P38 4.6l problem over 40mph

Hi there,
New to this site and hope its the correct place to post but wonder if anybody has any ideas on my P38 driving above 40mph problem.
Idles fine and accelerates up until 40mph great but after that it starts to ''jolt'. This happens above 40mph through acceleration and constant speed but stops when foot is taken off the accelerator.
It's as if theres a problem with 4th gear or the fuel injection or something but what do I know????
Has anybody experienced anything like this in the past?
Any help would be much appreciated

Ahhhhhh...
P38's are now all limited by law to a maximum of 42MPH.
Passed as a members bill last month.




But seriously.... get some diagnostic codes read on the beast. Have you checked your air filter and MAF sensor?

Ah good, thatll save on the old fuel bill. I was going to take him in for diagnosis but wonderd if I could get a heads up before I do. Air filter is newish, not checked MAF sensor

Throttle position sensor? Just to say something different! This has some control over gearbox.
But sounds like fuel to me. Check maf. Is it Thor or gems?

By 'jolt' do you mean misfire on all cylinders, in which case it could be ignition related.

Diplodino said:

Hi there,
New to this site and hope its the correct place to post but wonder if anybody has any ideas on my P38 driving above 40mph problem.
Idles fine and accelerates up until 40mph great but after that it starts to ''jolt'. This happens above 40mph through acceleration and constant speed but stops when foot is taken off the accelerator.
It's as if theres a problem with 4th gear or the fuel injection or something but what do I know????
Has anybody experienced anything like this in the past?
Any help would be much appreciated

Click to expand...

Thor / GEMS / diesel engine?
Manual or automatic gearbox?
Year might help too.

Is the jolt vibration or tugging or what? What happens if in low range?

Is it speed related or RPM related?

Sounds like a misfire when were the plugs changed last ?

Mine misfires like a b**ch when the plugs wear which is about yearly as it's on LPG

Whereabouts in Essex are you @Diplodino ?
What EMS is in the Rangie? GEMS/Thor ?

Sorry for the delay. It's a GEMS, 4.6l petrol automatic 1996.
I suppose you could describe it as a missfire but wouldn't that be at wouldn't that be at all speeds? All the plugs and leads were changed recently.
Its odd because if kept in manual 3rd gear it doesn't happen but in auto over 40 it does as if it's a problem related to 4th gear and above rather than RPM?

How about in Low Range?

If it is gearbox then @jamesmartin will know.

Not there that I know of in low range, not tested it above 40mph though!

Diplodino said:

Not there that I know of in low range, not tested it above 40mph though!

Click to expand...

Hard to get above 30 mph in low!