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rallas rallas is offline
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Join Date: Jun 2021
Car: 2016 BMW 435i
Default N55 on JB4 hitting limp mode and Boost Pressure Lower Than Expected code - 09-01-2021, 09:17 AM

I have a 2016 435i with EWG N55 and 8 speed. About 6 weeks ago I installed the BMS charge pipe and VRSF 6.5" competition intercooler. Only other mod is a K&N drop in filter. I installed the JB4 about a month prior to installing the intercooler and ran Map 1 with no issues. I would hit 12psi consistently on Map 1.

Around the time that I installed the intercooler and charge pipe I began to get occasional codes 104301/104302 for absolute pressure sensor, intake manifold plausibility, caster pressure too high or pressure too low while running map 1 or map 5. I thought I had boost leaks because none of the boost values seem to get close to the 12psi that I was seeing on Map1 before the intercooler install. I replaced every o-ring and seal on the charge pipe and intercooler and can't find a leak. I still cannot hit 12psi on Map 1 or even on Map5. If I run factory boost on map 4 it will run all day long with no issues or codes and the boost levels get to the ~8psi factory target without excessive wastegate duty levels.

I have noticed that the ign_x advance numbers will start varying on individual numbers when I run Map1 or Map5, but run the same on all cylinders on Map4. I don't see any indications of timing being pulled on all cylinders. We have good 93 octane in this area and have not had issues on my other turbo cars running the same 93 octane. I installed NGK 97506 plugs at the same time that I installed the JB4, gapped to 0.022".

I have noticed that AFRs can stay in the low 15s on 100% throttle runs and only dip to the low 14s which seem high to me. I know DI runs with higher AFRs under load, but I would expect to see it get in the lower 14s or 13s for high load. On Map4 runs I will see low 13s at high load and high rpm.

I have had 3 instances over the last 6 weeks where I hit limp mode and threw 120308 Boost pressure lower than expected code. Twice this past week. These are shown in the two attached logs.

For the log dated 08/30, I was initially just running map 4 with no issues, but changed back to map 1 and did a few pulls. The first two pulls seemed fine. On the last pull (end of attached log) I got the Drivetrain Malfunction-Drive Moderately message on IDrive, hit what felt like limp mode and code 120308 Boost pressure lower than expected showed up. Cycled power and it cleared and ran fine.

I did better 4th gear pulls this morning (see log dated 09/01) starting in Map 4, with no issues. Changed to Map 1 and did 2 pulls with no codes or limp mode. On these Map 1 pulls I noticed that I am only getting 10.8-10.9psi peak boost (as I have seen since installing the intercooler). wgdc only goes up to about 60. AFRs only drop to the low 14s at the end of the run. Fuel trims suggest that the ECU is trying to add fuel, but does not appear to be adding enough. Fuel pressures look good with fp_h staying around 18 at under load.

Then for the last two pulls I swapped to Map 5 since Map1 was not getting me into limp mode. The first Map5 pull was OK, but it did not get more than 11.2psi boost with the wgdc at 99. AFRs look about the same as the Map1 runs.

The last Map5 run it hits limp mode, gave the Idrive message and threw 120308 Boost pressure lower than expected code. During this pull it doesn't see more than 9.9psi boost and AFRs stay at ~15. Cycled power and everything went back to normal and I am back on Map4 till I get this crap figured out.

I am still not 100% convinced I don't have boost leak so I will be looking into smoking the intake components. I do need a peer check on these log files. I come from the world of turbo Miata's and Megasquirt, but all this fancy direct injections stuff is new to me. Any insights would be greatly appreciated.
Attached Files
File Type: csv P10_M4_R8_210901_0724 Map5 Limp Mode 2.csv (33.3 KB, 46 views)
File Type: csv P10_M4_R10_210830_0749 Map 1 Limp Mode.csv (30.3 KB, 44 views)
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