CDTi Auto performance lack

[goofysth]

Hello to all again.

I have two CDTi 75s, one is manual, one is auto.
Manual is perfect with performance, but Automatic is very sluggish and it lacks acceleration performance.

Basically, it has average performance below 2000rpm (but very similar to manual i have, so i assume that is what it is meant to be).
But, when i try to accelerate on steep or even slight hills it has very bad acceleration. Acceleration is specifically bad after 80 km/h (which is not the case on manual), no matter if i choose SPORT or any other mode.
I was travelling for 9 hours few days ago and it is a struggle to accelerate when it is important.

What i tried:
- Changed viton o-rings on both of them
- Did the leak back test on the injectors (everything OK)
- Checked injector imbalance values (all around 0.0)
- Changed MAF (previous one was bad according to values read on TOAF, and replacement improved performance slightly)

After all these, i compared results on the TOAF from both of them and boost pressure, inlet manifold pressure and fuel pressures (low and rail pressure) are the same on both of them.

Please, give me some ideas what can cause the problem and what to look after?

As well, i searched throughout the forum a lot, but didn't find a solution, so i decided to start a new thread.

Thank you all in advance

[grivas]

!

Originally Posted by goofysth

Hello to all again.

I have two CDTi 75s, one is manual, one is auto.
Manual is perfect with performance, but Automatic is very sluggish and it lacks acceleration performance.

Basically, it has average performance below 2000rpm (but very similar to manual i have, so i assume that is what it is meant to be).
But, when i try to accelerate on steep or even slight hills it has very bad acceleration. Acceleration is specifically bad after 80 km/h (which is not the case on manual), no matter if i choose SPORT or any other mode.
I was travelling for 9 hours few days ago and it is a struggle to accelerate when it is important.

What i tried:
- Changed viton o-rings on both of them
- Did the leak back test on the injectors (everything OK)
- Checked injector imbalance values (all around 0.0)
- Changed MAF (previous one was bad according to values read on TOAF, and replacement improved performance slightly)

After all these, i compared results on the TOAF from both of them and boost pressure, inlet manifold pressure and fuel pressures (low and rail pressure) are the same on both of them.

Please, give me some ideas what can cause the problem and what to look after?

As well, i searched throughout the forum a lot, but didn't find a solution, so i decided to start a new thread.

Thank you all in advance

Hey, I would disconnect the electrical cable to the MAF sensor and run the car for a few days as such then see what you get. Check your air filter is clean and replace as such. Check tyre pressures and add some injector cleaner to fuel, Forte or Millers. Then report back. Also ensure the intercooler elbow where you replaced the bottom rings is fully located so you are not looking boost, finally clean the EGR valve.

[goofysth]

Originally Posted by grivas

!

Hey, I would disconnect the electrical cable to the MAF sensor and run the car for a few days as such then see what you get. Check your air filter is clean and replace as such. Check tyre pressures and add some injector cleaner to fuel, Forte or Millers. Then report back. Also ensure the intercooler elbow where you replaced the bottom rings is fully located so you are not looking boost, finally clean the EGR valve.

Thanks for the reply.
I can do all these very fast, so i'll get back with the results.

[75Connie]

Originally Posted by goofysth

Thanks for the reply.
I can do all these very fast, so i'll get back with the results.

Don't do them all together. Make a change, then measure. Rinse and repeat.

Otherwise you'll never know what caused the problem.

I'd start with the MAF.

[75driver]

Originally Posted by goofysth

Hello to all again.



I have two CDTi 75s, one is manual, one is auto.

Manual is perfect with performance, but Automatic is very sluggish and it lacks acceleration performance.



Basically, it has average performance below 2000rpm (but very similar to manual i have, so i assume that is what it is meant to be).

But, when i try to accelerate on steep or even slight hills it has very bad acceleration. Acceleration is specifically bad after 80 km/h (which is not the case on manual), no matter if i choose SPORT or any other mode.

I was travelling for 9 hours few days ago and it is a struggle to accelerate when it is important.



What i tried:

- Changed viton o-rings on both of them

- Did the leak back test on the injectors (everything OK)

- Checked injector imbalance values (all around 0.0)

- Changed MAF (previous one was bad according to values read on TOAF, and replacement improved performance slightly)



After all these, i compared results on the TOAF from both of them and boost pressure, inlet manifold pressure and fuel pressures (low and rail pressure) are the same on both of them.



Please, give me some ideas what can cause the problem and what to look after?



As well, i searched throughout the forum a lot, but didn't find a solution, so i decided to start a new thread.



