Overboost problem, 2005 Patrol

[rayf3262]

That is interesting. How did you produce that?

Andrew

By dumping the CSV log files from ECUtalk into Excel.... and graphing the data.

 

[andrewk]

By dumping the CSV log files from ECUtalk into Excel.... and graphing the data.

Mmmm ...... that's easy enough, isn't it. If I didn't think I might have to buy an EGR valve soon, I'd probably go out and buy a laptop so I could do that.


Andrew

 

[rayf3262]

Mmmm ...... that's easy enough, isn't it. If I didn't think I might have to buy an EGR valve soon, I'd probably go out and buy a laptop so I could do that.


Andrew

If you can get the vehicle within about 40 meters of your desktop, a long cable would be a worthwhile try.. Certainly cheaper than a laptop.
Once its logging you can just go start the vehicle etc...

RS232 @ 9600 BPS

 

[andrewk]

Does anyone have a template for a blanking plate (ZD30 with stepper motor EGR valve) .......... so I can make one before I do any dismantling.

Mmm .... what a dummy I am. Nissan have those, don't they. They call them gaskets - and I'd need one anyway if I take the valve off. :doh

Andrew

 

[(RIP) PLANK]

Mmm .... what a dummy I am. Nissan have those, don't they. They call them gaskets - and I'd need one anyway if I take the valve off. :doh

Andrew

if its any consolation, i hadn't though of that either :doh

 

[Timbo_1975]

Have you yet blanked the EGR via a plate?

Bear in mind, doing so for testing will create other goings on, so dont confuse these with your original issue.

 

[andrewk]

Have you yet blanked the EGR via a plate?

Not yet. Slowly, slowly catchee monkee .......

I haven't yet obtained the materials to make one. I don't think cutting up a baked bean can is a good enough solution. I'll probably buy a small sheet of 1mm thick stainless steel off Fleabay.

Bear in mind, doing so for testing will create other goings on, so dont confuse these with your original issue.

I know it's likely to increase boost pressure at cruise by a few psi - or were you thinking about something else?

One other test I'm going to try before fitting an EGR blanking plate is to apply a fixed vacuum to the VNT actuator (by taking the vac supply off the actuator solenoid and connecting it to the VNT actuator instead). If I understand correctly, this will simply apply about 28 " Hg on to the VNT actuator which will lock the VNT lever up and hold the turbo vanes closed. As the turbo has become a small one, I'd expect it to perform well at small throttle openings but to run of of breath quickly at larger throttle openings. I wouldn't expect to see very high boost pressure at large throttle openings (because we now only have a small turbo). If we do see high boost pressure then it must be due to the EGR valve being stuck open when it should not be. If I don't see high boost pressure then .......... it's head scratching time gain. It is possible that I'll see an ECU 0905 boost pressure error due to lower than expected boost pressure at some combinations of engine revs/throttle. Note that I intend to do this purely on an experimental basis and will abort the test if I detect anything untoward happening.

I will also carry out one final check on the VNT actuator, to verify (as far as I can) that no one has tampered with its calibration before I bought the car. On tickover (vacuum on the actuator is around 18" Hg), the VNT lever is hard against the stop as expected. I want to check what vac level it takes for the lever to JUST reach/leave the stop (see test on page EM-1016 of workshop manual). I've no reason to suppose that it has been tampered with - the yellow paint looks original, but then again I have some yellow paint in the garage.

Subject to understanding the results of those two tests, I'll be making a move forward on fitting an EGR valve blanking plate next week.

Andrew

 

[Timbo_1975]

Right. Firstly you are not quite right with your anticipated result of holding the vanes in the closed position.

You will get VERY HIGH boost pressure, certainly in the midrnage (1500-2500rpm) under any sort of load, so be careful. You have a very small turbine housing and comparitively large compressor with the vanes closed up. When the turbine chokes from high exhaust pressure it will sort of control itself, but you will have overspeeded the unit at this point. With luck the ecu might have noticed and gone straight to limp mode, but we know how slow its response is.

Blanking the EGR with otherwise stock settings will definately result in higher than normal boost spiking, as there is more exhaust to go through the turbine and not via the egr.

A side effect will be the ECU *might* flag an egr low flow code, or a maf code, as it will not be seeing any reduced maf flow when it opens the egr valve which it is expecting.

From alittle experience with the ZD but alot of experience with the vw tdi, I can say that blanking the egr, and a software flash with decent n45 maps is the way forwards and yields huge gains both in terms of power, mpg, general running, and reduced egt's... infact everything is positive. It beggars belief that nissann actually let these out of the factory so poorly set up.

 

[andrewk]

Right. Firstly you are not quite right with your anticipated result of holding the vanes in the closed position.

You will get VERY HIGH boost pressure, certainly in the midrnage (1500-2500rpm) under any sort of load, so be careful.

Maybe I'd better give that a miss then

From alittle experience with the ZD but alot of experience with the vw tdi

One thing I've been trying to wrap my head around is that the VW Tdi folks seem to address boost pressure spiking by lengthening the VNT rod - but the Australian Nissan Patrol folks think it's right to adjust the VNT stop screw.

I haven't yet managed to wrap by head around the difference between the two - though it's obvious that adjusting the stop screw can only affect the point at which the turbo vanes start to open (it cannot have an effect if the arm is not in contact with it) - but lengthening the actuator rod can affect boost throughout the range.

Do you have any thoughts on this?

Andrew

 

[Timbo_1975]

Maybe I'd better give that a miss then




One thing I've been trying to wrap my head around is that the VW Tdi folks seem to address boost pressure spiking by lengthening the VNT rod - but the Australian Nissan Patrol folks think it's right to adjust the VNT stop screw.

