may not be 100% accurate but, without a BEF and the JB targetting say 20 psi the HPFP will be at 14 whereas, with a high load BEF and no other changes the HPFP drops to 11.

The 11 is right on the limit of what works OK so as soon as anything impact this, for example, a loss of traction, the value can drop sub 11 inducing misfires.

By reducing the Load Ceiling Main in the flash and thus reducing the amount of boost seen by the DME, the HPFP increases and can accommodate more fluctuations.

Form memory, the BMS high load flash uses a Load Ceiling Main of 180 and the FuelIt 200. Dropping to 150 increases the HPFP value under load to 12 maybe even 13 and the misfires are gone. For me this even allows traction control to intervene (which the high load BEFs really seemed to not like) and there are no problems.

Lowering the Load Ceiling Main does have other knock on effects though, so for example, fuelling in the BEF needs to be adjusted and for PI I needed to change the JB4 Fuel Bias otherwise trims would be way out.

There's also other things to consider. For DCT guys, DME boost impact DCT plate pressure. Form what I know, DCT plate pressure caps out at around a DME boost figure of 21psi. 200 on the load ceiling main, assuming other tables to do reduce boost, results in this. I think 180 is around 20 and the 150 I quoted above around 14. These are only approx but, what it does mean is that DCT guys may experience slip with a lower Load Ceiling Main value.

150 for me works OK but it does vary car to car and I know for others 150 at high boost results in slip. I am however not running the stock DCT flash so that may also be helping.

There's also something else at play. For example, if I run 140, at around 4 to 5K revs going WOT, the car will quite abruptly back off the power. Exactly the same as if you lift your foot quickly off the accelerator. There are no codes though. In summer, 150 at 23 psi solved this but not a 25psi. 155 at 25 psi solved it, but now the weather's colder and the car produces more power, I'm getting it at 155. Moving to 160 has resolved it but, for me, this is borderline where the misfires start.

There's also been some talk of back pressure, which may be a cause however, I don't think it's ** related. Yes, a c'less ** impacts positively but there was no change in misfires between the one I'm now running and stock.

With the setup as per my signature and a load ceiling main of 150 summer and 160 now the weather's getting colder, I can happily run 25 or 26 psi without issues - this is with 40 to 50% E, whereas the Fuelit and BMS BEFs can result in misfires if the boost target is set to >20psi. As I put at the start, this is based on my own BEF however, I have tried using the reduced Load Ceiling Main value on the BMS and FuelIt maps and it does seem to help.

What would be great, especially for DCT owners, would be a way to increase DME boost, independently control the HPFP value and independently control the DCT clutch pressure. Is that possible?

Hope the above helps.

UK 2011 - E82- 135i - N55 - DCT

JB4 | BMS OCC | N20 TMap | Fuel-It! PI | AIC6 PI Controller | Fuel-It! Fuel Lines | Fuel-It! Stage 2 LPFP | Continental In-line E Sensor | ER Charge Pipe | Pure Stage 2 Turbo | Pure High Flow Inlet | GFB DV+ | Richter C'less D/Pipe | Berk Race Full Exhaust | MFactory Pro Helical LSD (75% Bias Ratio) | eDiff Disabled Via Coding | MFactory Solid Diff Bushes | Diff Lockdown Bracket | Custom 98G0B BEF | NGK 5992s (0.020")

Last edited by keyap; 10-29-2016 at 08:59 AM..
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