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99 Turbo update - vroom vroom
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#11
 
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Re: 99 Turbo update - vroom vroom -
12-13-2004
, 05:13 PM
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Dave Hinz wrote: I thought it was just as it crossed over into the red boost, but it may have been also when I hit 6K RPM. I'll check tonight rather than second and third-guess my second-guessing. As you may have noticed, the 99T has a quite unusual boost control system that actually senses and controls the exhaust manifold pressure via a rubber diaphragm regulator. At high RPM's, (max BHP is at 5000 remember), I would expect that the added back pressure from the exhaust system will keep the needle away from the red area. If the rubber diaphragm is in good order and the wastegate valve isn't stuck, that is;-) |
header, and that has leaks.
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It's been a dozen years since I drove (a/this) 99 Turbo, until yesterday. The steering is a bit heavy, but it's a _very_ fast/responsive rack. Handles good, even on not so good tires. I plan to put on more than 3 miles tonight, but since it hasn't moved on it's own power in more than a decade, I'm going gently and cautiously. And double-checking that the wastegate is operational before you go all the way could be a good idea. I am on my second tranny and third head! A bicycle-pump will help you in revealing any leaks and perhaps you can hear the shaft moving as well. |
Dave
#12
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It's a _very_ abrupt cutoff; maybe I'm just hitting the rev limiter. Need to try again tonight and see what RPM it's happening at; I was watching the boost gage rather than the tach. The 99 fuel cutoff is really just the fuel-pump being switced off. I don't know how that feels since I don't have that feature, but I would think not quite as abrupt as total ignition misfire. The rev limiter is supposed to cut in at 6000 rpm and as far as I can tell from design, it will stay out until the rpms have dropped substatially. 6000 rpm is way beyond where I shift up and I have never experienced that. It is a simple spring-loaded centrifugal device in the distributor, quite easy to disable just for the sake of ruling out that possibility. It could be that the spring is getting old. Your original post indicates that it is boost related, not RPM. |
models. I've hit it before and it's very abrupt and unhealthy sounding as
you describe this one. The boost was set too high after replacing a turbo,
floored it and WHOOOSH *BANG* WHOOOSH *BANG* it's really amazing how quickly
boost can build up, it's *very* difficult to regulate it with the
accelerator pedal.
#13
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Volvo used a fuel pump overboost cutoff, at least on the 240 and 740 Turbo models. I've hit it before and it's very abrupt and unhealthy sounding as you describe this one. The boost was set too high after replacing a turbo, floored it and WHOOOSH *BANG* WHOOOSH *BANG* it's really amazing how quickly boost can build up, it's *very* difficult to regulate it with the accelerator pedal. |
I'm going to check to make sure the turbo bypass valve actually opens before
I wreck something. Too cold out there today to work on it, though.
Thanks,
Dave
#14
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Ah. I have no exhaust system on the car right now aside from the header, and that has leaks. Must sound interresting, Should give you more high-end boost than most 99's, |
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How do I check the wastegate with a bicycle pump, please? Locate the tube going from the exhaust manifold near where the tranny |
Disconnect it at the top cover, careful with the threads at the manifold
side, they are likely to be rusted and brittle.
Now you can verify that the diaphragm is intact by gently applying
compressed air onto the housing. There should not be significant leaks, as
that would flood the regulator with hot exhaust all the time, no doubt with
harmful results, I am not sure how much pressure is needed to crack open
the valve, especially not one that has been sitting for a decade, so if say
a moderate 10-15 psi is insufficient I would rather remove the four 4mm
(5mm? (no 4!)) nuts and the lid, thus gaining mechanical access to the end
of the valve shaft. Don't rotate it as that would destroy the expensive
rubber-diaphragm instantly! Check that it can be pushed in and that it
comes out again by itself.
BTW, the big, locked nut at the end of the shaft is of course the place to
adjust the boost. Increased spring pretension results in more boost.
You may want to go the other way at first. That will exersize the wastegate
system a bit extra too.
