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Old 26th May 2017, 15:06   #1
Bri R
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Default MG ZT CDTi: Poor torque pull

Hi All,

Wonder if anyone can help me. I have an MG ZT 135+ CDTi. I have had quite a lot of work done on the engine, but the pull and torque particularly on lower revs (i.e. between 1,000 to 2,500) is very poor since the work has been done. I’ve also noticed no response / ‘flat spots’ at around 1,000 and 2,600 revs on both acceleration and deceleration which I don’t think can be attributed to the turbo. Has any ZT diesel owner experienced similar, or have any idea what the problem might be please?

Listed below is the work I’ve had done in total (in addition to regular servicing):

- Replaced original Bosch MAF with new Bosch MAF sensor
- EGR bypass kit fitted
- Replaced PCV with new BMW modified kit
- Intercooler O-rings replaced
- New silicone intercooler turbo boost pipes from Jules fitted
- Exhaust ‘decat’ pipe fitted and particulate filter removed
- New in-tank diesel pump fitted
- Air inlet manifold cleaned and de-sludged
- K&N air filter fitted
- New fuel filter fitted
- Replaced injector seals
- Full engine ‘flush out’ and clean
- Accelerator pedal checked to ensure maximum acceleration achieved


I’m wondering if the new in-tank diesel pump I’ve just had fitted has failed already, so I will have this checked for low fuel pressure by my mechanic on his laptop diagnostics set-up – along with all the other possibilities.

Or I'm thinking as the layman that I am in car terms :-) that maybe with all the work done, it’s simply the case that the car is now in need of a remap or tuning chip and that I shouldn't be expecting the car to run any better before having this done?

To be fair, the car ran and pulled better before a lot of this work was done with just a little Millers diesel additive in the fuel and a good service – it was a real flying machine with plenty of low rev torque! Any help or advice would be much appreciated as it’s annoying that I’ve spent so much money on the engine and the performance is worse now. Many thanks.

Bri
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Old 27th May 2017, 09:06   #2
T-Cut
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You could try disconnecting the MAF wiring and see if things improve.

TC
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Old 27th May 2017, 21:19   #3
grivas
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Quote:
Originally Posted by Bri R View Post
Hi All,

Wonder if anyone can help me. I have an MG ZT 135+ CDTi. I have had quite a lot of work done on the engine, but the pull and torque particularly on lower revs (i.e. between 1,000 to 2,500) is very poor since the work has been done. I’ve also noticed no response / ‘flat spots’ at around 1,000 and 2,600 revs on both acceleration and deceleration which I don’t think can be attributed to the turbo. Has any ZT diesel owner experienced similar, or have any idea what the problem might be please?

Listed below is the work I’ve had done in total (in addition to regular servicing):

- Replaced original Bosch MAF with new Bosch MAF sensor
- EGR bypass kit fitted
- Replaced PCV with new BMW modified kit
- Intercooler O-rings replaced
- New silicone intercooler turbo boost pipes from Jules fitted
- Exhaust ‘decat’ pipe fitted and particulate filter removed
- New in-tank diesel pump fitted
- Air inlet manifold cleaned and de-sludged
- K&N air filter fitted
- New fuel filter fitted
- Replaced injector seals
- Full engine ‘flush out’ and clean
- Accelerator pedal checked to ensure maximum acceleration achieved


I’m wondering if the new in-tank diesel pump I’ve just had fitted has failed already, so I will have this checked for low fuel pressure by my mechanic on his laptop diagnostics set-up – along with all the other possibilities.

Or I'm thinking as the layman that I am in car terms :-) that maybe with all the work done, it’s simply the case that the car is now in need of a remap or tuning chip and that I shouldn't be expecting the car to run any better before having this done?

To be fair, the car ran and pulled better before a lot of this work was done with just a little Millers diesel additive in the fuel and a good service – it was a real flying machine with plenty of low rev torque! Any help or advice would be much appreciated as it’s annoying that I’ve spent so much money on the engine and the performance is worse now. Many thanks.

Bri
Hi there, first area to look at is the MAF sensor, disconnect it and go for a drive if things improve, then your sensor is goosed and it will need replacement, it is very important to use a GENUINE Bosch sensor no other will do and will fail soon.

A word to the wise, the BMW engine as fitted to the diesel variants is a superb engine, reliable and efficient as you would expect, STOP 'tuning' it the only thing it needs is a little more power/torque these are readily available it doesn't need special filters or bypasses or cleaning of manifolds, or de-catting, all it needs is a once a week hard drive, gentle driving a diesel kills it. make sure the engine is well warmed up before and drive carefully
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Old 27th May 2017, 22:04   #4
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I agree with T-Ciut and the above.
Just because something is new doesn't necessarily mean it's not faulty.
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Old 28th May 2017, 10:37   #5
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Exhaust ‘decat’ pipe fitted and particulate filter removed...


I was not aware that these cars were fitted with a Particulate filter ..
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Old 28th May 2017, 12:34   #6
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Make sure you have the correct bosch part number fitted, there are I believe 3 variants with different outputs....

if not already done the 160 map...

bypass kit fitted but is the remaining EGR manifold properly sealed off? leaks of exhaust gas lead to turbo lag and power loss...
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Old 28th May 2017, 20:16   #7
RogerHeinz57
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If the air cleaner is one that has oil sprayed over it, then the maf may be contaminated, egr bypass can also be a cause of power loss as I found my car hated it.
Tuning of these engines as already said is largely pointless as they don't really take to it much, the 160 map is good, but have learned that it is not really that great considering the options that have been made to fool various setting from standard.......
Has the air filter got a sock of fluffy style over the cone all the way round ? if not this is a major factor in the problems you describe as the air filter housing needs to have a certain amount of pressure, which if not there will stop things running properly !

Worth checking all the advice offered up here as it is mostly relevant to your concerns.
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