Overboost problem, 2005 Patrol

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cheers had heard of using a wire, but your process gives me confidence to try it.

so should i just get the code and post it for definition or do you have a link to all
the codes.

cheers
rich
 
ok tried and works though got bit punch drunk different codes coming off

may have got 7 different ones, incl. 9.5 i think, quite a few ecm codes
but may have mis counted, will try again.

its possible i suppose that some are old codes, there was a definitely
a 14.x think .1 which is a nats issue and have had strange alarm effects
in past.

will read em again then reset to clean slate, and next time light comes
on read it straight away.

those fast flashes are just that, blink and miss eh? wonder if better done
in dark.
 
ok, so definitely 14.1 nats, 9.5 boost , 7.3/4 pump/spill valve,
5.2 battery voltage high and 3.1 ecm failure,

was looking for 2.3 accelorater position but not seen having
had momentary power cut, but that could be the 9.5 i guess.

all gone now seen 5.5 all clear.

will print out list and keep wire in car to read next time.

saved few quid for now, just as well as hdd in pc bust so need
to replace it!!
 
FWIW, I did several thousand miles over the summer after Nissan fitted a new boost sensor, about 1500 miles of it towing a caravan - no problem at all.

Just before Christmas, guess what - 65mph on the motorway accelerating up onto the M66 from Haslingden and suddenly, the dreaded power loss when the 'Troll goes into limp mode. When I got home, I checked for ECU fault codes and yes, we have a 0905 code (boost pressure sensor). Weird or what .....

As the fault seemed exactly the same as before and as the motor is still otherwise running just fine, my guess was that the boost sensor (Charge Air Pressure sensor) had failed again. I rang Westway Nissan and explained what had happened and they agreed to change the sensor under warranty. I've been driving the car pretty gently and didn't experience the problem at all in January after the second new Boost sensor had been fitted - but earlier today, pretty much the same bit of motorway coming back from Haslingden and we get the sudden power loss again - and the 0905 boost pressure ECU fault. I'm now thinking that I just haven't got to the bottom of this yet - the fault must be something different - possibly a problem with a blocked EGR valve or some problem with the turbo wastegate or its actuator.

I'm pretty confident that West Nissan will not be able to diagnose the problem effectively. For sure they could just keep swapping stuff until the problem goes away, but that's likely to be way expensive. Just maybe the best (and possibly cheapest) solution is to take the motor to an expert. So, unless I can think of any better approach, I'm going to give Diesel Bob's a ring one day next week. If they can't diagnose the problem, no one can.

Ho hum ..............

Andrew
 
I dont know much about that sensor, or how it works, but it sounds as if something else is "wearing it out", if that makes sense?

good luck sorting it though, these are really annoying problems!
 
clivvy said:
I dont know much about that sensor, or how it works, but it sounds as if something else is "wearing it out", if that makes sense
Click to expand...

Yes, it makes sense - but I doubt that is happening (though I may be wrong) and think there may really be an overboost condition (as distinct from a phantom one resulting from a faulty sensor). My money now is on something else being faulty. I just don't understand enough about how it works (and don't have the test gear) to diagnose the fault myself - so I'm going to have to throw money at the problem. I just don't trust Westway Nissan enough to throw it at them. :(

Andrew
 
A minor move forward on this overboosting problem ......

I have now bought, but haven't yet fitted a boost pressure sensor. One of the natty electronic stepper motor ones. I'm still trying to suss out the least problematic way of installing it.

As the sun came out today, I decided to stick my head under the bonnet for a while to see if I could discover anything I'd previously missed. Anyway, I removed the vac hose from the VNT vacuum control solenoid, stuck it in my mouth and sucked hard. The VNT actuator rod moved smoothly to the end of it's travel & smoothly back again when I stopped sucking. It also stayed put if I blocked the hose with the end of my tongue.

I think I now know (probably):

a) There is nothing wrong with the vanes in the turbo. They are not stuck or sticky. (Does anyone want to buy an (unused) Innotec Chemical turbo cleaning kit??)

b) There is nothing wrong with the VNT actuator itself. At least, I now know that the diaphragm is fine and not leaking.

c) The vacuum hose between the VNT vacuum control solenoid and the VNT actuator is not leaking.

I'm beginning to think that, despite having already swapped the boost sensor (twice) for new ones, it still seems to me to be the most likely for being faulty. I'll test the boost sensor tomorrow (if it doesn't rain) - should be about 2V on one of the pins with the engine warm on trickover. Must get on with installing the boost gauge too .............

The only other option I can think of is a possibly faulty VNT vacuum control solenoid.

So ............. does anyone know how to test the VNT vacuum control solenoid. Is there anything else obvious I missed????

