FD3S:Twin Turbo Troubleshooting
Troubleshooting Sequential Turbocharger problems:
Primary Turbocharger
You first need to get the Primary Turbocharger working before attempting to fix anything on the Secondary Turbocharger. The Secondary Turbocharger requires the Primary Turbocharger to generate more than 8 psi of boost to operate actuators that control the Secondary Turbocharger.
When you first start looking around the engine bay you may notice more than a few vacuum hoses, well most of them are under the intake manifold, check out the colored vacuum hose diagram. Do not be too alarmed about this, as the trouble shooting typically narrows down to a couple of actuators and or hoses.
Primary Turbocharger Leaks
In order for the Primary Turbocharger to operate and generate more than 8 psi of boost check the items indicated on the Primary Turbocharger Leak Diagram. The items below are on the diagram and are listed in most likely to fail order:
Y-Pipe connector hose, (coupling)
* This is a very common failure part. This short hose, (coupling) will split and vent boosted air in copious amounts. The trick with this one is that when just looking at the part on the car it will look just fine. You need to remove the 90 degree plastic duct on top and completely remove the rubber coupling, then examine the rubber coupling by gently stretching it to see if there are any splits. Typically costs about $47 at dealer.
Check ~1" diameter hoses for leakage
* If you can rotate these hoses while attached, then the clamps are too loose. Get properly sized screw-clamps if the stock ones are not up to the job. New hoses will also help, but usually tightening the hose clamps is enough. A sign that there is air leakage is the presence of oily dirt on the aluminum casting around the hoses. New hose-clamps will set you back about $10 maximum for good ones. Note, clean up the oily dirt around the aluminum so that you will be able to see if these hoses start to leak again, (carburetor-cleaner works great).
Primary Turbo Inlet
* Typically collapses under high volume air through air cleaner into Primary Turbocharger. When the engine bay is hot the rubber is more prone to collapsing. Typical symptoms are having good boost at lower RPMs and then a loss of boost at higher RPMs, this is aggravated when engine warms-up softening the rubber allowing for easier and more complete collapse of the hose. Typically costs about $90 at dealer.
To/From Intercooler
* Same symptoms as the Y-Pipe coupler. When under boost, the hose-clamps prevent the hose from expanding due to the air pressure inside the hose. Do not under-estimate the force of 10 psi or more on 3" diameter hoses, what looks OK with engine not running may not work under boost conditions.
Air Bypass Valve
* Test for leakage and operation. At 14-22 kPa {100-170 mmHg, 3.9-6.7 inHg} of vacuum to the control port air will flow through the two larger ports. At 31.3 kPa {235 mmHg, 9.2 inHg} of vacuum to the control port the valve will be fully open. Note that the operating points of the Air Bypass Valve are different from the Charge Relief Valve. The Air Bypass Valve is essentially the factory blow-off valve. It is not computer controlled, but simply operates by the vacuum from the Intake Extension Manifold, (pressure = closed, vacuum = open). You will hear the Air Bypass Valve vent boost when you let off the gas and get a vacuum in the Intake Extension Manifold. Typically costs about $150 at dealer.
Charge Control Actuator
* When closed, this prevents Primary boost from going into the Secondary Turbocharger. This valve seals the air passage the same way as a throttle butterfly valve. This remains closed until 4,500 RPM AND Secondary boost pressure is the same or more than Primary boost pressure. There are two hoses on this actuator with one side connected to the Charge Control Actuator and the other side to the Primary Compressor. From 0 to 4,500 RPM the solenoid applies a Vacuum, Primary boost is greater than a vacuum, Charge Control Valve stays closed. Note, that the vacuum supply is from the Vacuum Chamber, thus leakage of the one-way check valve for the Vacuum Chamber will result in Primary boost applied on both sides of the actuator resulting in this valve opening when it should not, dumping Primary boost through the Charge Relief , Secondary Turbo and out the Charge Relief Valve. * A good way to test for this is to insert a tee fitting to the Vacuum Chamber and connect a vacuum/pressure test gauge. Then go drive, (preferably with someone to look at the gauges) and keeping below 4,500 RPM drive with Primary boost and see if the Vacuum changes. Note you want to be in a boost condition for a while, (at least 10 seconds) to see if there is any leakage, so 4th or 5th gear starting at 2,000 RPM on slight incline would be the best.
