Hi all,
this is my first post, we acquired our Disco II 2 weeks ago. I know similar topics have been covered before but I am not sure mine is exactly the same. So here it goes :

The engine (Disco II Td5 with auto trans from 2000) was behaving fine for the last 500km or so but yesterday I started perceiving a on/off pulsation in engine revolutions, when on highway at about 110km/h (say 65mph) and trying to accelerate a little hard. It actually first occured while on cruise control and in a rising highway slope. The engine accelerates and stalls and accelerates and stalls in a loop with about 1/2second intervals, like "vroum-__-vroum-__-vroum".
When accelerating "softly", it does not do this and i can pick up a bit of speed.

This pretty much repeats systematically on demand. Except at lower speeds (like 20mph) where it seems to rev fine. I'll try and do more tests today.
By the way, we did not have any extraordinary load on the car (pulling a small trailer but it did it also on the way back with empty trailer, and there's only 2 adults and two 2-yr old kiddos at the back, generally smiling about being in "La grosse voiture 4x4 de Maman").
Also, I actually remember someting slightly similar happening the week before, on cruise control in descending highway slopes, with this on-off-on-off behaviour which I then attributed to some confusion of the cruise control system when faced with increasing speed due to the descent.
But again, this is now not limited to when driving with cruise control, and I can repeat it "by hand" (or rather by foot) at will.

Voila, hope y'all can help if you ever experienced something similar to this precise trouble.

cheers
MB

Hi, if i was you i'd change the autobox oil and filter first of all, you must be certain about that before you go further with the diagnose, a session with a tester would be good as well, the autos are more sensitive to sensor inputs... unplug the MAF and see what happens, check fuse F2 in engine bay fusebox just to rule it out, you can also take the pipe from the bottom of the wastegate modulator and connect ir directly to the wastegate actuator valve to rule this out too... that's what comes in my mind on a first thought... aaaa, and if you didnt do it untill now check the ECU red plug for oil, if you find oil there replace the injector loom ASAP

sierrafery said:

Hi, if i was you i'd change the autobox oil and filter first of all, you must be certain about that before you go further with the diagnose, a session with a tester would be good as well, the autos are more sensitive to sensor inputs... unplug the MAF and see what happens, check fuse F2 in engine bay fusebox just to rule it out, you can also take the pipe from the bottom of the wastegate modulator and connect ir directly to the wastegate actuator valve to rule this out too... that's what comes in my mind on a first thought... aaaa, and if you didnt do it untill now check the ECU red plug for oil, if you find oil there replace the injector loom ASAP

Click to expand...

Excellent, thanks, I'll look into all these pronto and let you know.
Anybody else, feel free to chip in with more thoughts if any...
And have a nice sunday.
M

marcball said:

Excellent, thanks, I'll look into all these pronto and let you know.
Anybody else, feel free to chip in with more thoughts if any...
And have a nice sunday.
M

Click to expand...

Hi Marc, it sounds to me like the wastegate modulator is misbehaving. This is the electronic control which manages the operation of the turbo.

To check for this, take the car for a test drive, DO NOT USE CRUISE CONTROL.

Once the engine is correctly warmed up, try using full throttle in lower gears (manually select 2nd and then 3rd) and allow the revs to pass 3500. How does the engine perform? What if any, bad things are happening?


Dave

thebiglad said:

Hi Marc, it sounds to me like the wastegate modulator is misbehaving. This is the electronic control which manages the operation of the turbo.

To check for this, take the car for a test drive, DO NOT USE CRUISE CONTROL.

Once the engine is correctly warmed up, try using full throttle in lower gears (manually select 2nd and then 3rd) and allow the revs to pass 3500. How does the engine perform? What if any, bad things are happening?


Dave

Click to expand...