Andrew
 
Andrew as you are fitting a boost gauge have a read at the link as this will stop the overboosting once and for all once its been set up to what you set max boost to

http://www.chaz.yellowfoot.org/Manual Boost Controller.htm

The 2 graphs tell a story to me that Nissan have designed a system that is not fit for purpose and there are too many things (sensors)that can go wrong.

18psi seems to be the max boost that the guru's say is safe, but the standard curve spikes over 20psi.
I wonder what yours does when you fit the gauge. You can tell us what pressure brings in the MIL fault.

When I've hammered my 2.8, the max I've seen is 16psi. I know its a different set up. When I'm driving at steady 60mph it sits at 10psi boost.

Hope you get to the bottom of this problem as ThomastheTerrano is having the same issue.

Let us know how you get on with boost gauge etc.:thumbs
 
Here some checks for you to carry out after fitting your boost gauge.

If you have time, try to read this extract below. It comes from the TDi VW and Audi forum, but it is very relevant to our Patrols that use similar systems. http://www.tdiclub.com/

The main difference is that if you still have ECU control, you can go to 18psi at 2000rpm, but without ECU control, you should try to keep it around 10psi to stay out of the danger zone.

The purpose of these modifications is NOT to increase the steady-state boost pressure (which is already higher than the older vehicles use, and very close to the safe upper limit if the vehicle is "chipped") but rather to control the fluctuations of boost pressure characteristic of the stock boost control system, and to REDUCE the amount of boost pressure at low engine speeds in the interest of preserving the turbocharger by avoiding operation in the "surge" regime. This will actually *reduce* responsiveness at low engine speeds, but it is a necessary step to preserve the life of the turbo, if other modifications which increase fuel delivery at low engine speed have been done. These modifications are only useful if other modifications (e.g. injectors) have been made that result in either unacceptable exhaust smoke or power fluctuation due to fluctuations in boost pressure that the stock boost pressure control system cannot control, or unacceptably high boost pressure at engine speed below 2000 rpm. The VNT turbo must not reach full boost pressure until above 2000 engine rpm, and should preferably produce no more than about 6 psi boost pressure at 1500 rpm, to avoid operating the compressor in the highly damaging "surge" regime. Turbo manufacturers recommend staying at least 10% clear of operation in the surge regime.

Since the A4 cars do not have any small-diameter hoses which carry boost pressure, it will be necessary to install a suitable fitting to access boost pressure. This fitting should preferably be located as close as possible to the turbo compressor outlet, such as on the lower intercooler pipe ... remove the pipe from the vehicle to install the fitting there. In order to facilitate future removal of this pipe for timing belt changes, use some sort of quick-connect detachable fitting to your new boost signal hose.

Test Procedure for Turbo Calibration - Low Speed Regime

If you have an automatic transmission, you don't need to worry about operating the turbo in the "surge" regime. At full engine load, the transmission will either downshift to a lower gear or unlock the torque converter, and in either case, the engine speed will be above the critical zone. Nevertheless, it may be worth performing a test similar to what is described below, and confirm that the transmission downshifts if floored at 2000 rpm in top gear before the boost pressure reaches 18 psi, and downshifts if floored at 1500 rpm in top gear before boost pressure reaches 6 psi in response to smooth application of pedal.

On manual transmission vehicles, to test whether you have a potential "compressor surge" issue, install a boost gauge, and then in 5th gear on level ground, preferably at an altitude of not more than 1000 metres, abruptly floor the accelerator at 1900 rpm and note the boost response. Ideally, it should smoothly rise to a peak which is not more than 18 psi somewhere near 2000 rpm. Try tramping the pedal to the floor at engine speeds between 1900 and 2100 rpm. It should never exceed 18 psi in this speed range. Not even for a split second. If it passes the tramp-the-pedal test, try accelerating through that speed range starting at slightly lower speeds and try it in different gears - confirm that initially after flooring the pedal, the boost pressure is lower than its eventual peak when below 2000 rpm, and that the peak is not reached until 2000 rpm. If it passes THAT test, reduce speed to 1500 rpm, and see if you can get more than 6 psi boost at 1500 rpm (don't floor it at this speed unless a few initial tests at part load suggest that you can floor it without exceeding that pressure). If it ever exceeds 6 psi at 1500 rpm or 18 psi at 2000 rpm, or if the peak boost pressure - whatever it is set to - is reached before 2000 rpm (never mind what happens at higher engine speeds), then you have a potential "compressor surge" issue, and you should consider performing the "negative VNT adjustment". Turbo manufacturers recommend staying 10% clear of the surge regime, and if you get it so that it passes these tests no matter what you try, you'll be around 10% clear of the surge line. (Don't be surprised if a bone-stock TDI fails this test procedure ... no chip no tuning box no injectors no nothing. Stock calibration is extremely close to the surge regime and normal production tolerances may put it into the surge regime.)

