today my wife and i were heading down the island and we were behind someone running 40 in a 45... My wife went to pass, and when the gearbox dropped down and the rpm's jumped the car began to jerk.. the engine was studdering. it was almost like someone was turning the key on and off... power/no power/power/no power.....

any ideas on where to start...

oh, it is a 2003 xj8 with 75k... otherwise was running fine.

 

bumping this....anyone have any ideas?

 

I assume by your lack of comment that no CEL codes were set.

With the information provided a good guess is that the issue is electrical.

If you had an earlier year X308 the answer would be to start with the throttle body electrical connectors but we see few of the '00 - '03 with that issue. Never the less, removing and reconnecting couldn't hurt. Also the relay supplying power to the ECM has been a reported failure point. Remove, clean replace or swap a nearby relay.

Another WAG, check the large power connector on the front of the right firewall extension. It is a common electrical issue due to looseness or corrosion.

Could be another dozen issues but not enough information at this point.

 

thanks for the reply..
no codes were thrown.
i was out of town last week, so i was unable to do much in the way of checking connections. I will go through your list and see what i can find.

 

did anyone find out about this??? I'm having similar issue

 

how much fuel in the tank and is the filter new?

 

Could be the fuel pump-these do fail now & again...

 

New and new

 

Before we get too carried away, let's check the simple things first.
I had identical problems as you and found three things:
1.cracks in part load breather hose.
2. Slit in full load breather hose connection to cam cover.
3. The vacuum hose connection to fuel pressure regulator was bent double....obviuosly some noob had been in there before me!
Not to say that yours has these problems but by the sound of it, it is intake related and most likely air leaks into the intake system 'upstream' of the MAF will cause a lean running condition which ultimately leads to stuttering on acceleration...embarrassing at the least....especially in my case when overtaking a Mercedes! ;o]

 

Where is the fuel pressure regulator?

 

Fuel pressure regulator is at the rear of the left hand side fuel rail.
Standing at the left side of the engine bay, look towards front edge of the thrott;e body TB and you will see a small disc like item with a rubber vacuum hose on it.
Mine had been kinked over by some careless person.
Also check your purge valve and pipe work.
This is mounted on the firewall directly behind TB...a round device about 1.5" across witht he word jaguar on top.
Underneath there are two hoses...check these for security.
Also check the anti-resonance pipe attached to the left side of air trunking...this quite often fractures at the joint.
All these faults will allow 'Rogue air' into the intake system upstream of the MAF which cause the ECM to read lean....causing stuttering on acceleration.

 

Thanks!

 

Cleaning the throttle body and MAF never hurts. Be sure to use the
cleaner designed specifically for each one. The MAF is near the aircleaner
and easy to reach. The butterfly in the throttle body sometimes sticks
and causes the fuel/air mixture to get out of proper range.

I used to have a problem with oil leaking into the spark plugs holes. That causes the coil to short out. For some reason it was worse when accellerating going down hill. You can use a syringe and tubing to remove most of the
oil and then contact cleaner on the coil boot. I had to do that every
few months until fixing it correctly.

 

i wanted to reply that i found the issue from the origional post, sorry i did not reply earlier...

for us it was two fold. i first found a loose connection on the plug of the maf. I cleaned the plug contacts with electrical cleaner and re attached... problem got way better.... but still had issues under hard load.

For quite a while i have been getting the knock sensor CEL... i have never paid them much attention.. as i have never until recently had any performance issues.

Well i guess the sensors got worse or something, as i was continually getting the CEL.

I changed the sensors (a 30 minute job max... very easy...

BINGO... solved all my running issues and have not had a CEL in several months...

now if i could just find reasonably priced parking brake cables and parts...