Overboost problem, 2005 Patrol

[andrewk]

After behaving faultlessly (ish) for 40,000 miles and four years, my Patrol has started to behave oddly. Once the engine is hot, under load at just over 2500 rpm, it sometimes suddenly loses power. If this happens and you slowly push the pedal to the metal, nothing happens - if anything it goes slower. If you lift off and then press the accelerator again, it accelerates as normal. I've done a bit of reading on the internet and this behaviour is apparently a Nissan safety feature that is actuated if excessively high turbo boosting occurs - known apparently as "overboosting".

As a rule, machines misbehave like this if something is broken or is in the process of breaking. Does anyone has any idea what might be broken or breaking and how to fix it?


Andrew

 

[DEE]

What pump you got on that there truck mate

 

[andrewk]

Pump? It's a 3.0Di - a ZD30 - Y61

Andrew

 

[Timbo_1975]

VGT on these isnt it?

In which case, vanes sticking due to carbon I wouldnt wonder. You may be able to free it off by disconnecting the actuator then vigourously working the rod manually, otherwise you'll have to remove the turbo, and strip it (carefully) and clean the carbon by hand.

 

[andrewk]

In which case, vanes sticking due to carbon I wouldnt wonder.

If that were the case, wouldn't the overboosting occur when the engine was cold too? It doesn't.


Andrew

 

[Muckypup]

Dont know much but... I used to have an Escort RS Turbo that sometimes did the same thing but usually much higher up the revs. This was overboost, but was only kicking in because I had modifed the engine and it was running at up to double the standard boost.
Thought i'd blown my engine the first time i felt it, the drop in power nearly fired me through the windscreen :doh

 

[Muckypup]

Mine was caused by too much boost from the mods. Have you wound your actuator up for more boost?
When my overboost kicked in you had to stop the car completely and let it calm down for a minute or so before it would rev again. Sure its overboost?

 

[andrewk]

Mine was caused by too much boost from the mods. Have you wound your actuator up for more boost?
When my overboost kicked in you had to stop the car completely and let it calm down for a minute or so before it would rev again. Sure its overboost?

The motor is completely stock - no mods. I haven't touched the VNT actuator adjustment screw (and don't intend to).

You can test by driving until hot - then at 2600 rpm (ish) for 20-60 seconds, during which you get a sudden loss of power. Slowly pressing the accelerator pedal to the floor does nothing. This is a Nissan safety feature in the ECU that detects an overboost condition. Lifting off and then pressing the throttle pedal down again clears the fault and restores normal performance. It started behaving in exactly this way some time during Jan this year. Yes, I'm sure it's overboost. No mods to the motor - and it's only done 40,000 miles, so unlikely (I hope) that anything major is wearing out.

As it's easy to do, I'm going to change the MAF sensor, as it can play a role here. I'm told they often last only 40,000 miles. If I still have the fault after that (and can't find anything else amiss) I'll have to take it in to WestwayNissan or a diesel specialist and let them sort it out.

As it happens around motorway caravan-towing speed, I need to get it fixed soon.


Andrew

 

[Muckypup]

Hope you get sorted mate! :thumb2

 

[Timbo_1975]

I would imagine it is more likely to stick when hot due to expansion of the components?

A simple test would be to hook up a boost gauge, and go for a drive from cold!

 

[andrewk]

I would imagine it is more likely to stick when hot due to expansion of the components?

A simple test would be to hook up a boost gauge, and go for a drive from cold!

I don't really understand the logic behind that. How would an overboost condition be created if the turbo vanes were sticking? Wouldn't it result in a no-boost condition if the turbo didn't rotate?

I might get a boost gauge some time, but fitting one isn't really "simple", I think. Quite apart from buying one, sorting out where post-turbo to attach it and sourcing some fitting and tubing, I'd then have to find somewhere on the Patrol dash to physically fit the thing. Have you seen the dash on a post Aug-05 Patrol SVE? There's hardly a square inch to fit anything. I'm not so sure how a boost gauge would help me find the fault anyway. Surely, all it would do would confirm what I already know - that I do have an overboost condition.

From reading I've done, the favourite's seem to be a problem with the wastegate or split/holed vac lines. The MAF has to work too, methinks, but even though I've ordered one, I'm not confident that it's crackered - else I think there would be other symptoms too. Has anyone had an overboost condition on an un-modded Patrol (or Terrano) and managed to find the problem and fix it?

Andrew

 

[Timbo_1975]

I don't really understand the logic behind that. How would an overboost condition be created if the turbo vanes were sticking? Wouldn't it result in a no-boost condition if the turbo didn't rotate?
Andrew

On a VGT, there are movable vanes controlled by the actuator, which default to the closed position via a bloody large spring. If the vanes are sooted or sticking they cant open fully, or dont open fast enough in response to the boost rising, so you get an overboost condition.

I would personnally want to verify actual boost pressure via a gauge , as a diagnostic approach to determining whether the ecu is seeing what is actually happening, or whether the fault lies in the MAP sensor, a split hose, sticking vanes, or elsewhere.

 

[Thomas-the-Terrano2]

do you get an engine check light in any of this.

i sometimes get light on though clears when swithced off.
few times had the loss of gaining power, eased off and its reset.

the big hose from the turbo to the i/c has been pierced by the
plastic i/c cover once and doing a good impression of rubbing
again despite having filed away the 'corner' that did it last time.

currently got some foam trying to keep the 2 apart.

 

[andrewk]

do you get an engine check light in any of this.

No, not at all.

I'll check the intercooler hoses - thanks

Andrew

 

[andrewk]

as a diagnostic approach to determining whether the ecu is seeing what is actually happening, or whether the fault lies in the MAP sensor, a split hose, sticking vanes, or elsewhere.