Primary Turbocharger Control, (see Turbocharger Overview for more details).
Wastegate Solenoid / Actuator
* With only the Primary Turbocharger in operation, the Wastegate is NOT actively controlled by the ECU. Once boost pressure reaches about 10 psi, the Wastegate starts to open to bypass some of the exhaust around the Turbocharger, thus slowing down the Turbocharger. The Wastegate is not actively controlled by the ECU when below 4,500 RPM. The Wastegate solenoid is put in a fixed high duty cycle, (95% of the time on) which results in most of the air being vented from the Wastegate Actuator. At about 8 psi the Wastegate Actuator starts to move and by 10 psi the Actuator has moved enough to regulate the boost pressure to 10 psi. If boost is at 6 - 7 psi the pill to the wastegate could be missing, the Wastegate solenoid is not operating at 95% duty cycle, or the Wastegate is not mechanically connected to the actuator. * The size of the pill to the Wastegate Actuator in conjunction with the fixed 95% duty cycle of the solenoid controls the maximum Primary Turbo boost pressure.
Turbo Pre-Control Solenoid / Actuator
* This Actuator will direct some of the exhaust from the Primary Turbo to the Secondary Turbo. This re-directing of exhaust with the Turbo Pre-Control is also used as a method to Actively regulate Primary Turbo boost pressure, (instead of using the Wastegate). The Turbo Pre-Control is controlled by the ECU duty-controlling the Solenoid. The ECU controls the Turbo Pre-Control solenoid in a fixed manner based on RPM and boost pressure. * Another problem is that the Turbo Pre-Control door is slightly ajar robbing exhaust for the Primary Turbo. The solution is in properly setting the length of Turbo Pre-Control Actuator rod. Disconnect the rod from the the door by removing the C-clip, hold the door closed and set the length of the rod so that one half of the arm pin is hidden by the hole in the rod end. Then reattach the rod, you will have to pull on the rod in order to get the hole to go over the pin of the arm.
Turbocharger Exhaust
Exhaust Leaks
* Exhaust leaks between the engine and the turbocharger, (i.e. exhaust gasket), then the turbocharger will not be able to spin up as quick and/or not maintain boost pressure.
Exhaust Restriction
* Exhaust restriction after the turbocharger will show up as boost pressure drop-off at higher RPMs, (i.e. roll off after 6,000 RPM) the most common failure part here is the pre-cat, (sits between the turbos and the main catalytic converter). Due to the high exhaust temperatures, the pre-cats can start to fail in a plugged manner after about 50,000 miles. The common fix here is to replace the pre-cat with a down-pipe or have the pre-cat gutted. Note, check your area for emission laws with respect to the pre-cat before doing anything.
Secondary Turbocharger
You first need to get the Primary Turbocharger working before attempting to fix anything on the Secondary Turbocharger. The Secondary Turbocharger requires the Primary Turbocharger to generate more than 8 psi, (preferably 10 psi) to operate actuators that control the Secondary Turbocharger.
If you are at this point in your troubleshooting then a HIGHLY recommended tool to get is a hand-pump that can provide a vacuum as well as pressure, check out http:\\www.mityvac.com. Just about any local auto-parts/tools place will have these, also don't forget to get some "T" pipe fittings and some vacuum hose to allow tapping into various hoses. Basically you can attach this to the various actuators and solenoids to see if the they operate properly, much nicer than having to run the car to test things out.
Secondary Turbocharger Leaks
Assuming you have checked and verified the Primary Turbocharger for leaks there are several leakage paths specific to when the Primary and Secondary Turbochargers are operating, see the Secondary Turbocharger Leak Diagram. The item(s) below are on the diagram and are listed in most likely to fail order:
Charge Relief Solenoid / Valve
* Test for leakage and operation. At approximately 22.7-30.7 kPa {165-235 mmHg, 6.5-9.3 inHg} of vacuum to the control port air will flow through the two larger ports. Note that the operating points of the Charge Relief Valve are different from the Air Bypass Valve. The Charge Relief Valve vents boost during the pre-spin stage of the Secondary Turbocharger, (3,000 to 4,500 RPM). The Charge Control Valve isolates the Primary Turbocharger boost from the Secondary Turbocharger during the pre-spin stage. After 4,500 RPM the Charge Relief Valve is closed to allow Secondary boost to be added to Primary boost.
