I've been chasing this for months and I can't seem to put my finger on it. Everything is great (almost). I live in the Seattle area, and we have hills here. In my typical commute, there are two long downhill grades (nothing very steep), where I am 100% guaranteed to be put into Restricted Performance.

When I pull the codes, I get a plethora:

P0101 - Mass Airfow Sensor Circuit Range/Performance
P0193 - Fuel Pressure Sensor Input High
P0191 - Fuel Pressure Sensor Circuit Range/Performance
P1000 - Utter nonsense, have had this for years.
P2601 - Coolant Pump Circuit Range/Performance

- I put a new OEM MAF in a couple weeks ago.
- I thought I had the cowl water leak problem. I have effected a temporary fix (clear vinyl sealant tape - so ghetto). Maybe contact corrosion?
- I have a new Supercharger coolant pump sitting in my garage, awaiting my efforts.

I wiped the ECM trims this morning, put the transmission in Non-Sport mode, and drove like a normal sane person (which, with these cars is admittedly difficult).

Regarding fuel trims:
- I see what appear to be pretty "normal" LT trims being learned. Range is within "normal" (+-5%). ST trims look pretty normal. When the engine is cold, I see -10% (slightly too rich) at idle. On the highway, at a constant speed I see LT at -1 to -3%, and ST moving around in a range between -5 and +5%, which appears "normal".
- On overrun, ST trim shoots up to +20% and plateaus there. Seems like a "very lean" issue.

Regarding O2 readings:
- Warm engine, at idle, it oscillates between .01V and .02V. At 65mph, flat terrain, cruise control, it goes between .8V and .02V, which is normal as far as I know. The catalyst bed needs certain conditions, and the ST fuel trim reacts to the O2 sensor to produce conditions that vary between slightly rich to slightly lean in order to keep the catalyst happy.

So, what in the hell am I chasing? ST trims going to max deflection is in response to the O2 sensor voltage bottoming out. Low = Lean. This only ever happens on overrun. The idle ST and LT numbers are sane looking. So, what components could leak manifold vacuum on overrun?

Alternately, could this be failed O2 sensors?

I've had the battery checked. The tech said it's good. He said it was reading a tenth of a volt low. The battery has "Second" stamped into it, and appears to be from 2014. I have an Optima Yellowtop that I was thinking about connecting in parallel to the battery in the trunk to test.

The voltage PID shows >=15V, which should be the regulated output of the alternator. There is something to the notion that I may have a bad/failing alternator. Another member of the forum has the same "transplanted" XF fuel tank as I do, and experienced the same evap leak codes that I have, and his fix was an alternator replacement. Symptomology matches exactly with my EVAP issues. I was thinking "tank solenoid", since I can hear the damn thing surging when the evap tests happen, but... maybe that's a power delivery issue in disguise?

Thank you for wading through this very long rundown. Any and all help is appreciated

Ken

 

I'll think about the others but P1000 is not at all "utter nonsense" - why do you think it is? You should get P1111 if you quit clearing codes and fix things

You should only have 15V quite briefly when starting from cold. After that, more like 14. You want to be using a voltmeter to double check.

I'd also use the meter to check the battery voltage in the morning before you start the engine.

P2601 is not what you have. It's the INTERCOOLER pump and needs to work. Sounds like you have another pump, so that's good.

I'd ignore trims until they've relearned and then see what they are (parked, hot engine, LTFTs at idle then rev to 2500 or so and when settled see what they are).

The PCM knows what underrun is and what it can expect to see so don't over-think it. Expect it to shut off the injectors so lean is a given.

If you consistently get all those codes but a while back got none I'd be looking for a harness fault I think. Otherwise just fix them one by one and the IC pump is apparently wht you have so you may as well fit it.

 

Thanks, JagV8 - I see your confusion. I do have a new *intercooler pump* waiting to go in. Sorry, I mis-typed "supercharger pump", but rest assured I ordered the correct OEM part (C2C1314).

I'll go days and days with no problems as long as I drive flat, boring routes. No codes (except P1000), and certainly no P2601. Downhill for more than a quarter-mile or so, boom, RP and the other codes I mentioned - like clockwork. Absolutely reproducible.

P1000 feels like nonsense because it's essentially impossible for a DIY mechanic to diagnose which components are involved. P1000 is ALWAYS set. I know it means something, but I think it could also be a red herring to do with the XF fuel system components I have in my car (tank, pumps).

