Suddenly Lost Boost-Turbo Appears OK-'90

[Milanodan]

This is what I get for being lazy. Needed a starter for my '90 turbo. Normally I would do this job myself, but I got lazy and took the car to a small local shop. They have done good brake work for me before, but this time it's a disaster.

Pick the car up and the young mechanic who installed the starter said, "Your turbo isn't spinning up". Strange, because he shouldn't even be driving it after a starter installation.

Drove it home and sure enough, the familiar turbo whine on accel. wasn't there, and the boost gage didn't move. It also didn't accelerate like it should have--pulled like a good N/A Supra does. No tailpipe smoke either.

Installed a known good mechanical boost gage plumbed directly into the "intake air chamber", and can only get ~1 psi now. The mechanic had removed the air chamber to get more room to work on the starter, and I know he used a new gasket. Checked all 5 bolts; they are tight.

Pulled the turbo off, expecting to find broken wheels, etc. Nope, both wheels are fine and the shaft appears to have no end play. There is some radial play in the bearings, more than I think is OK. All the usual stuff is fine too--hoses, throttle opening fully, etc.

Anyone know a place where they can test this turbo before I have to spend big $$$ getting it rebuilt?

 

[Supracentral]

Installed a known good mechanical boost gage plumbed directly into the "intake air chamber", and can only get ~1 psi now. The mechanic had removed the air chamber to get more room to work on the starter, and I know he used a new gasket. Checked all 5 bolts; they are tight.

Your mechanic is an idiot. There's no reason to touch anything related to the turbo or intake in order to service the starter.

With that said, I strongly doubt you have a problem with your turbo. It sounds more like your knucklehead mechanic created a boost leak. Check ALL of the piping, trace the entire intake path. You've got a leak. And since you know knucklehead jacked with the manifold, I suspect that is exactly where your problems are.

Anyone know a place where they can test this turbo before I have to spend big $$$ getting it rebuilt?

Honestly you're wasting time and money there. I'll give you 10:1 odds that this isn't a turbo problem.

 

[TurboStreetCar]

Agreed, do a boost leak check and look for intercooler pipes not properly affixed and/or vac lines mising.

 

[Milanodan]

Thanks for the replies! I sure hope the turbo is OK. Yes, I now know the young mech. is a clown--what I didn't know is that he would be the one working on the car.

Given the large amount of airflow out of a good turbo, I'd think any air leak would have to be pretty big to lose ~8 psi, right? Also, the usual turbo whine on spool-up was gone. I found a fairly local guy who works on MR2's--of which I have a '88 supercharged one. I discovered the later turbo MR2's also use CT26 turbos--must have smaller trim. He is going to take a look at the turbo and give me his opinion, plus he told me who he uses to rebuild them in Texas. We'll see on Saturday.

This car had been rolled into a snowbank back ~'91 or '92, and was considered a total--didn't even break the windshield. It spent ~6 years in a body shop where the owner SLOWLY fixed it. I found it on eBay with 62,000 miles--paid $3200 in '05 for it. Flew (thanks, Delta-air miles) from Phoenix to Dayton Ohio and drove it back--no problem.

BHG a year later--fixed that myself, OK ever since. Car now has ~105,000 mi.

 

[SupraMario]

All I have to say is WOW, the starter isn't even on that side of the freakin engine bay.

 

[DigityD'87]

This is why no one touches my car. That truly sucks bro. Search up the thread on how to make a boost leak detector. Its a very simple procedure but I believe it does require a small air compressor. People claim to have spent just $25 at home depot making them.

 

[Milanodan]

Did some more checking and it appears the radial play in the shaft is more than I first thought. Also found a small, tight crack in the exhaust casting right where the waste gate seals, but it's not big enough to flow any exhaust.

The waste gate itself appears fine, including the flat seal area. It moves freely, and the actuator spring is fine.

I don't suppose anyone makes a direct bolt-on replacement turbo that has ball bearings? Don't need more boost, just long life.

Hmmm, a nice set of ceramic ball bearings----!

 

[Kevin]

make ur mechanic fix everything. since he wasnt supposed to drive your car anyway... and since u said that it was boosting before and not after he changed the starter.. he did something to fuck it up..

 

[Milanodan]

This repair shop is a small pretty non-tech. place--mostly a tire and small repair shop. I just got lazy (hell, I'm 68 years old) and thought they could do something simple like a starter motor--which IS hard to get to. So no way am I going back there.

Just got off the phone with the Texas rebuilding place and they agree-the turbo is OK. Told me my radial play is fine as long as the wheels don't rub--it's the axial play (thrust bearing) that would concern them.

SO, I am going to put this turbo back on, do the pressure/leak test, and cross my fingers.

 

[Milanodan]

Right after the starter replacement, I noticed the stock boost gage wasn't working, and I also could hear a new sound when idling--a hissing noise right behind the factory gage. I then teed a small tube into one of the vac. lines behind the drivers side of the engine (rear), ran it thru the firewall and used a known good mechanical gage. Discovered boost was way down to ~1 psi. I also noticed that when I pulled the gage out of the new tube, the hissing noise stopped. When I put my finger over the end of the open tube, the noise returns--every time. I've heard that there is NO vacuum line connected to the stock boost gage--it's electrical, but it sure sounds like a vacuum leak right behind the gage.

Then I removed the tee fitting and plugged the line directly into a small brass nipple I put directly into the rear of the air chamber--still only 1 psi. Anyone have a photo of the stock boost gage sensor/sender/whatever it is?

 

[Supracentral]

 

[Milanodan]

Thanks. All the wiring and vac. tube associated with it appear to be OK, but the sender is right where the "mechanic" was working.

I still don't understand what is making the hissing noise.

 

[Supracentral]

There are vacuum/boost lines all over the firewall. What you're describing is more than a "minor" boost leak. It's got to be a fairly large line, or the manifold itself is leaking.

 

[Milanodan]

Yup, these cars have vac. lines all over the place. I didn't mean to imply that a small vac. line could cause the loss of all that boost. Just seems strange that at the same time the boost was lost, the stock gage quit too. Idling w/o boost it should be pegged all the way down, but it just sits there just below the 0 mark. The hissing noise is a mystery too. BTW, it idles smooth as silk.

My friend is coming over soon to help me put all this stuff back together. We'll see what happens.

 

[Milanodan]

Turbo is back on and making full boost. We found a big hole in the mech. gage line I had run thru the firewall--soft silicon rubber tubing. Real clever of me! That's why I wasn't getting the boost on the mech. gage.

So now the factory gage is reading again, except it stays pinned all the way down to -4. At least it's getting some kind of signal where before it wasn't. Now all I have to do is figure out which wire carries the boost signal voltage up to the gage--must have a break in it.