VNT Linkage Adjustment

To slow down the rate of boost pressure rise at low engine speeds, using a 10mm wrench and suitable hand tools, release the locknut of the VNT linkage (located above the diaphragm housing on the turbo) and adjust it 1 turn in the direction of lengthening the linkage, then re-tighten the locknut. YOU ARE NOW YOUR OWN TURBO WARRANTY. (If your vehicle was hot-rodded such that this modification was needed, you were already your own turbo warranty anyway, but hopefully the turbo is less likely to blow apart now.)

NEVER NEVER NEVER shorten the length of this linkage to less than it was stock. Attempting to increase the boost pressure at low engine speeds, or attempting to get the turbo to accelerate to full boost faster (which will cause a massive overshoot) is asking for a blown turbo. It has happened, so don't neglect this possibility!!

Test Procedure for Boost Control System Response

After performing the above procedures, to test whether you have a potential "spike" issue, in high gear at 2500 rpm, abruptly floor the accelerator and note the boost response. In the ideal world, it'll go smartly to the boost setpoint (which is not more than 18 psi) and stay there, but in reality with the stock boost control system, you'll get some overshoot. If it overshoots and fluctuates wildly before settling down, you need to do something to control boost spikes. If it survived this test at 2500 rpm, try it at 3000 rpm. Remember that 18 psi is the safe limit for continuous operation at sea level and this must be de-rated in proportion to barometric pressure at higher altitudes. If you're scared by what you see (and if you drive like that!), you need to do something to control boost spikes!

A mechanical boost controller in parallel with the stock boost control system can be installed as per the Troubleshooting section of this FAQ, under the symptom "Fluctuation of boost pressure". It is critical that any vent hole in this boost controller be soldered closed to prevent a vacuum leak, and this boost controller will ONLY work in parallel with the stock boost control system so as to eliminate spikes. It cannot be used to raise the boost pressure beyond standard. Do not operate the standard turbocharger at more than 18 psi boost pressure at sea level. Do not operate an engine with a stock compression ratio at higher than 18 psi boost pressure.

Installation: VNT adjustment is straightforward for the home mechanic but you're playing with something that costs several thousand dollars to replace - that's the scary part. Boost controller and boost gauge installation is more involved due to the need to partially disassemble things in order to install the fitting and gauge, and get the boost controller calibrated. Professional installation may be possible but ordinary garage mechanics probably won't want to touch it. If your vehicle has side curtain airbags and a "double DIN" radio, you're going to have a tough time finding a place for a permanent boost gauge.

Advantages: For vehicles that have higher fuel delivery than stock, this provides a method of controlling the boost spikes and fluctuation that are characteristic of the stock boost control system, in order to avoid potentially dangerous operation of the turbo in the "surge" regime, and in order to avoid potential overspeed of the turbo or engine damage due to overboost conditions.

Comments: A boost gauge is MANDATORY if modifications are done to the stock boost control system.
 
Jocky,

That is VERY helpful. Just as soon as I've got the gauge fitted, I'm going to try out the testing regime for turbo spool up speed.

One thing I cannot understand, is how the 'Troll has managed to do 40,000 odd trouble-free miles if the VNT calibration needs adjustment. Something must have changed. The engineer in me keeps telling me that I should find out what that is. I know the turbo itself isn't excessively sooted up or the VNT mechanism would be sticky & it doesn't seem to be. The only other things I can think of that might soot up are the throttle body (can't imagine that can cause this problem) and the EGR valve. Maybe I need to check/clean those.

Whilst I have checked the vacuum hose to the VNT actuator, I haven't yet checked all the others. I suppose that it's still possible that the whole vacuum system is compromised due to a split in another hose. Its possible too that the VNT vacuum control solenoid is goosed - but I haven't yet worked out how to test that.

Modern motors really are getting way too complicated for their own (and our) good. Maybe I should buy an old V8 Range Rover with twin SU(?) carbs and a distributor - that I could fault find on with no problem!!

Maybe its time for a :beer

Andrew
 
Only glad to try and help.

Keep us posted:thumb2
 
andrew do you get your over boost at same sort of time or driving manner.

i seem to get it more if tootling along and then open it up, yet if go from
almost standstill, ok not exaclt a drag strip start then is fine.

tbh, wonder if gravity or g force involved somewhere as if accelerate out
of a roundabout, even trying to make progress by making as straight a
line thru the island with no other traffic about on it will come.
 
Richard have a good read at the test procedures. Sounds like it is spiking on spool up and overshooting and reaching more than 18psi before 2000rpm bring on the MIL:doh I know you've not got a boost gauge, but you can still do the tests at stated RPM and see if it faults.

:thumbs
 
I think it happens at around 2500-2800rpm under load.

