VW T4 Forum - VW T5 Forum banner

1 - 4 of 4 Posts

Premium Member
10 Posts
Discussion Starter #1
Hi all

In need of techincal expertise!

Bought a 2.5tdi AJT 88bhp T4 back in Jan, and currently doing the camper conversion thing!!

I expected a settling in period of replacing all sort of worn thing as its done 215k +! But im having a power issue!
Have spent hours poring over all sorts of threads relating to the topic and am now in need of guidance!

Problem is, its flat and gutless on hills. I live in Cornwal so there's plenty of them to choose from! I know its only 88bhp and done 215k +, but surely it should hold its own on hills in 4th?

This is all the stuff i've done so far to try and fix the problem:

  • All vac pipes changed leading from and to the N18 and N75
  • New MAF (Bosch)
  • Fitted new N75 (from VW)
  • Fitted decat exhaust
  • Done cage mod to MAF connector
  • Checked for leaks in boost hoses
  • Had air intake off turbo to check end float and free spining turbine
  • Fitted new o ring on air intake to turbo
  • replaced vac pipe to ECU (guess its for the MAP sensor)
  • Cleaned EGR valve
  • New air filter
  • New fuel filter
  • No blocked air intake

Have vag com and get this fault

17958 - Charge Pressure: Control Deviation
P1550 - 35-10 - - - Intermittent

Also have logged measuring blocks 3, 10 and 11. Graph below

From what i can tell the boost pressure seems to rise and then falls. It doesn't seem to vary with the calculated pressure.

I replaced the N75 most recently and was hoping this would fix it:(

I think im down to these options;

wastegate actuator leaking (not stuck as can move with hand)
faulty wire somewhere!

Going to use a mityvac (or similar) to test the actuator on the turbo.

Can anyone tell if my graph is normal or am i expecting to much from a 2.5tid?

So a big plea goes out there, HELP ME!

Premium Member
10 Posts
Discussion Starter #3
Thanks thevandidit, handy to know expertise are close at hand.

Thing is i was kinda hoping i could fix it myself?! Have learnt so much on the forum and enjoy skinning my knuckles!! Trying to save money for the interior too.

If theres nothing left to try though looks like a trip to see wiser folk!

Premium Member
10 Posts
Discussion Starter #4
Well after much thinking, searching asking around i seemed to have fixed the boost problem! Turned out to be a boost leak that was fixed with jubilee clips from sdroflaH!

I think the main leak was the plastic hose going from the maf to the turbo intake; they don't seem to fit very well and slop around possibly so that unmetered air is dragged in messing up the fuel/air mixture and possibly leaking boost too!

Anyway enough speculation, the graph below is with the leak fixed for people to compare if they have similar problems!
Notice the actual boost pressure rising and falling with calculated boost, unlike before!

1 - 4 of 4 Posts