Fault diagnosis help please!

[Jonboy_t]

Friend of mine has an '08 plate Astra diesel that is losing boost/power when going up an incline in 4th or 5th gear at motorway speeds - if you put your foot down, the engine management light comes on and it engages 'limp home mode'. He's had it in a Vauxhall garage but as it's not happening every time, they can't replicate it to diagnose it apparently. They've asked for him to bring it back next time it happens and they will put it on their diag machine.

I'm thinking that perhaps the EGR valve not allowing correct recirculation when under increased demand, so the engine throws a hissy fit. Either that or something like the wastegate not dumping pressure out and so the turbo cuts out because it's running at too high pressure.

I'm far from being a good mechanic though (I like playing with engines, but not very good at it!), so has anyone got other thoughts on what may be causing the fault?

[thinfourth2]

The wifes honda did exactly the same and changing the fuel filter solved it.

When diesels were simple changing the fuel filter solved many many problems

[andy-xr]

Split boost pipe? I'd be looking there first before it ends up in a conversation about injectors and fuel pumps!

[Jonboy_t]

andy-xr said:

Split boost pipe? I'd be looking there first before it ends up in a conversation about injectors and fuel pumps!

Good call, but apparently they have checked this - albeit visually.

[thinfourth2]

A fuel filter is a tenner plus labour to change

[Crafty_]

any error codes ? hold brake and throttle to the floor and turn ignition on, odometer will show codes.

Your diagnosis could be correct.

[Jonboy_t]

Crafty_ said:

any error codes ? hold brake and throttle to the floor and turn ignition on, odometer will show codes.

Your diagnosis could be correct.

I didn't know that!! I'll let him know and see if it comes up with anything. That might be the answer to the problem - I've got one of those code 'dictionary' things on my phone that should tell me what the code means.

Cheers for all your help on this guys!

[frosted]

I changed my own fuel filter and it took a whole of 10 minutes if that

[16v stretch]

Jonboy_t said:

Good call, but apparently they have checked this - albeit visually.

I +1 the boost pipes, take em off, give them a flex and have a good look, or some soapy water and a mate putting the engine under load should give you a better idea.

I would have thought if the EGR was sludged it would be pretty poor throughout the revs.

[thinfourth2]

16v stretch said:

I +1 the boost pipes, take em off, give them a flex and have a good look, or some soapy water and a mate putting the engine under load should give you a better idea.

.

Engines use lots and lots of air and not so much fuel

A split/collapsed boost pipe will starve an engine of air pretty quickly so i would expect faults in all gears.

A half choked fuel filter will give the engine enough fuel to produce max power for a short period however when you ask for max power for a longer period as in flat out in 4th or 5th it will use all the fuel in the clean side of the fuel system before starting to starve which will reduce fuel pressure and throw up error codes

[joncarpet]

had something very similar on my 53 Zafira 2.0dti. Low/no boost, limp home mode, then fine again. Even being facing downhill seemed to have an effect.
A recommended auto electrician found the fault code and a small split in boost pipe and all is sorted now!