Hello from Estonia,
please help me with my problem
Jaguar 4.0 v8 1999, rough at idle when hot, in the morning when cold works perfectly, in few last days when its hot it misfires badly and power is lost.
I have checked spark plugs- they are the right working colour bocsh super plus,
fr7dc+, ignition coils are working, i have cleaned idle valve and trottle body, but still misfiring when getting working temperature.
I have made diagnosticks but it show nothing- no mistakes.
Please help

 

Carioboy, welcome to the forum. Might I suggest that you go to the "New Member Section" and properly introduce yourself.

We really need the code(s) the vehicle is showing. Just a stab in the dark, maybe clean the MAF sensor.

 

diagnosticks show nothind, even check engine light is not on.

 

Probably a coil but could be an air leak (EGR? EVAP? etc). Maybe an O2 sensor (upstream most likely).

Used when the fault is occurring, an OBD tool (one that does "live data" such as elm327) can show you:
is it running CL (closed loop)
what the fuel trims are

Then check at 2500rpm.

Post all of what you find

If all looks OK (but we know it isn't), next look at O2 waveforms. Maybe just do the above then come back for suggestions from members.........

 

+1 with jagv8

Another possibility, a minor vacuum leak (as jagv8) mentioned above. On the these vehicles (both 6 and 8 cylinders) there are known failures with the hard plastic vacuum lines cracking in hard to see places. Again throwing darts in the dark.

For example our 3.0 had 1 of the IMT O-Rings (V8 engines do NOT have) leaking slightly, (the O-Rings would be associated with the vehicles vacuum), I had no codes as well, but there were other related symptoms that pointed me to them.

 

just tried to drive with it, started perfectly, drove about 10 miles all was perfect- went to the shop, came back started jag, it started to misfire, and when i press pedal to accelerate it misfires badly and no more power , i disconnected air mass sensor, no misfires but power is reduced when accelerate and rpm is jumping from 500 to 800.

 

You ran the vehicle without the MAF sensor plugged in? There were no codes while doing so?

 

It'll default, probably run OL (open loop), rich, may take a while to throw codes (if it does) - not least because it's OL.

If it runs rich long enough it'll destroy the cats of course.

Not a fix by any means!

 

made diagnosticks , shows p1000, and misfire, but doesnt show where is misfire.

 

To get P1000 you've cleared the codes. You lost the data on which misfire. It may or may not happen again. The reason it may not is that you cleared the data (not a good idea!).

You can either wait and hope it shows which misfire or start swapping coil(s).

You could perhaps try a jag dealer tool and look at its special data but this may not be cheap.