[Recker]

Just after a bit of feedback. My E90 335 is very rough on start up in the mornings. When i start it, the car will do a little shake for a few seconds. Did a bit of research and seems it could need the coil packs replacing. Has anyone else had this and am i on the right track?
Cheers

[vtl]

Sounds like leaking injectors if it only happens on cold starts. Excess fuel that has leaked over time in the cylinder takes a short time to burn off and the car will drive fine afterwards.

Get MHD and data log your cold starts, it's quite easy to diagnose by looking at the air fuel ratios

[Recker]

Originally Posted by vtl

Sounds like leaking injectors if it only happens on cold starts. Excess fuel that has leaked over time in the cylinder takes a short time to burn off and the car will drive fine afterwards.

Get MHD and data log your cold starts, it's quite easy to diagnose by looking at the air fuel ratios

Will try that. Thanks mate.

[aaron_]

If you haven't changed air filter, plugs or coils lately I'd start there. Clean the MAF sensor whilst you're at it. Do a walnut blast next. After that replace injectors. If non of that works drive car off cliff :-)


Also vtl, I'd like to find out about the health of my injectors. What numbers should I be looking out for off a cold start data log? I have a custom tune with MAF rescaled to accommodate my afe oiled intake. Will that affect my afr's?

[vtl]

Afrs on idle should be 14.7:1 which is 14.7 parts air, 1 part fuel. Larger numbers mean more air, meaning lean and less fuel, lower numbers mean rich and more fuel. There is an oxygen sensor which reads the afr on cylinders 1,2,3 and another on 4,5,6 on n54. On n55 you only have 1 O2 for all six cylinders

On a cold start, in the first 5-10 seconds the O2 sensors will be cold and won't give a proper reading. Once they give a proper reading you can use the afr readings to diagnose

While it's running rough a leaking injector will cause the afr to go rich (number lower than 14.7:1) and the afrs will be quite unstable. This is because there is an excess of fuel in the mixture. Once the fuel has been burned out it'll go back to 14.7:1. Classic injector leak.

[Recker]

Originally Posted by aaron_

If you haven't changed air filter, plugs or coils lately I'd start there. Clean the MAF sensor whilst you're at it. Do a walnut blast next. After that replace injectors. If non of that works drive car off cliff :-)


Also vtl, I'd like to find out about the health of my injectors. What numbers should I be looking out for off a cold start data log? I have a custom tune with MAF rescaled to accommodate my afe oiled intake. Will that affect my afr's?

" Drive off cliff " hahaha