VW T5 Vacuum pump readings

[jammyjambo]

Hi there

I can't see where else to post this so please correct me if it's wrong.

The tandem vacuum/fuel pump on a 2007 VW T5 2.5TDI. Does anyone know what vacuum readings I should be getting at idle and under load please?

I get underboost problems (limp mode) for the turbo and also the brake pedal feels a little harder than usual. To me this would imply a lack of vacuum pressure from the pump or a leak in the system.

The van has a new turbo, new N75, MAP and MAF sensors, intercooler, refurbed injectors.... smoke tested vacuum lines and high pressure pipes.

If it's not this then I'm still at a complete loss as to what causes the apparent turbo underboost fault code and then limp mode.

Many thanks if you can help,

James

[zollaf]

20 mm hg , same as a petrol car at idle, but inlike a petrol this reading should stay about the same as you rev it.

[jammyjambo]

Thanks for your post Zollaf.
I don't suppose you know what the fuel pressure out the same tandem pump should be do you?

James

[zollaf]

it was 100 psi iirc on the old 1.9 pd engines, so imagine it would be about the same.

[jammyjambo]

I've tested the output from the tandem pump and it pulls a good 30inHG. I disconnected every joint and checked that it pulls the same vacuum everywhere with no drop. All is good.
Across the N75 valve it sucks at about 22inHG to the turbo vanes. I assume this drop is just due to the internals of the N75 valve.
The valve works as I disconnected it and the turbo was very ineffective and it went into limp mode all the time.

So now that I've changed the Turbo, MAP, MAF, N75, checked the tandem pump, refurbed the injectors and had a new intercooler, does anybody have any idea what to check next?

All I can think of is whether it's fuel related.. Is there a way to check the fuel flow to the injectors.
If the ECU requests fuel but it can't deliver enough how can you check that?

My understanding of the 2.5 is now limited when it comes to fueling. So when you depress the accelerator, is it the throttle position sensor that then controls the opening of the injectors via the ECU?
My thinking is that the ECU sees that you want to accelerate, it then expects a certain boost pressure to be reached when more fuel is injected, this isn't reached because the fuel flow is limited for some reason, the MAP(inlet pressure sensor) then never reaches the ECU requested pressure, then it goes into limp mode.
I've probably got that all wrong...

Can someone please help?
I'm at a total loss of why it's so underpowered and goes into limp mode under load!

Thanks............

[Crasher]

What is the code number it is generating? Have you done a requested/actual boost graph test in Measuring blocks 011 zones 2 and 3?

[jammyjambo]

I have yes, and the actual boost pressure measured at the MAP is always considerably less than the ECU requested.

[jammyjambo]

PO299 is the code - underboost

[Crasher]

In Basic Settings 011, the revs are lifted and the N75 cycled, does the VNT actuator move up and down fully and smoothly in this mode? The boost display should change from approx 1000mBar to 1250mBar. If these are OK I would be considering a new genuine AMM but first of all I would do a 0.5Bar system pressure test but not many people have the equipment.

[jammyjambo]

The AMM was also recently replaced for a Bosch which I believe is what VW use and it made no difference unfortunately.
The high pressure system has also been pressure tested.
A new turbo was fitted that made no difference, and then some months later another was fitted as it was thought the initial one may have been faulty.

[Crasher]

There are a lot of Bosch forgeries around, check the sticker to see if it is made in China. I won't trust anything other than an AMM from TPS and even they can come faulty out of the box. Check the operation of the VNT rod in Basic settings 011.

[chrisfunfun]

hi, been reading this thread with great interest, as it came up in my internet search for the pump readings, yestdarday i was sat at the garage yet againm and my van had very similar problems and 2 garges could not sort it, long and short very similar to above post although his was 2 years ago and must now be sorted but no reply to the outcome so we had to do more work, as a stroke of luck we found my personal problem thats why im posting this as maybe help somone in futre, in the end the mechanic had the non return valve tested it all good, but we think was a copy as he turned it around and the van got full power and brakes back?? he took it off again to check and the arrow (flow) was facing the wrong way for the van to work correctly, if fiited with arrow in vacum flow direction, the van was usless. hope this helps as i nearly sold the van i was that sick of spending money and none of it worked. yesterday was my lucky day, i hope you all lucky.