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Turbo Boost Problem


Shifting Up
Hi all,

A couple of weeks ago I fitted a full width intercooler and uprated turbo (Allards phase 3 upgrade) to my 90. I have adjusted the fuel pump as per instructions and am pleased with the power gain so far.

Today I finally got round to setting the boost pressure as instructed. As anyone who has done this will know it is a fiddly job on a 300TDi, hence the reason for putting it off for a while. The maximum advised boost pressure in the documentation is 18.5 PSI so I shortened the wastegate actuator arm 3 or 4 turns from its factory setting and set out to road test it. The pressure gauge was fixed to the drilling at the rear of the inlet manifold and fed through the passenger window so that I could read it on the move. Unfortunately the maximum boost pressure I could manage even travelling up hill, flat stick was only 15PSI. No matter how I adjusted the actuator I could achieve no more boost pressure. I therefore removed the tube that connects the the wastegate actuator to the t-piece and plugged it to try to see if the actuator was faulty. No difference! There never seems to be enough boost pressure to open the actuator anyway. (by the way, the actuator also seemed fine when I connected it directly to a compressor to check its operation). I even tried a second pressure gauge in case the first was faulty

I have checked and rechecked all the hoses and cannot identify any leaks. I have also pressure tested the intercooler and hoses (by means of an ingenious contraption involving a compressor and several parts of an old inner tube). It all seems fine - inflated it to 20PSI and pressure held. All I can think is that either the new turbo is faulty (not likely I wouldn't have thought) or the wastegate valve in the exhaust manifold itself is bust.

Does anyone have any idea where I should go from here? I don't really want to replace the exhaust manifold without being pretty sure it's at fault.

If you have only just fitted the Turbo, give it a few days to settle down. They do seem a bit tight for a while. I might not be spinning at top speed yet. It needs running in, a bit like a new engine.

Check it again in a few days.

Maybe the spring in your acturator is not strong enough to hold more than 15 psi, is it a factory acturator or after market upgraded one? If you are using the factory one, I think shortening the rod will only result in reaching the boost much faster (at lower rpm) but the max. boost will remains the same as the length of the rod determind how soon to reach the boost and the spring in the acturator will determind how much boost it can hold.

I did had a same problem with my turbo volvo, the acturator just max out at a certain psi. but shortening the rod did provide a lot of low rpm power.
According to Allards, the actuator on the uprated turbo is the same as on the standard turbo. However, even with the pressure feed to the actuator blanked off (ie the actuator out of the loop), there is no difference in maximum pressure. I thought that this test would produce a dramatic increase in boost pressure (25PSI or so)
If you have had it all from Allards them can't they tell you want is going on.

As far as I can remember if you change the actuator length it should increase or decrease the amount of boost.

One thing are you sure your boost gauge is working correctly.

Out of interest what fuel pump alterations do Allard tell you to do?
I have spoken to Alan at Allards several times with no result. At the conclusion of the latest conversation I was basically told that I have a problem and he doesn't know what to suggest - smashing!

Shortening the actuator rod increases the pressure at which the wastegate valve opens and so increases maximum boost (and vice versa). However, the turbo/engine is not producing enough boost to open the valve, as evidenced by the fact that the max pressure is no different with the pressure pipe disconnected and the pipe plugged.

I have tried two different gauges (in case the first was faulty) with the same results.

At this stage I have only rotated the diaphragm in the fuel pump. This is the only adjustment Allards normally recommend (though others are sometimes applicable). I rotated it clockwise about 60-70 degrees. It could go more but I stopped at that since it was starting to smoke a little. I think I may try turning up the fuel a little, in case it is a fuelling problem that is causing starvation at high revs and hence not allowing boost to build up high enough.
According to Allards, the actuator on the uprated turbo is the same as on the standard turbo. However, even with the pressure feed to the actuator blanked off (ie the actuator out of the loop), there is no difference in maximum pressure. I thought that this test would produce a dramatic increase in boost pressure (25PSI or so)

So blanking off the actuator still cannot hold boost. Maybe the wastegate cannot be perfectly closed, still have a small gap to allow exhaust to leak through it, but since it is a new turbo I will rule that out, or double check all the intake piping, from turbo's compressor housing to the intercooler, then to the intake for leaks.

For testing the actuator, pump air to the actuator and see if the arm moves, as you hold the pressure, the arm will stay extended.

Give it a week or so as Chris suggested, the new turbo may need to run in.
Its not a matter of not holding boost. I can't get enough boost. It maxes out at 15PSI. I have double checked all the piping (and the intercooler) as I described in my original post. I have also already tested the actuator as you suggested (I've even replaced it with the original, just to test it) but no difference.

The turbo has been fitted for about 3 weeks now and has had a couple of fairly lengthy off road trips during that period. I will give it a little more time but I am not optimistic since Allards reckon I should easily be able to get the boost adjusted to 18.5PSI from new. They also reckon that without the wastegate actuator limiting the boost pressure (another test I have done) I should get 25+PSI whereas I can only manage 15.
Sounds like you have a leak somewhere.

As Allard say should be able to setting pressure from new.

I think you need to check all pipes.

This is one I think we all need to hear what the solution was when you find it good luck.
The problem is - where else could it be leaking? I have already checked the hoses, pipes and intercooler. First I disconnected the inlet and return hoses at the manifold/intercooler end. I covered one end with a circle of rubber cut from an old inner tube (fastened with a hose clip). I then covered the other end with the valve part of the inner tube (again fastened with a hose clip). I inflated the whole rig to 20PSI with my compressor and the hose/pipe/intecooler combination held the pressure (until one end blew off with a significant bang!) no problem.

I can't see any signs of leakeage at the manifolds (no sooty deposits or oil stains) and there is no sound of air leaking (which Allards say there should be for such a radical amount of compression loss). By the way, I also took off the fan to reduce the amount of noise/airflow during this test.

One other suggestion that has been mentioned is that the injector pump could be faulty (ie fuel is not atomising correctly). Is this feasible on a 3 year old 90 which has only done 17K miles? (I don't think there are any facilities in the Falklands that would be able to test this unless someone has a 'simple' way of testing).

******ed if I know what to try next!
Have you checked the hose from the air cleaner to the turbo. The hoses are known to de-laminate inside closing up reducing the air flow through. Perhaps less air less power = less boost been reached.
Hi, i am no expert in turbos but i was thinking maybe your not getting you total boost due to an exhaust problem, possibly due to the cat. im not sure but this may be food for thought for some of these other guys. Im very interested to find out the problem!! Good luck
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