I have been dealing with an intermittent loss of power on my '03 XJR for about three months now. Three months seems like a long time, but it represents about 800 miles, so not actually that long.

The first time I experienced it, it was remarkably repeatable, happening between 60 and 70 mph with light throttle... a standard freeway cruise. That's how it happened the first time, and for the rest of the day I could avoid it by staying under or over the speed limit. I didn't really have a sense of the cause. My solution each time it happened was to bury the throttle and everything went back to normal for a fair amount of time. Total mileage that day was probably 70 miles, so not a huge opportunity to experience the issue, but I was able to replicate it multiple times.

The second time it happened - maybe a week or two later - it was the same scenario, but this time I let up on the throttle instead and the car stalled. I coasted to the side of the freeway, cycled the key, and everything was back to normal. This was in the middle of the night, quite cold, and maybe 40 miles total driven. I put gas in it at 1am but at this moment I don't recall if that changed anything.

That weekend, I cleaned the MAF, replaced the air filter, replaced the O-rings on the PCV hose, and replaced the coolant temp sensor. I was thinking maybe a slightly off mixture - enough to mess with light throttle but not enough to affect power or trigger a CEL. That got me nowhere.

Third time it happened was the same as the first - 70mph cruise, loss of power, buried the throttle, everything was fine.

The last few weeks we've had a lot of rain, and last week when I went to put gas in the car I found the filler cavity was a swimming pool. Literally full of water, level with the body. The drain had become clogged, and the cavity was full to the top of water. I feel like that may be an important detail. I got the water out, took it home, and cleaned the drain... it's continued to rain, but no more swimming pool.

Today, the fourth time the issue has presented, things got worse. The car was occasionally stumbling while driving at low speed, but was fine on the freeway. At once point, sitting at a stop light, it flat out stalled when I rolled into the throttle. Today's total mileage was around 50 miles, half freeway and half low-speed (30mph) surface streets.

I'm not precisely sure where to look. Finding the fuel filter full of water certainly raises the possibility that there is water in the gas. By the same token, there was a swimming pool in there, and it seems like if it was leaking water in, it wouldn't have been a swimming pool. But, who knows?

At no point has there been a check engine light. I know on many cars loss of cam or crank sensor (especially) can not trigger a CEL as the car may confuse loss of signal with being shut down, but in this particular case, with repeated instances and twice stalling it seems like some error would get logged.

I've also been considering the possibility of a fuel pump issue. Both pumps run, and at idle there is good pressure. I've definitely had pumps slow-fail like this, but it's interesting to me that in most circumstances adding throttle has corrected the issue, and when it's twice stalled it's restarted immediately and without drama. Seems like a fuel pump problem would be *slightly* different, hard starts at least. I will comment the fuel filter is three years and 3,000 miles old.

Some may recall me posting last year about a failed throttle actuator. I've been considering that as well, but there's no real evidence that's the problem here... the TPS signals are still rock-solid, and I'd expect if it was an actuator problem I'd see a CEL. But, still, can't eliminate the possibility.

So, my question to you all: Any ideas on the nature of the problem or approaches to troubleshooting it?

 

When my fuel pump went out, the car was fine, started fine, and everything. But one day, after driving it for about 10 miles and turning it off, I went to turn it on again and stalled immediately.

For it to run properly, correct amount of air, fuel, and spark is needed, so I would check all components that control these things. You may want to check the basics, like your alternator, wiring, fuel pressure regulator, etc. Recall, that the XJR has two fuel pumps, so the second one kicks on when you step on the gas, keeping the fuel pressure/flow rate up.

I would first drain all the fuel in your tank, and put some new 91 octane gas in the tank.

What did the car do for a "sudden loss of power"? Low rpms?

 

Have you been saving all that up??

I'll have a stab at each issue, number one water in the fuel - did you say your fuel filter is full of water? if so, drain the tank and replace the fuel filter with a new one asap.

Reason being any water in the tank will sit and rot the pumps out at some point in the future.

Clear the drain by pulling the filter hat off and clean it with a tooth brush, poke a pipe cleaner down the tube itself, then flush with soapy water. If it's parked under trees, this is a yearly job.

Number 2 the car will post fault codes, it's doesn't have to peg a dash light, they're stored so instead of guessing plug an OBD reader in - you state the power loss is repeatable, go repeat it and note down the fault code in real time, it will flash as the car goes into restricted performance.

