Strange issue

[toby_w88]

Over the last few weeks I've noticed an issue every now and then that while driving along with light throttle input (to the point of no boost) it feels like the car is lurching slightly. I figured it was just related to the DBW and ignored it due to seldom occurrence. I have a scanguage with boost xguage so I can also monitor boost.

Today I got a injector module from DTUK and the issue has become very noticeable when on light throttle on no boost. If I maintain this level of throttle the car starts to lurch quite badly. Once I apply throttle and boost kicks in there is no issue but the issue does return next time you go back to light throttle.

tomorrow I'm going to unplug the box and go for a spin to see if the issue is still there, I suspect it will be given I experienced it (nowhere near as badly) for a few weeks before fitting the box.

I'm just wondering if anyone has experience an issue similar to this, I've read about the surging issue some people have had with the SCV but I'm not sure if its the same thing.

Cheers
Toby

[fridgie]

Scv could be the cause, also could be carbon build up in the manifolds. Most people with carbon build up find they get 'surgeing' around the 1800-2000rpm range.

How many km on the clock? Do you have an egr blank in? What sort of driving do you normally do (highway vs city vs full throttle ricer style)?

[Cowboy Dave]

Yeah sounds a bit like the surging that I get. For mine to happen it's typically 1800-2000 revs, usually under 60km and often when travelling up a slight rise. Would be interested to hear if your symptoms match that.

[Joe]

Are you in an ML or an MN Toby?

[Tony]

Another one. Hope the V6 boys don't find this.


Given it can only be fuel or air related. I'd be chasing the SCV, Map sensor and lower manifold swirl control.
Blocked filters etc more likely to cause issues while under load although can do this as our fuel supply pump runs at 100%
flow regardless the load. (Fuel recirculates)
On the Denso fuel system, this is where the SCV come in, it precisely meters the fuel to the high pressure rail pump. The SCV rest in full flow position then is in fact held closed to bypass fuel pass the CR pump when not needed. You can imagine what happens if they get sticky. (Not common any more as most have been upgraded.)

Swirl control....The lower manifold has four butterflies in it. This is designed to create a turbulence effect under light loads to promote more efficient combustion and increase low end torque. Carbon in this area can effect the swirl control and cause surging etc.

The Map sensor plays a big part in the fuel metering so the post and hose must be clear and functioning as it should.


Be interesting to run a data logger over the sensors and see whats going on when they do this. Data logging wont always pick it up either.

Just a thought, if you have a scan tool, next time this happens unplug the throttle body (It will code but run fine) and see if the issue goes away.

Keep us informed.

T

[toby_w88]

It's an April 11 build mn diesel, has about 24000 on the clock. No egr blank yet and about 90% highway kms

Going to pull the box out and go for a drive soon


Sent from my iPhone using Tapatalk... Coz apparently sigs are all the rage at the moment

[salt36]

[TUFF TROOP]

May need a injector recalibration. Have had a few at work do the same thing.

[toby_w88]

with the box removed the issue is still there, will get it booked into to get checked. also noticed it occasionally puffing out a bit of soot (under light load) while doing it.

as suggested by Tony, will pull the throttle body plug off after lunch and go for a quick spin to see if this affects it

[NowForThe5th]

Another one. Hope the V6 boys don't find this.

[toby_w88]

ok spent the last few hours trying a few different things

first off pulled the plug out of the TB DBW, could not reproduce the issue so reconnected it, issue was still not there. re-connected pdi box, after a while felt like the issue might be happening again slightly, so unplugged the DBW again and went for another spin, issue doesnt seem to be there so far, going to leave it unplugged for a few days and see if it occurs again.

as well as the scanguage I also have a bluetooth obd reader so I just ran scantool 1.13 on the car as well, with the throttlebody uplugged I get PO122 (didnt throw the engine light tho, scanguage couldnt see the code either) and curiously, noticed that while the tb is unplugged 'commanded egr' or something like that was reading at 0.0% at idle, tb plugged in was ~70%. Based on this I'm starting to think the EGR isnt used while the TB is unplugged. if this is the case, what benefits does the plugging the TB back in actually give?

[coxy47]

as well as the scanguage I also have a bluetooth obd reader so I just ran scantool 1.13 on the car as well, with the throttlebody uplugged I get PO122 (I think) and curiously, noticed that while the tb is unplugged 'commanded egr' or something like that was reading at 0.0% at idle, tb plugged in was ~70%. Based on this I'm starting to think the EGR isnt used while the TB is unplugged. if this is the case, what benefits does the plugging the TB back in actually give?

You are correct about the EGR. With the throttle disabled the throttle is permanently open so that the intake air doesnt go straight to the exhaust. The key benefit is that the throttle closes when the cars is shutdown to cut the air supply. If you shutdown the engine with it disconnected it wont close and hence you get a very rough shutdown. Personally id be concerned about this damaging the engine mounts long term but thats just my opinion.

[Tony]

As coxy mentioned, other than a big part of the EGR function as you have proven.(Hence causing issues with EGR blanking or malfunctioning EGR)...... It assist in a much smother shut down and helps prevent overrun.

I'd be taking it to the dealer and running the MUT3 over it. Could be a software issue in your case.

[Josh_Triton]

v6 doesn't have this issue

[toby_w88]

Yeah I'll book it in to get checked next week. It almost feels like when the turbo switches vanes and you get that extra kick