Lybra 1.9 jtd, actual boost pressure and loss of power

[capraa]

Hi All,

recently I'm facing a very strange problem with a Lybra 1.9 jtd 85kw engine.

At full throttle I notice a loss of power between 2.500 and 2.800 rmp. I did a log with multiecuscan and after many trials I found a strange behaviour with the actual boost pressure. Actual boost pressure tends to be higher than the desired boost pressure and it has a very high peak at rmp values close to the loss of power. I noticed that in conjunction with this peak there is a change in the boost control solenoid. Can be possible that the ECU reads a too high actual boost pressure (higher than the desired value) and acts on the boost solenoid to reduce the pressure?

Testing conditions:
- AC off;
- MAF replaced recently (even if I had a discussion with my dealer: I ordered a bosch 0281002309 but he gave me a 0280218113 saying that recent news indicate this as a replacement. Unfortunately on bosch website there is no evidence of this change and 0281002309 is still indicated as the only compatible maf for my engine).
- Engine in temperature (90 degree)
- EGR cleaned

What I need to understand is if I've to change the MAF (correct part. number this time) or I've to replace the boost pressure sensor as it reads incorrect values.
I attach a log file so that you can have a look if you like.

Please any help will be highly welcome.


Many thanks,
AleC

[Afgnet]

Check cracks in the intake pipe after the turbo, intercooler, etc...

[capraa]

Already done

All the pipes are ok, intercooler ok and recently cleaned, intake manifold cleaned,...


AleC

[alfa156sarajevo]

So you do not have any errors (DTC's)?
You only feel that lose power between 2500 and 2800 rpms?

Did you try to block EGR valve (to close it mechanically)?

[capraa]

No any error and at the moment EGR is closed (and indeed the only error listed is for the EGR).

It getting me crazy!


AleC

[TribesMan]

This is problem of turbo control vacuum system... Either you have some cracked vacuum pipes or the the vacuum solenoid that controls the VNT actuator is geting "slow"...

[capraa]

Vacuum pipes are ok and replaced recently.

Vacuum solenoid: it might be. Indeed the loss of power is non systematic but happens "randomly" mainly on full throttle. I just want be sure it is not the boost pressure sensor wich is getting broken to avoid a bad and unnecessary expence.

So you suggest the problem is the vacuum solenoid?

Thanks,
AleC

[tomsa]

Hello,
in my opinion the boost control works ok. It is normal to get an overshoot when you tip-in and at lower rpm you have at constant speed a higher boost pressure then disired because its in open loop control. At higher load/speeds it gets in closed loop control and for me it seems o.k. But your MAF values are nok, they are much to low. Either your MAF is defect or FES is measuring wrong values (kg/h instead of mg/i). Which ECU do you have?

Tomsa

[capraa]

Hi Tomsa,

unfortunately my ECU reports incorrect MAF values, as posted here: viewtopic.php?f=3&t=1357&p=3451&hilit=c91#p3451

Anyway from what I know there is a rough test for these ECUs and in accordance with it my MAF should be fine. Correct range for this test is reported below
on idle, EGR open: 27-32 mg/i
on idle, EGR close: 40-55 mg/i
full throttle, max rpm: 300-570 mg/i.

May be possible the problem is the incorrect MAF number, despite what said my reseller?


Thanks,
AleC

[tomsa]

Then don't believe is the MAF. Try to disconnect the MAF wire, then you should see in FES a default value from when I remember right about 800mg/i.
Try to drive and feel what's happening.
Which ECU do you have?

Tomsa