Hesitation under hard pull

[john]

Hi Guys,

Nagging tempremental problem with my XUD at the mo,

Factory fitted Bosch, 9mm with a few turns of the fuel screw
When doing a hard pull the power drops off for a moment before picking straight back up.

The boost guage is pinned to a steady 22psi but when it drops off it will spike upto 26 before shooting straight back down to 22 when the fueling comes back in.

This problem exists on straight diesel but is more evident when running on veg oil but I've changed the filters and cleaned the intank strainer with no effect.
I'm stuck as to wether its dragging in air or the fuel feed pipework is damaged/kinked, it has a small repair on the 90deg just before the grenade with some white stikaflex stuff... :\

Any thoughts on this would be appreciated!

Cheers,
John

[Harky]

More than likely air getting into the system somewhere, around the filter housing is a common place. Do you have to lift off the throttle and then back on to get the power back again?

[john]

No It just comes back by itself, although it can do it over and over on off on off sometimes!

Thing is it Dosnt knock, it just misses for a full turn. Why would the boost increase? My own reasonable grasp on all things sciencey dictates it would loose boost...

[petegledhill]

No It just comes back by itself, although it can do it over and over on off on off sometimes!

Thing is it Dosnt knock, it just misses for a full turn. Why would the boost increase? My own reasonable grasp on all things sciencey dictates it would loose boost...

had something similar with mine the fuel return banjo had a slide in that had stuck caused the feeling of fuel starv

[john]

had something similar with mine the fuel return banjo had a slide in that had stuck caused the feeling of fuel starv

Thanks for the heads up, googled this and its brought up an interesting theory!
I'll check this tomorrow at some point

[n0v0s]

You say it's worse on veg.. As it is gloopier stuff, the pump will increase suction/vacuum to draw the fuel in, and any air ingression will therefore become worse. Replace grenade and bodged pipe, job jobbed!

[Ruan]

I'd guess that's the wastegate just overshooting tbh, you've got the time for the lines to fill with air then the actuator to move, turbine wheel to slow down, then the pressure will drop...

[john]

I'm going to swap out the Bodged pipe/grenade before the weekend.
Keep meaning to weld the wastegate on the T2 too

[Ruan]

What's the latest obsession with welding T2 wastegates?

It's kinda pointless, it's just something that everyone went on about for months and then it became a fad... If you intend to have your car as a daily car, I highly recommend against it, you just need to actually shorten the actuator arm or increase the spring pressure...

All it does is strangle the engine at high RPMs - yes, it'll give you a massive peak midrange, but you're just likely to overheat turbos, precups, heads... These engines aren't exactly the best for high heat levels, they really don't like it, and welding closed the wastegate just accentuates this and gets things red hot... You can get away with it on larger turbos, they've got such big turbine wheels, there's little to no restriction anyway...

Everyone assumes these engines are just invincible, but they just aren't... They do NOT like high temperatures...

[john]

Here's a thought, could it be sucking in a soft boost pipe?

[john]

Epic bump I know, but thought I would post the solution to this problem!

Changed the grenade+pipes to no avail, lump of clear pipe between filter and pump showed nothing.
Turned out that a washer was missing off the bolt/union thing on top of the feed line on pump itself!

No apparent leaking from it and was a right bastard to pin down, my next step was to guess a ruined seal somewhere in the pump itself and replace the entire Bosch pump!

Glad it's running fine now, just debating wether to T25 it, or try squeeze one of the TB28's I have laid around down the back!

[Harky]

Good to hear you got it sorted. I had problems with that same copper washer only a couple of weeks ago!