Thread: Strange behaviour

Originally Posted by Blknight.aus

on the off chance, work out the throttle position required to cause the fault then chuck it in low range and see if the throttle position changes.
If it does it at the same RPMs but different throttle position oil in the harness is the main culprit

If it does it at different RPM but the throttle position remains the same then its the TPS.

Tried this today: hi range error @ 2500 rpm, lo range @ 4000 rpm (approx). looks like it is the TPS, then?
One questions, though: it does the same also when I engage cruise control. Does CC use the TPS to regulate car speed? Sounds a bit silly to me, but then again I am not car designer ...

Georgie

Mine did it yesterday after a Friday night of wading average 2 foot of floodwater whilst getting home, one puddle took me by surprise and had a big splash. Today I checked the air filter, and immediately bought a new one. I was complete, but slightly soggy on one corner and torn. Yes the rest of the airbox was dry. My car had only travelled 200km's since the big splash.


Car had only done this once and hasn't done it since. May be a co-incidence.

I would also make sure that the wastegate is not stuck closed, this will cause an overboost condition and momentarily the ECU will shut off fuelling to avoid engine damage. Just get a pair of multigrips and see if you can move the wastegate actuator rod away from the actuator, extending it against the internal spring pressure. It is quite difficult but it should move smoothly . If it is sticking, soak the shaft where it goes into the manifold housing with CRC or similar and move it manually for a while to free it up.

This also fits with the high and low range check, as the engine will not work hard enough in low range until high RPM to cause enough boost for the wastegate to try and open. You will never get a wastegate to open on a diesel engine without load applied, IE driving up a hill or driven hard.

This is not uncommon and will cause bad surging and sometimes a very quick miss, like a petrol engine having its coil lead momentarily disconnected.

JC

thanks, justinc, will try to have a look.
i will need to consult the RAVE disk first to see which part you mean.

georgie

OOPS, sorry. The wastegate actuator sits on top of the turbocharger housing, in front of the heat shield and has a rod coming out of one end with an adjustable ferrule in the middle of it. This rod goes partially under the exhaust heat shield where it is attached to the wastegate flap controlling 'lug'. The actuator has a small 3.5mm rubber hose going to it, and this is the pressure hose that forces the actuator rod out under boost and the rod opens the wastegate, bleeding off excessive boost.
I should also mention at this point that Disco's have a wastegate duty cycle controller switch, and this is bolted to the side of the A/C compressor and controls the bleed of pressure through this little hose to the actuator via signals from the ECU. These can sometimes fail, but the symptoms can be far more annoying, IE NO ability to accelerate at all, 'limp mode' Check engine lamp and poor starting etc.

Hope this is of some use G

JC

justinc,

staring is excellent, acceleration is there (up to the point where the stupid on-off thing occurs), so i hope the situation is not that bad an can be remedied with a bit of wd 40 ... or a new TPS at the worst.

again thanks for your help.

georgie

Just as an aside, IF you had access to a diagnostic tool, like RCL or testbook etc, a Throttle pedal potentiometer fault will show up as a 'driver demand circuit 'error, whereas a sticking wastegate can sometimes display an 'overboost condition'. This will mostly be a 'soft' or intermittent code.


JC

nope, no way.
however: is testbook a purpose-built tool, or simply a piece of software on a standard notebook? in that case, where do i get the software from?

georgie