Ken

 

Yeah, I figured it eventually and you may as well fit it

P1000 is a status not an error. But it should change to another status (P1111) if you let it. You can ignore P1111 but should not have P1000 indefinitely - though the fault(s) may be why.

If you give it a few days without clearing codes (and without disconnecting the battery) do you get P1111? If not, see which OBD monitors are not set as that may be a clue.

Right now the P2601 and dubious voltage worry me most.

If you have time, study the electrical guide (see www.jagrepair.com) to see if the various items reported happen to share a harness - you'll have to study a bit though. (And hope they don't and especially that it's not the one behind the front bumper.)

 

I'll do the following things tomorrow morning:

- check voltage of the battery before starting the car
- log voltage for a bit, maybe every minute for 5 minutes, after startup - using my voltmeter - to see if it fluctuates from 15V. If it doesn't, does it feel safe to say that the battery is on its way out, and that "tenth of a volt" is significant?
- Order a new fuel pressure sensor.

I'll do a few varying load drive cycles at different RPMs to give the ECM something to learn, and check LTFTs tomorrow afternoon/evening when I get home.

This may have nothing at all to do with anything, but I was not getting the fuel pressure errors until recently. I ran the tank down to basically empty, then went to the local race track and put in 5gal of 110 octane [That was a LOT of fun, btw, the car is a different animal] After that, I started using one of the reputable octane boost additives to liven things up a bit above our local 92 premium pump gas (Royal Purple Max Boost). The high RPM behavior was livened up quite a bit. Then I started getting the fuel pressure codes. It was time for a new fuel filter anyway, so I replaced that. Clearly it made no difference. I quit using the Max Boost. Also no difference. Perhaps the additive fouled the sensor? That particular sensor also sits right in the drip-zone for the famous cowl leak, which is why I went down the route of abating the leak.

One other thing. If I put the car in neutral and coast down these hills, I see no codes and no RP. If I downshift and keep the revs above ~1600, their occurrence is significantly abated as well. If I leave the pending codes in place and drive it while in RP long enough to get a snapshot data frame, the RPM is inevitably in the 1600 range. There happens to be a kind of "rough spot" in the rev band there. If, parked, I rev up and through that area, there is what I would call an above-average amount of vibration (not jarring, or cylinder-miss type shaking) for a car of this level of refinement. Everywhere else, it's turbine-smooth (a little lope at idle, but I'd expect that given this engine's likely cam profile).

Ken

 

One more thing that I remembered. A while back - 6 months or so - I used to ONLY get the P2601, and it would immediately throw me into RP (makes sense - no intercooler = dangerous hot air going into the engine = engine goes boom). Clearly RP is tied to that code, and the others are probably symptomatic of something else (or several something elses). I hate hate HATE driving the car in RP; it's so boring and gutless. So, I clear the code and wait a few seconds for RP to go away. Funny thing, though, is that when I was ONLY getting P2601, it would still happen when cruising down a long gradual hill.

I've never seen P1000 go away, even before I was getting 2601 - so I should check the OBD monitors again and see what's going on there.

I'll report those back tonight.

Ken

 

Interesting.

It's tough to diagnose with several faults so fix anything you can then see what occurs.

 

41 minute drive home last night, I ran a PID log:

- Voltage PID never dropped below 15v.
- Fuel pressure sensor flatlined a few times (0 psi)
- Fuel pressure sensor maxxed out at 70.05 psi for several minute stretches.
- LTFT bottomed out at -15% a few times
- O2 voltage exceed 1v
- O2 wideband lambda > 1.0 (hit 1.3) for a disturbing length of time
- Threw all the same codes and went into RP about halfway home, in one of the predictable downhilll sections. I pulled off, let the car idle while taking some screengrabs of the conditions. I cleared the codes because I felt I could also provoke the strange mixture behavior on the next mild uphill grade (I was right).

Started getting stumbles and power-loss while cruising at 1600-ish rpm. I switched down gears while in cruise control at 56mph, and got power drops and stumbles in all gears. Upon arrival at home, I ran the log trace and let the car idle in the driveway. O2 voltage was .8v for a good couple minutes, and then slowly dropped down to .01v and fluctuated there. While it was dropping, the car was stumbling, idling rough, and tried to die a few times. Fuel pressure readings dropped to zero at a few points (could be a data read error, don't know).

