How to check out the CT26 Turbo condition

Introduction

The biggest requests that come to me is how to check the condition of the turbo. So I've written this page so that the DIYer can perform a moderate check on the turbos current state. You will need to learn some turbo terminology & physics, thats unavoidable, but I promise to keep it to a minimum. (Skip to the bottom if you already know all this.) Whoops! I apologize but for some reason the Checking the turbo section was cut off on the web site for some reason. It's there now!!

TURBO 101

Before you go headfirst into checking out the turbo, you should know a few things, especially how it works.
Everyone basically knows a turbocharger on an engine which yeilds to more power right? Well how does it do this?

The turbo charger is actually a device consisting of two main components, a compressor and a exhaust turbine. (see illustration) Each section has a specially shaped wheel with fins, connected to each other through a single rod. The compressor wheel is on the air inlet side while the exhaust wheel, called a turbine, resides in the exhaust flow. The turbo works in this manner:

1)Hot and fast (high energy)exhaust gases are forced through the turbocharger's exhaust turbine section, which creates rotational movement of the turbine wheel. (Many think it moves because the gases are hitting it, but in actuality it's the high energy gas expansion from cooling).
2) As mentioned the turbine wheel is connected to the compressor wheel, so the compressor wheel (similar to the turbine wheel but opposite) moves at the same rate (proportionally). This movement of the compressor wheel, forces air into the engine at a higher rate than the engine would by itself (which normally is under vacuum). This allows more air in the cylinder per power stroke. This also creates heat, I'll discuss later.
3)More air means more fuel can be added.
4)More fuel to burn allows greater power per stroke, and produces hotter exhaust gases.
5)These hotter gases in turn move the turbine and causes it to spin faster creating even more boost.

So at higher RPMs you produce more exhaust energy for the turbo and thus produce more boost (up to a point). At full boost the turbo can spin in excess of 45,000 RPM (NOW THATS FAST). Smaller turbos spool up faster (less rotational intertia) than larger ones also.

Wastegates

Naturally you can see that the boost would keep going up (or creep) to the limits of the compressor, engine, exhaust rate or any of the above. This effect is also called positive feedback. Additionally the higher the boost pressure, the more fuel you need. If you go lean (no fuel) you can kiss that engine good bye. Therefore the boost level must be controlled. This is handled by a device called the Wastegate. It is actually a door (or valve) that opens and shuts out exhaust air from actually entering the turbine area of the turbo. When it's open it allows air to go straight out the tailpipe(well almost), and thereby "wasting" energy. While closed it directs the exhaust to the turbine, which it must pass by to get out to the exhaust. So let's look at it during a typical operation:

You wanna pass up this SUV, so you romp on the gas.
The engine's computer senses you want more power, and closes the wastegate.
Exhaust gas enters the turbine and begins to turn or "spool" up (50,000 RPM +).
As it spools up the compressor pushes more air into the cylinders.
The computer dumps more fuel in producing more power
The wastegate will monitor the pressure build up, and will open as soon as the set boost pressure is reached.
The wastegate then begins to actuate between open and closed to keep the boost pressure regulated.
You've blown away the SUV and you back off the throttle, the wastegate stays open.

In the MR2 Turbo the Wastegate is vacuum controlled, with the amount of vacuum correlating to a specific boost level (although not linearly). This vacuum line pressure can be adjusted creating lower or higher desired wastegate set points, and thus alter boost level. Be carefull when modifying this, if you create a condition that prevents the wastegate from doing it's job, you could destroy your engine!!! The last thing to keep in mind is the wastegate can only flow so much air, and if you exceed this you'll start getting boost creap. Thus the larger the turbo & boost you typically need larger wastegate. Also, as a side note, if you never seem to get any boost the wastegate may be bad.

So you with me so far, but still don't know why you have an intercooler, blow off valve (BOV), or even why the darn thing is so expensive to buy or fix!!!!