The 03 is an AJ27 with TPPS & TPS, either can and do go into restricted performance before any codes are logged, then it just gets worse. But an unmetered air leak is another possible, along with faulty O2 sensors - take your pick at this point.

 

May have a P1582 stored but a tool that fauils to tell you it's there. It's a sort of flight data recorder as to what was happening as the car stalled.

I'd have a look at fuel trims (see the many threads). And if you don't have an elm327 probably worth getting one (for trims and to see if P1582 / other codes are being hidden by what you have now).

 

On every car I have ever owned, a failing fuel pump has presented when trying to start the car... whether the car dies and won't restart, or simply won't start after sitting, point is that I've never had a fuel pump stop and start randomly while driving, but always restart. That is why I doubt the pump(s). The fact that pressure is rock-solid while running the pumps "manually" via the relay supports the idea the pumps are fine.
I don't know how better to describe loss of power... the car slows, the engine slows, everything slows while my foot hasn't moved. Like invisible brakes.
I'm pretty good at auto repair. I generally don't reach out until I'm at a place where experience is worth more than talent.
Not filter, filler, the place where you put fuel in the tank.
I have multiple high-end scan tools. There are no codes stored, no codes pending. There have been no dash warnings, including the "restricted performance" warning. As I mentioned, the car is not aware anything is wrong.

Edit: This is what caused me to possibly suspect a crank sensor... I've seen numerous cars with dying problems be a crank sensor, since the ECM doesn't really distinguish a loss of crank signal from a normal shutdown. However, I've almost never seen a crank signal come and go like this or, if it does, it's almost always worse when hot and that doesn't seem to be true here.

My Autel did not find a P1582 and I'm inclined to believe it, but I guess even if it's there I don't have a way to access that freeze frame data, so I'm kinda hosed there. I've been trying for a long time to find a clone VCM/IDS to buy, but come up empty. Seems like I missed my opportunity on buying one of those.

 

Just a random idea:

Hard starting is not the only failure mode of fuel pumps. Sometimes they can supply moderate fuel flow but lose their ability to provide higher flow rates. Your symptoms make me wonder if Fuel Pump 1 is beginning to fail and cannot supply enough fuel to maintain speeds above 60 mph. Perhaps at 70 mph Fuel Pump 2 is kicking in and all is well? Somewhere I've read the conditions under which Fuel Pump 2 is engergized but a quick search of my literature didn't find it. I did find this from one of the AJ26/AJ27 Engine Management System manuals:




Cheers,

Don

 

You are not alone!

A long time ago I remember reading that in the XJR sometimes #1 fails entirely but people don't notice because #2 has more or less taken over and is doing all the work.

I'm able to run each via relays and I get pressure in the rail, but I haven't dismissed this as a cause. Even though I have now observed the failure at low speed, the fact that rolling into the throttle always gets me back going again, which seems like it'd be consisted with #1 having an issue and additional throttle energizes #2. I too was trying to find the criteria for #2 to see if any of this made sense, but couldn't.

Monetarily I'm fine replacing the fuel pump, and with 110k on the car I'm kinda interested in doing it... it just sounds like a bear on the '03, where the whole tank has to come out. I've read the threads, seen the toilet pipe tool, but I'm still nervous about access & releasing the fuel lines. :| Maybe I will call around and get some insane estimates from shops to encourage me.

 

I would clean the throttle body connections before locking in on the fuel pumps.

 

Change the fuel filter. Back in the day when GM cars had those crappy Rochester carbs with the thimble sized fuel filters, engine cut out was a common problem and always traced to the fuel filter.

 

The throttle body itself was replaced less than a year ago, everything in there is spotless. I have a sense of what a failed TB feels like, and while that was honestly my first thought when this issue set in (another bad TB), it really doesn't feel like that. And, unlike the first/last time, no codes and no "restricted performance" warning. All the OBDII data off the TB (like TPS resistance and voltage) appears correct.





Yeah, but the Jag has a gigantic Bosch (or maybe mine's Mahle) filter, and it was replaced three years and 3,000 miles ago. Plus, the problem comes and goes seemingly at random. I don't really see how more throttle would cause a filter to unblock. :|

 

Change fuel filter...it can be defective.... or full of **** !!!!

 

The OE filter was actually a GM AC Delco.

It was driving at a steady highway speed that I first noticed mine going out ... it was an ever so slight vibration that go a bit worse and I understood it was the engine. I really thought I had a coil acting up. It was so intermittent and hard to notice that taking it in was pointless.