Thank you all in advance

Are both cars the same from factory?
Ie are both 115bhp or 130bhp?
Or is the auto perhaps 115 and the manual 130 bhp.
Has either one been remapped?
Both of the above points alone may account for an appreciable difference.
However, If you’ve had the auto car for a while, and are now noticing a decline in performance, that’s another issue, most of the suspects which you’ve already looked at.🤔
What maf did you purchase?
Anything other than a proper Bosch one may be a waste of time.
Are MAF readings “within spec”...sorry I don’t have figures to hand, but you should be able to get them on here somewhere.


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[goofysth]

Are both cars the same from factory?
Ie are both 115bhp or 130bhp?
Or is the auto perhaps 115 and the manual 130 bhp.
Has either one been remapped?

Both cars are 130bhp from factory, but i am not sure if one of them is mapped. How can i check that?

What maf did you purchase?
Anything other than a proper Bosch one may be a waste of time.
Are MAF readings “within spec”...

Yes, i took the proper Bosch one.

sorry I don’t have figures to hand, but you should be able to get them on here somewhere.

Now, the figures are very good, around 490mg/hub when 700rpm and around 670mg/hub when 3000 rpm.
Those values are within the range (almost perfect).

When we speak of MAF values, what i found on TOAF is that "Real air mass" values are equal for both cars, but "Required air mass" values are different.
For example when revved to 3000RPM as a reference:
Car with manual gearbox - MAF values:
- Real air mass: 650 mg/hub AND Required air mass: 433 mg/hub

Car with automatic gearbox - MAF values:
- Real air mass: 670 mg/hub AND Required air mass: 961 mg/hub

So, the Required air mass are 'very' different. What is Required air mass at least and is this a sign?

Thanks again...

[grivas]

Originally Posted by goofysth

Both cars are 130bhp from factory, but i am not sure if one of them is mapped. How can i check that?



Yes, i took the proper Bosch one.



Now, the figures are very good, around 490mg/hub when 700rpm and around 670mg/hub when 3000 rpm.
Those values are within the range (almost perfect).

When we speak of MAF values, what i found on TOAF is that "Real air mass" values are equal for both cars, but "Required air mass" values are different.
For example when revved to 3000RPM as a reference:
Car with manual gearbox - MAF values:
- Real air mass: 650 mg/hub AND Required air mass: 433 mg/hub

Car with automatic gearbox - MAF values:
- Real air mass: 670 mg/hub AND Required air mass: 961 mg/hub

So, the Required air mass are 'very' different. What is Required air mass at least and is this a sign?

Thanks again...

I would disconnect the MAF sensor electrical wiring plug and run the car for several days as such then report back.

How do you know the MAF sensor is a genuine Bosch sensor?. Also you could swap the MAF sensors between cars and then see?.

[marinabrian]

Look at the live data of the MAF while very gently increasing the revs from tickover.

If the mass airflow readings drop to <350 mg/stroke then increase the revs to over 2000 RPM briefly and then release the throttle pedal and allow the car to idle.

Then note the MAF readings, do they recover within five seconds to circa 495mg/stroke, or does this take considerably longer?

The off load figures you quote look to be well within spec, nigh on perfect in fact, so I suspect the EGR operation is the problem here

By the way I always disable EGR operation before resorting to unplugging the MAF, because unplugging the MAF also disables EGR operation, so a completely perfect MAF sensor can be classed as poor, when in fact what is happening is the EGR sticking

Brian

[goofysth]

Originally Posted by marinabrian

Look at the live data of the MAF while very gently increasing the revs from tickover.

If the mass airflow readings drop to <350 mg/stroke then increase the revs to over 2000 RPM briefly and then release the throttle pedal and allow the car to idle.

Then note the MAF readings, do they recover within five seconds to circa 495mg/stroke, or does this take considerably longer?

The off load figures you quote look to be well within spec, nigh on perfect in fact, so I suspect the EGR operation is the problem here

By the way I always disable EGR operation before resorting to unplugging the MAF, because unplugging the MAF also disables EGR operation, so a completely perfect MAF sensor can be classed as poor, when in fact what is happening is the EGR sticking

Brian

Thanks Brian,

I accidentally deleted previous message.
I'll do the thing you mentioned.

As well, how can i disable EGR operation you said?
And how to repair EGR if that is the case?

Thanks

[marinabrian]

Originally Posted by goofysth

Thanks Brian,

I accidentally deleted previous message.
I'll do the thing you mentioned.

As well, how can i disable EGR operation you said?
And how to repair EGR if that is the case?

Thanks

Unplug the electrical connector to the actuator solenoid, this will disable operation of the EGR

Generally speaking failures of this type are caused by the carbon break of the pushrod which operates the valve, becoming clogged to the point it scores the guide tube inside the EGR.

Cleaning the EGR may help matters, but simply unplugging the connector will suffice for testing purposes.

So follow the vacuum hose back from the diaphragm on the EGR toward the engine, the actuator solenoid is connected to this

Brian