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Old 06-10-2008, 07:54 AM   #1 (permalink)
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Question 525 TDS Inconsistent Turbo

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?

Last edited by 525TDSBeast; 06-10-2008 at 07:56 AM.
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Old 06-10-2008, 09:06 AM   #2 (permalink)
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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.
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Old 06-10-2008, 12:17 PM   #3 (permalink)
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Cheers buddy

Thanks for your time and help matey, will check all of that out!
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Old 06-24-2008, 08:51 AM   #4 (permalink)
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Smile intermittant turbo ?

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
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Old 07-25-2008, 11:48 AM   #5 (permalink)
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Originally Posted by 525TDSBeast View Post
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

Last edited by porka; 07-25-2008 at 11:50 AM.
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Old 08-05-2008, 12:22 PM   #6 (permalink)
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forum.bmw5.co.uk • View topic - porka's 525 TDS boost problem
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Old 08-18-2008, 11:43 AM   #7 (permalink)
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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.
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Old 08-21-2008, 01:25 PM   #8 (permalink)
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Originally Posted by 525TDSBeast View Post
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.
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Old 08-23-2008, 12:22 AM   #9 (permalink)
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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]

Last edited by ///Ramon; 08-23-2008 at 12:27 AM.
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Old 08-24-2008, 10:59 AM   #10 (permalink)
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Originally Posted by 525TDSBeast View Post
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!
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Old 08-25-2008, 09:53 AM   #11 (permalink)
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It looks quite difficult to access the turbo and check the pipe you mention. What is the easiest way to get at it?
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Old 11-29-2008, 05:45 PM   #12 (permalink)
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Hi there

Well, the weather has now got cold and the turbo definitely works when there's cold air getting into it. Was wondering whether that gave anyone any further ideas as to what the problem might be - would the intercooler be something that I should check? Is the sensor affected by air temp?

Any help greatly appreciated 'cos now that I've had turbo for a while I'm really not looking forward to going back to being without it in the summer...

Thanks
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Old 12-25-2008, 07:54 PM   #13 (permalink)
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I still have the same problem too and have given up as I have checked pretty much everything, lol. Indeed, its a lot less of a problem in cold weather.

MAP sensor connected or disconnected = no difference

NEW MAF = no difference

Connected/disconnected all temperature sensors = no difference

NEW Injectors = no difference

Boost pressure is good, only down a tiny bit when running slow as is to be expected with less fuel...

Therefore, its not actually a turbo problem, but something is cutting the FUEL !!

So logically, fuel pump or injector pump. The fuel pump definitely works as I can hear it. So it must be the injector pump $$$

Only other option is that for some reason the fuel pump is cutting out sometimes but then surely temperature wouldn't affect it.

I did replace the fuel temperature sensor in the injector pump but the only thing that cured was that the mpg reading on the computer is now correct...

I'm still open to suggestions but generally can't wait to get my hands on a 530d
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Old 12-26-2008, 11:30 AM   #14 (permalink)
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Reading this I am thinking that if the engine has boost then the ecu/inj pump should supply fuel to run the extra air or it will run lean and overheat.The best place to ask about any pump issues is to ring P.B.ASHER in southampton (do a google search),I had them recon my e34 pump and a chat on phone with them and they will be able to tell you if it is a inj pump problem. I did wonder if it could be engine temp related in any way,my e34 will not take full throttle and will pull away steady until it has run for a while,a lot of searching around the net informed me that this is to let the gearbox warm up a bit before heavy use,under the inlet manifold the m51 has I think 2 temp sensors and a 3rd which does the temp gauge,could this 'low power feel/feel like lack of boost' be the system cutting this cold engine/steady acceleration until part warm into play on a hot engine ??? due to dodgy sensor or wiring ??.Generally taking the tops of these pumps is to be avoided unless the top is drilled and pinned to ensure that it goes back on in same position,half a mill out and sometimes the engine will not run or run very rough or not at all.I tried on mine when the potentiometer was failing to try to get it to run off the portion of its worn track to stop a shakey rough tickover,moved it about .30mm back towards windscreen and it then poured out black smoke at tickover and was undriveable.
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