Intercooler

Unfortunetly, at least while physics rule, compressing air builds pressure, pressure is heat, and excessive heat is bad for an engine. Higher temperatures increase the risk of detonation. Not to mention air at higher temperatures is less dense and than colder air, and therefore produces less power in the motor. Having high temperatures also create more wear and tear on an engine, which is why the MR2 Turbo is somewhat less reliable than a normally aspirated one. An intercooler is much like your radiator except meant for air, in which cools the heated compressed air back down to tolerable temperatures, which increases power. The larger the intercooler the more air it can cool. Intercoolers also can become "heat soaked," which decreases it's ability to cool the air because the difference in the intercooler temp and the air temp is smaller. Have you've ever noticed that a MR2 Turbo (or any other)takes off with a little more ummph after idling for a few mintues??? This is because the intercooler is no longer heat soaked, and keeps the air colder than while it was chirping along with hot air at 3500 RPM. Any time you increase boost your going to create more heat, and you should upgrade to an intercooler that cools more air. This also increases reliability and power of stock 3s-GTE, put does lower the pressure a smidge.

Blow Off Valve(BOV)

If you've ever driven an MR2 turbo you've heard a kind off "psss" or "hisssss" during shifting under boost. That noise is the blow of valve venting compressed air out. HEY, why are we venting out good compressed air?? Well imagine what happens when you shift:

You take your foot off the gas which closes the throttle plate
with the intake manifold closed, the air has nowhere to go
This builds up allot of pressure (and pressure = heat) 'cause the turbo's still spinning
The pressure then probigates back to the compressor wheel, with an effect like trying to grind a turkey with the garbage disposal.
Least to say the longer this occurs the more it slows the turbo down and puts high stress on the turbo's components.
The boost will come down as the turbo slows
Enter the BOV, it senses the pressure build up, and opens up the line venting it to the outside world in a big "Hissss" or back into the inlet of the turbo.
The venting releives the pressure and the turbo doesn't slow down
now your back on the gas and you've got immediate boost (although lower than before you shifted)available because the turbo didn't spool down.

Typically the more boost you can produce, the more you need to vent during shifting, which can lead to bigger BOVs. The MR2 Turbo is setup to vent the air back into the intake, which produces less noise than an atmosphere vented one. In racing cars a BOV may not be needed cause the mechanical punishment may be acceptable, but for our use a BOV is great for keeping the turbo alive longer.

The problems with turbos...

In today's world we've improved technology to the point that engines are running up to 9K RPM for commercial sports cars. Do you relasize how hard that is, getting things moving that fast? It's tuff and the turbo is a 45,000 RPM BEAST(Actually this was incorrect it can reach 110,000RPM). As my professor used to say "speed costs money, how fast you wanna go?" The materials that make up the compressor wheel must be extremely rugid and leight at the same time. The heavier the material the longer it would take to spool up. Then you come to the very special design of the "fins" on the wheels. They are specially shaped and curved to optimize for either compression or vacuum rotation (compressor & exhaust wheels respectively). The bearings that two wheel and shaft assembly must rotate on must also be highly durable to heat and 100,000RPMs. Typically these are oil cooled, with some turbo's also having water cooled ability. All in all the turbo is built to last, with the bearings and other seals taking there toll. In fact all turbo's that are shown to have some bearing or seal wear early, typically only require those components to be replaced. These pieces are pretty affordable, so how come they charge 500$ to rebuild it. Well for one, it's extremely hard to take apart without the right tools, and another is the high speed balancing. You heard right "BALANCING." Everyone has their tires balanced right? Well those only go about 1220RPMs at 80mph. So how do you expect to buy a little DIY turbo rebuild kit and expect to have it balanced right? Ok, so there's more intertia in wheels than the turbo but still, 1220RPM VS. 110,000 RPMs...you do the math :P. There are currently only a couple equipment manufacturers that make machines to properly balance turbos. So the rebuilder will perform this balance and check to maintain all other components are fine. A single turbo can last a long time, if you watch for the signs, and check your turbo every 6,000-10,000 miles.

Checking the condition of your TURBO

Ok so you know a little about turbos now and you feel enlightened & ready to check out the turbo right? What!!! You skipped that part?? Don't worry I'll explain how to check it all without allot on lingo. Unfortunetly the BGB and other guides are a PASS / FAIL type of testing procedure, and this just isn't good enough. The approach I have taken is to evaluate the current CONDITION, and how long in it's life cycle the turbo and it's systems are at. Many Toyota mechanics are quick to say "Yeah your Turbo is gone and blah, blah, blah..." meanwhile they are thinking *CAACHING* easy money. In fact from talking to other turbo car owners, dealers seem to aim their first sites at the turbo, even though the real problem might be ignition, Blow off Valve or even a simple Vacuum leak. As I mentioned above the two components of a turbo that will fail first are the seals and bearings. Once those go...well I'll tell you the effect of these as we check 'em. I recommend doing this test before you purchase a MR2 turbo. O.K., let's get our hands dirty.

