Has anyone experienced a similar problem to this,it’s driving me crazy.when I start it up I get exactly 8 seconds of it running as sweet as a nut but then it goes into limp mode and seems to lose boost and won’t let me rev past 1500rpm.this can be overridden by flicking the ignition key back 1 place and then forward again which will allow another 8 seconds and so on.the annoying thing is that the fault disappeared for 4 weeks and then reappeared again when I needed the truck the most.tried the usual suspects ie fuel filter etc but everything seems fine.totally baffled.it might sound daft but could the exhaust brake be kicking in?
Why not just take it into MANs, and get them to put it on to their Diagnostics computer.
I had a Saab car that did exactly what you describe, they put it on their computer and it was a faulty sensor of some sort…job sorted.
If you leave it, it will more than likely eventually fail, and break down one day in the most inconvenient far away place, and cost you a mint for recovery and repair.
Being in limp mode on a busy motorway aint ideal. 
Only way is get it connected to the computer or you will be fiddling with / changing random parts. Plenty of people got diagnostic stuff apart from MAN. Almost certainly is a sensor / wiring thing.
Where are you located ?
Dave comber:
Has anyone experienced a similar problem to this,it’s driving me crazy.when I start it up I get exactly 8 seconds of it running as sweet as a nut but then it goes into limp mode and seems to lose boost and won’t let me rev past 1500rpm.this can be overridden by flicking the ignition key back 1 place and then forward again which will allow another 8 seconds and so on.the annoying thing is that the fault disappeared for 4 weeks and then reappeared again when I needed the truck the most.tried the usual suspects ie fuel filter etc but everything seems fine.totally baffled.it might sound daft but could the exhaust brake be kicking in?
Before you go down the diagnostics route you could check all the multiplugs under the front grille, there are 5 and if some of the pins get corroded this can lead to a breakdown as you describe, also check the flywheel sensor is clean (on top of the bell housing held in with one 10 mm bolt) There are also non return valves in the diesel lines (just at the N/S/R of the engine block) check they aren’t stuck too, other than these simple checks it plug in & see what happens.
Will it keep a constant tick over speed & does the EDC light come on when the fault occurs?
Almost certainly will be a sensor that puts it into limp mode , get it on a diagnosis system .
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MAF sensor usually results in a limit to the number of revs it’ll do and a derating of the power but as everyone else has said, take the ■■■■■■ thing to a garage and pay them for a diagnosis instead of just randomly chucking parts at it. You could even get one of those cheap OBD-II fault code readers from Ebay and read them yourself although they’re a bit limited compared to manufacturer’s software.
manski:
Only way is get it connected to the computer or you will be fiddling with / changing random parts. Plenty of people got diagnostic stuff apart from MAN. Almost certainly is a sensor / wiring thing.
Where are you located ?
I’m In Hinckley, Leicestershire
1970commer:
Dave comber:
Has anyone experienced a similar problem to this,it’s driving me crazy.when I start it up I get exactly 8 seconds of it running as sweet as a nut but then it goes into limp mode and seems to lose boost and won’t let me rev past 1500rpm.this can be overridden by flicking the ignition key back 1 place and then forward again which will allow another 8 seconds and so on.the annoying thing is that the fault disappeared for 4 weeks and then reappeared again when I needed the truck the most.tried the usual suspects ie fuel filter etc but everything seems fine.totally baffled.it might sound daft but could the exhaust brake be kicking in?Before you go down the diagnostics route you could check all the multiplugs under the front grille, there are 5 and if some of the pins get corroded this can lead to a breakdown as you describe, also check the flywheel sensor is clean (on top of the bell housing held in with one 10 mm bolt) There are also non return valves in the diesel lines (just at the N/S/R of the engine block) check they aren’t stuck too, other than these simple checks it plug in & see what happens.
Will it keep a constant tick over speed & does the EDC light come on when the fault occurs?
Thanks for that.yes the edc light comes on intermittently during the fault.yes it will tick over perfectly
Dave comber:
manski:
Only way is get it connected to the computer or you will be fiddling with / changing random parts. Plenty of people got diagnostic stuff apart from MAN. Almost certainly is a sensor / wiring thing.
Where are you located ?I’m In Hinckley, Leicestershire
Sent you a pm, might help. You are a long way from us unfortunately.
Please help me! Same problem