A/F ratio adjustment??? - The Unofficial BMW M5 Messageboard (m5board.com)

Fordkoppie · 2nd November 2009, 21:38

HI everyone,
My S38B36 engine is now finally run in after 1200km of not taking it over 4000rpm.
So yesterday i floored it and took it for the first time over 4k and then, DISAPPOINTMENT!!
It goes nice up to 5000rpm and then chokes(does not want to go any further) when 'Wide Open Throttle' is achieved.
What was strage to me is that if you floor it and lift your foot just 1 - 2 mm up, then it revs smooth all the way to 7000.
I then bought a set of new spark plugs and it was better but the point of trouble now doesnt start on 5000 anymore but the same problem now arises at 6000rpm. it still goes smooth when just OFF W.O.T.
To check, i drove it with a gas analyser and the a/f ratio stays on +- 14.7 the whole time, but as soon as it is on W.O.T it overfuels the engine completely starting at a/f 12.9 at 3000rpm and rising up to a a/f ratio of 10.5 at 6000rpm where it starts choking.
What went wong??

Could the software go corrupt while standing without a battery for 4 months?
Can the mixture be adjusted or reset at all, because it seems to me that the allen adjustment screw on the MAF only affects idle and very small throttle opening?
This is now after i tried new: plugs, ht leads, distributor cap, rotor, MAF with no effect exept the plugs that extends the problem a 1000rpm further down the rpm range.
Thanks in advance
Chee"RS"
PS- the south african versions had no lambda sensors, nor cats, nor air pump, nor egr

marekd174 · 2nd November 2009, 23:23

Check your throttle position sensor as well as the ECU temperature sensor.

XaQ · 3rd November 2009, 04:47

Mine is doing the same thing! I haven't been able to diagnose it properly yet, but after I fixed my tach I realized it was hitting a brick wall at about 5000-5500 rpm. I'll try lifting off the throttle to see if it'll go to 7k.

Fordkoppie · 3rd November 2009, 20:19

Thanks, but how??

Cyrus · 3rd November 2009, 22:40

I just finished doing an S38B36.

Throttle switch was not working properly and it was SLOW.

You need a simple diagnostic check which shows a datastream. Just look for the throttle switch going to full load. If it remains on part load then either the throttle cable needs slight adjustment or the switch is not working.

The amount of power your missing on a 3.6 is around 20hp if your throttle switch is not working.

Same goes for the temperature sensor, you can see if it's working with diagnostics. If it's not working the ECU will cause massive over fuelling.

Your problem is sensor related.

marekd174 · 4th November 2009, 01:15

You can check it using an Ohm meter. The spec for the ECU temperature sensor is (value at 20C ambient is 2300-2700ohms, at 80C operating temp is 300-360, it's the same part as an E30 325 and lots of other cars). The TPS
(also same as E30 325e/M3 or E28 525e if with rectangular plug, located at the #1 cylinder throttle body) can be checked by seeing that the resistance at idle is 0 ohms and at full throttle 0 ohms. I can't think which pins at the top of my head, but a search should answer that for you.

Fordkoppie · 4th November 2009, 17:25

Is the ecu temperature sensor the one on the waterjacket above the exhaust, or the one in front of the engine , or the one in the air intake filter box?

marekd174 · 5th November 2009, 00:44

Quote:

Originally Posted by Fordkoppie

Is the ecu temperature sensor the one on the waterjacket above the exhaust, or the one in front of the engine , or the one in the air intake filter box?

The ECU temp sensor is the one in the waterjacket above the exhaust. The one in the intake is the intake temperature sensor.

XaQ · 5th November 2009, 05:56

My TPS isn't indicating WOT. It was good last time I checked it, must be an intermittent failure.

Tomba · 5th November 2009, 14:11

It seems his throttle switch is working fine (does the resonance flap works?), particial cruise = 14,7 AFR and @ WOT it enriches to much fuel. Also if his water temperature sensor was not right would it be running 14.7 @ particial load? (i don't think so). Because the car has no lambda sonde it won't adapt fuel AFRs. Maybe the wires of the water temp. are interrupting the signal (quite common). Therefore you better check the resistance at the sensor self and the pin connections at the DME. If it deviates to much you know your wires are the cause.

Maybe to much fuel pressure (check fuel pressure particial (3bar - x bar vacuum) and full load 3bar), leaking injectors or less air : bad cam timing, blocked air filter.....

I have the same problem with my E30 323i when i am on LPi (gas), seems my ecu adapts the mixture to lean and causes a to poor mixture @ full load / high particial load (still tries to adapt to 14.7 AFR). Base injector constant or conversion from petrol opening signal to LPi opening signal in the LPi ecu seems responsable, i need to change it.