Secondary Turbocharger Control, (see Turbocharger Overview for more details).
At this time you should have the Primary Turbocharger functions completely, and checked the Secondary Turbocharger for leaks.
Turbo Pre-Control Solenoid / Actuator
* To prevent a drop in boost pressure when the Secondary Turbo begins to operate, the Secondary Turbo is made to spin prior to providing boost. The Turbo Pre-Control is controlled by the ECU duty-controlling the pre-control solenoid. The ECU controls the pre-control solenoid in a fixed manner based on RPM and boost pressure, (i.e. boost pressure regulation).
Turbo Control Solenoid(s) / Actuator
* The Turbo Control Solenoid / Actuator is one of the more complicated actuators as it requires both vacuum and pressure to operate properly. This actuator is controlled by two solenoids, (both are wired together to the one ECU output) one solenoid applies pressure to one side of the actuator and the other applies vacuum to the other side of the actuator. With pressure on one side and a vacuum on the other side of the actuator, the speed of the actuator is improved. A typical problem is loss of Secondary boost in 1st or 2nd gear at 4,500 RPM, but reliable operation in other gears. This points to one side of the Turbo Control Actuator not getting it's pressure/vacuum, so it will still operate but not quickly enough. * No vacuum to one side of the Turbo Control Solenoid / Actuator is a common failure. This is typically caused by the one-way valve that supplies vacuum to the Turbo Control Solenoid / Actuator through the Vacuum Chamber. The one-way valve will leak, allowing manifold pressure to leak into the vacuum while under boost
Charge Control Solenoid / Actuator
* When closed, this prevents Primary boost from going into the Secondary Turbocharger. This remains closed until 4,500 RPM AND Secondary boost pressure is the same or more than Primary boost pressure. There are two hoses on this actuator with one side connected to the Charge Control Solenoid and the other side to the Primary Compressor. At 4,500 RPM the Charge Control Solenoid switches and changes from the Vacuum Chamber to the Secondary Compressor. Once the Secondary Turbo is producing the same or more Boost than the Primary Turbo, the Charge Control Actuator's spring will allow the it to open, allowing the both the Primary and Secondary Turbo provide boost. Note, that the vacuum supply is from the Vacuum Chamber, thus leakage of the one-way valve for the Vacuum Chamber will result in this valve opening too soon.
Wastegate Solenoid / Actuator
* With both Turbochargers are in operation, the Wastegate is actively controlled by the ECU to allow exhaust to be bypassed around both of the Turbochargers to allow control of boost pressure. Once boost pressure reaches a set value, (i.e. 10 psi) then the wastegate starts to open to bypass some of the exhaust around the Turbochargers, thus slowing down the Turbochargers. The Wastegate is controlled by the ECU duty-controlling the Solenoid.
One-way Check Valves, Chambers, and Tanks
* There are several one-way check valves that are essential to proper operation of the Secondary Turbo coming on-line and staying on-line.
* Here is a list of the solenoids and related actuators and where they get their air supply from. Also an explanation of how these air supplies operate. There is a Pressure Tank and a Vacuum Chamber, each of these are supplied air through an one-way check valve.
Air Supply Turbo Pre-Control Solenoid and Turbo Pre-control Actuator Primary Wastegate Solenoid and Wastegate Actuator Primary Charge Relief Solenoid and Charge Relief Valve Vacuum Charge Control Solenoid and Charge Control Actuator Vacuum Turbo Control Solenoid and Turbo Control Actuator Vacuum and Pressure
Air Supply
* This column indicates where the solenoid and actuator gets it's air supply from.
