Hi Guys,

Actually this is about my MG ZTT with the same M47R engine and I thought I'd get your thoughts on this problem...

Just returned from holiday driving across France, through the Pyrenees and then across Northern Spain. Spotted a lot of Freelanders - especially in the Pyrenees - I'll show you a picture of my favourite later

So the problem: usually the car goes extremely well. Pretty seamless between low revs with a fairly subtle but noticeable transition when the turbo comes on song. But in the recent hot weather, the car felt more sluggish (it was loaded 4-up, with camping gear etc. mind!) but ran okay. But in the mountains, the poor engine was staggeringly sluggish below 1800 rpm. In fact - and I've not ever come across this before, I'd find that the car would decelerate if you put your foot down! Too much fuel, insufficient air I would think. Dropping a gear or two and getting the engine above 1800 rpm would rescue the situation.

The problem certainly got better on returning down to sea level, but was still present in the heat (saw temperatures of up to 42.5 Celcius on the external thermometer - thank goodness for effective air conditioning!). Not quite as bad as at 2000 metres, but not normal.

Interestingly now the temperatures have fallen down to the mid 20s, the car feels much more normal (and it isn't carrying the camping gear any more!)

On interrogating the ECU, no recorded faults. The MAF appears to be functioning - not sure whether the numbers are appropriate or not - but probably not bad enough to cause major problems under most circumstances.

The injector trim settings reveal that injector 1 is being trimmed quite differently to the others - so that's a problem, but I doubt the problem causing the appalling off-boast performance.

The intercooler to turbo hose has been replaced with a good silicone item some while ago (the original rubber hose had had it). I haven't looked at the intercooler O-rings - but they were replaced just a couple of years ago - and the engine performance now is not bad...

So in summary poor off-boast performance at altitude and in heat with a distinct feel that the car was possibly over-fueling (although no observable smoke in the rear-view mirror).

Any ideas? I am pretty sure that this is not normal! Cheers

Doesn't sound right. Do a check on high and low rail pressures, also check the boost pressure and come back with some numbers.
You need idle and full power figures if you can get them.
Has the EGR been eliminated? If not the inlet manifold could be full of goop.

Thanks Nodge

Ahem, the EGR might not be quite standard But historical crud can't be discounted I guess.

I'll see whether I can get some numbers - not sure that the tool will provide all of the ones you mention (I don't recall them - and if I had seen them, I'd definitely have looked). The fuel pressures may need direct measurement - I don't think I have the equipment to do this (I have a 3-bar gauge, but not one for the high-pressure fuel circuit). I'll let you know what I can find

Interestingly, the car is a little reluctant to start when hot (takes a fair amount of turning over on the starter). In tank fuel pump can be heard to run, but I would not be surprised to find that this a part of the problem - I've had to rebuild it in the past and they're comically weak on the Rover 75/ZT. But always thought that injector leak back was more likely to account for this particular problem, but mention it here again in case it has bearing.

Also, it has been remapped to 135+ bhp spec. Allegedly it's "160" but I doubt it (not had it on a rolling road), but it does go really rather well when going strong

PS picture of my favourite FL1, snapped in the Pyrenees - a 2 litre L series I’d guess, handsomely loved and abused and clearly well-used:

What year is it? I'm assuming it's post 2004, so potentially not OBD2 compliant.

2003 and not EOBD compliant. My pscan can read the ECU

at altitude and in heat

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maybe ..
high ambient air intake temps + less oxygen at altitude
ecu won't deliver the fuel demanded due to the intake temp.
made worse by altitude .. and hill climbing ..
( i.e slower speed .. not much air flowing thru intercooler
( add engine bay heat on top of outside temps ..
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Yes, I agree: exactly the worst conditions - but modern vehicles are tested under such conditions. I’m really not exaggerating when I say that below 1800 rpm, pressing the accelerator actually caused the car to gently decelerate!

Something isn’t right, but at lower ambient temperatures at closer to sea level, performance has returned... Could it even be something odd like crank case pressure breathing? i.e. filter clogging up???

I’m really not exaggerating when I say that below 1800 rpm, pressing the accelerator actually caused the car to gently decelerate!

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that line is what prompted my train of thought

just had in mind what mine used-to-be-like under certain conditions ..
( i.e. very hot and humid uk ambient temps .. and before i did the intake mod )
then added another 15-20c to the ambient temps + altitude + terrain + vehicle load ..

you write "off-boost"
does the MG ZTT have a variable vane turbo like the hippo td4 ?
if not .. i'd guess that would add to pre-1800 rpm slugishness
( in those conditions you encountered )
just a guess ..

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rob_bell said:

Yes, I agree: exactly the worst conditions - but modern vehicles are tested under such conditions. I’m really not exaggerating when I say that below 1800 rpm, pressing the accelerator actually caused the car to gently decelerate!