I haven't yet managed to wrap by head around the difference between the two - though it's obvious that adjusting the stop screw can only affect the point at which the turbo vanes start to open (it cannot have an effect if the arm is not in contact with it) - but lengthening the actuator rod can affect boost throughout the range.

Do you have any thoughts on this?

Andrew

Yes. Lengthening the rod on a gt1749v numbs the boost response and gives the ecu alittle more time to catch it. At any point, the vanes are slightly more open than they might have been orignally.

Adjusting the stop screw on a gt2052v only alters the base closed point and the fully open poistion. It does nothing to alter response.

 

[andrewk]

I've just finished measuring MAF voltage against engine revs (again!!!) for the original genuine MAF that was in the car from new (for about 40,000 miles). I took about 50 readings and plotted them as a scatter graph in a spreadsheet. Most of the points you can see comprise several identical or very similar readings.

Isn't that interesting. I *think* I'm getting near to a solution. Something weird is happening about 3200 rpm. This is also about the engine speed at which the overboost error occurs. On full throttle, boost pressure sharply rises to about 25 psi and the ECU records a boost pressure error.

My tentative conclusion is that the EGR valve is partly open when it should not be and is, therefore, faulty. If the inlet manifold were excessively pressurised by exhaust passing through an open EGR valve at high engine revs, this would explain high boost pressures I've been seeing and the odd MAF voltages at high engine revs. As a second check, I will repeat the same test with a different MAF. If I get the same results then that must make the diagnosis that the EGR is faulty certain.

Assuming I do get similar results with the second MAF, I need to decide whether to block the EGR valve or replace it with a new one. The air filter is a little mucky, so I'm going down to Westway Nissan on Monday to buy a new one. Whilst I'm there, I'll get (or order) a gasket for the EGR valve (to use as a template for making a blanking plate) - and get a price for a replacement EGR valve. Unless the price for the EGR valve is a lot less than I expect, I think I'll have installed a blanking plate before the end of next week.

Problem solved? Dunno ....... but I will soon.

Thanks very much for all the contributions to helping me understand the problem and arrive at a solution. I really appreciate it.

Cheers
Andrew

 

[andrewk]

Yes. Lengthening the rod on a gt1749v numbs the boost response and gives the ecu alittle more time to catch it. At any point, the vanes are slightly more open than they might have been orignally.

Adjusting the stop screw on a gt2052v only alters the base closed point and the fully open poistion. It does nothing to alter response.

I think I'm very close now to deciding that I'm going to block the EGR valve. Immediately after that I've some testing to do and then have to devise a strategy for recalibrating the VNT actuator. The recalibration strategy has to involve very small adjustments that can be reversed to the original settings if necessary and a lot of testing. Isn't this going to be fun .......

Andrew

 

[Jocky]

Keep us posted and hope you get it sorted:thumb2

I've been tinkering with mine and fitted a manual boost controller to hold the wastegate shut to maintain boost for longer:augie


:thumb2

 

[Karinofnine]

Is this a really stupid thing to say, but, why couldn't you fit a dump valve? (before the turbo, and particularly if you were going to block the EGR valve)

 

[andrewk]

Firstly, I don't know anything about dump valves - so I'd have to do some research to understand the implications of what you are suggesting and decide whether it makes sense for this application. Mine is a Y61 with a ZD30, having a VNT turbocharger.

Secondly, I need to discover/confirm what the cause of the overboost problem is before doing anything. I don't think I should be treating a symptom rather than a cause. It seems most likely that it is a faulty EGR valve that is the cause and I may yet simply replace that or have it replaced.

If I do decide to block the EGR valve, this should solve the high revs/large throttle overboost error by itself. I will/may need to do something else to limit boost at cruise to a sensible level. At the moment, it doesn't exceed 15 psi - but if I block the EGR valve, it will probably rise by at least a few psi. Providing I'm careful, the simplest and cheapest way to do that is to adjust the VNT calibration by either lengthening the VNT rod a bit or by winding in the VNT lever stop screw. As I have a boost gauge fitted, this should be do-able without having to buy anything else. Providing I keep detailed records of exactly what I've done it is reversible too.

If, after blocking the EGR valve and adjusting the VNT calibration, I find that I still have problems with boost pressure at cruise or an overboost error then I'll have to do something else - buying a recent Defender County springs to mind (or emigrating)

Andrew

 

[Karinofnine]

Some information about EGRs and turbos (and other stuff) here

http://users.on.net/~aschulze/ZD30/ZD30 Y61 Reference Document - BW.pdf

 

[rayf3262]

That drop off in airflow at 3200 rpm is most odd...
Was this done while diving or static?

 

[andrewk]

That drop off in airflow at 3200 rpm is most odd...
Was this done while diving or static?

They were measured with the car stationary in neutral. A DMM was used at the MAF terminals. Yes, the airflow fall-off is odd.

I think that the EGR valve is open at high engine revs (and also at large throttle openings). It should be closed. Uncontrolled exhaust gasses are pressurising the inlet manifold (via the open EGR valve) which reduces the intake airflow via the turbo and intercooler. The MAF senses that intake air mass has fallen, so its output voltage falls.

If my spare MAF measures the same (and I think it will, because I get an identical overboost error/limp mode at the same engine revs with that too) then that, I think, confirms the diagnosis.

I strongly suspect that if the EGR valve were blocked (or if I replace it with a new one) then the MAF voltage against engine revs will be fairly linear - as it says it should be in the workshop manual.

Andrew

 

[Jocky]

Some information about EGRs and turbos (and other stuff) here

http://users.on.net/~aschulze/ZD30/ZD30 Y61 Reference Document - BW.pdf

Great doc and loads of info from the Patrol guru's:thumb2

:clap

 

[Thomas-the-Terrano2]

so whats an egr run at as i would sooner keep truck stock.