We'll start out by doing a physical check of the turbo. I recommend taking the corners easy the day you plan to do this, I'll explain why later. Wait 'till the car is nice & COLD. WARNING: You will be in and around the HOTTEST parts of your MR2's engine, DO NOT perform these tests if even just WARM, and always use rags and other hand arm protection. All you will need is a phillips screwdriver/or 10mm wrench/driver, and some pliers. Loosen the intake pipe elbow brackets, that connects the Air Flow Meter (Big Black/metal Air filter BOX on the left) to the intake tube to the turbo with a screwdriver or 10mm socket/wrench. (Pics coming soon) Remove the Blow OFF Valve(BOV) recirculating tube from the BOV. The BOV is that black device on the tube that runs accros the back of your valve cover to the intercooler. I Don't recommend removing this metal tube from the intake pipe going to the turbo, as that clamp is INCREDIBLY hard to get back on/off while still on the turbo. Remove the PCV tube from the Valve cover to the turbo intake pipe. Now you should be able to loosen the last tube clamp holding the turbo intake tube to the turbo. It may take a little twisting and then it should pull out straight to the left. Now we'll have a look at the intake "mouth" of the turbo, and compressor fins. Additionally the tube from the intercooler to the throttle body section should also be removed.

(1)Look to see if there is a standing puddle of oil on the turbo intake. MR2s naturally have a little oil here from oil/oil gases that came out of the PCV pipe from the valve cover. During Hard right hand cornering oil will shift to the left of the head and leak out the PCV into the intake tube. Many have replaced this tube with a K&N Vented Catch can to reduce this, but that's another discussion. Now, back to that puddle (if you have one). NO OIL - to maybe a 1/8"-1/4" puddle is probably normal. Puddles larger than this indicate either medium-hard cornering during your last drive, or that the oil seal(s) on the compressor side of the turbo are leaking.
(2)Look in the Throttle body for puddles of oil also. There should be none to VERY VERY LITTLE here. If an excessive oil puddle was present at the turbo and here then your turbo has begun to wear through it's seals and are literally SPITTING oil into the system, which reduces your octane level. This really pushes your ignition system, and causes poorer acceleration and starts to guck up your intake fast. The bigger the puddle the worse your turbo seals, even BEARINGs are, and the closer to the end of the turbo's life your at.
(2)Look at the intake tube for Oil/carbon residue, with a thin layer being normal, but a buildup additionally supporting that you have a bad seal in the turbo. If you have oil puddles and buildup in the tubes and throttle body, just imagine what the bottom of your intercooler looks like!!!!
(3)Now Shine a light at the oil residue in the intake and all air tubes, and look for TINY, almost dust-size particles of metal. YES METAL. As you'll soon see, the turbo's bearings/seals can be so worn, that it allows the compressor fins to hit the turbo housing. This friction chips away metal from the fins and spits them everywhere!! THIS IS VERY BAD!! Metal in the engine will wear down rings, cylinders, rod & main bearings, etc...the list goes on and on, and the engine is most likely already damaged. The turbo is DEAD & Unless you plan to buy a new engine...I wouldn't purchase the car. If it's yours, count on a rebuild sometime soon.
(4)Still with me? Ok, shine a light into the turbo intake such that you can see the fins. If there are carbon deposits on the fins, then again it's sucking in allot of oil and/or reciculated gases from either a leak elswhere or the turbo seals are bad or going.
(5)Now for the touchy feely stuff. In most cases you don't have the time or acces to a dial gauge, so we'll go by feel. This is the final determination of the life cycle state of the turbo. Using a non-lint rag on your hand, reach into the turbo intake, and feel for the fins. Rotate the fins(part of the compressor wheel) CW. You should feel NO DRAG WHATSOEVER. If it was sticky at first and then rotated, then your turbo shaft bearings are going/gone and it's probably at 85-95% of it's life. If it is free running from the begining then you've passed this step.
(6)Ok now, move your hand to the middle of the wheel to the bolt. Check the axial (IN & Out) play. This is a good test for the seals & bearings, but primarily the seals. A good "touchy feely" method I've used is that if I can feel movement, then it fails to be in spec. The TOYOTA BGB says the AXIAL PLAY is to be 0.13mm(0.0051 in.) or LESS. Most people cannot "feel" this small amount so if you "feel" movement you can definantly say it's out of the spec. If you have a dial guage you should use that instead. Ok, so you say "If it's out of spec, how long do I have?" Well, I will explain all that later below. Most turbos I've tested unless within 60K miles of being rebuilt will fail this "feely" test. BE SURE not to just think there is movement, be SURE there IS movement.
(7)Now, we'll check radial play (UP & DOWN). Again using the "feely" method if you notice movement, the bearings/seals are definantly bad. You can use a dial gauge as the BGB says through the top oil inlet...consult the BGB for this. The Radial play should be 0.18mm(0.0071in) or less.

