Car:   Octavia 2 1.9 PD BXE

 

Have posted in General Maintenance as I don't expect this to be model specific 

 

Following long running saga trying to get car to run right (several other posts but briefest description - down on power and hesitant / missing when warmed up) I tried disconnecting the EGR valve. Valve not removed just disconnected and plugged the pipe from the vacuum solenoid block to the EGR actuator, car runs better like this.

 

Thinking out loud here but to my mind that still leaves 3 options.

 

1) Faulty EGR valve

Have checked actuation with hand held pump and gauge. It holds pressure, valve opens under vacuum and closes when vacuum removed. Realise this is not quite the same as actual operating conditions though.

 

2) Faulty N75 valve inside the vacuum solenoid block

Still not sure how to test this. There are instructions on net regarding how to test Individual N75 valve. But I still can't work out how to test it as part of vacuum solenoid block

 

3) Incorrect signal into N75 valve

 

Any way of narrowing it down?  As the EGR valve and vacuum solenoid block are expensive to replace 'just in case', particularly as I have already replaced turbo and MAF sensor.

 

Alternatively any other possible culprits?

 

I have access to full VCDS

 

Thanks

 

 

 

 

 

sounds like it wants a good clean out  from memory it doesn't operate when cold,    it may not be completely closing  worth a look  is it vac ASV also or electric

sounds like it wants a good clean out  from memory it doesn't operate when cold,    it may not be completely closing  worth a look  is it vac ASV also or electric

Thanks 

 

Coincidentally as you were typing the above I was out cleaning the EGR valve.

 

Had not done this myself previously as garage said they had done it - still pretty caked though. I guess by 'clean' they meant squirt something into the induction system and hope for the best. I removed the valve and did a more thorough scrape and scrub with carb cleaner.

 

Attachment shows it refitted doing a final vacuum test on valve. 

BTW Starts to open at 11 inHg  fully open at 21 inHg 

 

Not tried it out yet so we will see how it goes.

 

Thanks again.

sounds like it wants a good clean out  from memory it doesn't operate when cold,    it may not be completely closing  worth a look  is it vac ASV also or electric

Should have said ASV is electrically actuated (did not realise some were vacuum) obviously can't observe it directly in normal running but with hose removed and car not running valve is fully open, start engine - the valve stays open, switch off engine valve briefly closes then opens and stays open. As far as I am aware this is what it should do but as ever if anyone can confirm this (or otherwise) it would be appreciated.

 

Thanks

you got it  :beer:

EGR cleanout may have improved things a bit but not a fix unfortunately.

 

Back to looking at log of all blocks at idle, comparing them with others on the net from PD engines considered to be in good health the difference that stands out is:

 

Group 11

Engine Speed (G28)                         819 rpm

Boost Pressure (specified)               1091 mbar

Boost Pressure (actual)                    898 mbar

Charge pressure control duty cycle  83% 

 

What would be likely cause of discrepancy between specified and actual pressure?

 

Took some vacuum readings with engine running - using a Y connector so that I could tap of for a reading but still leave the vacuum circuits complete.

 

At idle reading on pipe to EGR valve actuator 12.5 inHg

 

At idle, reading on pipe to control turbo is 18 inHg

At 2500 rpm (no load), reading on pipe to control turbo is 15 inHg

 

THese don't seem right to me but my thinking may be wrong. Anyone know what I should be getting here?

 

Thanks

Should also have said with car engine idling the MAF sensor can be unplugged and plugged back in again with no discernable change in engine note - Not sure if this points towards anything / rules anything out.