Hello all. At the outset, I do want to appreciate the wealth of information on this forum and the always ready to help community. I need help with trouble shooting a starting issue on my 2018 xjr575.

It all seems to have started when the car started dying down occasionally upon start up. Cold engine or warm engine starts did not seem to make a difference. It wasn't all the time and initially it seemed that it needed a few cranks before the engine fired up. It finally threw a check engine light and I took it in to the dealer. Did not have a diagnostic tool at that time. Initial diagnostics at the dealer gave a code for low fuel rail pressure at the dealer and they recommended replacing the HPFP pumps (apparently a common issue with these cars according to them at high mileage - mine has a shade over 99,000 miles on it and has been good so far). They did check the concerned sensor and reported that the sensor is okay. Initially, I had wanted to replace the HPFP pumps myself but found it very difficult from under the car. I had posted a few posts on a different thread pertaining to the HPFP pump replacement issues that I was having. Suffice it to say, when the pump # 1 would not come off easily (as it should), I finally threw in the towel and had the HPFP pumps replaced by the dealer. They did not report any other issues and replacement went as usual according to their report. I do tend to trust them since I have been with them for > 8 years and they have been pretty decent all along.

Post the HPFP pump replacement, all seemed well for a few weeks. Then the symptoms have recurred that are almost identical to what the car was doing initially prior to the HPFP replacements, with one difference - no CEL this time. When I hit the start button, the car seems like it cranks up but it doesn't "hold" and the engine dies down. It does not do it all the time. It will crank up and idle just fine at times and then other times it will crank but the motor dies down. When it does start up, it idles as usual and runs just fine including city drives, highway speeds, throttle response and WOT on ramp runs (which are always so much fun in this one). No discernible misfires, rough idle or any other running issues that I can hear or feel. I have done some preliminary investigating that I will list below.

Battery - on the voltmeter, it's reading 11.95 - 12.16 V at baseline and between 14.5 - 14.8 with the engine running. So assuming this is not an issue.

It does seem to crank up, so I am guessing that the starter motor is okay. I do not know how to test it and am open to pointers if there is a way to interrogate it via a bidirectional diagnostic tool ( just recently purchased the icarsoft V4.0 with JLR preloaded on it).

Replaced both engine air filters.
Cleaned both MAFs down-stream of the air filters with the CRC MAF sensor cleaner spray.
Both HPFPs replaced recently as noted above.
Spark plugs were replaced a couple of months ago as part of routine maintenance.

Bought the icarsoft (JLR preloaded) V4.0 bidirectional diagnostic tool last week and ran the preliminary diagnostic scan last night. The only code that showed up was labelled as "historic" for the low fuel rail pressure - presumably the pre-HPFP replacement code. No other active codes.
On the diagnostic scan - all 6 O2 sensors are showing a pass status. The "misfire" diagnostics on each cylinder are showing a pass with no misfires detected. The AFR is showing up as "pass".
It has some seat climate control module codes for the rear seats, but I am assuming that is likely from disconnected rear seat connectors on the wire looms as I have the rear seat off (both the bottom and back) when I had to get to the emergency trunk release direct 12V connector due to my stupidity of disconnecting the negative terminal of the battery when trying to work on the fuel pumps and closing the trunk like an idiot. Also, the seat is off since I am trying to get to the rear speaker / sub woofer on the rear shelf to try and fix / replace a blown / rattling rear speaker.

To summarize, I now have a car with the above mentioned issue with no CEL and no codes on the diagnostic scanner that I have. Last night, with the tool wired into the OBD portal on the car, I cranked up the car twice and it started and idled. I tried to pull any live codes and nothing showed up. So now I am at my wit's end and do not know how to proceed further. Any pointers / help would be greatly appreciated. I would hate to just throw parts at it, my mind's all over the place - failing injector / injectors, maybe a bad spark plug from the recent replacement (was done at the dealer), bad / stuck throttle body?? I don't know if its related but the dealer did recently perform the intake valve cleaning procedure a couple of months ago but the car ran just fine after that until the initial issue showed up more than a month later, so , don't know if its related.

I did search this forum but could not find a relevant thread on this. Hence starting a new thread and any help appreciated. Apologies for the long initial post. Love this car and would really like to get it back to its usual good health.

 

JLR wants 12.6 VDC after the car has sat all night. Yours is below that and that's a red flag! How old is the battery? Any chance it's the original battery? Might not be your problem but I would replace the battery first thing.

Sure sounds like a fuel problem. What are your fuel pressures? Without hooking the car up to the JLR SDD system you may not be seeing everything.

One long shot idea? There is a fuel pressure/temperature sensor located on the back end of the passenger side fuel rail. Not common but we have seen a few guys have a failure of that sensor without a code.



I have it labeled pressure sensor because JLR is not clear about all this sensors does. After one of the failures we found out that it also measure the fuel temperature.
Sorry I don't have the part number.
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Good points.

Battery - its a JLR battery, original to the car. Those readings I posted are after the car has sat in the garage for just over a week. Have hooked it up to a battery tender last night and plan to take it off today and see what the battery reads.

Am trying my best to not take it in to the dealer. I don't know of anyone who has the JLR SDD system around me other than the local dealer. I am in the DFW area. If there is a reputable Jag mechanic around here, I would welcome any recommendations.

Regarding the sensor - if it is a failed sensor, then would the car not have an issue at every single start up? Its the intermittent nature of the problem (amongst other things given that it runs great once it starts) that has me puzzled.

 

+1 on the battery. 8 years is good run on a battery.

wombat

 

Any pointers other than the battery?

