Technical JTD low power, error P0235 & multiecuscan boost log

[klaasdc]

Hi all,

I have an Alfa 156 JTD 115 and a Multipla JTD 115, but the engine on the Multipla feels very "flat". On the Alfa you get a shove when flooring the pedal, but the Multipla just seems to struggle to get get up to speed.
At some point on the highway I suddenly got an Engine Control Fault on the dash and could barely keep up with traffic. Eventually that cleared itself and I could get home safely.


With multiecuscan I then checked for error codes and there was P0235 and P0236.
I decided to replace the EGR and the MAP sensor (both were gunked up with oil/tar) as the EGR would not respond when toggling it from multiecuscan. As the car also never showed more than 2 bars on the temperature scale, I replaced the thermostat at the same time.

Now the engine heats up properly, but it still drives like crap. Eventually I again got it into "limp home" mode when driving it >3000 rpm. This time the only error code was P0235.

I decided to make some logs with multiecuscan of the boost pressure, see attached.
It looks like the measured boost pressure is often higher than or lingering much longer than the desired boost pressure. I'm not sure if what I see is still plausible, and what parts I need to look at next.
With multiecuscan I also tested the VGT actuator on the turbo and I estimate it does move about 1cm in and out.

Any ideas?

 

[widemouthfrog]

I feel your pain! It's a common problem.

Check all of the junctions in the small bore tubing that connects the MAP sensor,solenoid boost valve etc. It sounds as though you've got a leak somewhere in those small vacuum pipes. I had exectly the same symptoms that you describe several years ago, and also replaced the expensive sensors. The fix for the problem was actually a short length of rubber tube (cost: 20 pence) that two of the small pipes push into. It had a tiny split in it and wouldn't hold vacuum. Going into limp mode when you hit 3,000rpm is typical of this fault. There are lots of threads on here about it.


Travel on the VGT actuator sounds a bit shy, but not much. You could just have a tiny vacuum leak somewhere.

Good luck!

 

[klaasdc]

I feel your pain! It's a common problem.

Check all of the junctions in the small bore tubing that connects the MAP sensor,solenoid boost valve etc. It sounds as though you've got a leak somewhere in those small vacuum pipes. I had exectly the same symptoms that you describe several years ago, and also replaced the expensive sensors. The fix for the problem was actually a short length of rubber tube (cost: 20 pence) that two of the small pipes push into. It had a tiny split in it and wouldn't hold vacuum. Going into limp mode when you hit 3,000rpm is typical of this fault. There are lots of threads on here about it.


Travel on the VGT actuator sounds a bit shy, but not much. You could just have a tiny vacuum leak somewhere.

Good luck!

Thanks!
I will look at all the small tubing. Could not find anything wrong with those to the turbo actuator and solenoid so far. Maybe I'll try to attach a brake bleeding kit to see if I can hear a leak.

 

[klaasdc]

Problem solved!

Double checked all the pipes but no issues there. Eventually tested the turbo actuator using a brake bleed kit and it barely moved 1cm. Seemed more like slack on the mechanism than moving the actuator.
So I decided to remove the turbo and indeed the mechanism was completely seized. I did not manage to separate the turbo to clean it (too much rust), and opted to trade it in for a refurbished one instead. Car now finally runs fine.

During the test drive, one intake pipe clamp was not tightened fully and started whistling + sputtering some oil on the engine block. I suppose this oil comes from the breather pipe at the inlet. Maybe I need to investigate this further.

 

[widemouthfrog]

Good to hear that it's fixed. You may find that the intercooler is full of black goo. Giving it a good soak (in petrol, if that isn't forbidden these days) can help to purge it. It will certainly help induction breathing. Let it dry out well afterwards to avoid interesting after-effects on the engine

The concertina rubber pipe that runs to the bottom intercooler stub will very likely be half-full of the same black goo.