Only Happens in 4 Low

[siringo]

Here's a very strange one.

2010 D40 King Cab.

This only happens in low range 4th gear. It happens on the flat, up hill, downhill, under load and coasting. Every other gear is OK, 2WD, 4WD, high and low range, this just happens in 4 low.

While in 4 low, the motor surges. It's like, spurt, normal, spurt spurt, normal, drops away into turbo lag, normal, spurt, drops away and almost cuts out, comes back, spurts, normal etc etc etc. I asked some mechanic mates while away on a trip and they had no idea. I can only think it's something like the computer not knowing what to do when the motor is matched to that gear.

I have no idea at all. Any help much appreciated.

 

[longy509]

not sure what it is but mine does it aswell i think there was athread a while back with a few other people having the same problem

 

[siringo]

That's good news longy, coz if more people have the problem, Nissan should/may know about it, so I should be able to get it fixed.

Also reassuring to know others have the same prob and that it's just not a problem with my vehicle.

Thanks mate.

 

[BravoBrad]

same problem here.. really noticeable on flat ground where you are just holding speed (ie not accelerating)

 

[siringo]

That's funny, we all drive Kingcabs.

When I find out what it is, I'll post it up here.

 

[morticus]

Never noticed it in mine... It just whines a bit.

 

[nathand22]

My old THAI built DUAL CAB also did that exact thing from new, BUT the new SPAIN built doesnt do it at all. It seems to only be the THAI models that its happening with.

 

[Old.Tony]

We took ours up to about 45-50km/h on dirt in 4LO to see if the cruise control could be engaged in 4LO (just answering a curiosity question, we don't normally use cruise control in 4LO!). I'm absolutely confident we would have been in 4th at least - smooth as silk. Again, Spanish dual cab, not a Thai-built or KC.

I'd go as far as suggesting that it's not the fact that the space behind the front seats has anything to do with vehicle performance, it's probably something peculiar to the Thai engine. As to what is causing it, it's an odd one. It's behaving like a bad turbo actuator. I wonder if there's a logic error between gearbox/transfer and turbocharger, so that when 4LO signal is on, and gearbox registers 4th gear, the ECM does stupid things with the turbo, or even fuel rail pressure?

Can you put the Torque application to work for us, and graph the turbocharger boost pressure and fuel rail pressure against each other while you're cruising steadily in 4LO/4th gear? Maybe something will be revealed? I don't know where else to start.

 

[Tappet]

2011 King Cab here and mine does it to. Not that i'm worried about it. Should be in high range by then anyway.

I think that is good educated guess tho Tony, some kind of logic error.

 

[Rumpig]

Speedlimited in low range maybe?

 

[siringo]

Thanks for the help guys.

I'll try and graph those 2 values this arvo.

 

[siringo]

Some graphs

Here are some graphs off Torque...

Fuel Rail Pressure over time.

low range 4th gear @ 2000 rpm

low range 5th gear @ 2000 rpm

I also noticed that the surging is nowhere near as pronounced when driving on bitumen, so if you get Nissan to look at the problem, do it on a dirt road!

 

[siringo]

Another

This is an interesting one, all in low range 4th gear at around 2000rpm

Started driving off road, threw in the clutch (shown by the dip in the middle) then picked it back up driving on the bitumen...

The first section may be a bit enhanced as I was driving down a cow track, so it was bumpy anyway, so the foot went up and down on the accelerator a bit, but it was smooth on the bitumen. This really shows what the surging is like from the 50 second mark onwards..


I drove home about 20k's on dirt road and monitored the fuel rail at different times in different gears and the only gear where the fuel rail pressure was erratic was in 4th low range.

So what governs the fuel rail pressure????

 

[Old.Tony]

Fuel rail pressure is managed by the ECM, the little box near the right-hand bonnet hinge.

The graph is really interesting. It could be the result of several things. Fuel rail pressure sensor reading scoring badly against throttle position + vehicle speed + engine load + engine rpm would be the first logic problem I'd be looking at. I wonder if you could replicate the engine load + vehicle speed + throttle position in 2HI and see if there's a similar response, which might discount the 4LO being involved. In 2HI/4HI, the torque isn't multiplied so minor variations wouldn't be as noticeable.

If the fuel rail pressure variation is still there in 4th gear in 2HI/4HI, then I wonder if it's something to do with the neutral position sensor and not a logic problem at all?

 

[nathand22]

What i noticed with my old Thai D40 was that if i really stood on the go peddle while in low 3rd or 4th it would accelerate smoothly as normally BUT when i tried to just maintain a speed in those two gears the surging would come back and i would go back to HIGH range.

 

[siringo]

What i noticed with my old Thai D40 was that if i really stood on the go peddle while in low 3rd or 4th it would accelerate smoothly as normally BUT when i tried to just maintain a speed in those two gears the surging would come back and i would go back to HIGH range.

Yep, exactly the same as mine.

 

[siringo]

Fuel rail pressure is managed by the ECM, the little box near the right-hand bonnet hinge.

The graph is really interesting. It could be the result of several things. Fuel rail pressure sensor reading scoring badly against throttle position + vehicle speed + engine load + engine rpm would be the first logic problem I'd be looking at. I wonder if you could replicate the engine load + vehicle speed + throttle position in 2HI and see if there's a similar response, which might discount the 4LO being involved. In 2HI/4HI, the torque isn't multiplied so minor variations wouldn't be as noticeable.

If the fuel rail pressure variation is still there in 4th gear in 2HI/4HI, then I wonder if it's something to do with the neutral position sensor and not a logic problem at all?

Matching the speed would be difficult as in 4Lo you do around 15-20 km'h and 4Hi it's a lot faster, but I could match the revs. I'll try that tomorrow.

If it's a logic problem, then it's a logic problem through all these, or many, of these Thai models. What do/can we do about that???

I'm starting to think I may have to find a friendly Nissan service centre and see if they go through whatever list they have of known faults for the Thai builds and look for this problem.

I wouldn't be surprised if they say "yep, documented fault, we'll replace the ECM"

But equally, I wouldn't be surprised if they said "Never heard of that problem before"

Is there a neutral position sensor on a manual box??? Assuming there is (and I'm not doubting you Tony), what effect do you think that could cause???

 

[siringo]

Mmmm, just googled this problem and there are few links. One is to another thread on this site from Geoff, with the same problem, he drives a D22 I think. And Woody said it happened to him as well.

 

[siringo]

2WD 4th gear @ 2000rpm

Here's a Torque fuel rail pressure graph while in 2WD 4th gear at 2000rpm ...

Pressure is fairly regular. The dip in the chart is due to slight road undulations..

 

[Old.Tony]

That is proof positive that it's not simply because it's in 4th gear. The initial variations had the fuel rail jumping from 5K psi to 9K - that's an amazing variation - and in 2HI it's probably not scratching the 7500-8500psi mark in variation.

(For the avid reader accustomed to petrol injection fuel pressures of 80 to 200psi, the common rail diesels in these cars have extraordinary fuel pumps that can drive the rail pressure to 30,000psi which is nearly twice the pressure at the bottom of the Mariana Trench, the deepest part of the ocean on the planet).

Much of that variation is going to be the ECM's variations to provide test data for the oxygen sensors in the exhaust.

It looks like in 4LO that the variations are exaggerated. Why? Why in 4th gear, and why only around 2,000rpm?

The ECM knows if you're in gear or not (it has to, because it inhibits the choice of 4LO unless you're in neutral). I don't think there's a variation in the gearbox between 2HI/4HI/4LO - that's all inside the transfer case. Nothing inside the gearbox should change.

And so we come back to a logic problem. Are they using a CAN signal that is incorrectly identifying itself, or is the signal coming from the transfer case sensors cross-linked into the HO2S in the exhaust, or the turbo actuator (vacuum)?

It'd be wonderful if you could manually control the turbocharger vanes, and disconnect the vacuum lines and still have some boost. That would at least discount that.

I wonder if FB could have a squiz at the internal database and see if there are any issues relating to this?