I think the first step in diagnosing a fault on a system of any kind is to understand how it's supposed to work and I'm not there yet.

There seems to be two basic options:

1) The ECU is receiving incorrect inputs and is initiating the overboost safety feature when it should not. I know the ECU measures throttle position, engine speed and air mass (via the MAF) but how does it measure actual boost pressure? Is there a sensor somewhere?

2) The ECU is receiving correct inputs and is correctly initiating the overboost safety feature. Overboost might actually exist because:

a) The turbo's vanes are gummed up or the VNT actuator is crackered
b) The wastegate is gummed up or its actuator is crackered
c) A vac hose is holed or split, so even though the turbo, wastegate and actuators are OK excessive boost still occurs

As an aside, the only work carried out on the 'Troll around the time the overboost fault first occured was to install new 12N and 12S sockets (for the caravan) up under the rear bumper to replace those whacked on a laning trip in N.Yorks in December. The battery was disconnected for an hour or two while I did that job. I know that if the battery is disconnected for more than 20 mins then the ECU will reset to factory defaults and then re-learn the engine setup - but I don't know whether that can be relevant to the current overboost fault.

Andrew

 

[Timbo_1975]

I feel you may not be grasping the method of control and feedback the ecu has.

On the 3.0, actual boost pressure is measured via the MAP sensor. This allows the ECU to cycle the VGT actuator solonoid such to control boost pressure. The solonoid is switched rapidly on/off (%duty cycle) and air-wise is fed from the inlet manifold.

Standard boost pressure should be 1.0-1.2bar with the system active. With the connector removed, you should have about 0.6bar.

The MAF in this case has two main functions:

a) to provide feedback deviation for accurate control of the egr system (egr active = drop in air flow in through the maf)

b) to signal when the engine goes from off load to partial load, so the ecu knows when to start to control the VGT solonoid. (also helps the ecu to decide when to operate the intake swirl flaps)

Although you dont have the MIL lamp on, if the limp mode is actually being triggered by an over boost, then you should have a DTC 0905 code present.

If the MAF was returning a bad signal then DTC 0102 will be present.

Have you checked for codes? If not, do so, then report back.

Hope this helps. Tim.

 

[andrewk]

I feel you may not be grasping the method of control and feedback the ecu has.

I'm certain that is so :lol

On the 3.0, actual boost pressure is measured via the MAP sensor.

Now I'm (even more) confused. I've got a workshop manual (exactly as the one used by Nissan dealers). There are no references to a "MAP sensor" anywhere in the manual. The only reference to a "Manifold Absolute Pressure" sensor (MAP) is in "SAE J1930 Terminology List" (glossary of terms) but not anywhere in the body of the documents themselves. Are you sure that a Patrol actually has one - most references I've seen suggest that diesel motors usually have a MAF or a MAP sensor, but not both?

There are references to a "Charge Air Pressure Sensor" - but the manual says that "The charge air pressure sensor detects pressure in the exit side of the charge air cooler. The sensor output voltage to the ECM increases as pressure increases. The charge air pressure sensor is not used to control the engine system under normal conditions."

This allows the ECU to cycle the VGT actuator solonoid such to control boost pressure. The solonoid is switched rapidly on/off (%duty cycle) and air-wise is fed from the inlet manifold.

Unless the workshop manual is telling porkies, the 'Troll ZD30DDti engine doesn't have a MAP sensor that does that.

The MAF in this case has two main functions

I've just fitted a new MAF and taken the 'Troll out for a test drive at the same speeds, on the same roads, that caused the overboost fault previously. At 2600rpm where the fault occured (and where it is said to occur in the Patrol4x4.com Reference document here http://users.on.net/~aschulze/ZD30/ZD30 Y61 Reference Document - Colour.pdf) everything was fine -- but giving it a bit more umpty at circa 3000rpm, I get exactly the same power loss. Changing the MAF has had an effect but hasn't cured the problem.

Ah well ........ it needs a service in a thousand miles or so anyway, so I'll book it in at Westway Nissan and see what they can find. Maybe it's time I visited the bank manager too.


Andrew

 

[Timbo_1975]

The charge air pressure sensor = manifold absolute pressure (MAP). Same thing.

 

[andrewk]

The charge air pressure sensor = manifold absolute pressure (MAP). Same thing.

The manual does say that it isn't used to control the engine "in normal conditions".

I went shopping a while back and came back home via a route that I could use to check again whether the Nissan overboost safety feature (i.e. the power loss) would be triggered after a spell at 2600rpm. It certainly has not been so far - maybe it's fixed - but I need to do some more testing.

I also need to ponder why I thought that I still had a similar problem at 3000 rpm after changing the MAF. What actually happened is that after not triggering the fault at 2600 rpm, I was thinking "Whoopee, it's fixed!!" and booted the motor up the hill, accelerating to 3000 rpm (ish) when something that felt similar happened. The road was quite steep & wet and I was accelerating hard. It is just possible that I was kidding myself and what actually happened was we had a bit of wheelspin on black ice - it's been around freezing here most of the day.

Anyway, tomorrow, I'm going to take it for a wander along the M62 from the Oldham turnoff, to the M66 and back up to the Saddleworth turn off. If I can't replicate the fault then I'm going to regard it as fixed.

Watch this space ...........

Andrew

(PS Thanks for your help)

 

[andrewk]

I went for a wander today - from home up the A627M and east along M62 to the Saddleworth turnoff then back home. The 'Troll behaved impeccably no matter how I provoked it.

Unless it's playing games with me, it increasingly looks like it might be fixed. The new MAF sensor cost a mere £60 delivered off Fleabay.

A result (probably) :thumb2

Cheers
Andrew