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Old 09-12-2007, 03:40 PM   #1
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Base Boost Adjustment - FAIL !

I went to adjust the base boost in my '89 convertible. Pulling the APC box I get maybe 1/4 into the yellow under full throttle. IIRC stock base boost is 5.5 psi, which is 1/2 of the yellow or so.

I have a modified APC box which when installed in any other c900 turbo easily boosts well into the red. In the convertible, it manages only to get to the top of the yellow.

So under the car I go. I shortened the rod as much as I could. After 2 or 3 complete turns, the rod itself stopped moving, and the whole rod assembly starting turning (and turning it at that point was not making it shorter). Figuring that was as far as she goes, I stopped. The rod was noticeably shorter than it had been before.

But when I went to test drive, there was absolutely no change at all in boost behavior. Still 1/4 yellow at best, and with the APC box, still maxed out at the top of the yellow.

So what's the deal? Busted wastegate?

As an aside, the very small C clip at the bottom of the connecting rod fell into the chassis and disappeared into the void where all lost pieces go. I was able to wrap the wire around the connection and it seemed pretty well secured, but is that something that I should sorry about replacing?
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Old 09-12-2007, 03:49 PM   #2
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are you sure the rod was not just spinning inside the wastegate? with those old rusty wastegates, you got to grab the rod at the wastegate spring side with a vice grips or something, then turn the nut while the rod is still attached to the wastegate at the turbo side.
Could be that the actuator is just shot, or the T3 is all full of cracks... but it sounds like the rod was just not made short enough.
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Old 09-12-2007, 07:23 PM   #3
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What he said. You really need to connect up a calibrated gauge.
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Old 09-12-2007, 07:47 PM   #4
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Well, there was enough shortening in the rod for me to expect some change in the way the car drives, or notice a change even in the uncalibrated stock gauge.

When I say there was no difference in how the car drove or what the gauge displayed, there was absolutely no difference. Not even a tiny, possible, little, "missed it if you blinked" kind of difference.

From what I read online, three full turns is like 1.5 psi difference. Which ought to show up some how, if it's really there.

I'll try some more with the vise grips. But my gut tells me that's not to change anything either.
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Old 09-12-2007, 09:09 PM   #5
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If you're measuring basic boost, 3 vs 4.5 won't feel like much, which is why you need a calibrated guage.

I also don't think it's particularly linear, based on my experience. Most likely the reason why it would be low is because the spring is getting tired in it's old age, which could also throw of the official ".5psi per turn".
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Old 09-12-2007, 09:46 PM   #6
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yeah those really old wastegates are almost always all worn out. got to shorten em up quite a bit to get even normal base boost of 5.5-6 PSI...
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Old 09-13-2007, 06:18 AM   #7
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Hell even on my Viggen the adjustment nut was pretty rusted to the rod. I had to use some Liquid Wrench and channel locks on the rod while turning the adjustment nut to break it free.

If you're sure it did shorten the rod and nothing happened, you should check for a vacuum leak.
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Old 09-13-2007, 06:45 AM   #8
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Funny, I did this exact thing last night, too. But damned traffic around here, there was only one stretch of road where I hit full boost in 3rd (I was en route to pick the gf up from the metro, no time to tool around). I didn't see any more boost, but then again the car wasn't hot yet, and it needs to be to seal up the leak in my exhaust manifold I heard that it's not good to tighten the stock wastegate act. rod to far, limits wastegate travel or some such nonsense, what are the other options? I was thinking MBC between the APC solenoid and the WGA...will that help with "tired springs"? Before I adjusted it, baseboost was "very little into the yellow," didn't really have time to see how far I got it now. Is a new WGA my best option for a 'tired spring'? What's this "helper spring" nonsense? That sounds cheap and good...
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Old 09-13-2007, 07:15 AM   #9
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I heard that it's not good to tighten the stock wastegate act. rod to far, limits wastegate travel or some such nonsense, what are the other options?
See the recent TSL thread about wastegate springs. It's true you do not want to make the wastegate actuator rod too short because it will start to reduce the maximum amount that it can open. This can lead to base boost creep. Say you have 7PSI between 2000-4500 RPM's, but then it will rise up to 12 PSI by redline.... very un-safe especially with a stock ECU.