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It does sound odd.
An engine at high altitude will make less power, than at sea level even if it's turbocharged. The turbo can only boost the air that can get to the turbine. So if engine bay temps are high and atmospheric pressure low, the engine will make less power.
However I can't see what putting your foot down harder would reduce power production.

The only way I think would be if you over-fuel for the available air available. It may be that the 160 remap is the problem, but, as mentioned, I didn't see any plumes of smoke that you might expect if this were the case? But it may be that I missed it?

I didn't get a chance to run the live data diagnostics last night - hopefully will get a chance tonight

Hi Nodge,

Spent a little time playing with live mode measuring rail pressure (RP), low pressure supply (LPS), inlet manifold pressure (IMP), MAF-measured (MAP-M) and MAP-requested (MAF-R).

All measurements were performed with engine hot, stationary. Hit idle speed was 600rpm. All units are kPa except the common rail pressure, which is MPa.

Engine speed | RP | LPS | IMP | MAF-M | MAF-R
600 , 30 , 352 , 102 , 453 , 800
1000 , 30 , 348 , 103 , 472 , 438
1500 , 34 , 346 , 107 , 487 , 370
2000 , 41 , 340 , 112 , 512 , 397
3000 , 57 , 330 , 136 , 600 , 660

I can put this into a spreadsheet later and maybe graph it.

The common rail pressure goes up with rpm, particularly over 1500rpm (from 30MPa to approaching 60MPa).
Concomitantly, the inlet manifold pressure goes up from a little over 100kPa to 136kPa. Similarly, the measured MAF goes from 450 to 600kPa. I’m interested at the didparity between the measured and requested MAF - would be interested to know what is deemed normal?

Were those figures taken when driving or just holding the revs with the vehicle stationary?

If the figures are when driving the MAP looks ok.
I'd expect to see anything from 0.9Kpa to 140Kpa.

MAF looks to have a limited range, if the integer is in Milligrams Per Stroke. I'd expect to see 400 mgps to around 1200 mgps.

The high rail pressure looks very low if it's an on the road reading.
I'd expect to see 25,000Kpa at idle to over 125,000Kpa at full power.

Sadly my diagnostic system cannot log data (I’ve been pestering Philip about this for a long time!) - so in the interests of safety, these are all stationary figures after driving to get the engine fully up to temperature.

I’ll check the MAF units when I get home - but I think what you’ve suggest sounds about right.

Am I looking at a failing MAF and LP fuel pump? These are the usual suspects on these cars. Bosch car parts eh? Might be better off with Lucas

rob_bell said:

Am I looking at a failing MAF and LP fuel pump?

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The MAF looks weak but the LP rail holds 330Kpa, which is acceptable.
Does it get it's performance back if the MAF is unplugged?

Performance is “okay” at the moment: I could disconnect to see if it changes. The real problem was found in the Pyrenees - and I’m back in London now, so difficult to reproduce the conditions!

Perhaps I’ll try a new MAF (pricey!) ans see how I go...?

rob_bell said:

The real problem was found in the Pyrenees - and I’m back in London now, so difficult to reproduce the conditions!

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You'll definitely struggle to find anywhere in London that's as high as the Pyrenees.
It could be that the problem is a non-problem back at normal altitudes and moderate temperature.

rob_bell said:

Perhaps I’ll try a new MAF (pricey!) and see how I go...

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Just unplug the MAF and try it before you spend on a replacement. Unless you know the MAF has travelled a good distance, as they will slowly degrade over time.
If unplugging the MAF makes a noticeable difference, then thats 's potentially your problem.

Thanks Nodge. I’ll try unplugging and see what changes.

The MAF units shown in picture below:

rob_bell said:

Thanks Nodge. I’ll try unplugging and see what changes.

The MAF units shown in picture below:View attachment 155851

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So it's in milligrams per stroke then, which is a standard MAF measurement value. The diagnostic is showing the measured air at the MAF is less than the engine's requirements. This could well be why you were down on power. The M47R has an anti black smoke programme. This limits fuel to the engine if the measured air mass is less than expected. Basically there can never be more fuel than the available air to burn it. So if your MAF was returning a low signal, the EDC will limit fuel (and power) which you noticed.
It's definitely worth unplugging the MAF to try it. When the EDC doesn't get the MAF signal, it fuels the engine based on MAP, RPM and throttle position. No EGR takes place and no anti smoke programme is used.
Running without the MAF will put the MIL on as no EGR can take place, it' an emissions warning, nothing else.

Makes sense - but screen shot above is cold idle. When hot, measured MAF is generally higher than requested (1000-2000rpm) - so on that basis, the anti-smoke is unlikely to be the issue???