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SVreX
SVreX MegaDork
7/12/14 1:51 p.m.

The car is a turbo Miata with megasquirt.

The turbo is a TD04H.

I've got no boost. The car has been sitting for a while.

I'm reading a reasonably healthy 18 in-Hg of vacuum at idle. If I no-load rev it, it will move to about 5 in-Hg of vacuum.

If I rev it under load, it will max at 0. This is a standing still load- I have not launched it on the street. With the brakes applied and car strapped down, I cannot develop boost at any rpm.

OK, so I started searching. I found significant leaks at virtually every joint in the piping. Fixed them. No improvement.

Turbo spins freely. No play in the shaft, no grinding noises. No scraping, or metal shavings.

Boost gauge works. I disconnected the tubing, pressurized the line, and read boost.

I disconnected the piping from the turbo, and held my hand over the outlet while running. I could feel air flowing, but not at significant pressure. I could seal it with my hand, including when revving.

So, I am thinking waste gate. I can move the actuator rod with some resistance, but I am hearing a lot of rattling inside the housing. I am waiting for the car to cool down to pull apart the exhaust, but I am betting on the waste gate being broken/ loose/ stuck open/ etc.

Any other thoughts? Any other ideas on diagnostics?

I know I should launch it on the street under a real load, but shouldn't I be able to create SOME boost standing still?

Armitage
Armitage HalfDork
7/12/14 3:48 p.m.

I've never tried to do what you're describing but it seems like a TD04H-sized turbo should make positive boost under normal driving load at somewhere around 2500 RPM, depending on displacement. It may not be possible to get those conditions standing still. One trick we used to do with DSMs is to drop the rev limit down to something like 4500 or 5000 RPM, then sit at WOT at the tree. That'd spool up the turbo to 5 or 10 psi by the time we dumped the clutch. If you have an aftermarket ECU you might be able to investigate doing something like that as a test.

Oh, and if the boost control on that car was tuned with all those vacuum leaks present, you might encounter a boost spike when you first get on it now that they're all fixed.

edit: I see it has megasquirt, you should be able to enable stutterbox and test.

kb58
kb58 HalfDork
7/12/14 4:17 p.m.

Sounds like you've done a decent job of self-diagnosing it. Agree on finding out what's going on with the wastegate.

MrJoshua
MrJoshua PowerDork
7/12/14 5:26 p.m.

The engine may be revving faster than the turbo. It has a decently lightweight flywheel. I just tested revving while sitting in the wife's '02 WRX (lol kindle autocorrects WRX to SEX). The boost seemed to be a factor of time it took to rev. Flooring it from idle gave me measurable boost from ~4500RPM up. Starting at 2000RPM gave me 0 boost by red line. The WRX idle rev is a bit sluggish from 850-2000RPM so the whole rev took significantly longer which I think gave the turbo more time to spool up.

MrJoshua
MrJoshua PowerDork
7/12/14 5:29 p.m.

IIRC that downpipe is a giant PIA to unbolt. If you go that route I hope it gives you the answer.

Dr. Hess
Dr. Hess MegaDork
7/12/14 6:34 p.m.

If the waste gate is OK, you need to try it on the street. I never had boost on the Esprit (RIP) without the car moving.

Vigo
Vigo PowerDork
7/12/14 6:58 p.m.

It's almost guaranteed to have something to do with the wastegate puck.

MrJoshua
MrJoshua PowerDork
7/12/14 7:45 p.m.

While you're at it I'd say check the manifold for cracks just to be sure.

SVreX
SVreX MegaDork
7/12/14 8:00 p.m.

I think the waste gate rattle was a clue.

When I opened it, first off I found the bolts loose to the housing, and a leak around the exhaust gasket. Then I found the waste gate was not closing all the way.

Still haven't put it together- I'll keep you posted.

MrJoshua
MrJoshua PowerDork
7/12/14 8:08 p.m.

Awesome! Problems are good/solveable! I the wastegate rod length adjustable? Which gasket?

SVreX
SVreX MegaDork
7/12/14 8:32 p.m.

Yes, the rod is adjustable. It appears I will use up all of it's adjustment.