 

I suspect that the voltage drops by crank too low for accuracy injector operation.
12.1v is low voltage for any modern vehicle. (not only XJ)
If you have jumper cables: You can try to add power for a battery on trunk from other (fully charged) battery or from another vehicle and then try to start up. If your engine starts Ok: You just need a new battery.

 

If all y'all's prediction is true - a.k.a - a new battery, then I will be a super happy camper.

 

Speaking of battery replacements, does the hive have a recommended brand? Apparently the icarsoft V4.0 has the battery registration functionality for the BMS registration. Would rather get a good brand and do it myself instead of the dealer.

Any pitfalls to avoid when installing a new battery?

 

Duracell Group 49 AGM.

@$240

wombat

 

perfect. That's exactly the one I was going to pick after reviewing a few today. Hopefully I can get it in this weekend and I'll report back.

 

"Varta" is the OE on my XJR 575 - changing the battery is as simple as on any other vehicle.
No need for dealer to do it - may have to reset window auto function

 

I use the H8 battery from Walmart.
Better warranty and Walmart's are everywhere so no warranty problems if needed.
Walmart EverStart Platinum H8 Battery
$189 and a 5 year warranty and 850 CCA.

On a side note my 2014 XJR OEM battery lasted 10.5 years! The longest I have ever had a battery survive. The funny thing was it was still working fine and so was the crappy start/stop system. I just thought it has done it's job and waiting for a failure was a fools errand!
The above battery has been in a year or so with no problems.
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Thank you all for all the inputs . Here’s the update from tonight - after being hooked up to a battery tender (deltran) for 24 hours over the weekend with the tender showing green lights ( charging complete) , I let the car sit in the garage from Monday onwards . Tonight , about 2 days in , checked the voltage on the battery with car off and only the trunk open , it is reading 12.33 V. Tried starting the car , it started up just fine on first crank or “on the button” to borrow lingo from the classic Jaguar world . Idled normal , no misfires. After 10 minutes of idling , checked the voltage at the battery again - 14.43 V, fluctuating between 14.12 and 14.43V .

As someone said before , the battery is Varta labeled JLR and original to the car. So I am guessing it’s an aging battery ? Since it’s not holding 12.6 V or higher after a charge ?

 

If the 12.33 v reading you got was with the battery still connected, that's not far off being a good battery still - dont forget, the telematics are a constant drain on the battery when the car is not in use.

 

yes , that reading was with the battery fully connected to the car . I am going to muster the courage to drive it to work today and see how it goes. I am carrying the diagnostic tool , voltmeter and the NOCO jump starter kit I have with me in the car … lol … might as well throw in the tire inflator for some good juju. I’ll report back later today

 

Well that's the thing. Is your battery bad? No but it is borderline. Since JLR has a published value of 12.6 VDC there must be a reason. So this may or may not fix your problem but it is a starting point.

When the car is running the voltage reflects the alternator so those numbers have no value unless you have a charging problem. Those numbers just show that yes the charging system is trying to return the battery to some level of charge. It use to charge the battery to 100% and stop. But with the BMS stuff the battery life is modeled and the charge level of the battery can be anywhere from around 75% to 100% charged. The BMS even discharges the battery at certain intervals to get a reading of battery health.

We have seen many batteries that start the car but yet still give the car odd codes. So replacing the battery is kind of a CYA thing.
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How is the low fuel pressure reading when the issue happens? I'd be much more inclined to believe your pump is not holding pressure and bleeding off, causing the crank and die. A bad battery won't cause a loss of fuel pressure or fuel pump faults.

 

I will try to see if my diagnostic tool that I have (its the icarsoft LR V 4.0) can actually read the numeric fuel pressure when its hooked up to the OBD port in the car. I will try it this evening and report back. Just to ensure that I understand you correctly - are you referring to the HPFP pump/s or are you talking about the low pressure fuel pump (sending unit) that is in the fuel tank?

Also, the code for low fuel rail pressure has not returned since I had the HPFP pumps replaced. But almost exactly identical symptoms ("crank and die") returned about a month later as mentioned in my initial post. HPFP replacement was performed by the dealer. Curiously enough, although the signs/symptoms were almost identical, the car did not throw a CEL this time, has never thrown a CEL after the HPFP replacement and no codes are showing up on the diagnostic scanner that I have currently. Hope this helps.

Any input appreciated.

 

Low pressure in the tank. You should have a separate sensor value for that pressure, before the rail pressure. When the car is off and hasn't run for a while, they should match when you first open a door or ignition on and the in-tank runs, it will put about 90psi into the fuel rail, which is enough to get the engine to kick over until the HPFPs can build up the pressure they need to reach, say 800-1200psi at idle. The logic for the testing of the sensors is unreliable at best. The pump is run for a set time and the car assumes it has pressure, it somewhat ignores the sensors during actual cranking as the values would be too high for just the LPFP, but not up to the normal HPFP driven rail pressures until the rotate enough times. I've also seen those rail sensors give bad readings with no fault codes. Best bet is using SDD or whatever you have with a datalogger function, watch all your fuel pressure sensors and see what you get. Post the graphs here and we can try to be of some help.

 

These are some really good pointers. Allow me to ask a noob question (and I will look into it myself too) - would you know off the top of your head if the icarsoft LR V4.0 bidirectional OBD tool has this functionality of quantifying these fuel pressures +/- graphs? Asking because I do not have access to a SDD scanner short of taking it to my local dealer. I do not necessarily mind the diagnostic fee that the dealer charges, but thought I would ask. If there are SDD / datalogger kits that can be purchased, then happy to do that too. I am in the DFW area, so if there are reputed Jag specialist shops, then I am open to recommendations.