525 TDS Inconsistent Turbo

[525TDSBeast]

Hey

Have an E34 '95 525 TDS Touring with 127k on the clock - great car. Had it from my uncle who looks after his motors and it runs great, except that the turbo only functions intermittently. Sometimes you hit 2,500rpm and a nice big surge of power hits you (probably more often when cold, but wouldn't swear on it) and the rest of the time the acceleration is totally linear and frankly crap. As a result I never trust it for overtaking cos if the turbo doesn't kick in then I'm screwed!

My garage (local Bimmer specialist) has suggested replacing the turbo, but I don't understand why the turbo would work sometimes and not others if it was duff?

Is this a 'replace the turbo' issue or is it likely to be caused by a faulty sensor? And if I do replace the turbo, can I get a bigger one and have MORE POWER MWAH HA HA HA!

Finally, issue with the fuel feed - if the tank gets more than half empty I start getting air bubbles along the fuel feed (the less in the tank, the more bubbles). An RAC guy I spoke to said that the fuel pipe sometimes splits and air gets in, but my garage says replace the sensors - any thoughts?

[darkhorse737]

intermitent operation on turbo:

1) wastegate stuck in open;
2) if there are any visible leaks, it's possible that the oil interferes with proper operation of the turbo;
3) the ceramic seal may be damaged or leaking, causing exhaust gas to leak into the intake side;
4)sensors are a possible area of fault too...
5) exhaust leak between exhaust manifold and turbo (?)
6) could also be the impeller bearings(in relation to #3 being damaged. (if this be the case, sometimes you'll hear the turbo whine, and sometimes you won't)

Before you decide on changing the turbo which is by no means cheap... i would rather suggest that you visually check the operation yourself.

- bigger doesn't always mean better. There are limitations to turbo efficiency...

Fuel feed - fuel pipe inside the tank splitting at the seam is possible(it's happened to me a couple of times on trucks.... BUT, even when you have bubbles in your lines, for as long as you don't sputter our or performance isn't compromised, you have nothing to worry about. M-Benz diesels perpetually have bubbles in the inline filters and it doesn't affect operation.

[525TDSBeast]

Thanks for your time and help matey, will check all of that out!

[Bigmac]

I had the same indications on my machine 525tds 183000 miles, a intermittant " in fuel tank" pump was the cause, replaced now all is fine

[porka]

Originally Posted by 525TDSBeast

Hey

Have an E34 '95 525 TDS Touring with 127k on the clock - great car. Had it from my uncle who looks after his motors and it runs great, except that the turbo only functions intermittently. Sometimes you hit 2,500rpm and a nice big surge of power hits you (probably more often when cold, but wouldn't swear on it) and the rest of the time the acceleration is totally linear and frankly crap. As a result I never trust it for overtaking cos if the turbo doesn't kick in then I'm screwed!

My garage (local Bimmer specialist) has suggested replacing the turbo, but I don't understand why the turbo would work sometimes and not others if it was duff?

Is this a 'replace the turbo' issue or is it likely to be caused by a faulty sensor? And if I do replace the turbo, can I get a bigger one and have MORE POWER MWAH HA HA HA!

Finally, issue with the fuel feed - if the tank gets more than half empty I start getting air bubbles along the fuel feed (the less in the tank, the more bubbles). An RAC guy I spoke to said that the fuel pipe sometimes splits and air gets in, but my garage says replace the sensors - any thoughts?

Hi, I have exactly the same inconsistent power on my 525tds too. Have you managed to get it fixed ?

Also, highly recommended forum.bmw5.co.uk • Index page

[porka]

forum.bmw5.co.uk • View topic - porka's 525 TDS boost problem

[525TDSBeast]

Hey

Sorry for slow response - am changing jobs and am a bit tied up.

Have just had full service done on the car. My garage rigged it up to the diagnostics and the system came back with error 54 - Boost sensor. They reset it and it worked as it should briefly but is now back to how it was before.

You apparently can't get the sensor separate from a whole new turbo and that is £900 odd a unit retail. Unless anyone has any bright ideas as to how I can fix this without dropping that much cash then I think I'll just leave it, annoying as it is!

Any suggestions much appreciated and sorry once again for non-response.

[MADDOUG]

Originally Posted by 525TDSBeast

Hey

Have an E34 '95 525 TDS Touring with 127k on the clock - great car. Had it from my uncle who looks after his motors and it runs great, except that the turbo only functions intermittently. Sometimes you hit 2,500rpm and a nice big surge of power hits you (probably more often when cold, but wouldn't swear on it) and the rest of the time the acceleration is totally linear and frankly crap. As a result I never trust it for overtaking cos if the turbo doesn't kick in then I'm screwed!

My garage (local Bimmer specialist) has suggested replacing the turbo, but I don't understand why the turbo would work sometimes and not others if it was duff?

Is this a 'replace the turbo' issue or is it likely to be caused by a faulty sensor? And if I do replace the turbo, can I get a bigger one and have MORE POWER MWAH HA HA HA!

Finally, issue with the fuel feed - if the tank gets more than half empty I start getting air bubbles along the fuel feed (the less in the tank, the more bubbles). An RAC guy I spoke to said that the fuel pipe sometimes splits and air gets in, but my garage says replace the sensors - any thoughts?

The air getting in half full tank is caused by the 'o' ring on lift pump failing that gives a seal when the pump is fitted into its holder inside tank,had this happen to me,the 'o' ring pipe in pipe join sits at half tank level.My tds did not run well with air in lines,I realised it was 'o' ring when I would travel round large roundabouts and engine would run better.

[///Ramon]

the air bubbles are a result of the fuel line up pump. When the pump have to work harder (when almost empty or a quarter full) it is getting difficult.. at final it will stop pumping up diesel..

it is easy to replace. Just take out the backseat and behind the passengerseat you will find the pump under a round cover.

I had the problem with my E36 325i M50 B25 and with my E39 525TDS, for the first one i wrote a technical document. Although it is in dutch and for the M50 engine (it is quite simular), it is illustrated with pics.. zo you don't realy need the text

replacing fuel pump [E36]

[chrisb]

Originally Posted by 525TDSBeast

Hey

Sorry for slow response - am changing jobs and am a bit tied up.

Have just had full service done on the car. My garage rigged it up to the diagnostics and the system came back with error 54 - Boost sensor. They reset it and it worked as it should briefly but is now back to how it was before.

You apparently can't get the sensor separate from a whole new turbo and that is £900 odd a unit retail. Unless anyone has any bright ideas as to how I can fix this without dropping that much cash then I think I'll just leave it, annoying as it is!

Any suggestions much appreciated and sorry once again for non-response.

Hi my first post here I hope it's useful. I had the same Turbo problems on my 525TDS with the same diagnostics error code. The "boost pressure sensor" turned out to be the MAP (manifold absolute pressure i think) sensor which is the small (1" square) sensor mounted closest to the round socket where the diagnostics plugs in. It is also next to two vacuum sensors but has a braided hose going to it rather than the 'smooth' ones on the vac sensors. The other end of this braided hose attaches directly underneath the inlet manifold.
When I took the pipe off the bottom of the MAP sensor both the sensor and the pipe were full of black liquid. I took the pipe completely off right at the manifold (fiddly to get back on) and cleaned it and the sensor out and since then the turbo has worked like a dream, i didn't even need to replace the sensor! I hope this works for you!
chris

[stevecvo]

It looks quite difficult to access the turbo and check the pipe you mention. What is the easiest way to get at it?