Overboost problem, 2005 Patrol

[andrewk]

just remembered that last year my rac pal couldnt get his works lappy to connect to troll and he had various software, ended up reading codes with the wire method
and counting mil light flashes.

Yep, that's what I've been doing

please post some pictures of the dawes valve conversion.

I installed a boost pressure gauge a month or so ago. The dawes installation should be easy - just tee into the pressure hose going to the gauge sensor for one end of the dawes - and then from the other end of the dawes to a tee in the vacuum hose that goes to the VNT actuator.

The principle is simple, once the boost pressure rises above the level that the dawes valve is adjusted to, it starts to open. This reduces the vac to the VNT actuator which moves the VNT lever and the boost falls a bit. Effectively, all the dawes will be doing is lopping the peaks off the boost pressure so that, hopefully, it will not rise above about 15 psi (and so, again hopefully, we'll not see an overboost error).

Once I get the dawes valve - probably take two or three weeks from USA via Customs and Excise - I'll fit it, clean up the installation of the boost gauge and replace the bright blue vacuum hose with black so it looks a bit more professional - and then I'll take a photo or three.

Cheers
Andrew

 

[andrewk]

I think this great long saga is now close to a conclusion. After another adjustment of both the stop screw and VNT rod length on the turbo, I now get .....

In neutral (hot): Increasing revs slowly from idle to 3500 rpm, boost rises to a peak of 8-10 psi around 3200 rpm and then falls backl. No error.

M62 uphill: At 70 mph in 5th, up steepish hill towards the Saddleworth turnoff, boost pressure is steady at 13-14psi. If I lean on the throttle a bit, it rises to 15 psi. No error.

After leaving the M62 and heading towards Oldham up the steepish hill towards the transmitter at Windy Hill, in 3rd gear and accelerating at half throttle boost pressures is steady at 15 psi. If I then floor the throttle at 2800-3000rpm, boost pressure spikes to 20-22psi but then falls back to 15psi as the revs rise towards the red line. No error.

I haven't towed the caravan since the latest adjustment, but there has been no overboost error. I'm quietly confident that it's OK now. I'll still install the Dawes valve when it arrives and adjust it to try and keep boost spikes down to 18 psi.

Fixed?? Dunno - but maybe I will soon. I'll keep you posted.

Andrew

 

[Thomas-the-Terrano2]

sounds good Andrew, take it that is without the dawes valve kit.

does performance feel any less as a result.

perhaps can sort a meet and show me as like to try but feel
so out of my depth.

 

[andrewk]

sounds good Andrew, take it that is without the dawes valve kit.

Yes. I haven't yet received the Dawes valve. It'll take a while - its from the USA. I'm not expecting it for a week or two yet.

does performance feel any less as a result

No, performance is fine.

perhaps can sort a meet and show me as like to try but feel
so out of my depth.

Yes, maybe we should - Sheffield is near enough. You have to remember, though, that the problem I had was because someone (previous owner) had been fiddling with the turbocharger VNT calibration. I don't think that is the case with yours, is it? Have you any reason to suppose that the problem is caused by the turbocharger itself? Adjusting the stop screw or VNT rod length will make things (MUCH) worse if the fault is caused by something else. If the problem is a failed or failing MAF, ignoring that could result in the engine blowing.

Have you had an overboost error for as long as you've had the Patrol? Has it been modified in any way? Remind me, do you have a boost gauge installed?

Andrew

 

[Thomas-the-Terrano2]

no boost guage, though would, just a bit fearful of messing with the
whole induction area of car, happy as far as doing stat, even helping
do water pump though.

it wasnt always doing it, started about 4 months in in 2009, after
plenty of no issue towing.

came on solo one day on A55 when needed bit more throttle to
overtake.

as for mods, no idea, though when gasket and pistons were done
engineer said some one had been in before to some degree. also
several of the fan shrouds were broken ok they are fragile as ive
bust an already sprained one. (retaining fastners)

some of shroud is broken too, so someone was clumsy before me.

the car seems to souond different every time i drive it, not
parnoid but gettng there, think always listening and looking
at guages and check lights, never did with terrano.

love it and sort of hate it at same time, yet just like t2 never
needed to come home on a breakdown truck.... always gets
us there and back.

 

[andrewk]

no boost guage, though would, just a bit fearful of messing with the whole induction area of car

Yeah, me too. I only did because I had little option.

Firstly, have a close look at the turbo's VNT linkage. You should see an adjuster on the rod and also a stop screw with a locknut behind and to the right of the adjuster. You should see some yellow (sometimes white) paint on them put on by Garrett in the factory. If the paint is there and the paint on the adjusters and locknuts lines up and doesn't look to have been disturbed then leave the adjusters well alone.

One possible - and I believe it happens quite a bit with motors that have done a few miles - is that the VNT vanes stick. The lever at the bottom of the rod should be at the bottom of its travel with the engine switched off. With the engine hot, it should be at the top of its travel and touching the stop on tickover. Also hot, if you rev to about 3200 rpm, it should fall back to the bottom of its travel.

You can also check for vane stickiness by pushing the lever up with your finger. It's quite hard to do - but it should move smoothly both up and down. You can also check that by applying vacuum to the VNT actuator. The easiest way to do that is to follow the black hose from the actuator back to the VNT control solenoid and (carefully) pull the pipe off at the solenoid end. Using a pair of MK1 lungs, suck on the end of the hose. You should be able to lift the lever to the top of its travel (its not hard). If you stick your tongue over the end of the hose with the lever at the top, the lever should stay where it is. If it does, the hose is OK and the VNT actuator doesn't leak.

Once you checked all that, especially if you suspect that the turbo vanes are a bit sticky, get yourself a 14mm open ended spanner. It will just slide onto the VNT lever. Using the spanner, give the lever a really good wiggle up and down. I have heard that sometimes this can relieve the stickiness. After you've done that, go give it a blast and see if the problem is cured.

If everything seems OK so far, your next port of call is to checkout the MAF sensor. For that, you need a multimeter - preferably a digital one. If you measure between the centre pin (red wire) of the MAF and ground (battery ground), you should get about 2V with the engine warm and on tickover (mine is about 1.85V). If you gradually increase engine revs, the voltage at the MAF should rise. It should be well over 3V by the time you hit 3000 revs. (you could graph it and post in on here - or compare with mine earlier in the thread, maybe)

I'm sure there are other possibilities, but sticky turbo vanes and a failing MAF are the most likely - so a good starting place for testing.

Andrew