Vacuum
* Vacuum is supplied from the Vacuum Chamber, this chamber is supplied with a vacuum from the Intake via a one-way check valve. This one-way check valve allows the vacuum chamber to keep a vacuum while the intake becomes pressurized from the Turbochargers during boost.
Vacuum Chamber
* This is a black plastic tank that is buried between the alternator and power steering pump. Kind of difficult to see, removing the Pressure Chamber helps to see it, has one hose connection, and should have a hose attached, (Engine View Picture). This hose comes from the rats nest of metal tubes, and there is a one-way check valve between the rats nest of tubes and the Intake. This one-way check valve can start to leak after a while, causing loss of vacuum to various controls when under boost for a while. A way to troubleshoot this one-way valve leaking is to note a gradual loss of boost and then drop the throttle long enough for your boost gauge to indicate at least 20 inHg of vacuum then slam the throttle back down again. If boost is back up to what it should be then replace this one-way check valve. Basically what this does is "recharge" the vacuum chamber when you let off the gas, allowing actuators to operate properly while the vacuum is still present.
* The vacuum one-way check valve goes from the Intake manifold to the Vacuum Chamber via the rats nest of tubes, (Mazda Part# N390-13-995A). This has a layer of three paper like filters on each end for separating any oil from the air.
Primary
* Primary air is supplied directly from the Primary Turbocharger compressor, no one-way check valves or pressure tanks. Note that the Primary Turbo must be operating and generating more than 7 psi of boost to be useful for any of the solenoids or actuators.
Pressure
* Pressure is supplied from the Pressure Tank, this tank is supplied with pressure from the Primary Turbo's compressor via a one-way check valve. The one-way check valve allows the pressure tank to keep a pressure when the Primary Turbo is not producing boost and/or during the Secondary Turbo coming on-line. Note that the pressure tank requires the Primary Turbo to be operating and generating more than 7 psi of boost to be useful for any of the solenoids or actuators.
Pressure Tank
* This is a black plastic tank that is located above and between the alternator and air-pump and in front of the intake. Kind of difficult to miss, has two hose connections on the driver's side, and should have two hoses attached, (Engine View Picture). One hose comes from a one-way check valve between the Pressure Chamber and the Primary Turbo Compressor outlet, remove the Pressure Chamber to see this one-way check valve. The other hose goes to various solenoids that require pressurized air. It is VERY common for either one of the hoses to the Pressure Tank or the one-way check valve to pop off due to pressures greater than 12 psi that the tank holds due to boost spikes and the hoses becoming old.
* The pressure one-way check valve goes from the Primary Turbo Compressor to the Pressure Tank, (Mazda Part# N390-13-995A ). This has a layer of three paper like filters on each end for separating any oil from the air.
The normal boost pattern and a method of testing is as follows:
Note this was originally developed for Mazda dealers, and has since been slightly modified as per feedback/questions from various people that have used this.
1) Steps should be done in order. Failure of any step will require further inspection prior to continuing.
* WOT = wide open throttle * KOKO = Key On Key Off
2) Verify engine is at operating temperature.
* Remove Double Throttle Actuator vacuum line * At operating temperature, no vacuum should be present with engine idling. * Re-attach hose
3) Check engine vacuum at idle
* Vacuum reading should be above 15 inHg with Air Conditioner OFF. Typically 17 inHg to 19 inHg for a stock engine, and for a ported engine the vacuum readings are more in the 16 inHg range.
4) Check no-load operation of Primary Turbocharger, (note that the best way to test the car for boost is step 7, but you need to pass this test/step to be able to perform test 6).
* Briefly accelerate engine to WOT in neutral, (From idle, punch the gas, get the RPMs above 5,000 but less than redline), about +4 psi should be obtained as you pass from 3,000 to 4,000 RPM.
o If you do not get this you most likely have a leak of the boosted air. This is anywhere from the turbos to the intake manifold. See Turbo Leak Diagram for helpful hints.
* If get about +4 psi, then have another person watch the Turbo Pre-Control Actuator rod for movement during this test.