OK!! NOW you've finished checking it over, either by my "feely" method or an exact method using a dial Gauge. So how do you tell how far along the turbo is? First I'll describe what I consider the turbo's life span:

0-25%- Turbo is like new and in Specifications, no oil leakage, 100% power& spool up
26-50%- Still in Spec, VERY slight oil leagage, 95% power/ 100% spool up
51-60%- Turbo may be out of spec, but may not be felt by "feely" test, Slight oil leakage, 90% power & spool up CAUTION: Just because it passes the "feely" test does not mean the turbo is good, a dial gauge is then needed to be sure.
61-70%- You can now sense movement with my "feely" method. 85% Power/ 75% Spool up
71-99%- Movements around 0.5-1mm can be felt by "feely" 75-80% Power/ 65-70% Spool up
100% - Compressor wheel hitting turbine housing, throwing metal. 60-75% power / 50% Spool up

Most of these numbers are Fly by the seat feeling/approximations and aren't verified, whatever you choose to do with your turbo is up you. This comes from my experience with my MR2 Turbo, that the turbo ran in my car for 160K miles (YES it was the ORIGINAL TURBO).

Power is specifically the total output the turbo can deliver. Say it pulled 9 PSI when new...it might be down to 7 PSI. THATs 25%. (By the way the normal boost range stock is 7.1-11.8 psi, 49-81kps. Spool Up refers to the amount of time the turbo takes to SPIN up to rated speeds. IE. 50% means it now takes twice as long from when it was new to spool up to X RPM.

If you've used my touchy feely test, and found movement, then your turbo can be anywhere from 60%-100% of it's life. The amount of play really determines where from 60% the condition of the turbo really is. Mine didn't have movement at 70K but did at 86K...I still had it in my car at 160K, and at that time I coud feel between .5-1mm of movement!! The turbo was so bad then it spat so much oil that the ignition could keep up under any real boost. I'd say if you can feel movement under .25mm(thats 'tuff) Your at 60% and .5mm 80% & 1mm your at 90%, while metal particles indicate totally dead, not even rebuildable without a new compressor wheel turbo. In all I would recommend rebuilding the turbo SOON if you can feel movement. However, as I have indicated you can wait longer, but that means more and more oil get's into your engine, performance goes down, and your ignition system gets more and more overtasked. From when I could feel it at 86k miles I went to 160K before rebuilding it(Hey money was tight), mine wasn't flying metal, but it couldn't keep pulling off the 14PSI I cranked it to and I was replacing the ignition components like mad.

The BOV & Other items to look/test for...

Here are some other little tidbits to aid in the verification of the turbo being a problem while running. Also a quick way to seeing if your Blow Off Valve is going bad.

Install a boost gauge and monitor your STOCK boost and see if it's repeatable, and steady. If you find boost falling of quickly while keep the throttle down, the turbo is having problems...this can be due to bearing resistance, or that the BOV is failing to say closed at the high boost levels.
When the car is cold listen for Clacking when bliping or on the throttle (sitting still is best). Usually the clacking stops after it's warmed up (1-2 minutes or so). This is a definant indication your BOV needs to be replaced. Toyota wants 175$ for this part so I recommend a performance aftermarket like Blitz or Zen.
If your car hesitates under full boost it could be your ignition system. If you replace your plugs,rotor, wires, & cap. And the problem continues then your turbo is spitting allot of oil, reducing your octane level and the ignition simply can't fire the cylinder. Rebuild the turbo and your problems should clear up.

Well that's all for now. If ANYTHING is unclear just send me an e-mail to MR2MKII@aol.com. I hope this has & will help!!