MAF Sensors
 

Today in traffic my car started pulsing at idle and I was experiencing a loss of power at low RPMs. Seems like a MAF sensor to me, but reaching the MAFs on these cars seems to be a nightmare. Can they be accessed from the wheel wells and do I actually have to pull the front apron?

Perhaps you should invest in the Workshop Manual. It can be purchased from vendors on the Internet for less than 30$US.

Or downloaded in PDF format from here, for $0 - JagRepair.com - Jaguar Repair Information Resource

The MAFs are located in the air filter housings (one for an XK, two for an XKR) which are located behind the front bumper (fender?) and in front of the wheel arch. You'll need to lift the front end, get the undertray off, undo at least the lower half of the wheel arch liner and tie it back out of the way. Then you can access the air filter housings - the MAF is on the top/rear side in the short tube between the housing and the pipe that runs upwards toward the top of the engine bay.

Check for fault codes before you do anything, if the MAF is dodgy you'll likely see a code related to it. If you do have to replace the MAF then you can save about 50% of the Jaguar dealer price by buying the corresponding Denso part - at least on the 4.2 XK/XKR, the MAFs are manufactured by Denso.

Or download from this forums "How-To" sticky link with other useful technical documents see post #3 https://www.jaguarforums.com/forum/x...k-links-20091/

And here's your classic check the battery voltage at rest before spending a dime on anything.

Done. Got a brand new battery the other day.

Did installation of the new battery fix your driveability problem?

When? Did it change the symptoms?


Mini-rant time.. Is it just from texting, or does the younger generation not realize that the more interesting info they put out there regarding their problem, the better and quicker resolution they'll benefit from?

:icon_doh:

No, new battery was installed about a month ago. Charge seems normal at the battery posts. Tried doing a hard reset today while I wait for new filters to arrive, but one of the cable tightening bolts broke on me, so tomorrow I'll have a verdict on that one.

More or less assumed it could be gathered that I am still having problems if I didn't acknowledge their resolution. I'm aware that I'm new to this side of the forum and you may not be familiar with me, but I'm no stranger to the XJS forum and I have had no trouble communicating with the folks on there. Please don't be so hasty with the judgement.

OK, a few more questions:

1. Have you measured battery voltage after the car has rested overnight and remains IG-OFF?
2. Is the check engine light or any other warning lights or messages on?
3. Do you have the Jaguar SDD software to retrieve any logged fault codes?
4. Since you posted on May 29, has the driveability problem been intermittent or constant?

Sorry for the late reply. Got super busy with my cross country move, didn't have time to mess with the car yet. Hoping to tackle it this week. I haven't measured battery voltage after sitting overnight, probably should give that a shot. The check engine light is on. Just had the codes scanned today. Getting P0193, P0088, and P0087. Drivability has been intermittent for sure. If I restart the car it clears up.

P0087: fuel rail pressure too low
P0088: fuel rail pressure too high
P0193: fuel rail pressure sensor circuit high input

Fuel Pressure Sensor and wiring harness both look okay. Ordered a new sensor anyway because the compatible Mustang part was so cheap. If that doesn't fix it I'm inclined to check out the MAF sensors next, because I've already got new filters to put in and otherwise what could it be? Pump and fuel filter?

If you can replicate the problem "upon demand" and while the car is parked, then I would suggest putting a fuel pressure gauge on the fuel line so that you can see what is the fuel pressure when the loss of power issue occurs. You are looking for 55 psi minimum.

If the fuel pressure can be seen to drop when the issue happens then I would conclude the sensor is accurately reporting a problem with the fuel pump.

Since the problem is intermittent I would not think the fuel filter is the problem.

The fix might be as simple as replacing your engine air filter, particularly if it's dirty or not genuine OEM Jaguar. You have only one, since you have a 2007 XK. See these threads:
https://www.jaguarforums.com/forum/x...sensor-161155/
https://www.jaguarforums.com/forum/x...ptions-122210/

Y.Y.You're joking. I was under the impression I needed 2. Shoot, already bought them. That would mean I only have one MAF sensor then, is it on the driver's sideY

I can't replicate it on demand. I always replace pump and filter at the same time. You think that's the culprit then?Y

On the left side of the car. LHD and RHD within the same model, makes "driver's side" a poor identifier.

I'm an idiot, thanks.

Since the fuel tank has to be dropped to access the fuel pump, I would say that you should obtain evidence that the pump is actually the problem (evidence such as a low fuel pressure reading) before you invest in the effort to replace the pump.

So, I pulled the fender liner, replaced the Air filter (Which was dirty) and cleaned the MAF sensor. Had a solid two days of perfect driving. Had an hour drive to the airport the other night and the same problem reared its ugly head. The hunting/stumbling only occurs at intermittently at idle, and disappears after a restart. Once I reach highway speeds I'm sitting pretty. The car drives as normal. No fluctuation in RPMs and my gas mileage stays in to high 20s/low 30s. If the fuel pump was at fault wouldn't it cause issues while highway driving too? I also was not aware of the OEM jaguar only thing when I bought my air filter. I put a Beck/Arnley unit in. Is that really a huge problem source?

Watch fuel trims at idle both when OK and when not.

Check every sensor you can via live data for plausibility, again in those two cases.

Like JagV8 said, check your fuel trims. Look at this article to help make sense of what you're looking at/for:
https://www.autoserviceprofessional....for-you?Page=2


Possible relevant quote from article.
"Since the amount of air flowing through the vacuum leak doesn’t increase, the leak has less affect on air/fuel ratio at higher speeds and loads, so LTFT will come down as engine speed goes up. When you look for vacuum leaks, don’t forget the various “calibrated vacuum leaks” like crankcase ventilation, the evaporative emissions (EVAP) purge valve and, if equipped, air-shrouded injectors."

So where are we with replacing parts and verifying the original complaint and codes are still relevant? Also still curious about the voltage after sitting overnight.

Pressure high, low and sensor out of range all point to towards the sensor, the wiring or a control problem in how the sensors input is interpreted. Just shutting the car off and restarting it to me points at how the input is being interpreted.

Maybe a dumb question since I haven't researched it but how does the 4.2 control fuel pressure? Mechanical dump valve like so many other early gen vehicles or control the fuel pump speed like later model stuff.

Ah crud. My OBD-II scanner is not advanced enough for any of that. Can you recommend a model for me?

Replaced Air filter and cleaned MAF sensor. seemed to have fixed the problem for a couple days. Gonna throw the new fuel pressure sensor in tonight. I'm definitely leaning towards it being a sensor issue, the shutting off and restarting thing gave me that idea as well.
I'll have to wait until tomorrow night to get the 24 hours at rest battery reading.
To my understanding it's the latter with a pump controller (C2C35672)

elm327 should do but there are dozens or hundreds.

I have the Icarsoft LR2 and it's OK but not stellar. You can compare a couple displays but it's difficult to set up and the read out is in text only so you are stuck with what it reads when it reads it which is confusing for a fluctuating idle etc.

Page 1645 of the X150 S/M is interesting in its description of how the ECU talks to the pump driver.

We can probably conclude that it is not a fault with the pump though, correct? When I've had pumps fail in the past it effected highway driving as well. The symptoms also seem to go away after a long drive.

Battery at rest is 12.47 after sitting for a few hours. I'll report back with over night readings tomorrow. Gonna check the sensors on my new OBDII tonight

Well this got stranger. I'm still a novice with using an OBDII scanner for diagnostic purposes. (this is pretty much my first car made after the cold war). All the codes were the same as before. I used the OBDII to check fuel pressure and it came back hovering around 36 psi. Even though the car wasn't having the fault. The engine was running normally and smoothly. There's no way that's possible, so I swapped the fuel pressure sensor out for a new one and now it's hovering around 44psi, even at 2500rpm . Couldn't figure out how to get to the fuel clipping menu yet (just got the device tonight). I also couldn't get the car to start acting up. I reset the CEL with the OBDII and it did not turn back on even though the car was only at 44psi supposedly. So what now? Could it be a weak fuel pump? I'm stymied.

I would look into an actual pressure gauge and do some comparison testing. I assume there's a Schrader valve somewhere on the fuel rail to tap into.

Isn't it possible the sensor is the culprit and was providing bad readings to the ECU?

It's a feedback based closed loop system. ECU looks at power demand inputs and decides what pressure to feed the injectors then tells the fuel pump driver how hard to drive and then looks at the sensor to see what's going on. Somewhere in that chain of events there's a problem.

ECU
Pump Driver
Pump
Plumbing
Sensor
Wiring between anything

It can't be the sensor because I swapped that out and I'm still only getting 44psi which is too low.


ECU
Pump Driver
Pump
✓Plumbing (I can't see this being the problem in a car this new)
✓Sensor
✓Wiring between anything (This may be a preemptive check mark, but the wiring in the hostile environment of the engine bay that I have checked has been fine)


Oh man, the other three options look costly. Would a new ECM need to be married to the car by a dealer? I'm gonna go ahead and order a new pump driver because I did end up finding one really cheap near me.

Will do. I'll try and acquire one tonight

Quit wasting money on parts until you have some idea what's wrong. Until you actually know what pressure is at the rail everything is still suspect. You could have corrupted data from the sensor or PWM problems from the ECU to the driver. From experiences garnered from the forum over the past year all of this can still fall back against the battery. The X150 is a fickle beast when it comes to electronics and controls. At least you aren't paying a shop to misdiagnose it yet.

Did you read the section of the service manual on the fuel system?