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Little power at low gear & high rpm

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Little power at low gear & high rpm

Postby njoshea » Sat May 14, 2022 1:05 pm

I see variations on this theme on other posts, but not quite the same problem. Here goes:

I have a 2005 Mk6 2.4tdci. I had the turbo replaced recently, and wow-wee, it goes like the clappers now at the top end of the speed range.
But, in low gear & high rpm its a shocker - low power, blowing black smoke at high rpms & a deeper, throaty note to the engine at those high rpm's.
So, diagnosis time:
1) I checked the EGR - it was filthy. I installed a blanking plate to see what would happen, and it ran like a charm (whats that telling me? No good ideas - any theories?)
2) The EGR must be stuffed. so I replaced it with a new one & removed the blanking plate. No change - back to poor performance at low gear/high rpm.
3) OK, is it starved of air when it needs it most? I replaced the airfilter and confirmed air & intercooler hoses were good. No change - still poor performance at low gear/high rpm.
4) Hmm, is it the exhaust side? I went to a muffler shop, they checked both catalytic converter and mufflers. They're all good.

Ive run out of ideas. Any other thoughts out there? Cheers.
2005 Mk6 2.4L 101kW TDCI
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Re: Little power at low gear & high rpm

Postby knobby1 » Sat May 14, 2022 9:16 pm

Have you had the codes read..?? Glow plug light flashing..??

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When I die, I want to go peacefully in my sleep like my Grandfather, not screaming like the passengers in his car..!
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Re: Little power at low gear & high rpm

Postby njoshea » Sat May 14, 2022 11:46 pm

No engine light warnings.
No codes from my scan tool. But, I'm reading on here there are scan tools and then there are scan tools. So, upgrading my capability to use FORScan at the moment.
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Re: Little power at low gear & high rpm

Postby apartransit » Sun May 15, 2022 8:20 pm

Not sure if helps, but try to check pressure demanded from pump to injectors. This could help if you se huge pressure difference between pressure provided and pressure demanded,pressure regulator is faulty.
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Re: Little power at low gear & high rpm

Postby knobby1 » Mon May 16, 2022 4:56 am

apartransit wrote:Not sure if helps, but try to check pressure demanded from pump to injectors. This could help if you se huge pressure difference between pressure provided and pressure demanded,pressure regulator is faulty.


Mk6 TDDi doesn't have a fuel pressure regulator like the Mk7's.

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2008 2.4L RWD 170+PS 6-speed 350 LWB High Roof.

When I die, I want to go peacefully in my sleep like my Grandfather, not screaming like the passengers in his car..!
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Re: Little power at low gear & high rpm

Postby njoshea » Mon May 16, 2022 6:11 am

Some musings while I wait for the modified ELM327 to turn up...
The improved low gear/high RPM performance with EGR blanking is telling me something...
Turbo is 'new' (reconditioned), EGR is new, cylinder rings were replaced a couple of years ago, injectors were called good at the same time, silencers & catalytic converter are clear. Is there any other mechanical item Ive overlooked?
Assuming the 'hardware' is good, then I guess it must be sensors...looking forward to the code reader turning up!
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Re: Little power at low gear & high rpm

Postby knobby1 » Mon May 16, 2022 6:48 am

njoshea wrote:Some musings while I wait for the modified ELM327 to turn up...
The improved low gear/high RPM performance with EGR blanking is telling me something...
Turbo is 'new' (reconditioned), EGR is new, cylinder rings were replaced a couple of years ago, injectors were called good at the same time, silencers & catalytic converter are clear. Is there any other mechanical item Ive overlooked?
Assuming the 'hardware' is good, then I guess it must be sensors...looking forward to the code reader turning up!


Mk6 TDCi's are known for pumps eating themselves.

Lord Knobrot
2008 2.4L RWD 170+PS 6-speed 350 LWB High Roof.

When I die, I want to go peacefully in my sleep like my Grandfather, not screaming like the passengers in his car..!
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Re: Little power at low gear & high rpm

Postby njoshea » Fri May 20, 2022 11:51 am

FORScan is pretty cool. I went for a run and plotted some data:

test-19-05-22.jpg


Nothings leaping out at me yet. Although...Engine Cylinder Temperature (ECT) looks kinda low doesnt it?
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Re: Little power at low gear & high rpm

Postby njoshea » Wed May 25, 2022 2:22 am

Well, the engine temperature was too low - the thermostat was buggered.
So, engine temps are back up where they should be now, and while vehicle performance does feel better, the fundamental problem of black smoke on accels remains.
Per the suggestions on here, I'll investigate fuel demand vs actual next.
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Re: Little power at low gear & high rpm

Postby njoshea » Sat May 28, 2022 5:40 am

Hang on a moment...whats this??