5) Check vacuum chamber's storage ability with engine off
* Pull off vacuum hose at Charge Relief Actuator
* Should hear air entering hose vacuum, re-attach hose
* Start engine - briefly accelerate engine to WOT in neutral again
* Turn engine off - KOKO 6 TIMES
* Watch Charge Control Actuator work each time
* Watch Turbo Control Actuator work each time, (need to crawl under the car to see this one)
6) Check Pressure Tank's pressure storage ability with engine off
* Pull off one of the hoses of Pressure Tank
* Should hear air leaving tank (pressure), re-attach hose.
o There is a one-way check valve between the pressure tank and the Primary Compressor housing that feeds the pressure tank, this one-way check valve or a leaky hose or solenoid valve will cause Pressure Tank leakage.
7) Road test with boost gauge
* Drive to third gear with normal acceleration * Accelerate from 35 MPH at WOT until passing 4,500 RPM * A slight and smooth increase in power should be felt at approximately 4,500 RPM. This will be about 65 MPH.
RPM PSI 3,000 10 4,500 8 as secondary turbo comes on 4,500 + 10 recovers almost immediately 6,000 + 8 and holds to redline
These readings indicate normal operation. Readings will vary with altitude and temperature, (i.e. lower temperature = higher boost).
If you are having intermittent problems when hot, then try driving the car hard, parking the car, allow it to heat soak for a minute or two, perform these tests with everything very hot.
Rebuilding and/or replacing the Turbochargers
OK, you have found out that the Turbochargers do actually need to be replaced, (major bummer). I read somewhere that anyone with a turbocharged car should really look at the turbocharger(s) as a "consumable" part, much like clutch, brakes, etc... this may make you feel better but will not help with the cash-flow situation.
If you have a Mazda dealer than knows 3rd Gen RX-7s then they can do most of the work for you. Typically the Mazda dealer removes the turbos, then sends them out for re-build at a turbo re-builder, then the Mazda dealer puts the re-built turbos back in the car. Ask them how they go about doing this and if they have done this before and used the turbo re-builder before. These are very important questions to ask and get satisfactory answers to.
If you do not know of a good Turbocharger re-builder, then look in your local Yellow Pages directory under, hey you guessed it "Turbochargers". Phone everyone listed and ask them if they have worked on your type of Turbocharger for the 3rd Gen RX-7, (they are made by Hitachi, model HT12). There are basically two types of turbocharger re-builders, one will just work on the turbo cartridge and you get to remove this from the RX-7 specific exhaust and compressor housings. The other type of re-builder will accept the whole RX-7 turbocharger assembly. Both have their advantages and disadvantages.
Turbocharger cartridge re-builders will cost you less for the re-build of the turbos, but you will need some special tools to remove the housings and some set-up jigs to have everything re-align when putting everything back together. The other thing is that typically there will be cracks in the cast iron exhaust housings, typically around the wastegate, where the exhaust enters the housing from the engine, and around the exhaust wheel of each turbo. These cracks can be anywhere from benign to irreparable depending on how deep and where they are located. Any cracks that are where the exhaust wheel is is generally considered irreparable. For around the wastegate these can be welded up or some shops can machine and put an insert in. Note that any of this type of welding must be performed at a shop that does this kind of work, see Turbocharger assembly re-builders. So in the end, you may spend about the same amount of money, except that it will not be all in the same place. Another disadvantage, is that re-assembling the turbocharger into the RX-7 housings requires lining up oil in/out fittings and compressor outlets with respect to the exhaust manifold attachment plane, non-trivial and requires measuring or adding alignment marks of the various parts prior to disassembly.
Turbocharger assembly re-builders will cost you more but you get the complete assembly under warranty. It is very important that the place you use has experience with the 3rd Gen RX-7 turbochargers, because there are a bunch of non-obvious things that a first time re-builder will not realize about re-assembly of the turbos and the housings as mentioned in the previous paragraph, (i.e. alignment of oil in/out fittings and alignment of primary and secondary compressor outputs).
Note, it is VERY common to loose the inline pills that are between the Primary Compressor and the Wastegate and Turbo Pre-Control Actuators when having the Turbochargers replaced. Typically the re-builder will replace all hosing on the Turbocharger, and it is non-obvious that there are restrictor pills in the hoses.
