Stall in reverse downhill when come to stop
 

Does anyone have any ideas about the stalling issue I'm having with my 2010 XF 5.0 V8? Here are the details:

• First start of day (cold start) but not necessarily cold outside. Temps have been as high as 60s or in the 20s.
• Backing down driveway on slight downhill, maybe 15 degrees from horizontal
• Hit the brakes and come to full stop (usually because a car is passing by on my street)
• RPM drops to 0.
• Car stalls
• Check engine light comes on
• I can "save" it if I take my foot off the brakes or switch to P.
• Restarts no problem in same spot on driveway
• After restart it will run in reverse at a stop no problem
• No codes
• Dealer had it for 3 weeks and could duplicate issue but had no idea
• Dealer opened case with JLR but still no idea
• Dealer suggested 5 hours of time to take apart car and check fuel lines
• Coolant temp sensor replaced by dealer just on a hunch but no help
• Petrol flange checked out okay (I had seen a video about a stall caused by a short on some electric connector on the flange)

I have some videos of it happening but they are too big to upload. I'll try to cut them down and upload. Has anyone experienced this stalling issue or have any idea of the root cause? I really appreciate any help.

If the MIL is on there will be code(s) even if some tool(s) won't reveal it/them.

Cutting out can be various things such as an air leak (perhaps related to braking).

Thanks JagV8. What tool are you referring to? The MIL comes on solid when the car stalls but it goes off on restart. Also appreciate the tip about the air and braking. I’ll look into it and please let me know any more specifics you may have.

Ah... in that case maybe it won't have a code. The earlier cars would normally have such as P1582 (records lots of data when e.g. a stall occurs) and you'd need SDD/IDS to decode it. I don't know for yours, sorry.

Live data from stall - help needed
 

Had stall this morning while recording live data on ALR 539B code reader. Data readout is attached. Stall was at frame 18 (out of 23). I've looked through the data but I have no idea how to interpret it. The most dramatic change I see just before the stall is in CATEMP11. It drops from over 900 (in frame 17) to 400 (in frame 18). I'm not sure if this means anything or if this data change is a clue to the cause or is a symptom. Also see load % go from 40s to almost 80, MAP goes up, and TP_R goes down right before stall but no idea what any of this means either. Can you please review the data and let me know if anything jumps out at you? I really appreciate any help or insight.

It's a puzzle, not least because we can't see which original thing causes which others.

I'll try "thinking aloud"...

MAF drops to zero, which will mean no fuel is injected and a stall is inevitable then.

But why does MAF do that? I don't think the data shows that (but I could be wrong).

I suspect an air leak might do it, or the throttle closing, or an intermittent MAF signal.

Suppose it's the throttle, it could be any of a few causes, e.g. because the car (well, the PCM) thinks there's no/less demand (e.g. the accelerator pedal input says so, presumably in error), or the throttle plate itself could jitter a bit.

In case it's a sudden air leak... something flexing? A crack opening?

When this happens I’m coasting backwards down my driveway with my foot barely on the break, then I hit the brakes to stop full (about frame 17) and it stalls.

Things will flex, vacuum will be used as well, so probably related to one of them.

I’m curious. Did you ever get this issue resolved?

2011 XFR - I just had this exact thing start happening to mine, which is how I stumbled on this thread looking for answers. Cold start, after rpms settle for roughly a minute or two, throw it in reverse and start backing down the driveway (its not steep but also not level, hardly an incline), about 15 feet into reversing the rpms stumble and if I don't "catch" it by going full brake it will stall. Fires right back up though an no issues when warm or on the rest of the drive. Hoses all look good, nothing obvious, no check engines lights. It's truly odd and definitely hope someone could shed some light on this if they also experienced it.

An intermittent air leak maybe e.g. something opens when in reverse as the engine moves a little.

I'd suggest possibly the brake booster vacuum is leaking down overnight, the first application of the brake delivering a larger-than-normal amount of air into the intake system which increases manifold pressure (i.e. loses vacuum), cold engine sensitive to the resulting lean mixture. Just a theory, possibly worth investigating.