R400D: Curious misfire

[aerobod - near CYYC]

Looking back at my old 992 traces John, I have Short Term Lambda Control Status and Final Injection Time, but Adapted Fuel 1, Adaptive Map Output or TPS Fuel + Trim would probably show a change in fueling, too.

[John Vine]

Thanks, James. 

I've found Short Term Lambda Control Status on my log.  For the future, I've amended the page to include the other four panels you listed.  I guess that will help the next time I investigate an O2 sensor failure!

This graph is the same as the first one in #47, but with Target Lambda and Short Term Lambda Control Status (STLCS) overlaid:

 

The Target Lambda plot starts at 1.0, but every so often drops to 0.0 (at 36:31, 36:46, 37:16 and 37:20).  When this happens, the STLCS appears as the green/yellow vertical bar. The corresponding Data Controller field showed "Disabled by Target Map".  I've no idea what that signifies (if anything) but it does seem to coincide with the engine cuts.  In case it's relevant, the STLCS bar at 37m 40s reads "No Sensor Type Selected".

At least this exercise is broadening my Easimap knowledge (I think).

JV

[aerobod - near CYYC]

Hi John, the "Disabled by Target Map" is a consequence of using significant throttle movements after the dip in the Lambda sensor voltage and is more during the recovery after the "cut" by the looks of it. This is normal behaviour in moving between closed loop and open loop Lambda control. I think it will be difficult to determine the exact failure mechanism without fuel injection values, although the circumstantial evidence certainly points to the original Lambda sensor being faulty.

Although there are different mapping conditions that disable closed loop Lambda control, the primary mechanism is the target lambda map vs RPM and Throttle Site. Typically above about 4500RPM and Throttle Site 7, the target Lambda will be 0.0, which indicates control should be disabled. 

[Geoff Brown]

From conversation here & a couple of PMs with JV it seems the Lambda Sensor was the culprit. 

Should it be something that is changed at a certain mileage/calendar point considering the stress it comes under in a Seven exhaust ? Especially when a cat pipe is fitted & considering in general the 2.0L Duratec in higher output form tends to run just a tad rich.

The sensor is obviously an 'on condition item'. Research on line brings up all sorts of 'recommendations' to change between 60,000 & 100,000 miles. BOSCH quote a probable up to 40% increase in fuel system efficiency if the sensor is changed at a suitable time but do not state at what point.

With no arbitrary replacement information I suppose it is a case of 'if it ain't broke don't fix it'. 'When it breaks fix it'. And carry a spare in the boot when touring ?

[John Vine]

Thanks, James.  That's really helpful, and adds to my slowly increasing knowledge.  Next time, I'll have the injection info logged.

And carry a spare in the boot when touring ?

I think that's a wise precaution, Geoff, and is certainly what I do.

JV

 

[cobar]

Unfortunately, Caterham doesn't mount the O2 sensor in an optimal position for longevity. The various aftermarket WBO2 controller manufacturers and Bosch all recommend positioning it at least 10% above horizontal to avoid moisture generated during cold start up from pooling on the sensor. In contrast, Caterham places it below horizontal. For my upcoming build, I plan to have the sensor mount relocated to address this.  This doc is a good read on sensor mounting best practices: https://wbo2.com/lsu/LsuInstal.pdf 

[John Vine]

I hadn't realized that the angle of dangle was so marked:

Thanks for the PDF link.  It deals with wide-band sensors, but can we assume it applies equally to narrow-band sensors?

JV

[aerobod - near CYYC]

The narrow band sensor is just as vulnerable to thermal shock from condensation as a wide band sensor. I think the mitigating factor for Caterhams is that they are more likely to be driven on fine warm days than other vehicles, compared with a high humidity and cold winter day, so the probability of exhaust condensation in any quantity is lower.

[StevehS3]

I imagine the pops and bags on overrun don't help either (if applicable). 

[Geoff Brown]

#59 - Don't forget the flames !!

[John Vine]

Hi James,

I added the extra panels you suggested, and recorded another in-flight log of about 55 mins, including a 10-min stop.  The car ran impeccably throughout.

This shows a 25-sec snapshot:

 

Traces (from the top):

Green - Short Term Lambda Control Status
Purple - Adaptive Map Output
Orange - Lambda
Brown - Engine Speed
Dark Blue - Final Injection Time
Purple - TPS Fuel + Trim
Light Blue - Adapted Fuel 1

(the last three all pretty well coincide)

My query relates to the traces between 47:06 and  47:10 (around the vertical pecked line).  Lambda is flat and the bottom three are zero.

What (if anything) do these traces suggest? 

JV
 

[aerobod - near CYYC]

Hi John, it looks like you took your foot off the throttle and the revs were above a certain fuel-cut limit. I'm not sure what that limit is in the locked Caterham ECU, but I have it set to 3000RPM in my map. This will cause Lambda to go lean (high value) as fuel is not injected until the engine speed drops to that limit if the throttle stays closed. The fuel injection times show that no fuel is being injected during that "coasting period" from 47:06 to 47:10 and also during the gear changes when you take your foot off the throttle, but during the gear changes they are brief enough that the Lambda doesn't get a chance to be detected as lean due to some fuel still in the inlet tract.

[John Vine]

Many thanks, James. 

Looking at the timeline, I was probably descending a steep hill at the time on the overrun, with foot firmly off the gas.  

JV