D2 apparent turbo lag?

Hi, has anybody got any thoughts please on this problem with my 2004 Td5 manual Disco? It is all standard, 93k miles, FSH and still has the EGR valve fitted and working. It appears to suffer from turbo lag (more than normal) below 1500 RPM but otherwise goes perfectly well. I found some time ago that if I disconnected the MAF sensor the problem disappeared even though the MAF readings on my Hawkeye were what I'd expect. More recently I've fitted a new MAP sensor, MAF sensor and wastegate modulator (all OEM items, no aftermarket) but nothing made any difference i.e. a definite flat spot with the MAF connected, pulls well at low revs with it disconnected. All other readings on the Hawkeye look good as far as I can tell and no faults logged. The easy answer is just to drive around with the MAF disconnected, which is what I've been doing for the past year or two, but it's bugging me now and I'd just like to get to the bottom of it. Any ideas? Thanks.

What make was the MAF.. ? As our Sierryferry says, if its not a genuine one, its a lottery. I replaced mine with a genuine LR, but I still have the symptoms you have. Havent got to the bottom of it yet as too many other bits to catch up on...

It was a Siemens VDO. But- 2 years ago I also fitted the one off of my previous Disco which I'd had from new and still had the original factory sensor. It gave the same symptoms so in my mind it's pretty hard to fault the MAF sensor. I'll standby to be proved wrong though!

OEM as in original equpiment manufacturer?
If so that is not a 100 percent sign its a pukka part.

My 2001 used to like its in tank fuel pumps, the gauzes on the pump also used to block up.

Also the throttle pedal had a worn part on the track and that caused lack of power, Iirc it has two sets of tracks, one measures 1 to 100 and the other 100 to 0, so long as they both agree the ecu is happy, if they dont it sulks.
Turbo wastegate seizes or rather tries to.
Egr is well worth blanking off, it may be working, but it may not be closing fully.

I liked the car, but fcuk me there was always summat wrong with the bloody thing.
The D3 is a piece of pssi in comparison!

You should take a look into the EGR to see how gunked up it is eventually get rid of it, on facelifts a quite common problem is that the catalyst is clogged and restricts the gas flow so the turbo can't spin up well... go somewhere where the noise it's not an issue, undo partially the downpipe to have a gap there and go for a short drive...if it runs better you have the answer

Thanks Lynall, some things to have a look at there when I get home this evening. The fact that I also had a factory MAF sensor fitted which showed the same symptoms pretty much rules out the sensor in my mind. I'm going to put my MAF sensor on my girlfriends 2003 G4 to see if the fault transfers with it- but I have to put the cylinder head back on first- it's on it's way back from having a cracked injector port welded up. I know my pump is OK as I had the tank out a couple of months ago and the pump and tank interior were as clean as a whistle. Interestingly though, I had to change the injector seals on Saturday as the car was getting intermittently hard to start in the morning for the previous week. The copper washers that came out weren't in bad shape but I did find a lot of carbon particles in Nos 3 & 4 injector ports which I can only imagine were deposits from combustion gasses leaking past the washers. That also explains why the starting problem was intermittent- if the engine stopped with compression on Nos 3 or 4 cylinders it would bleed off past the washers and push fuel back to the tank. If not, it would start normally.
I'll check the throttle position later with the Hawkeye. I think the EU3 models actually have a triple track and it all looked good last time I looked but worth looking again for the time it will take.

Thanks Lynall, some things to have a look at there when I get home this evening. The fact that I also had a factory MAF sensor fitted which showed the same symptoms pretty much rules out the sensor in my mind. I'm going to put my MAF sensor on my girlfriends 2003 G4 to see if the fault transfers with it- but I have to put the cylinder head back on first- it's on it's way back from having a cracked injector port welded up. I know my pump is OK as I had the tank out a couple of months ago and the pump and tank interior were as clean as a whistle. Interestingly though, I had to change the injector seals on Saturday as the car was getting intermittently hard to start in the morning for the previous week. The copper washers that came out weren't in bad shape but I did find a lot of carbon particles in Nos 3 & 4 injector ports which I can only imagine were deposits from combustion gasses leaking past the washers. That also explains why the starting problem was intermittent- if the engine stopped with compression on Nos 3 or 4 cylinders it would bleed off past the washers and push fuel back to the tank. If not, it would start normally.
I'll check the throttle position later with the Hawkeye. I think the EU3 models actually have a triple track and it all looked good last time I looked but worth looking again for the time it will take.

sierrafery said:

You should take a look into the EGR to see how gunked up it is eventually get rid of it, on facelifts a quite common problem is that the catalyst is clogged and restricts the gas flow so the turbo can't spin up well... go somewhere where the noise it's not an issue, undo partially the downpipe to have a gap there and go for a short drive...if it runs better you have the answer

Click to expand...

Thanks Sierrafery. I'm thinking along the lines of eliminating the EGR valve as there is, I believe, a direct link with the MAF output. I'm going to mechanically lock it closed and the air valve open and see what happens. I'm not in a rush to get rid of it as I can see diesel emissions getting more and more attention at MoT time in the future as diesels become less popular environmentally. Besides, all my driving is on windy country lanes (low speed, high power, hence why this "MAF" flat spot is a problem) where the EGR valve is, or should be, rarely open anyway. I'll see how clean it is when I do that, but when I changed the MAP sensor a while back, it wasn't gunged at all. The new one did put a little bit more spring in it's step though.
Interesting thought re the CAT- I hadn't considered that, but I then can't understand how unplugging the MAF would suddenly clear it. I'll put it on my list of things to try though- I've been around long enough to know that logic is often buried deep and hard to find!
My gut feeling is that with the MAF connected, either the wastegate is being opened at low revs or the ECU is restricting fuel flow. I'll try and get some more quantative data to go on.

Watch the ambient pressure(AAP) reading , it should be very close to MAP at idle and drop up to 4 units under heavy throttle, that sensor delivers the AAT too for Eu3 management but that reading is not displayed by diagnostics even though it's important... as about the MAF, unfortunately the only 100% certain way to rule it out is with NEW Genuine LR sensor, "OEM" means nothing these days: https://www.landyzone.co.uk/land-rover/d2-td5-cutting-out-when-warm.326582/#post-4193511

Sierrafery, could this be the fault that's causing my low power issues ?

NANOCOM - TD5ENG.APP - TD5 ENGINE fault file

(2,8) AMBIENT PRESSURE CIRCUIT, (LOGGED LOW).

Yes it can cos the AAP fault sends the ECM to ''limited boost" default, replace the AAP sensor

Part number MHK100820L or MHK100600L ? Both parts are listed. Is it worth the extra £££ for a genuine part, and Im already guessing your answer....

Mines a late 2003 TD5.

Is it a typo on LRCAT, because it mentions Air-Con sensor for this part.

MHK100820L for Eu3 this one has decent price compared to the other, genuine LR is the best for any sensor but if you find it too expensive at least buy a premium branded one cos there are many versions of it as it's used by Rover and BMW too

New sensor ordered from local LR dealers...

Let's see if it knocks another issue from the ever growing list...

New part collected. £65 genuine from Land Rover. Why pay over £100 at my local Land Rover indy parts place. Genuine spares from LR are reasonably priced. Just have to see if it solves my issues...

No different.... best start my own thread. Sorry for hijacking this one....