engine goes rich when cooling fan is off. Please help :(

[Alessio]

I have a newly built b18c turbo engine. I went to my tuner who tuned my p28 s300. The engine ran really good with an AFR on idle at around 15-16 ( I have to get the car to emissions test). I returned home and parked the car. The morning after I started the car and idle was really crappy with an AFR of 10!!!. So I called my tuner to see if there was a problem. We noticed that the car ran AFR 10, from cold start and when the cooling fan kicked in, AFR went suddenly to 15-16, then when the cooling fan stopped, AFR dropped at 10 again. Checked all ground points and they all seem to be fine, the only mods to my cooling system are a mishimoto thermostat and fan switch.

maybe someone here has encountered the same problem.

Thank you very much.

Alessio

[lowblow]

Pls Check Altenator and Battery if is in Good condition.

[Alessio]

I've checked all the ground points till now, but I had the same result. I will try to change the battery to see what happens but I think the battery is fine. Thanks for your reply.

[Alessio]

changed the battery to a new one to be sure its ok. I also added a new ground wire going from cylinder head to negative battery therminal, but got the same result. Please someone try to suggest me what it might be as I cant find the source of the peroblem.

when the fan kicks in, there is no change neither in MAP value and neither in battery voltage (as seen on smanager). The thing which is happening is that the values in fuel table shift. to explain to you better, when the car is idleing 800rpm, it has 10AFR, on the fuel table a group of values are highlighted in red (the values which the map is currently using), duty is 2%, injectors 2ms. When the fan turns on, the red highlighted group on the fuel table shifts a colum to the right and revs at around 1000, afr goes suddenly to 16, duty around 1%, injector 1ms.

now my tuner set the car to run 16afr as I have to take the car for emissions testing.

please help.

[Spunkster]

You need to make sure you have the injector dead times set properly for your injectors. This will cause the issies you are describing when there is more electrical load.

[Alessio]

I don't think its about dead times, because when the fan starts, there is no change in battery voltage (as seen on the Smanager). Still haven't solved the problem yet.