So, I go for another short drive to verify the fixed thermostat results in correct Engine Cylinder Temperature (ECT) - it gets to ~90degrees - tick, looks good.
I also logged EGR and Turbocharger Vane vacuum solenoids as well, and, bugger me, I get this:
test-28-05-22.jpg


Its flat zero throughout the test drive - this tells me the EGR valve isn't being commanded (via vacuum) to do anything! Does that sound right to forum readers??

FORScan describes this EGR variable as:
Exhaust Gas Recirculation Valve Duty Cycle
This parameter represents the variable duty cycle to the normally closed EGR vacuum solenoid. This solenoid varies the vacuum applied to the EGR valve.


So, I ask the forum - if its reading zero does this mean the EGR valve is always open (letting exhaust gases in to the inlet manifold) or always closed?
Note - the EGR valve itself is new. A few weeks ago I had it blanked for a few days to see if running performance improved, and it did.
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Re: Little power at low gear & high rpm

Postby knobby1 » Sat May 28, 2022 9:55 am

njoshea wrote:Hang on a moment...whats this??

So, I go for another short drive to verify the fixed thermostat results in correct Engine Cylinder Temperature (ECT) - it gets to ~90degrees - tick, looks good.
I also logged EGR and Turbocharger Vane vacuum solenoids as well, and, bugger me, I get this:
test-28-05-22.jpg


Its flat zero throughout the test drive - this tells me the EGR valve isn't being commanded (via vacuum) to do anything! Does that sound right to forum readers??

FORScan describes this EGR variable as:
Exhaust Gas Recirculation Valve Duty Cycle
This parameter represents the variable duty cycle to the normally closed EGR vacuum solenoid. This solenoid varies the vacuum applied to the EGR valve.


So, I ask the forum - if its reading zero does this mean the EGR valve is always open (letting exhaust gases in to the inlet manifold) or always closed?
Note - the EGR valve itself is new. A few weeks ago I had it blanked for a few days to see if running performance improved, and it did.


It's NOT engine cylinder temp, it doesn't have a cyl temp sensor....if it did, cylinder temps would be in the hundreds.....it's engine coolant temp, or more correctly Cyl head temp, the sensor is in the back of the cyl head and just senses the temp of the aluminium.

Just blank the EGR off on the Mk6, it won't throw a fault code. They're usually more trouble than they're worth.

Lord Knobrot
2008 2.4L RWD 170+PS 6-speed 350 LWB High Roof.

When I die, I want to go peacefully in my sleep like my Grandfather, not screaming like the passengers in his car..!
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Re: Little power at low gear & high rpm

Postby njoshea » Sat May 28, 2022 12:10 pm

Sure I can blank the EGR, but I'd rather not.
I'll be checking the EGR solenoid functionality next, any other suggestions out there would be appreciated!
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Re: Little power at low gear & high rpm

Postby njoshea » Fri Jun 03, 2022 10:27 am

Checked the EGR solenoid (energised it) - it worked. Checked supply voltage as well - all good there too.
Checked the turbo solenoid as well since I was frigging around in that area - it checked out too.

It must be PCM commands then - investigating that next.
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Re: Little power at low gear & high rpm

Postby marc1234567 » Sat Jun 04, 2022 9:34 am

njoshea wrote:Sure I can blank the EGR, but I'd rather not.
I'll be checking the EGR solenoid functionality next, any other suggestions out there would be appreciated!



it is fair enough wanting to get ro the bottom of it all but what do you think will be the downside to blanking the egr? I think the default for the egr is closed. This is based on me taking one off and looking and seeing g it was closed.
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Re: Little power at low gear & high rpm

Postby njoshea » Sun Jun 05, 2022 7:16 am

marc1234567 wrote:
njoshea wrote:Sure I can blank the EGR, but I'd rather not.
I'll be checking the EGR solenoid functionality next, any other suggestions out there would be appreciated!



it is fair enough wanting to get to the bottom of it all but what do you think will be the downside to blanking the egr? I think the default for the egr is closed. This is based on me taking one off and looking and seeing g it was closed.


Thanks marc, I guessed as much.
Other than the legality of it, and the fact the engine thinks its receiving an air/fuel composition that it isn't - then, nothing.
I don't like hacking another engineer's solution without the full facts in front of me (he says, eyeing the blanking plate and socket set anyway)

Went for another test drive - I now notice that at low power & RPM's <2000, the engine runs very rough and occasionally what sounds like engine knock. It gave me a fright - disengaging power immediately (push in clutch) stopped the noise. I then continued driving by maintaining RPM above 2000 for the rest of the way - no problems.
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