M20 AFR problems.

[digger]

I am running a stock m20b25 in my 325is apart from a powerchip.

The first graph shows:
- 2 runs with Powerchip and all esle setup as i arrived (red and blue curves)
- 1 run with Powerchip after the guy adjusted the AFM spring tension(later returned it to its original setting) after finding someone had tampererd previously(green curve).

notice the leaning out at 95-100 kph (:( ) What could cause that?

The second graph shows
-2 runs with powerchip in a different ECU and a different AFM (two curves with highest kw at 4900 rpm.
-3 runs with standard chip in same ECU as first graphs.
-1 run where he stuffed around a bit which can be ignored (obvious one).

notice how the two chips, ECU and AFM showed the same LEANING OUT characteristics at 4800RPM. The powerchip only showed gains at 4300-5200 rpm where the AFR was where it is supposed to be at a reasonably low 13's. The days were >30 degree celcius and uncorrected so i am unconcernecd about the power output (which peaks at 4900rpm) which is down 20% (need a top end overhaul).

I have new pump, stock inj, FPR, ignition equipment (plugs cap rotor and wires) seem to be in good shape.

I later took my car to a experienced BMW guy and he connected up a motec computer thingy with an O2 sensor in the tail pipe. He drove me around on the street and we looked at the digital readout of the AFR. it started at 14.7 at low rpm and steadily lowered to 14.4 at fuel cut-off. It confimed its running lean but showed no dips and rises like the gas analyser at the dyno place.
He also said that my injectors are too small (new stock ones) and that my AFM was ok interms of those diagnositic tests anyway.

What is causing those dips and rises as i have seen another 325i with the same shape AFR but propertionally richer.

Any ideas what to do?

[Jordan]

Your fuel injectors are your problem.

[digger]

Your fuel injectors are your problem.

I have stock brand new injectors and i am thinking the same, but what has me questioning the idea is that if you look at the 2nd graph at 4700 rpm it starts to lean out and then at 5900 rpm its starts to richen up.....why would it do that? Its not a very gradual change either which would be expected if the flow rate was a bit too small.

I tended to think that it was the AFM at the time due to the almost random pattern but if anything it should be running rich (spring tension is low and the output is 4.5V when flap is fully open)

Also the 2nd place i took it to (where we physically drove around the streert with an O2 sensor up the pipes) didn't show that leaning out and richening up characeristics (very strange) it just ran lean (14.7 richening up slightly to 14.4 at redline) the whole time which is hinting at the injectors.

I have put some 18lb injectors in and it drives and sounds different (probably slightly rich) but i'm going to leave it until i do the head and a few other mods and get a piggy back Unichip to give some decent AFR control.

[RobertK]

the 17.5lb or 19lb Bosch injectors are probably your best bet.

[SpecM]

the 17.5lb or 19lb Bosch injectors are probably your best bet.

-17.5 lbs = m50 squirters, correct?

[digger]

latest results with 18lb injectors all else stock.

one run stock chip another with P'chip

[silversleeper]

what car did u pull the 18lbs injectors from? and what is a p'chip?

[digger]

some Ford (EA Falcon) and P'chip = Powerchip.


Chip is for sale as i am moving up to Unichip piggyback on Thurs.

I'd guess and say the chip is best on a standard 325i as it has not been set for my bigger injectors so its way too rich but still manages to equal and sometimes exceed the stock chip purely due to the revised timing with proper fuelling it would be a good mod along with the much better responsivesness.