Diagnosing Common Problems

The GT-Four is blessed with the legendary Toyota reliability but it is not invincible.
Inevitably, as with any high power 4WD car, the driver will be faced with a problem sooner or later.

In these pages we hope to help solve some of the more common ones

To narrow down the range of options please choose your car model below

Common problems
Suspension Braking Gearbox
Engine Check Engine Light Turbo

Clunk From Rear When Accelerating Or Changing Gear

This is a common problem on the GT4, and is generally caused by movement in the rear differential.
It is caused by a failure/breakdown of the stock differential mounting which has a large rubber bush in it. Over time this rubber slowly fails until it allows the differential to move creating the characteristic clunk

There is an excellent write-up on diff cushion replacement here on gtfours.co.uk

Light Clunk When Reversing

If you are suffering from a light clunk when braking in reverse do not worry. This is actually not a problem as such but is a feature of the brakes used on the GT-Four
Th calipers allow the brake pads to move slightly when wheel rotation direction changes. So you get a light clunk the first time you brake in reverse and a light clunk first time you brake going forwards. Othen than a quick visual inspection to make sure that the brake pads are correctly seated in the calipers and all of the brake pad retaining pins are in place there is nothing more to do.

Car Pulls Or Wanders

This could be something very simple, or very complicated!

Crunch When Changing Gear

There are many reasons why this might happen from simple to expensive!
If it happens on all gears then the problem is very likely to be clutch related as it is rare to experience gearbox related problems in all gears
The first thing to check is clutch pedal adjustment to make sure that the clutch is dis-engaging correctly

If this is in order then then it is possible that the clutch pedal bracket in the drivers footwell has snapped. This is seemingly quite a common problem on ST185 variant models and has been occasionally reported on other models to.
To inspect you need to get into the drivers footwell "upside down" so that your head is down by the pedals. This can be a painful experience and requires a certain amount of wriggling.
When you get there check the bracket that the edals are attached to. You are looking for a crack in either end of the support which allows the braket to move and hence prevents full clutch dis-engagement

If this fails then read through the clutch related issues section below and see if anything there seems amiss

If the selection problem is related to only one or two gears then it's likely to be one of two things :-
The linkages could be worn. This is best diagnosed from inside the car. With the engine off put the car in any gear and try to "wiggle" the gearstick. If it moves in any direction by more than about 1/2" then there is play in the linkages which could be causing the problem
The play problem can be solved quite simply although it is a fiddly job. The linkage cables are attached to the gearbox selectors with 2 rubber bushes which, over time, degrade and become loose. The solution is to replace these bushes, either with OEM Toyota parts or aftermarket replacements.
Shown below are a set of stock (worn) Toyota bushes alongside a set of aftermarket replacements
Replacement Vs Toyota bushes

If the bushes do not seem worn or replacing them does not help the problem and you have exhausted all simple clutch maintenance problems then it is quite possible that the problem lies within the gearbox itself, likely a worn synchromesh. Tackling this sort of problem goes beyond the scope of simple home maintenance!

Clutch related issues

Problems with the clutch can cause a number of different issues with the car from difficult gear selection to slippage
Unfortunately most problems will require inspection of the clutch assembley. This in turn requires removal of the gear/transfer box from the engine. Not a task for the fainthearted but it is possible for the enthusiast DIY fan
Some common symptoms

Poor fuel consumption

Firstly how do you define poor?
Well a well setup car should return 25+mpg with sensible driving. If you have removed your lead boots and still cannot get near this you may have a problem!
There are a number of potential reasons for this:-
For ST165 and ST185 models any leak in the vacuum system will cause overfueling. If it is a small leak it may not be obvious!
However, a common cause is a failing O2 sensor. These do degrade with age and mileage. It is one of the common causes for poor fuel consumption
It is possible to test the sensor if you have a voltmeter

Low Boost

It is difficult to make an exact diagnosis of this due to the fact that there are so many cars out there running modified boost levels. The good news is that reduced boost is not always a sign of a blown turbo! Turbo failure generally tends to be either catastrophic resulting in no boost or non boost effecting (blown seals etc)

Some common tricks and tips:-
Number 1 most important test. CHECK FOR ERROR CODES (follow THIS LINK. The ECU has a number of strategies for dealing with engine problems and boost reduction is one of them. If you are running an EBC try switching it off. This might allow you to establish the base actuator assuming you haven't got boost creep problems
If you are running a relief valve or bleed valve remove and inspect them. Bleed valves can becone blocked and relief valves can become sticky. In both cases a visual inspection and good clean might solve the problem
Other Things you can try to diagnose actuator problems:-

Over Boost

Boost Creep

Boost creep occurs because fundamentally the turbo wastegate is too small
This means that even when the wastegate is fully open there is still to much exhaust flow through the turbine which in turn produces more boost
The normal symptoms are a boost curve which rises in line with rpm. It is quite common to see boost creep sufferers who have 0.6 bar boost at 3000 rpm and 1.5+ bar boost at 7000rpm even when running wastegate actuator pressure only. This is a sure sign of boost creep
So what causes it? I have a stock turbo so why am I suffering?
It is almost always caused by improvements in the engine breathing systems. That means free flowing induction system in conjunction with a free flowing de-cat exhaust
The exhaust is the main culprit. As the exhaust system is improved exhaust gases are able to exit the exhaust system easier. This also means that they can flow through the turbo that much faster which leads to boost creep
So how do I fix it?
It depends ;)
There are a few avenues of attack. Some good, some bad