The gasket for the waste gate/ exhaust turbine housing cover, which technically should not effect it (it is in the waste stream after the turbine), but I guess it could have an impact, if it made the flow easier through the waste gate.

MrJoshua
MrJoshua PowerDork
7/12/14 8:53 p.m.

IIRC one of those gaskets is really hard to make seal or find or something. I think Miataturbo.net was the source of information on which gasket is hard to make work.

SVreX
SVreX MegaDork
7/13/14 7:56 a.m.

Adjusted the waste gate last night. Also found a lot of loose exhaust connections, including the joint between the turbo and the manifold.

Checked carefully for cracks in the exhaust manifold.

Got it all back together and tightened up last night. Didn't start it 'till this morning as a courtesy to my neighbors.

Only had a minute or two to check this morning, but still nothing. I'll put it on the road this afternoon.

SVreX
SVreX MegaDork
7/13/14 7:56 a.m.

It did make better sounds this morning...

Fueled by Caffeine
Fueled by Caffeine MegaDork
7/13/14 1:07 p.m.

Awesome.

dansxr2
dansxr2 Dork
7/13/14 4:15 p.m.

Is a TD04H kinda big for a Miata? I have a T3/T04E on my F2T MX-3, it comes on hard at 3-3500. For DD status I'm considering going to a T3 Super 60 later on.

turboswede
turboswede GRM+ Memberand UltimaDork
7/13/14 4:26 p.m.
dansxr2 wrote: Is a TD04H kinda big for a Miata? I have a T3/T04E on my F2T MX-3, it comes on hard at 3-3500. For DD status I'm considering going to a T3 Super 60 later on.

Depends on whether it's a 1.6 or a 1.8.

I know the TE04H is sized for about a 1.6, but Chrysler used them on a 2.5 because they didn't want to pay for the Garrett VNT's anymore. Not sure how that compares in size to the TD04 though.

Vigo
Vigo PowerDork
7/13/14 4:57 p.m.
Is a TD04H kinda big for a Miata?

That would be a resounding NO. It's just that the miata community in particular is unusually hung up on tiny turbines. By anyone else's standards, it's borderline too small.

SVreX
SVreX MegaDork
7/13/14 7:46 p.m.

Well, I put it on the road.

Now I've got too much boost!

If anyone wants to know, you can't read boost standing still on a Miata with a TD04.

Oh, and if anyone wants to know, 20 PSI is too much in a car that has virtually nothing sorted out- even the seats weren't bolted down.

NOW, I can get to work!

SVreX
SVreX MegaDork
7/13/14 7:49 p.m.
Vigo wrote:
Is a TD04H kinda big for a Miata?
That would be a resounding NO. It's just that the miata community in particular is unusually hung up on tiny turbines. By anyone else's standards, it's borderline too small.

I'm gonna agree with Vigo on this.

Even though I've got a bit much to handle right now, it is not about the size of the turbo, it's about the sorting of everything else. Once I get the suspension, steering, boost control, engine tune, harnesses, etc. etc. etc., it will be just about right.

MrJoshua
MrJoshua PowerDork
7/13/14 8:07 p.m.

There was a boost control valve attached with zip ties to the engine lift point at the front of the valve cover when we sold it. Bypassing it should get you back closer to stock Greddy boost. (6psi IIRC). A quick Google search about greddy turbos did mention the stock wastegate diaphragm being lousy.

SVreX
SVreX MegaDork
7/13/14 9:33 p.m.

Yeah, I know there is a manual boost control.

I'll start playing with it. I think I'm wanting to lock it in at about 12 psi, so I can start dialing in the other frankenstein aspects.

MrJoshua
MrJoshua PowerDork
7/13/14 10:10 p.m.

20 psi=I'm jealous

SVreX
SVreX MegaDork
7/14/14 11:08 a.m.
MrJoshua wrote: 20 psi=I'm jealous

It was pretty unhappy there...

...for now.

dyintorace
dyintorace GRM+ Memberand UberDork
7/14/14 11:11 a.m.

I hope you're able to use the MS to dial in launch control. I always thought that would be so cool to use on the drag runs.

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