Hi there
I'm new to the forum., but have read alot of things on here on the past as I own and xf, xjl and xk8 so often need to read the jag forum.

A quick bit of help if you can. I am experiencing a problem where my 2002 4.2 xk8 is bogging down or loosing power when I floor the throttle. Initially the car grumbles then falls back to idle. I can nurse the car up to motorway speeds but there no power at all.

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​​​​​I'm thinking of starting with the fuel filter as I don't see that in the history. The car recently got a throttle body by previous owner. No lights display on the dash when the engine is bogging down.

I have an icarsoft jag specific reader but only gonna hook it up tomorrow. Has anyone any ideas on where to go after the fuel filter.

Cheers

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Welcome to the forums Tuifly767,

First thoughts are the recent Throttle Body - especially if it was a used one rather than a refurbished one with a new TPS.

You mention 'motorway' so I assume you are in the UK. Our fuel supplies are generally OK and blocked fuel filters are rare although not unknown. More likely is a failing fuel pump or an air leak on the inlet trunking causing weak mixture.

Speculation only and hope the iCarsoft will show some helpful codes.

Graham

 

Check fuel trims (even if no codes).

 

Hi guys thanks for the feedback and help. Yes im in the UK. (live in NI). So no fault codes flagged. Il look around the intake area for leaks. What are the normal idle fuel trim values and underload values at say 3000 rpm? Is there a table anywhere?

I noticed mine on idle were:
Long trim b1 1.6%
Short trim b2 3.1%
Long trim b2 0.8 %
Short trim b1 0%

Il be reading while driving later today. To see what happens with full throttle.

 

Also check fuel pressure, especially when it misbehaves.

 

OK fuel pressure reading was 381 kpa idle dropping to 294kpa when misbehaving (floot down).

The fuel trims largely stayed negative.

I had a look at throttle valve as I noticed a high pith hum coming from the throttle assembly. But appears to be operating correctly, responds to throttle and looks reasonably clean.

​​​​​​Inspected air intake ducting, no holes. Checked I couldn't see any loose connections around air assembly.

I reassembled and restarted

Same problem.

I disconnected MAF and engine died, reconnected all good.

I cannot get the thing to throw up a code or dash light.

I noticed when I put my foot down while driving on the test run earlier that the engine didn't fall to idle it just refused to go over 3,500 revs and hung at 70mph but if I let up on the throttle the car very very slowly accelerated.

 

Well my 1st thought would be fuel filter different car but you're describing textbook clogged fuel filter symptoms.Its a cheap quick replacement and hey you'll get instant feedback when you try to blow through the old filter.

I hope it turns out to be something this simple 4u.

John

 

Hopefully someone can say whether thy are OK. I'm doubtful (I feel they should NOT drop).

So it thinks it is overfuelling based on MAF (& other sensors).

Could be MAF but also could be such as blocked cat(s).

-ve trims means you're not looking for air leaks at this time.

Which of P1000 / P1111 do you have?

If P1000 many codes cannot be flagged.

Still could be bad MAF / blocked cat(s).

 

Hi there many thanks for the excellent info.

The only code appears to be P1000-reset yet to be performed.

Yes im certainly coming to the same conclusion regarding the Cats, as I found another link on the forum with someone experiencing very similar symptoms and it turned out to be a blocked cat.

https://www.jaguarforums.com/forum/x...-104614/page2/

Is there anyway to rule out the maf without buying one to test?

I was going to disconnect both ends at the bottom of the cats as suggested in the link above and feel the pressure.

On a hunch I did a bit of go ogling for new cats and seem to find alot of 4.0l ones but not 4.2l, are these different for 4.2? If so, has anyone any idea where to get 4.2 cats. Il do further checks today to try confirm it's them, but certainly starting to look that way.

 

Can we rule out it being a partially clogged air filter or a partially clogged fresh air intake?

 

I will double check this to make sure nothing blocking the air intake and filter, checked from filter to intake but will confirm filter forward today.

 

Ok I have put it back on the icarsoft computer after doing a bit of reading into cats and things to look out for, im not used to diagnosing cat converters but basic research told me to look at the O2 sensor switch rate of S2 (after the Cats) and so i focused on looking at the SI and S2 values of the Banks. I also displayed fuel pressure and MAF sensor data, just to try see a picture.

The data below is approximate from changing values. The engine as left to run idle for 5 mins before taking these readings.