Hi Dave,
thanks for this precise input which I just got this evening.
The good thing is I have actually tried these steps earlier this morning (on the long road back from picking up three baguettes...). I also took two 40 minute drives in the afternoon as we're in the middle of a move to a town nearby.
Here's the new factual tidbits :
- I tried pushing the engine a liiiiiitle bit when cold, and did get no stutters. I did not insist.
- once it was officially warm, I pushed the engine a bit and did get the stutter.
- as I kept going farther and farther, the stutter seemed to be less marked, meaning I could get to a point where i'd accelerate a little bit more than fully smooth, and the engine revs would get into a soft wave rather than a stutter (stuttering more pronouncedly if I pushed harder).
- after a good 20 minutes on the highway (the engine temp was already horizontal-warm before I got on the highway), the whole pattern seemed to have gone, meaning I could push the throttle strongly and get no stutter. After exiting the highway, I noticed the same, i.e. no stutter or wavy acceleration.
- having left the car for an hour or so, I picked it up again and the engine temp gauge was still horizontal-warm, but the stutter was there again. And again, after 20 minutes on the highway, the stutter was gone.
- now, the other thing that's bothering me is that i'm wondering if the engine is not somehow a bit too mellow. It's hard to say as I've know it for only 500 miles or so, and my other car has a very zesty 4.0L bmw petrol v8 (sorry for boasting but I love that machine). The deal is that the Td5 is struggling to keep 110 kph on the highway on cruise control (I had a friend's rusty trailer attached and did not want to push my luck too hard to 130) whereas I remember it holding a 135 even on ascending slopes a week before. And if I really punch the throttle once "fully warm with no stutter", it sort of gets to 3500rpm for a short while (2-5 seconds) with little impression of acceleration ("seat of my pants" sensor) but wont go farther, and the auto trans rapidly upshifts so the usable rev range seems to be 2000-3000 rpm. It's sort of ok and manageable, but it is not exactly impressive or lively, and I feel like that one (and only) time that I pushed the engine last week, well it had a more rounded sporty audi 5-cyl turbo feeling to it...
- oh, and I did teh equivalent of your steps this morning and well I can't remember exactly, but I think with the trans on "1" it revved up quickly of course, in "2" it did the same and I think on "3" it did stutter. Or maybe rather it was that it seemed to struggle to go beyond 3500 rpm in "3". I'll retest that tomorrow and let y'all know.

I'll try and locate the wastegate tomorrow evening and see if it is stuck, but I do welcome any further interpretation based on the above...

could stutter be ecu sensing over boost

Hi Marc, well first of all I wouldn't call it bragging, more of an admission, that you have a 4.0 BMW. Now if it was the V8 4.2 Jaguar engine that would be entirely different

I digress...............................pushing an engine whilst it is cold really tells us nothing, but you were obviously quite thorough in your tests, so we can discount any cold engine problems.

With an autobox car you need to select 2nd or 3rd rather than using D to do these tests.

I'm assuming that you don't have a diagnostic terminal such as Lynx, Hawkeye or Nanocom?

If that is the case, then apply a 'process of elimination' approach. The engine is misfiring when you demand more of it. This could be caused by:

1. Insufficient fuel supply;

2. Inappropriate turbo control via the wastegate and it's electronic controller;

3. Insufficient air supply or incorrect signals from the MAP (Manifold Absolute Pressure) sensor on the inlet manifold.


So, have you changed the fuel and air filters within the last 4 weeks? If not, buy a set from Paddocks : DA6004P | Filter Kit - TD5 - Premium Brands

Next, identify the MAP sensor, it's the small black plastic thing in the middle of the picture:



remove it from the inlet manifold, clean it with aerosol brake and clutch cleaner such as: Toolstation: Brake Cleaner 400ml

Get plenty of this in stock it's mighty useful. So give the outside and the inside a really good clean with this stuff then allow to dry, then re-install and test-drive.



We'll move on as necessary.

Cheers
Dave

IMO untill the injector loom(oil in the red plug) and the autobox oil/filter are not ruled out other things might be in vain, these two things both are temperature sensitive and can give those symptoms, the overboost would be the same regardless of engine temp

Sorry guys,
super busy at the moment. I ordered the filters and brake cleaner, will look into the red plug this weekend.
Thanks again for all the constructive input
More soon...