S65 AMG misfires (not the usual)

[alexanderfoti]

I can imagine!

Unfortunately, like the rest of the UK, we have ground to a half because of a small bit of snow. None of my bits have arrive so will have to be on hold for a bit.

 

[alexanderfoti]

Can anybody help explain my fuel trims above.

I THINK that selfadaption in idle speed range = Short term fuel trim and that the value is representative of injector open time adjustment.

Therefore, at idle, the car is removing a small amount of fuel from the left bank, and slightly more fuel from the right bank. Is that correct?

Additionally, my Self-adaption in lower and partial = Long term fuel trims?

If that is correct, it would indicate that its removing fuel from the left bank and adding a small amount of fuel to the right bank.

Is this accurate?

 

[alexanderfoti]

To satisfy my curiosity I checked with an OBD standard reader and it gave me.

STFT Bank 1 - -7.81%
STFT Bank 2 - -4.69%

LTFT Bank 1 +0.78%
LTFT Bank 2 -0.78%

So bank 1 (right bank) is being enriched and Bank 2 (left bank, one with misfires) is being leaned out.

Those match my DAS value interpretations. I wonder if it is as simple as a dodgy o2 sensor, as:

This car has no MAF's (MAP speed density calculations)
No air leaks in the vac system (vac tight for 2-3 minutes)
No air leaks at all, entire intake system is boost tight to 25 psi.

 

[LostKiwi]

Does this help?
http://www.austincc.edu/wkibbe/lambda.htm

You can easily test for a bad O2 sensor by disconnecting it. That will force it to run off the map. I would clear adaptations first as they will remain in use and if bad will force more bad running.

 

[alexanderfoti]

Does this help?
http://www.austincc.edu/wkibbe/lambda.htm

You can easily test for a bad O2 sensor by disconnecting it. That will force it to run off the map. I would clear adaptations first as they will remain in use and if bad will force more bad running.

Thanks, Cant do full load test with the o2 disconnected though, it will be in limp mode.

Will have a read through that tomorrow.

 

[LostKiwi]

Might need Dyno time then. Correlate lambda and emissions.

 

[oigle]

I always thought O2 sensors were only effective at idle and on cruise to obtain the best economy. Under full throttle, where your problems lie, they are ineffective. My knowledge base is many years old :-(

 

[LostKiwi]

I always thought O2 sensors were only effective at idle and on cruise to obtain the best economy. Under full throttle, where your problems lie, they are ineffective. My knowledge base is many years old :-(

To be honest that was my understanding too. When cold the car runs open loop (map only) then as it warms up at around 70c it switches to closed loop (lambda control) and will stay on lambda control unless full throttle is asked for (when it again goes open loop).

 

[alexanderfoti]

I always thought O2 sensors were only effective at idle and on cruise to obtain the best economy. Under full throttle, where your problems lie, they are ineffective. My knowledge base is many years old :-(

It's true, they are, but long term fuel trims that are learned over time are applied globally to the mixtures, even under full throttle or other situations that wouldn't be using o2 correction.

If the car is leaning out the mixture whilst in closed loop, and its added -10% to the short term fuel trim during closed loop and this ends up being there long enough to end up in long term fuel trims, then this - 10% trim will end up being applied as a base to ALL mixture formation.

I think my explanation makes sense but I am not great at explaining it.

 

[oigle]

As I said, my knowledge base is rather old...like me!!

 

[alexanderfoti]

Backpressure tester arrived today.

cats not blocked.

I played about on the weekend though. I always had a slight rough idle on cold starts. Smooth running showed 25+ faults on cylinder number 10 when cold for approx 30 seconds. Compression test etc on that bank was all good so I dismissed it.

If I reset the adaptions and do a cold start with the o2's unplugged, it doesn't do it. Suspect O2 sensors are lazy or biased!

Waiting on new o2 sensors to confirm.

 

[alexanderfoti]

New O2 sensors fitted. Fuel trims are now in the positives on both banks.

OBD reading :

LTFT Bank 1 +4.45%
LTFT Bank 2 +3.78%

It does jump around a bit, but I suspect this is because I watching it while driving.

I haven't had a chance to try full throttle acceleration in 2nd, as traffic has not been permitting.

Will keep this thread updated.

 

[LostKiwi]

That looks a bit more sensible

 

[alexanderfoti]

That looks a bit more sensible

I agree, car has larger intakes and not standard, so makes sense that its adding fuel while driving around off boost.

 

[LostKiwi]

More to the point it shows a balanced fuelling regime. On the old r129.066 a bad O2 reading (it has a single lambda in the cat) can be down to an issue on one of the banks creating an issue on the other one causing a self perpetuating fault. For example if one side has an air leak the O2 sensor will richen the mixture for all cylinders creating an over rich condition on the other side as the sensor averages the two. Nett result one side runs lean and the other rich which can then create random misfires.
At least yours separates the two banks (as long as the ECU fuels each bank independently on the basis of individual O2 sensors).

 

[alexanderfoti]

More to the point it shows a balanced fuelling regime. On the old r129.066 a bad O2 reading (it has a single lambda in the cat) can be down to an issue on one of the banks creating an issue on the other one causing a self perpetuating fault. For example if one side has an air leak the O2 sensor will richen the mixture for all cylinders creating an over rich condition on the other side as the sensor averages the two. Nett result one side runs lean and the other rich which can then create random misfires.
At least yours separates the two banks (as long as the ECU fuels each bank independently on the basis of individual O2 sensors).

I agree, leaning out one side and enriching the other never seemed right to me. Have high hopes for this.

My cold start rough idle is still there though, Smooth running shows 15-20 faults on cylinder number 10 when cold, does it when it drops off high idle.

Not plugs, ignition, cold compression test gave 125psi. Thinking a possible bad fuel injector. Only does it under light load, if you put it in drive straight away it doesn't do it.

 

[LostKiwi]

125psi seems low to me - I'd expect over 165psi. What were the other cylinders?

What's the compression ratio? As a rule of thumb I work to 8:1=140psi, 9:1=165psi, 10:1=190psi ideally (unless it's fitted with race cams when they will all be lower).

 

[alexanderfoti]

125psi seems low to me - I'd expect over 165psi. What were the other cylinders?

What's the compression ratio? As a rule of thumb I work to 8:1=140psi, 9:1=165psi, 10:1=190psi minimum (unless it's fitted with race cams when they will all be lower).

9:1 ambient temp 3 Degrees

Engine was stone cold though, would expect higher on a warm engine.

If it is indeed low, may confirm my dodgy valve theory.

 

[LostKiwi]

Compare to another couple of cylinders and see what that shows up.

 

[alexanderfoti]

Compare to another couple of cylinders and see what that shows up.

Ah I remeber now, I did that already!

Number 11 and number 9 where all 125psi as well, so I stopped worrying about it.

Edit: of course, the gauge could be off a bit as well!