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Old 9th November 2019, 21:20   #1
Geoff130
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Default CDTI power drop over 300RPM

I recently bought a cdti to save it from the scrapyard and while fixing MOT failures ( brake pads, discs, handbrake, rear jacking point and number plate lights) I also fitted a new air filter, viton O rings, silicone intercooler hose from Jules, cleaned the EGR and intake manifold, oil and filter and fitted the correct fan with new brushes. It's now passed it's MOT and pulls well up to 3000 RPM then it struggles to rev any more. Is this normal for a diesel? I've had the 1.8 and still have my ZT190 so can't really compare it with the others.
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Old 9th November 2019, 21:22   #2
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Could be a dodgy MAF sensor.
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Old 9th November 2019, 22:19   #3
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I don't know if it's related but there is a smell of the exhaust inside although It doesn't sound like the exhaust is blowing
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Old 9th November 2019, 23:26   #4
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Have a check under the bonnet at the big pipe on the passenger side front, that comes from the bottom connection to the air cooler.This is the main pipe that carries the air from the turbo to the engine, for splits. Also have you checked the EGR that the pipe goes to . This gets clogged up with coke. Easy enough to take off the pipe at the top end for a look. How many miles has it done?
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Old 10th November 2019, 00:27   #5
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I rarely take my CDT over 3,000RPM, I will get more acceleration by changing up with the same throttle opening. Pressing harder on the pedal above 3,000 doesn't do much except use more fuel and make more noise. 3,000 rpm in top gear equates to 90mph.
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Old 10th November 2019, 00:36   #6
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Quote:
Originally Posted by bl52krz View Post
Have a check under the bonnet at the big pipe on the passenger side front, that comes from the bottom connection to the air cooler.This is the main pipe that carries the air from the turbo to the engine, for splits. Also have you checked the EGR that the pipe goes to . This gets clogged up with coke. Easy enough to take off the pipe at the top end for a look. How many miles has it done?
Roughly 180,000 miles, I replaced the old intercooler pipe with a new one, I also cleaned the EGR and inlet manifold, there was about 10mm of coke in it.
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Old 10th November 2019, 00:42   #7
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Quote:
Originally Posted by Comfortably Numb View Post
I rarely take my CDT over 3,000RPM, I will get more acceleration by changing up with the same throttle opening. Pressing harder on the pedal above 3,000 doesn't do much except use more fuel and make more noise. 3,000 rpm in top gear equates to 90mph.
That's what I was asking really, is this a normal response or is there something wrong with that's causing this.
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Old 10th November 2019, 00:56   #8
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The longer stroke, heavier crank and flywheel of the diesel engine in general tends to give it these characteristics. I have had many older diesels, the free-est revving being the 2003 Audi 1.9TDI, but even that was unrewarding above around 3,300 rpm. My CDT is the standard 115 bhp. Once it's through its MoT, I intend to have it remapped for more power and efficiency - watch this space.
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Old 10th November 2019, 01:03   #9
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Quote:
Originally Posted by Geoff130 View Post
I recently bought a cdti to save it from the scrapyard and while fixing MOT failures ( brake pads, discs, handbrake, rear jacking point and number plate lights) I also fitted a new air filter, viton O rings, silicone intercooler hose from Jules, cleaned the EGR and intake manifold, oil and filter and fitted the correct fan with new brushes. It's now passed it's MOT and pulls well up to 3000 RPM then it struggles to rev any more. Is this normal for a diesel? I've had the 1.8 and still have my ZT190 so can't really compare it with the others.
No it is not normal, mine is an auto, and will happily rev to the red line whilst in sport mode (it is not a pleasant experience to me, as I consider myself mechanically sympathetic, so rarely use the sport mode).

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Originally Posted by trikey View Post
Could be a dodgy MAF sensor.
^^^^^^^^^ this would be my first port of call. Try unplugging the MAF, and see if this improves the response, and if it does, then a replacement (Bosch only, do not be tempted with cheaper alternatives - BMW M5 V10 uses the same insert and is normally quite a bit cheaper, carefully swap between the housings)
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Old 10th November 2019, 01:03   #10
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Quote
The longer stroke, heavier crank and flywheel of the diesel engine in general tends to give it these characteristics. I have had many older diesels, the free-est revving being the 2003 Audi 1.9TDI, but even that was unrewarding above around 3,300 rpm. My CDT is the standard 115 bhp. Once it's through its MoT, I intend to have it remapped for more power and efficiency - watch this space.


That's something I was considering but I wanted to know the car is working as good as it can before getting a remap. I'll be interested to hear how you get on.

Last edited by Geoff130; 10th November 2019 at 01:06..
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