P1557 Charge pressure control

hydo14

Member
During the week I got limp mode and the with obdeleven I got a P1557 Charge pressure control: positive deviation fault code.

Today I put the car up in ramps and had an inspection of all the charge hoses for any splits or cracks as well as looking at the intercooler in case that has burst at the crimps and all of this looks okay.

Next step was looking at the vacuum hoses to the turbo again these all look fine and are connected securely. So then carried on working my way around to the inlet manifold and here the EGR has a lot of oil all over it. Could this be a source of my problems or have I missed something?

The anti shudder valve looks pretty manky so I will try and wriggle the whole EGR assembly out to clean it anyway - though this is probably futile...
 

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audifan

A2OC Donor
EGR would not cause this issue. Are you sure that the intercooler end cap has not split? Recheck all the plastic / rubber connections to the N75 valve as that is what controls the turbo pressure. The whole system is very sensitive and any leak will make the system faulty. Carefully check the 2 pipes as they pass down the bulkhead before they reach the turbo ( one on the turbo pressure green coloured and the other to the waste gate actuator ). Then check all 3 connections onto the N75 are tight. Actually worth now replacing the pressure rubber pipes as they are now well used. Does the fault clear when you cycle the ignition?
Ref your EGR valve, contentious issue but I would replace it as where the oil has stained the outside indicates the oil is getting out the shaft. Many people would just isolate it or machine it out. Be warned if you clean it that it really is horrible gunk to get off everything it touches. And to clean it properly you need to remove it from the engine , so easier quicker and cleaner just to fit a new one.
 

hydo14

Member
Cheers for the advice @audifan I shall give all the above another check over tomorrow as I had left the car up on the axle stands. The limp mode does go away with a key cycle and then the car seems fine for another few hundred miles or so until it happens again.

I have ordered a new EGR anyway as there's something unhappy with that one with all the black goo coming out of it.
 

hydo14

Member
Project update: The hose that runs from the turbo to the N75 looked fine however when I gave it a wiggle to check that it was connected it pretty much disintegrated in my hand, looks like replacement hoses are in order and then hopefully this will sort it out.

There wasn't anything else to report, the intercooler ends seem absolutely fine and I would expect to see a bit of oil on the intercooler as there's a small amount in all the charge hoses.
 
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audifan

A2OC Donor
Better to replace all the rubber braided pipes not just the N75 but also the N239 and N18 as they have all aged. Make sure you force them over the thinner plastic tube far enough and that they also all fit tightly onto the solenoids. When replacing the pipes to the turbo do one line at a time to prevent them getting fitted to the wrong location.

This diagram shows the routing and the lengths of tube required...



If the intercooler ends were split, the error message would have been negative deviation i.e. loss of pressure. Your message means the turbo is not dumping off enough pressure. I suppose that could end up blowing the end caps in time....
 

audifan

A2OC Donor
7Zap is a bit flaky just now but this is the diagram of the pipes but not the required dimensions...

1612723886228.png
 

hydo14

Member
Thanks all, think I've got it all sorted now. In the end there were a number of issues:
  • Oil leaking out of the shaft for the butterfly valve shaft for the anti shudder mechanism. New EGR sorted this
  • Very very tired braided rubber hoses that attach the various vacuum/pressure hoses that run to the intake, n75 to the hard plastic lines that run down the bulkhead. These all needed replacing at both ends. I used some generic 3.5 mm inner diameter braided NBR hose
  • The green wastegate hose was split so I think that was the source of the leak and the above issues
 

Un4tural

Member
I was looking at getting some replacement hose and struggled to find ID for the vacuum lines, cheers for that! Mine are not disintegrating but will do them for due course due as had an intermittent hiccup now and again with boost pressure.
 

hydo14

Member
I figured that the plastic hard pipes are 4mm outer diameter so 3.5 mm inner diameter would give a nice tight fit. It was hard to measure the ones I took out as the rubber had gone all gooey and barely held it's shape.
 
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