The data was as below:

Idle:

• Airflow MAF : 5.10
• O2 Sensor B1-S1: 0.29ma
• O2 Sensor B1 S2: 0.530V (Fluctuating Alot As low as 0.105 up to 0.790)
• Lambada B1 S1: 1.015

• O2 Sensor B2-S1: -0.34ma
• O2 Sensor B2-S2: 0.640V (Fluctuating but less than the first As low as 0.425 up to 0.725)
• Lambada B2S1: 1.030

At 2500 RPM

• Airflow MAF : 14.39
• O2 Sensor B1-S1: 0.10 ma
• O2 Sensor B1 S2: 0.600V (Fluctuating Alot As low as 0.520 up to 0.805)
• Lambada B1 S1: 1.013

• O2 Sensor B2-S1: -0.20ma
• O2 Sensor B2-S2: 0.690V (Fluctuating but less than the first As low as 0.530 up to 0.690)
• Lambada B2S1: 1.070

At 2500 rpm fuel pressure was 378 Kpa, intake manifold pressure 23.0 Kpa, 6.3% Throttle position.

The switch rate of the S2 sensors especially on B1 S2 stands out to me, Am I just seeing too much into this data or is it suspicious? Any thoughts or suggestions are always welcome.

 

Thought I would Share the videos of me doing this to show the switch rates im seeing, incase it helps. (The readings chosen are over 2 pages in the computer)
Apologies i was holding my 15 month old son as he fell to pieces when i tried to sneak out to the garage for 10 mins, so you hear me a few time trying to entertain him haha.

Video 1 (Idle Readings)
Video 2 (2500 RPM Readings)

 

On a 4.2l engine, the fuel pressure is available over OBDII. It should read 55psi pretty much at all times.

You should probably focus on the trim numbers, easier to interpret than current/voltages.

The AFM for our cars is common to a bunch of models at pretty cheap, you might want to just get it.

A smoke test would probably help find air leaks. The intake pipe is a common place for leaks.

 

I was going to suggest looking at the intake pipe! Seeing if it has any holes causing a air leak. I just recently replaced my intake tube because it had a giant hole in it from the plastic failing. The hole caused my XKR to be very slow and not accelerate to higher speeds

 

I don't think a smoke test is called for. In post #4 he reported the fuel trims were near 0 at idle.

 

I will certainly have another look, but i took the ducting all off, and all appeared ok after close examination.
Fuel rail pressure is 55 PSI when at 2000 RPM, When it boggs down, fuel pressure seems to remain at 55 PSI. I will grab a MAF sensor and see if that does the trick.

 

Update:
MAF sensor will be checked later today (new one out for delivery). I tried getting the bottom end of cats loose to see if it helped (In case cat(s) are blocked) but the bolts are well seized and rusted on them, even after some rust release on there.
I have car booked into an exhaust shop on Tuesday (earliest I could get), As I feel they will have a better shot of getting the back of the Cats off with it on a lift.

If it is the Cats, seems that the only option is a universal cat or the Nameless ones, as the originals are very difficult to find (Lots for the 4.0 Litre but cannot find any for the 4.2 L).

Any thoughts until then to keep troubleshooting?

I was looking on JTIS as well as other sources, the MAF readings seem within the normal, The fuel pressure seems normal, the fuel trims seem to dance around the 0 and remove fuel when bogged down.

 

Changed the MAF to a new one, no change.
I also confirmed i had one with same part numbers in the airbox off my old stype in the garage, and it also made no difference, all the same part numbers by Denco.

 

If the throttle body as been messed with, you might want to do the $0 reset procedure. In the bin next to the brake booster, you should see the end of the gas pedal cable going to a semi-big spring-loaded sensor. Adjust the slack in the cable as needed. Then go inside the car, turn ignition on, engine off, and exercise the gas pedal fairly slowly along the entire travel, from the top all the way down to the floor. Do that a few times. This supposedly re-teaches the ECU the range of values for the sensor. Then test your acceleration again.

FWIW, the throttle angle and even maybe the gas pedal sensor are likely available over OBDII. Might be worth a look. I have never tested this myself, but if you remove the intake pipe, you should see the throttle move as the gas pedal is depressed (ignition on, engine off). You might want to check that all of that is smooth and making sense, e.g. that the gas pedal to the floor corresponds to the throttle plate being open all the way and the throttle position reading 100%.