Negative long term fuel trim

J

Joez4

Member
 West Midlands
2004 2.2 m54 running negative long term fuel trims
Car has had new plugs, coil packs, vanos seals, thermostat, water pump, rebuilt fuel injectors and new continental maf.

Bank 1 has a multiplicative mixture adaptation of -4.52

Bank 2 has a multiplicative mixture adaptation of -5.07

Catalyst monitor will not set but the bmw drive cycle to set it isn't easy to follow especially when the roads are busy, also keep getting fault for Bank 2 sensor 2 heater even tho car completes o2 heater monitor. I have 4 new oxygen sensors for the car but I'm on the fence about changing them as by all accounts they are very difficult to remove.

Dme reports current atmospheric pressure as 1000.94 Met Office app for my area states 1010.02 portable weather station I have states 1010 also.
Car runs and drives fine and for all I know it's always run negative or something related to the work I've done to the car has caused it.
 
The Approx 10kPA difference will only cause a very slight enrichment of your fuel system. Nothing near -5%. A broken Baro Sensor will have a high difference of several 100 kPA.

Personally, I would not worry about the -4% to -5% fuel trims. They are in the safe range and the DME is keeping control of the mixture correctly.

I had a 2.0L Z3 (M52TUB20) that ran -5% to -6% total fuel trims all the time I had it. Tried many things to improve it and could not. New Pre-cat O2's did not improve it, nor did a new MAF. I just learnt to live with it.
 
NZ00Z3 said:
Personally, I would not worry about the -4% to -5% fuel trims. They are in the safe range and the DME is keeping control of the mixture correctly.
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I agree. Total 5% fuel trim (per bank) in either direction is normal and acceptable.
 
Yeah I think it is acceptable also, the car is maintaining the ideal mixture like you say it's in safe range, just curious as to why it needs to pull fuel, I know of all the reasons why that is but don't have the tools to test them all, just hoping it's not a sign that my cats are getting blocked
 
Joez4 said:
just curious as to why it needs to pull fuel
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The DME is keeping it the safe range so the cats are not having any excess fuel getting to them. shouldn't be a problem. There's a ton of reasons that it could be like simply having slow responding lambda sensors, or leaking fuel injectors, bad MAF, etc. But until something actually goes bad it's not worth worrying about.
 
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