One day it just died -- and it was clear what the problem was.

 

It is possible that the intermittent fault is caused by overheating on the ECU. Im not sure if the XJR has one but most model ECU's having a cooling fan attached to the board just like a CPU on a computer. The next time you get an interruption place your hand on the ECU if it is to hot to touch then that is possibly your fault occurring. Place a wet rag on it to cool it down and then try a restart. If it went away then you may have located your problem.

 

It's been pretty chilly here, so it seems an ECM overheat is unlikely, but I will definitely check it if the opportunity arises.

Which it has not! I've only done another 100 miles or so, but the problem has not repeated itself amongst multiple "it's definitely gonna happen" trips. So weird.

However, today something else happened: While sitting in a brief bit of traffic (OH NO! IT'S RAINING!) The CEL illuminated. I was kind of happy about that - maybe something to do with the problem! Of course I did not have my scan tool handy, but when I got home I pulled the codes: P0172 and P0175, "mixure too rich" in each bank.

The freeze frame data oddly shows STFT at -3% (within reason) but the LTFT at a whopping -20%. That is very weird I think... like a problem came and went. Most of the rest of the freeze frame makes sense - 6mph, 584rpm, 190 degree coolant temp, IAT 60-something degrees. But, the MAP sensor showed 6.8psi which seems suspect... I don't know what it should be, but creeping in traffic (D, no significant throttle input, 6mph) I don't think that's right... We are at 40' above sea level, so I'd expect vacuum, although being supercharged maybe slight pressure... 6.8psi seems very wrong.

Since it was both banks at the same time, it's fair to rule out things that exist on both sides, like O2 sensors, injectors, coils, plugs, etc. It necessarily has to be something upstream, which would point to MAF or MAP. A post-MAF air leak would likely cause a lean issue so I think that's off the table. I believe there is one FPR per rail (?) so a stuck regulator seems unlikely. Coolant temp and IAT both were expected.

Can anybody comment on what the MAP should look like at idle? A faulty MAP or MAF could definitely explain both the stumbling issue and these recent CELs.

(Sadly, I neglected to note the MAF reading... I don't know how I missed it )

 

The big -ve mean it's running (very) rich and trying to compensate. It's near to flagging rich codes.

Faulty MAP tends to flag codes.

Faulty MAF, not so much. It could be dirty so under-reading.

I'd say 0.01% PCM (aka ECM). They are very reliable.

 

it *is* flagging rich codes - P0172 and P0175.

But if not the MAP and not the MAF, what?

 

Hi thesameguy,

Please use your User Control Panel (User CP link above left) to edit your signature and add your Jag's year, model and engine info so we don't have to scroll back to your first post to be reminded. Thanks!

At the link below you can download the Powertrain DTC Summaries manual which gives possible causes of each diagnostic trouble code:

Jaguar X308 DTC Summaries 2001-2003

Here's pdf page 17 from the manual:


Symptoms like yours are sometimes the result of multiple components or systems operating out of spec. I can't recall if you've checked, but a very common cause of rich running is a Coolant Temperature Sensor (CTS) stuck at a resistance the ECM interprets as "cold," so the ECM continues to apply cold-start fuel enrichment even after the engine has reached full operating temperature. You can test the CTS with an ohmmeter to confirm that its DC resistance conforms to the table in the EMS manual when the engine is cold and again when it is hot.

A stuck-open coolant thermostat can also contribute to rich running.

Cheers,

Don

 

I meant: faulty MAP tends to flag codes - for the MAP! You're not getting those so it's probably not faulty.

 

If the injectors are dirty they will spit instead of spraying, which loads the cylinders with raw fuel: try a good fuel system cleaner (Gumout or Lucas' most expensive, BG44, SeaFoam). Clean the MAF, the throttle plate and bore, change the air filter.

 

Buuuut... if people read the first post they would know I had replaced the CTS.

The cooling system seems in-spec. The upper radiator hose is hot, needle is where it should be, new CTS indicates a stable 190 degree operating temperature. Given the cold weather last week (<60F) I think if the thermostat was stuck open I'd see much lower temperatures.

I read the factory P-code explanation, which basically points out the obvious but does nothing further. Is there a section which explains performance of these sensors that I have overlooked? I'm really hung up on the MAP sensor reporting 6.8psi at idle. That just doesn't seem right.