Charge Pressure Control - What's going in on here?

 

Car Octavia 2 1.9 PD BXE

Still trying to work out why engine missing/surging and poor/non starting when hot

 

Was looking at the idea that Engine note should change when you disconnect MAP sensor  - No discernable change in engine note when disconnected or reconnected.

 

Looking in more detail I looked at Group 11 - Charge Pressure Control, while also looking at vacuum in line from solenoid valve block to turbo actuator. Gauge was connected with a 'T' so function of vacuum line should not be disturbed.

 

So as table below describes, ran at idle then disconnected MAP sensor then reconnected.

 

What struck me was that Boost pressure at idle is less than specified - aware that they will not always match perfectly but I presume this deviation is outwith normal limits.

 

Then although disconnecting MAP sensor changed CPDC, vacuum to turbo actuator and actual boost pressure, reconnecting MAP sensor made no difference to readings (stayed as they were when it was disconnected). Switching engine off then on again caused the readings to go back to almost exactly initial values.

 

I am thinking this is not quite right and hopeful there are some clues in here, but don't quite know what to make of it. Any ideas appreciated.

 

Thanks

 

 

 

 

VCDS RPM is not continuous - goes up in steps . Presume engine speed must have been right on boundary between these two values as it was alternating between 819 and 840

Edited 4 June, 201610 yr by Octy0GG

Just realised something else may not quite be right here.

 

Other sources suggest that with engine idling when you disconnect MAP sensor the Manifold pressure reading should momentarily drop to 400mbar then rise to match atmospheric.

 

Admittedly this was for VW T4 but appears to be similar Bosch MAP sensor. 

 

Is it your understanding/experience that 1.9 PD BXE should exhibit the same behaviour? as clearly mine does not.

 

Should be said that the MAP sensor is a new genuine Bosch part - That's not to say that it or associated connectors and wiring couldn't be faulty.

 

Fitted new MAP sensor to replace faulty one which was reading well under atmospheric (by about 200mbar) with engine off.

The new one is within 10mbar of atmospheric with engine off which I understand to be within acceptable limits.

 

Thanks

Edited 4 June, 201610 yr by Octy0GG

Regarding the readings not returning to initial state until the engine has been switched off then on again, It has been suggested to me that this is required as a 'reset' for some readings. Anyone know for sure if this is the case here?

 

Thanks

not sure why you'd expect any boost pressure at idle   I would be looking at temps sender and a sticky egr valve 

not sure why you'd expect any boost pressure at idle   I would be looking at temps sender and a sticky egr valve 

Thanks

 

Not so much that I had any particular expectation of what boost should be at idle - more just that I expected actual boost pressure to be a lot closer to specified boost pressure. Are you suggesting that the specified boost pressure of 1091.4 mbar points to an error? Anyone know what this could be indicative of?

 

EGR valve is new, actuation has been checked with hand operated vacuum pump and with VCDS output test. Vacuum lines have all been checked with vacuum pump.

 

 

Plot of temp sensor output attached here seems OK. This one was done stationary at idle and took a long time to heat up, intake temperature did rise but that would have been due to no air flow. Did another temp. plot while driving - heated up faster and intake stayed close to ambient.

I would guess that your guage isn't that accurate/ or with in a margin of error @ approx 1/10 of a psi ( what range is it and when was it last caibrated?)   I can't see it being a problem,  re air temp it will go up rapidly once you start to raise pressure, bike pump effect

Hi

 

Not a mechanical gauge 'actual' boost is from VCDS and therefore reliant on MAP sensor and wiring.

 

I realise therefore that, despite the MAP sensor being new and a genuine Bosch part, this 'actual' reading may not really be the actual boost . For this reason I am looking at getting a mechanical boost gauge to measure boost directly. Decent ones don't seem cheap, looking at Mocal or Racetech. Not keen on making a hole to allow connection but cant see any other way.

a-hhhh  :sun: