300tdi Boost pressure?

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Disco Moneypit

Disco Moneypit

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North Derbyshire / South Yorkshire
Hi chaps,

I have already done a quick search on this matter, but i cant seem to find a definative answer......


A little background info first. My 300tdi is falling of boost, accompanied with a weird whistling noise. I'm guessing that I either have a loose or split hose, or faulty acutuer or something. The intercooler was removed and flushed out when I did all the welding work a while back and the sedimeter drained. Since then I have only done some very mild green laning, so I am confidant that it isn't all silted up.

I have bought a boost gauge to fit so that I can get an idea of what figure I am starting with, but what I don't know is what figure I should be aiming for? Could any of you guys help?

The vehicle uses about 1/4 litre of oil every 1000 miles, (I check all fluids weekly, doing around 500 miles per week), and fuel consumption is dropping rapidly. I used to get 500-540 miles from a tank, but now get 360!

I will also be doing a compression / leak down test, although I don't expect to get any bad news from this.


Oh, and it's a 96 300tdi XS. Manual box, EGR blanked off, running on 215/70/16 Insa M/Ts.



In advance, many thanks.
 
Do your tests for a start, my guess would be a split air hose - but you've not mentioned excessive black smoke which I'd associate with this.

I'm pretty sure I read somewhere the normal boost is 14psi (about 1 bar) but that seems a bit low to me. When you do your compression test, do it once dry then get an oil can and give each cylinder 3-5 squirts and test again - if the pressure rises significantly (more than 30-50psi) the piston rings are suspect, if it stays lower than it should be the valves are suspect. Hope that helps, may also be worth setting the valve clearences before you start.
 
Thin_trucker said:
Do your tests for a start, my guess would be a split air hose - but you've not mentioned excessive black smoke which I'd associate with this.

I'm pretty sure I read somewhere the normal boost is 14psi (about 1 bar) but that seems a bit low to me. When you do your compression test, do it once dry then get an oil can and give each cylinder 3-5 squirts and test again - if the pressure rises significantly (more than 30-50psi) the piston rings are suspect, if it stays lower than it should be the valves are suspect. Hope that helps, may also be worth setting the valve clearences before you start.
Click to expand...

Many thanks.

Yes, it is a little rattly, but I was putting this down to a leaking exhaust / inlet manifold. But on the other hand as I cannot remember when the valve clearances were last checked, I shall set them first.

Once again, cheers.
 
Thin_trucker said:
Do your tests for a start, my guess would be a split air hose - but you've not mentioned excessive black smoke which I'd associate with this.

I'm pretty sure I read somewhere the normal boost is 14psi (about 1 bar) but that seems a bit low to me. When you do your compression test, do it once dry then get an oil can and give each cylinder 3-5 squirts and test again - if the pressure rises significantly (more than 30-50psi) the piston rings are suspect, if it stays lower than it should be the valves are suspect. Hope that helps, may also be worth setting the valve clearences before you start.
Click to expand...

Not a good idea with a diesel. :doh:
 
Disco Moneypit said:
Hi chaps,

I have already done a quick search on this matter, but i cant seem to find a definative answer......


A little background info first. My 300tdi is falling of boost, accompanied with a weird whistling noise. I'm guessing that I either have a loose or split hose, or faulty acutuer or something. The intercooler was removed and flushed out when I did all the welding work a while back and the sedimeter drained. Since then I have only done some very mild green laning, so I am confidant that it isn't all silted up.

I have bought a boost gauge to fit so that I can get an idea of what figure I am starting with, but what I don't know is what figure I should be aiming for? Could any of you guys help?

The vehicle uses about 1/4 litre of oil every 1000 miles, (I check all fluids weekly, doing around 500 miles per week), and fuel consumption is dropping rapidly. I used to get 500-540 miles from a tank, but now get 360!

I will also be doing a compression / leak down test, although I don't expect to get any bad news from this.


Oh, and it's a 96 300tdi XS. Manual box, EGR blanked off, running on 215/70/16 Insa M/Ts.



In advance, many thanks.
Click to expand...

Hi there a couple of observations:

1. The tyre size you quote is incorrect for a Disco TDi 300, they should be 235/70/16, or 205/80/16. Your tyres will give an under-reading on your speed and mileometer of about 4%. So when you think you've done 400 mls you actually only done about 380. Also, the Insa Turbo's are good mud tyres but will affect your mpg quite negatively.

2. Turbo boost as std on a TDi 300 engine is, according to Rave "12 - 15psi measured at the wastegate T-piece."

If you have worries about turbo and hoses, take the hoses off and examine them inside and out, there sounds to be a leak or internal delamination going on.

If in doubt, replace.

Good luck

Dave
 
Soloby Rob said:
Not a good idea with a diesel. :doh:
Click to expand...

Never heard that one, and that's how I was shown at college (qualified mechanic) BUT, you learn something new every day and all that; what makes it a bad idea? Not being funny with you mate, I want to know that's all.

edit; Ah, think I see where you're coming from, you should avoid this with a hot engine as the oil may fire like the diesel normally would.
 
Last edited:
thebiglad said:
Hi there a couple of observations:

1. The tyre size you quote is incorrect for a Disco TDi 300, they should be 235/70/16, or 205/80/16. Your tyres will give an under-reading on your speed and mileometer of about 4%. So when you think you've done 400 mls you actually only done about 380. Also, the Insa Turbo's are good mud tyres but will affect your mpg quite negatively.

2. Turbo boost as std on a TDi 300 engine is, according to Rave "12 - 15psi measured at the wastegate T-piece."

If you have worries about turbo and hoses, take the hoses off and examine them inside and out, there sounds to be a leak or internal delamination going on.

If in doubt, replace.

Good luck

Dave
Click to expand...


I stand corrected. mine are 235/70/16's.

With the M/Ts on, fuel range dropped closer to the 500 mark on an average run, compared to nearer 550 when I had the Pirelli Scorpions on it. But recently the range has dropped and dropped with each tank full.

The vehicle will come on boost, but show it any sort of a hill, even a slight rise in elevation on the motorway, and the revs just fall away. You then change down to 4th at about 2500rpm, blipping the throttle mid shift, only for the revs to fall away again. Into 3rd, same thing.
 
Disco Moneypit said:
The vehicle will come on boost, but show it any sort of a hill, even a slight rise in elevation on the motorway, and the revs just fall away. You then change down to 4th at about 2500rpm, blipping the throttle mid shift, only for the revs to fall away again. Into 3rd, same thing.
Click to expand...


It's sounding more and more like a fault, not a tuning issue. First place I would go would be the fuel sedimenter - bet it's full of crâp.

You know where to find it, right?
 
Afternoon chaps.


The sedimeter, (located near the OSR wheel), was drained a couple of months back, for what I expect to be the first time ever! Unbelieveable the amount of crap that came out of it. I changed the fuel filter at the same time. I couldn't remove the sedimeter at the time because the nuts were rounding off, but I did let a good couple of litre of clean diesel drain through it.




During the time that the car was off the road being welded up, I spent an entire day cleaning out the rad and the intercooler. I have also replaced a couple of the hoses with new silicone ones.



My moneys on a loose or damaged hose somewhere, or a dodgy acuter, but we will see.....




Thanks for the advice chaps. I will report back once I have found the problem.


Cheers.
 
You need to get the sedimenter cleaned out properly . Snotty jelly stuff inside moves around and blocks yer fuel flow.
 
The reason behind not using oil to recheck cylinder compression in that you can and often do get detonation of the oil, and never clean the internals of a intercoller with anything remotely resembling a fuel as again you run the risk of uncontrolled engine rpm till it uses all the cleaner, I remember once an apprentice thought he was being really effcient and rinsed a wire mess air cleaner with parrafine on a GPO LDO van totally oversped the engine with catastophic results, the poor lad went as white as sheet and had to be sent home, when the engine was stripped we made a trophy from some of the spectacular scuptures extracted from the block.
Dev
 
Wolseley1800 said:
Hi,
I have the same problem on a 300tdi auto.
Can you point me in the direction of the hoses you are talking about?

Cheers
Click to expand...

The hoses in question are the rubber hoses that go between the turbo unit and the inlet manifold.

There is a short 90° elbow directly from the turbo , onto a metal pipe; then a short straight hose between the pipe and the bottom of the intercooler; the last hose goes between the top of the intercooler and the inlet manifold (this may be part metal part rubber if the vehicle has not had the De-EGR mod).

The hose that fails most often is the 90°elbow - if it feels too soft just replace it.
 
Well have ordered the pipes as I think I have found the problem.
The top hose is the original and who ever sealed the small hose did a crap job as all the boost is exiting through it
 
the other thing to watch is whether the jubilee clips are still holding, a few years ago I had similar problem on a bit of machinery, we changed hoses, rebuilt filter boxes all sorts, in the end it was a couple of budget jubilee clips that werent holding up - buy quality clips the few pence you save just arnt worth it
 
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