Datalog BMW 135i Cold Start Rough Idle (fine when JB4/MHD removed)

Phillstine

Lurker
Dec 6, 2021
13
0
0
Hi Guys,

I've been having a problem with my car for a while and have replaced loads of things to no avail.

On starting only when cold and left for over 24 hours the first start up is rough and stumbles and misfires badly for 10 seconds.

I've replaced Injectors to Index 12
HPFP replaced
Low pressure Sensor replaced
Sparkplugs replaced
Coil replaced
Vanos Solenoids replaced
Inlets Walnut Blasted
New Turbos

I don't get any codes, I notice that when starting it's fine until the JB4 wakes up (Needle Sweep) then starts running poorly so I removed the JB4 and it would start fine every time. I then Mapped the car with MHD and the problem is back, flash back to stock starts perfect again.

Is there something in the fuel tables on MHD/JB4 that effects start up different to stock?



Thanks you in advance for your help!
 
Last edited:

KClemente

Corporal
Nov 26, 2019
213
99
0
Ride
E90 335i
Is your cold start still enabled? Your timing is hitting deep into the negatives which will slow the idle down and then the PID will try and raise timing and then get caught into a loop.

What spark plugs are you running and with what gap?
 

Phillstine

Lurker
Dec 6, 2021
13
0
0
I currently have cold start delete running as it stops the roughness being so aggressive until you put it into gear (bringing the rpm up). Without cold start delete it will sometimes be so bad it will stall.

The plugs are just the standard Bosch plugs, no adjustments to the gap. Although I had the problem before I changed the plugs and it ran fine on the old plugs for a good few thousand miles.

Thanks
 

BloodyZ4

Lurker
Mar 17, 2021
17
6
0
Germany
Ride
Z4 35i DCT
Can you log Laufunruhe?

I had a similar issue, turned out one of my new index 12's was faulty.

That way you can identify which cylinders are causing the issue. Then start with swapping plugs/coils on that cylinder and see if it moves to the swapped one. If not it’s the injector.