--
Frode
#15
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Dave Hinz wrote: Ah. I have no exhaust system on the car right now aside from the header, and that has leaks. Must sound interresting, Should give you more high-end boost than most 99's, but I don't think that is the source of your problem. |
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How do I check the wastegate with a bicycle pump, please? Locate the tube going from the exhaust manifold near where the tranny dipstick is located to the aluminium top cover of the regulator housing. Disconnect it at the top cover, careful with the threads at the manifold side, they are likely to be rusted and brittle. |
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Now you can verify that the diaphragm is intact by gently applying compressed air onto the housing. There should not be significant leaks, as that would flood the regulator with hot exhaust all the time, no doubt with harmful results, |
Pushes down on the diaphragm to open the bypass valve, yes? An elegant
solution.
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I am not sure how much pressure is needed to crack open the valve, especially not one that has been sitting for a decade, |
which should be the same enough for these purposes (yes?), it looks like,
well, a valve valve. Could be stuck to the seat, could be stuck
along the stem. Probably want to take the top off as you mention just to
check that, being that head gaskets aren't cheap and all.
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Don't rotate it as that would destroy the expensive rubber-diaphragm instantly! Check that it can be pushed in and that it comes out again by itself. |
things anyway.
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BTW, the big, locked nut at the end of the shaft is of course the place to adjust the boost. Increased spring pretension results in more boost. You may want to go the other way at first. That will exersize the wastegate system a bit extra too. |
it travel more and un-sticky itself, in thory at least. Sounds reasonable.
There'll be more updates, oh yes, I guarantee it.
Dave Hinz
#16
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Ah, so this is how it measures the boost pressure, through that line. Pushes down on the diaphragm to open the bypass valve, yes? An elegant solution. Not very precise, but less prone to oscillations. I'm sure the fact that the |
99-engine's reputation for "ketchup-effect".
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So if I turn down the boost until I get a feel for everything, that'll make it travel more and un-sticky itself, in thory at least. Sounds reasonable. |
-------------------------------------------------
PSI Bar Turns in/out to obtain correct
12.5 .86 1 out
11.9 .82 3/4 out
11.3 .78 1/2 out
10.7 .74 1/4 out
10.15 .7 0 (Correct value)
9.6 5 .66 1/4 in
9.0 .62 1/2 in
8.4 .58 3/4 in
7.8 .54 1 in
-------------------------------------------------
Another thing just came to my mind:
Back in the days when this was my only car, I reduced the pressure to .5 bar
or so, since I ran out of spare heads. This resulted in an annoying noise
that I chased for a year before I realized it was the wastegate valve
hammering the seat almost from idle. Had a minor crack in the exhaust
manifold removed and welded without any effect amongst other things!
--
Frode
#17
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Ah, so this is how it measures the boost pressure, through that line. Pushes down on the diaphragm to open the bypass valve, yes? An elegant solution. Not very precise, but less prone to oscillations. I'm sure the fact that the valve opens in the upstream direction most likely contribute to the 99-engine's reputation for "ketchup-effect". |
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So if I turn down the boost until I get a feel for everything, that'll make it travel more and un-sticky itself, in thory at least. Sounds reasonable. Some info from Heynes no. 247, p 246 ------------------------------------------------- PSI Bar Turns in/out to obtain correct |
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Another thing just came to my mind: Back in the days when this was my only car, I reduced the pressure to .5 bar or so, since I ran out of spare heads. This resulted in an annoying noise that I chased for a year before I realized it was the wastegate valve hammering the seat almost from idle. Had a minor crack in the exhaust manifold removed and welded without any effect amongst other things! |
and leave it there. It should be zippy enough as it, I should think. What
is the output of this engine, 160 Horsepower or so, right?
Dave
#18
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I'll probably set the base boost (wups, boost I mean) to normal spec and leave it there. It should be zippy enough as it, I should think. What is the output of this engine, 160 Horsepower or so, right? |
US model: 135 bhp @ 5500, 216 Nm @ 3500 rpm @ 0.5 bar, cat. yes?
UK 145 bhp @ 5000, 235 Nm @ 3000 rpm @ 0.7 bar, no cat.
Compression ratio: 7.2:1 !
Note!
Pressure switch actuating pressure: US0.7 bar, UK 0.9 bar.
FYI, I operate it at 0.8-0.9, unleaded 95 octane since mid-80's, no problems
except wheelspin in rain when careless (short wheelbase). Rust is my main
problem, so...
--
Frode
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