Thread: TD5 Inlet Manifold pressure

DOH!!!

It's just dawned on me.. the ambient pressure.. it the air pressure the weather guy on telly talks about. right?


So that changes the question.... I think cutting out at around 245 kPa is telling me things cut out at around 1.4 bar or boost ( 140 Kpa).


So am I right in thinking that could be wastegate modulator or something like that?


Sorry if some of this sounds stupid... I am still learning what goes on with Turbo diesels.. and I really want to understand whats happening under there...

Cheers,
Mark

you're about on the money....

one sensor tells the ECU how much air pressure there is in the airbox (the bit that holds the air filter)

and another tells you how much pressure youve got in the intake manifold....

Quite why it wants both bits of info is a bit of a mystery to me because for a turbo diesel all that really counts is the pressure in the inlet manifold and the temperature.

It makes sense for an NA engine to have both especially a petrol engine.

Originally Posted by Bytemrk

Hi guys,

Since doing the EGR and silicone hoses I have been tinkering with my Nanocom, trying to get a better understanding of what happens under the bonnet.

I am currently finding if I give the motor a big right foot it goes really hard then cuts out and goes agian.. etc I suspected it was the ECU saying too much boost.

Looking at the Nanocom it seems to be doing it when the inlet pressure is getting to around 245kPa.

Now the bit I can't work out.. is that the Nanocom is also telling that the Turbo Inlet pressure is 103KPa at Idle and same when turned off! It's showing ambient Pressure of around 101 KPa

Am I missing something here , but shouldn't the manifold pressure be very minimal - especially with the motor not running!

I am suspecting either what the Nanocom is telling me is BS... or maybe I have a faulty Manifold Pressure Sensor?

Can anyone tell me if they see big holes in my logic?

Mark

Your lucky its not the manifold pressure sensor! They are around $500 new!!

Ambient pressure should be about 100kpa and manifold pressure should be about 100kpa at idle I think.

I just tested my boost modulator by bypassing it. Seems like its a bit more responsive so I think mine isnt functioning right. Not much more power though...

Angus

I bypassed the modulator and got no real change.. if anything it doesn't run as well.

If I flatten it, around 2500 RPM, I get this sort of cutting out effect, yet if am less aggressive on the throttle.. it powers along beautifully..going straight past 2500RPM with no hesitation.

This sort of surging seems to happen at around 235 kPa inlet pressure.

It's certainly not undrivable.. because I very rarely flatten it.. but when I do I want it to go!.. not hesitate.

Any other ideas?

Turbo hoses? Oil in loom? Fuel pressure regulator (got any dripping diesel?)? Clogged fuel filter - get any cheap dirty diesel on a trip?

Angus

Forgive me if I am wrong here, but I thought the ECU will go into a overboost situation around 1.2-1.3 bar, so if you are getting up to 1.4 you're doing well. I think there are some electronic gadgets out there to stop the surging, but I would just back-off the wastegate adjuster a little to stop the overboost from happening. Mine never gets above 1.1 bar before the wastgate opens and it drops back to 1 bar.
The ECU has been flash upgraded, and I think I'm near the clutch's limit on torque, so I haven't brought the boost up to around 1.25 bar, but I might in the near future just to see how it goes.

Fraser

Originally Posted by McDisco

Turbo hoses? Oil in loom? Fuel pressure regulator (got any dripping diesel?)? Clogged fuel filter - get any cheap dirty diesel on a trip?

Angus

New silicone hoses.. no sign of oil in the Loom and no dripping diesel... But I will take a look at fuel pressure and clogged filter - it's just about due for a service.

Thanks Angus.

Mark

1.4 bar is about right, but perhaps just a little high, so I expect the engine is experiencing fuel cut-out due to prolonged excessive boost which typically occurs on full throttle at around 2500 rpm. This can be caused by a faulty (sticky or stuck) boost modulator, wastegate actuator, sticky/siezed wastegate or faulty pressure hoses.

If you have wound-up the wastegate actuator arm then its time to start winding it back but it would have been wound-up quite a long way to cause this. You can easily test the modulator to check that boost pressure gets to the wastegate actuator with the ignition off, and that there is no path from the low pressure side to the actuator at the same time. Any other condition is faulty.

It could also be a faulty fuel pump that's not delivering full pressure, but the 2500 rpm spot is very typical of fuel cut-out due to excessive boost.