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Loss of revs, power then stall, when cold.


RobinB5

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When I drive my S4 from cold (or after only a couple of minutes or so warming up), after a minute or so of driving I get a loss of power, revs drop then it stalls. Restart immediately and the problem either happens only once again, or doesn't reappear at all. When driving off after a longer warm-up, the problem never occurs.

I took an Espritmon log today when this problem happened. The only correlation I could find was that the start of the loss of power occurred the first time the system went from Open Loop to Closed Loop:

image.thumb.png.b33ece313b534e4a0b86dc0bd7a7e73b.png

Revs drop to below desired idle value, increasing TPS has little or no effect, then the engine stalls.

In this case after a couple of restarts, the problem goes away, the O2 sensor enters its 'wobbling all over the place' phase at the next open/closed loop change and all is good:

image.png.b5c06117b3ea055bc6158ab4b3e0e9eb.png

As the engine stalled, a few seconds after the problem manifested itself (drop in revs regardless of TPS etc.), a QDM-B error was thrown. Last time the same thing happened an O2 sensor error was thrown. 

It would be interesting to understand under what circumstance does the O2 sensor voltage start to wobble all over the place (indicative of good operation), why this happens on a closed to open loop condition when there is no subsequent problem, and why the first time my car goes from closed to open loop, and the stall occurs, is my O2 sensor not reporting the wobbling signals yet?

Note that when the car is fully warmed prior to driving (coolant temp @ 82degC) this issue does not occur.

Dodgy O2 sensor that needs to be warmed up prior to being able to signal correctly?

Any guidance or explanation would be very welcome! Thanks in advance :)

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I have no experience with Esprit mon (cross fingers, not had a problem yet).

 

But I think it is interesting that the AFR goes up, the IAC goes up (makes sense) but the Injector pulse width also rises.  Also Why does the Spark advance rise, that may  be normal operation to prevent stall.

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The spark advance rises to the value set by the 'Spark Reference Angle' parameter (74.9 degrees) because the engine speed dropped low enough to revert to EST Bypass mode where the ignition module determines the spark advance and remains there when the engine stalls.

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23 minutes ago, sailorbob said:

You say this is a cold start problem but the Espritmon screenshot shows a warm start, which is correct? Also, have you figured out which quad driver circuit is causing the QDM-B fault?

It happens when not completely warmed up, this time it had been started for a minute or so prior to the espritmon recording,  the stall happened about a minute after that. Not hunted down the QDM-B fault yet, but that is thrown a second or so after the stall had happened, in fact I think it could even be thrown as I switch the ignition off. 

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The QDM-B error is probably due to the ignition being turned off and therefore not relevant.  Note that the 'CL' LED does not indicate that the fuelling is being controlled in closed loop mode, merely that closed loop mode is permitted if the appropriate conditions are met.

I believe the stalling is caused by the 'CL Correction Term' value dropping significantly, possibly to a zero value from that screenshot. This big question is, naturally, why is that happening.

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Yes, that blue line. It is a multiplier of the 'Base Pulsewidth' (aka BPW) and is derived from the lambda sensor input and is used to cause the switching of the A/F ratio about the stoichiometric A/F ratio.

I suspect the lambda sensor could be cause of this problem. If the ECU is seeing a rich mixture that does not lean off as the BPW is leaned out it will keep on leaning out until you get the stall if this happens before the ECU decides there's a problem with the sensor. Check the datalog and see if this is indeed what's happening.

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So I've noted from other logs, when enough time was allowed for the coolant temp to settle at ~82 then drive off, with no subsequent stalling, that the integrator line was flat up until CL was permitted, then the O2 sensor does its wobbly thing and the integrator line wobbles around a bit.

In this case the O2 sensor didn't really change much at the open to closed CL point, seemingly correlated with the subsequent stall. These sensors need to achieve a certain temperature before they can measure O2 levels, is that correct? Some come with internal heaters, others rely on being heated up by the exhaust gas. I don't know what type the Esprit has. If the latter, then can it only go closed loop when it gets hot enough? In this case, does the ECU think it's up to temperature, goes closed loop, but the O2 sensor is not ready to sense, sends a crap signal back then screws up the fuelling logic? Or am I thinking too much about a subject I know too little about! :)

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I'm not sure how to check the datalog from Espritmon, other than what ever is presented in its gui. I've not installed Freescan, would that yield some more detailed info?

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I've also noticed that the O2 voltage reading, just after I started the car after the stall, both times, read 1.1V. Considering these things should only go up to 0.9V, it does rather look like it's not a happy bunny. Think I'll order a new one anyway. Thanks again @sailorbob

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The Esprit uses a Zirconia type heated lambda sensor. The heater is used to reduce the warm up time of the sensor. It also allows the sensor to be mounted farther away from high thermal loads such as that created by the turbocharger and keep the sensor hot when it may otherwise cool down during times such as an extended period of idle.  The Zirconia type can output a voltage between 0 V and 1.1 V and from some datalogs I have just checked it occasionally does go over 1.0 V.

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Espirtmon doesn't indicate the actual values, just this bar plot:

image.png.d5aa5933117a4a9fff7ab09f277fe211.png 

From the manual 'Red bard above the line indicate compensation for engine running lean, below the line compensation for rich'. So from what I understand if there were no red bars, BLM would be 128. It's a little below for cell 1 and 5, more for 16 and 17. 19 is the idle one, right?

One other point to note, the previous 10+ year old battery on the car that I used for the last 12 months would drain quite quickly. I charged it each time before having a spin, there was a chance it might have totally drained between drives. Last week I put a new battery in, so the battery was obviously disconnected for that. It's certainly busy learning at the moment, if the battery did drain totally before, possibly often, maybe most journeys were the start of the learning process? Just a thought. Even so, don't think it should stall when learning?

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In later versions of Espritmon I have added the capability to save the first 1 KB of RAM to disk in the file espritram.bin. This is done when you press the v key.

In this file the whole table is available. The contents of BLM cell 0 is at location 0x0016, cell 1 at 0x0018 etc.

Good luck,

Erik

 

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6 minutes ago, sailorbob said:

I think you meant to say cell 1 is at 0x0017 :)

Hi Bob, I will recheck, but from what I remember there is always a byte between the stored BLM values, so the 0x0018 was intentional, not a typo. I first need to find my original source of information.

Erik

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@sailorbobhere you go. (The spikes for both integrator and BLM don't show up on Espritmon (maybe some kind of filtering going on)). Generally, BLM drops to ~60% and back up a few times before and whilst problems occur. But no worse than when the O2 sensor kicks in and it goes closed loop for the final part of the drive where no problems are experienced again. 

image.png.c36768e338960b4cc2936d13dedc8488.png

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I think we can say with almost certainty that the Integrator dropping to zero is causing the stall.

You have an oddity with the BLM values too as the graph above shows the maximum being almost hit a couple of times and I'm guessing the minimum being hit three times (I say guessing because you aren't running a standard S4 calibration and the 'BLM Min' (aka KBLMMIN) parameter appears to have been altered).

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Well @Barrykearleyfound that this S4 is running an S4s memcal, don't know if that has a bearing. Generally @sailorbob, is it fair to assume that the lambda sensor is a bit buggered, leading to dodgy Integrator values, leading to the stall when it first 'can' go from open to closed loop, and so would benefit from being replaced?

image.thumb.png.b47b2bb2cce55c3700d03026450b1d32.png

And finally, many thanks for all your input, it is very much appreciated and I've learned loads :)

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