Pop a wastegate spring on there, and you can get correct base boost out of the thing as well as have a correct length wastegate rod.
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Old 09-13-2007, 07:20 AM   #10
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Yeah, I don't see why people think that an extra spring on the wastegate is a bandaid, no-good fix. The no-good fix is to make the WGA rod super short, you end with boost creep as DeLorean pointed out.

The reason the wastegate is not holding boost is because the spring inside is not stiff enought to hold the boost, so adding another spring, or replaing the spring inside is the better fix rather than making the rod so short that the WG can't open fully.
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Old 09-13-2007, 08:59 AM   #11
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So the external "helper" spring (Home Depot Mod) would work just as well on a C900 to adjust base boost?
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Old 09-13-2007, 09:18 AM   #12
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Some additional data points after re-examining the situation this morning:

1. the rod is as short as it can be. It's not rust or dirt or anything, it's all the way short. The 11mm nut at the end of the rod will continue all the way down to the actuator, but the rod itself stops about 1/2-to-3/4 of an inch short of that.

2. still 1/4 yellow boost max, at WOT, with the rod in this position (actually that's generous, it's probably more like 1/5 yellow)

3. no apparent vacuum leaks, without being incredibly thorough, a quick look shows no split lines

4. I took the vacuum hose off the actuator, which should produce uncontrolled boost because the actuator never gets a signal to open the wastegate. That worked. I did not dare try WOT given how high the boost was going - I was easily getting into the red and climbing with 1/3 throttle.

I think this boils down to a very weak spring that needs replacement.
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Old 09-13-2007, 09:22 AM   #13
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Quote:
Originally Posted by amish_geek View Post
So the external "helper" spring (Home Depot Mod) would work just as well on a C900 to adjust base boost?


first you'd want to try getting good base boost without it... if you have to make the actuator too short to get correct base boost, then adding a wastegate spring (or just replacing the wastegate actuator) is the next step.
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Old 09-13-2007, 09:23 AM   #14
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Yeah I think I'm in the same boat greg, but I dont have the time or the patience to open up the WGA. I'm gonna try the helper spring, maybe this weekend, I'll try and take some snapshots if it works.
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Old 09-13-2007, 12:40 PM   #15
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Greg I've got an extra T3 wastegate actuator laying around and no T3 turbos so if you would like it, its yours. My forgetful self still has not sent out a box to Palmer, hopefully tomorrow, so I could throw it in there.
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Old 09-13-2007, 12:48 PM   #16
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Quote:
Originally Posted by 90SPG View Post
Greg I've got an extra T3 wastegate actuator laying around and no T3 turbos so if you would like it, its yours. My forgetful self still has not sent out a box to Palmer, hopefully tomorrow, so I could throw it in there.
Thank you, that's very generous - I'll take you up on that.
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Old 09-13-2007, 12:50 PM   #17
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I have a t3 turbo with shaft play, attached to a wg. Not sure if these turbos can be refurbed and changed for any signifigant power gain. But this would be a good canidate.
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Old 09-13-2007, 05:14 PM   #18
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Greg, you should also go to the local checker, and pick up a cheapo boosties gauge. I think they are about 20 bucks...


It's real easy to hook up, and we can swap between both of your cars for "tuning Purposes"


Also, Phil, if you wanna toss that into "the box" I'll make sure Greg gets it.
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Last edited by Palmer; 09-13-2007 at 05:40 PM. Reason: STFU GREG
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Old 09-13-2007, 05:17 PM   #19
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Porpoises? Why would I want to tune porpoises?

What? Purposes, you say?

Oh, never mind.

/Emily Litella
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Old 09-13-2007, 08:03 PM   #20
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Nice thing about the C900Ts, you can remove the drivers side speaker grill and reach in and disconnect the vacuum hose from the stock boost guage and temporarily connect it to a calibrated guage. I've got a 3 or 4" gauge that I used for those purposes. Of course, I don't ever work on C900s anymore so I haven't used it in several years.
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