Transit mk6 90 t350 rwd rocking when flat out

[Connor444]

Hi recently brought a transit w reg (think a 90) t350 rwd recovery truck and when up to speed 60-70 and foot flat to the floor it starts what i would describe as rocking like it's excelerating then decelerating not drastically but enough so the passenger notices but when lift off the pedal an inch it's fine
Any ideas would be a great help
Thanks

[knobby1]

Is she screaming her head off at 70mph...?? Do you have a tacho or know what sort of rpm she's doing at the time?? At 70mph and a short diff ratio...she might be on the rev limiter..!

Lord Knobrot

[Connor444]

Hi
No revs fine when flat out don't sound like it's reving it's nuts off
No tacho either
It's kind of like it's got more to give in speed but fuel or something is saying no
It can happen from 60-80 just a little strange also sounds like a tractor lol had a few transits too and from sound and way it drives something ain't right

[Connor444]

No idea on rpm either

[knobby1]

Fuel filter replaced lately?? Pedal could be duff....Timing solenoid may also be on it's way out, fairly common on the TDDi engines....you may need to get the codes read before doing anything costly.

Lord Knobrot

[wronghole]

Speed limiter set at 70mph perhaps

[Connor444]

No idea on fuel filter will try that first
No limiter as does it at 60 70 and 80 think it's when it's under a big load from hills or flat out etc
As for rest will check those over and see if anything comes up on computer
Thanks

[Frag]

Blocked fuel filter will cause those symptoms...