The signs point to a rich condition, but I'm not sure of the cause.

I haven't driven the car today, but I have an errand to run this evening. I'll do a voltage reading then, directly off the battery, before starting up.

Ken

 

You look to be drowning in yet more data but what do you plan to do with it? I cannot see the point at all.

 

After sitting overnight, the battery voltage - using my Fluke - reads 12.24v. I believe a charged battery should read 12.6v, yes?

This was after a 41 minute drive home and sitting overnight.

So, it looks like I will need to rule in a bad battery. The last time I had it tested, it was "a tenth low". Now it looks like it's worse.

Ken

 

Seems like my plan is this:

1. Replace the battery (will do this tonight if possible)
2. Clear the ECM and drive it.
3. Re-evaluate if needed.

Current possibilities (besides bad battery):

- Failing O2 sensors (could the cats be shot?)
- Wiring harness issue, affecting multiple systems.
- Something more exotic and, therefore, less likely.

Ken

 

Yes, but did you fit that IC pump?

 

Not yet. It's on the (extended) list, but I'm wondering if the pump circuit range/performance error is due to the battery. I'm not ignoring the pump, but I think it goes somewhere after #3 in the list. Battery feels like #1 priority

Ken

 

Looking at the electrical diagrams in this document: http://www.jagrepair.com/images/Auto...cal-2005on.pdf

It looks like everything that is throwing codes is either on the Engine Harness (PI)[all the sensors], or the Front Harness (FH)[the IC pump]. The vehicle harness connects to the engine harness at PI41, and the front harness connects to the engine harness at PI42. The plugs, it seems, are adjacent to one another, at the bulkhead, passenger side. This is one of those drip locations for the cowl leak. There may be a correlation, or there may not be - just putting that out there.

After I get the battery in tonight, we'll see how she acts and proceed from there.

Ken

 

New battery on board. Voltages look great. Static voltage, engine off: 13.6v. Charging voltage, about 14-ish.

Reset the trims and drove around long enough to get new, stable trims. I got the following codes:

P0101
P0193

LTFT
@2500rpm: +3% (both banks) [STFT was -2%, so 1% total trim]
@1500rpm: +18% (bank 1) +5% (bank 2) [STFT -2%]
@Idle: +18% (bank 1) +9% (bank 2) [STFT -1%]

Pretty lean.

Ken

 

Another drive:

LTFT @ Idle (bank 1/bank 2): +16/+12
LTFT @ 1.5k(bank 1/bank 2): +20/+8
LTFT @ 2.5k(bank 1/bank 2): +0/0

P0101 - Mass Airfow Sensor Circuit Range/Performance
P0193 - Fuel Pressure Sensor Input High
P0191 - Fuel Pressure Sensor Circuit Range/Performance


No hills on this drive. All flat valley. Felt lean, too - throttle was not as snappy.

Doesn't act like the "classic" vacuum leak (big positive trims at idle, lower/zero trims at 1.5k)

What am I looking at?

Ken

 

I doubt it's finished learning yet.

 

No doubt, but still - those large LTFT are not good. I went back and looked at my data. If the fuel pressure sensor is acting up, could that be my culprit here? I mean, if the thing is reading falsely low, the computer might open up the injector pulse to compensate and we'd be too rich. Conversely, if the thing was reading falsely high, the computer might shorten the injector pulse and cause a lean condition. I see fuel pressure readings of over 70psi when the average for this car is supposed to be something like 55psi.

I'm going to rule out vacuum leaks tomorrow. I'll try the water bottle trick first and hit the likely offenders. I'll fix whatever I find, but I think I'll call my local Jag dealer and get a fuel pressure sensor. It's right on top, easy to reach, may as well

Thanks,

Ken

 

Water bottle is a poor way. Smoke test or use a burnable gas.

Nothing looks like fuel pressure but give it a chance and fix things before doing more.

 

Ken, you are ahead of me technically, but we do have the same car, same year, so what the hell.

I spend more than I should by being pro-active, checking/changing suspect parts based on info from this forum. Not good for my bank account, but the Jag is quite trouble-free.

I saw from one of your posts that fuel pressure sensor varied from 0 to 70 psi, and wonder about the fuel filters. With everything humming beautifully I had my filters checked - they were FILTHY.

My $0.02 worth, forgive if you have already been there.

OH, btw, agree with JagV8 about the intercooler pump.