[ard5040]

Would greatly appreciate any constructive input here. The car is an '07 335i with 126k, mt, fbo, catted downpipes (being replaced with AR catless in 2 weeks), jb4 map 6 18psi @6000 rpm, new oem tubos. HPFP, index 12 injectors, fuel rail, coils, plugs, intake manifold, vanos solenoids replaced within last 12 months. Haven't replaced map sensor or boost solenoids. No existing codes, logs run prior to cold weather were fine. The problem started with the cold air temps, below 40 degrees. After warm up, accelerating to 4/4500 in 2nd, 3rd no problem. Shifting into 4th or 5th, between 35 & 4000 I get the half engine, reduced power warning. But there's no loss of power. DME apparently resets and light/message turns off after 45 seconds. After that initial warning, the car revs to 6k in all gears with no warning. I've read that this is not uncommon with jb4 in colder climates. True? Is there a fix?

[muncie21]

Move to FL

Just teasing. I have a similar setup FBO w/JB4 running Map 5 (auto tune) and didn't notice any cold-start/drivability problems this winter.

You'll prolly need to provide the revision of your JB4 for people to be able to help out much. The 'other' N54 site has a section dedicated to JB4 issues, perhaps ask your question over there too.

[Mike@N54Tuning.com]

Originally Posted by ard5040

Would greatly appreciate any constructive input here. The car is an '07 335i with 126k, mt, fbo, catted downpipes (being replaced with AR catless in 2 weeks), jb4 map 6 18psi @6000 rpm, new oem tubos. HPFP, index 12 injectors, fuel rail, coils, plugs, intake manifold, vanos solenoids replaced within last 12 months. Haven't replaced map sensor or boost solenoids. No existing codes, logs run prior to cold weather were fine. The problem started with the cold air temps, below 40 degrees. After warm up, accelerating to 4/4500 in 2nd, 3rd no problem. Shifting into 4th or 5th, between 35 & 4000 I get the half engine, reduced power warning. But there's no loss of power. DME apparently resets and light/message turns off after 45 seconds. After that initial warning, the car revs to 6k in all gears with no warning. I've read that this is not uncommon with jb4 in colder climates. True? Is there a fix?

Did you scan the car for codes? Turn off auto code clear (if its on) and then get a code readout. JB4 should not have any issues in cold climate / weather.

Mike

[ard5040]

Originally Posted by Mike@N54Tuning.com

Did you scan the car for codes? Turn off auto code clear (if its on) and then get a code readout. JB4 should not have any issues in cold climate / weather.

Mike

No codes

[Mike@N54Tuning.com]

Originally Posted by ard5040

No codes

There has to be a stored code if you got a reduced power warning, unless the JB4 auto clear is on.

Mike

[mike@x-ph.com]

Originally Posted by Mike@N54Tuning.com

There has to be a stored code if you got a reduced power warning, unless the JB4 auto clear is on.

Mike

+1

[ard5040]

auto clear is not on, and no stored or pending codes, I broke down and paid the dealer to run diagnostic and came up empty

[SlimE92]

Originally Posted by ard5040

auto clear is not on, and no stored or pending codes, I broke down and paid the dealer to run diagnostic and came up empty

Doesn't sound right at all did they run the scan in front of you. Whenever you get a reduced power notice a code is always stored as a fault or ghost code