Recently my engine 4.2 ,shakes for the first few minutes at startup.

Ive gone about the normal tasks of cleaning the throttle body, Mass air flow

sensor, new air filter, run through several tanks of fuel with seafoam, and

with Lucas fuel treatment. Nothing seams to help. Ive bought a new fuel filter

to put on as the last resort. The car runs puurfect after a few minutes, but

after sitting for more then 8 hrs it shakes at startup Someone told me on

older jags there is a cold start sensor??

Any ideas? Thanks!!

 

Have you checked for OBDII codes?

 

I checked with a OBD 2 scanner and got one pending code of p1111
I read thats a normal code is this correct?

 

Yes, that is normal.

I would suggest checking the spark plugs wells for leaking fluids (oil or water) and also inspecting the spark plugs themselves.

Also, if your OBDII reader can do real time monitoring, have a look at the long term trims, the coolant temperature and the fuel pressure (only available on 2003 and later cars).

 

What should the fuel pressure be at? I owned a 2003 Lincoln LS v8 that had issues with the coils because of the the gaskets around the plugs would leak oil, causing them to foul out. I know the LS engine is a similar to the 4.2 do they have similar issues?

 

Fuel pressure is electronically regulated on the 4.2L and should be about 55 PSI on a normally aspirated engine.

Yes, these engines have the same issues with leaking seals in the spark plug wells. Also, particularly if the engine has been washed, there could be water in there also.

 

Monitor your ST and LT fuel trims immediately upon startup, you'll notice something immediately if something is amiss. Anything over say...8% and its a vacuum/unmeasured air leak getting into the engine. If you do have one, there's lots of threads and videos around here showing you how and where to locate them. It could be a crack in the air pipe, it could be a leak at the TB gasket, etc. good luck, most of us have had to chase more than one of these down...me included.

 

Did you find out what the problem was?

 

Thanks for checking!
Unfortunately I have not been able to fix this issue. The engine shake seems to clear itself after 2-3 minutes of idle. Ive done all that was recommended. Ive changed the fuel filter, checked the coil packs to see if oil had pooled in the spark plug wells, monitored the the air to fuel mixture and oxygen levels via OBD2. No fix any other ideas?

 

Try a can of BG-44K in a full tank of gas.

 

I have put a can of bg44 in thanks whitexkr and it seems to have helped only done a 100 hundred miles but im sure its working.

 

my engine is much smoother on startup now but i can still feel a shake, do you think i should use another can? or try the injector cleaner fluid instead of bg44 again?

is it ok to keep using this stuff in our engines?

 

Both my 05 XJ and XK do the same thing on start up, but as soon as the rpm begans to drop, the shake go's away.

I just assume it is a fuel start up (rich) issue and could be adjusted, but it hasn't gotten worse or improved now for over 5 years, so I don't worry about it. It's been my experience over the years that on a issue like this which last at top's 3 or 4 seconds, having someone (dealer or whatever) mess with it, will screw someting else up. Since they run like sweet tea afterwards, so be it.

Chuck
05/ XK8 Conv.