* Driving up a steepish hill in 3rd can cause it.
* Accelerating hard from the Haslingden turn-off in 4th and 5th uphill onto the M66 to overtake slow moving traffic has caused it.
* Blitzing up the M62 to the Saddleworth turnoff (fairly steep for a motorway) in 4th & 5th always causes it.
* Towing a caravan south-bound up the M6 towards the Shap turnoff at 50-55mph in 4th caused it

I think it'll always happen if the engine is under load at 2500-2800 rpm for maybe half a minute (maybe less). To get home from Oldham, I have to drive up a steepish hill - sometimes I go up in 3rd (at maytbve 2500 rpm) and sometimes in 4th. In traffic, I might have to keep lifting off anyway, so sometimes I haven't actually noticed the limp/error occur, but it has and the 0905 error code (overboost) is stored.

Andrew
 
andrewk said:
I think it happens at around 2500-2800rpm under load.

* Driving up a steepish hill in 3rd can cause it.
* Accelerating hard from the Haslingden turn-off in 4th and 5th uphill onto the M66 to overtake slow moving traffic has caused it.
* Blitzing up the M62 to the Saddleworth turnoff (fairly steep for a motorway) in 4th & 5th always causes it.
* Towing a caravan south-bound up the M6 towards the Shap turnoff at 50-55mph in 4th caused it

I think it'll always happen if the engine is under load at 2500-2800 rpm for maybe half a minute (maybe less). To get home from Oldham, I have to drive up a steepish hill - sometimes I go up in 3rd (at maytbve 2500 rpm) and sometimes in 4th. In traffic, I might have to keep lifting off anyway, so sometimes I haven't actually noticed the limp/error occur, but it has and the 0905 error code (overboost) is stored.

Andrew
Click to expand...

sound very similar to mine, tbh its so torquey in 3rd even with van on that can
attack hills that would have seen me drop to 2nd in terrano whislt on flat or risk
running out of steam and digging for gears.

in fact its the same island then up a ramp i think does it every time with van on
and similar scenes elsewehre, came back from cleethorpes, ok pretty flat but never
came on, but no situation like had on outbound.

it certainly does nt comoe on standing still reving the bits off it, so a load is definitely
part of issue, thing is busy navigating island or whatever im not looking at rev
counter. often look down fews seconds later and sure enough its on for rest of trip.
 
no just sharing the pain with you!

was waiting to see if still there after rebuild as guess is.

thinking back, it didnt do it when i first bought the troll
in march 09, towed several times and was in june 09
running solo back to caravan site it did it then nothing for
some time, plenty of towing again then found these 3rd
gear islands and ramps were a common.

last summer when i'd changed water pump and stat but still
got some heat from unresolved HGF we towed to mid
wales without it coming on then it did it solo again. its
been illusive and hgf has had blame seemingly incorrectly
to long.

looking for a simple fix, dont like mods, but hey after spending
on rebuild dont want anything else to fail me now.

seriously think will need some help to sort, mind got my rac
buddy and engineer that did rebuild and all good advise here.
 
A bit of a move forward on this. I have now installed a boost gauge (stepper motor, electronic type) in the cab and connected it to power and have run the signal cable into the engine bay. I have yet to connect the gauge sensor into the intake airstream - a job for tomorrow.

As the gauge is a dual purpose vacuum/boost gauge, it occured to me that it might be interesting to see what the ECU & VNT control solenoid are asking the turbo to do by temporarily teeing into the hose between the solenoid and the VNT actuator and using the gauge to measure the control vacuum in the hose - and then have a drive around and see what's happening.

1) At tickover, the VNT lever is at the top of its travel (or near - I haven't checked with a feeler gauge yet) with the vacuum gauge reading 18-19" Hg. I *think* this is pretty much what it is supposed to do.

2) Over a gentle run of about 5 miles on mostly small throttle openings, the vacuum readings stayed at or near 18" Hg. It only fell below that reading if I leaned on the throttle. Even leaning hard on the throttle (at any engine speed & gear) rarely took the vacuum reading below 10" Hg (maybe to 7 or 8" Hg) and then only momentarily if I suddenly floored the throttle pedal. I suspect (but don't know) that this is normal behaviour).

3) I headed towards a junction onto the M62 heading east (motorway/highway heading up the Pennine Hills). Before going onto the M62, I stopped and cleared an 0905 ECU fault code. I tried to keep a fairly steady speed around 65mph (2600-2700 rpm in top) up the hill on maybe half throttle or so. Though I didn't notice any reduction in performance (though maybe I was daydreaming), on a couple of occasions without any change in throttle opening, the vacuum wandered back & forth between 14-15" Hg and 10"Hg. Lifting off the throttle and then reapplying sent the vac straight back up to 10"Hg. When I got back home, I discovered that the ECU had stored another 0905 code.

I can't help wondering why the vacuum never goes (much) below 10"Hg - and why when the 0905 overboost occurs it doesn't go back up to 18-19"Hg. Does anyone have any insights on this?

Andrew
 
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