All Trac and GT-four Troubleshooting

Having trouble with your All Trac or GT-four?

Read over this Q&A page and see if you can find your problem. If you would like to see how to perform maintenance to fix these problems see the Maintenance Page.

Find your particular problem below:

Clunk from Rear End

Most likely this is the Rear Differential Mount. There is a large rubber bushing that surrounds the rear differential. This part is put under tremendous stress. Once the rubber is cracked or broken it can no longer stop the differential from shifting under acceleration. This shift is what causes the clunk you hear. Replacing this mount will solve the problem.

Low Boost/Loss of Power

If you notice suddenly that you have lost power, check for engine codes. If you do not receive an error code, it may be turbo related. The turbo makes power by driving exhaust energy through the turbine. If the exhaust energy does not reach the turbine you will not receive as much power. The wastegate flapper door can have cracks around it which will cause internal exhaust leaks. This is very hard to determine because once full boost is achieved, the performance is fine. It will just take longer to reach full boost. If you are noticing little to no boost, you may have a wastegate actuator problem. They can go bad and if so will open very easily with little boost. Also some cases have been found of the actuator arm actually becoming disconnected from the turbo charger.

If the turbo system checks out there may be another problem. The Turbo has a valve (Turbo VSV) that switches from low to high boost under normal conditions If this valve is stuck in low mode then you will be stuck with low boost. You will know to suspect this problem if the car performs well otherwise, but just has a lower boost figure than normal.

Sluggish When Cold

This actually is quite normal. The computer will limit the boost and retard timing when it detects cold conditions. This is a safety feature of the car so that you will not be stressing the engine when it is cold. If you notice that it takes longer and longer for the car to get out of cold mode, then you may want to test the sensors that report temperature to the ECU.

Hesitation under boost

If you have noticed that your car works fine when not in boost but then stutters or hesitates when under hard acceleration (or boosting), it may be fuel related. The most common problem is the fuel filter. In a lot of cases the fuel filter has never been changed, and is dirty/clogged. This is a relatively cheap replacement and should be suspected first. If that doesn't fix the problem, the next thing to try is a general tune up. Finally, if you are still having problems look at the fuel pump. Especially for the ST165, you must realize that the fuel pump is over 12 years old and could be performing poorly. Some tests performed on old used pumps showed they were only operating at about 15% flow versus new (extreme case).

Smoke from Rear after/during boost

If you (or someone else) notice that white smoke comes from the back while boosting, this is most likely the turbo. The seals could be bad on the exhaust side and during boost when oil pressure is high, the oil is entering the exhaust system. The turbo will need to be rebuilt with new seals if that is the case.

Smoke from Rear after/during idle

If you notice white smoke pour from the back after idling for some time, this is most likely the valve seals in the head. When idling the oil will drip into the combustion chamber and burn. When you accelerate from a stop all of this oil and smoke will burn and come from the rear. The car does not smoke after driving because the combustion process is hot enough to burn the oil completely. This is not a terribly serious problem, but will get worse over time. This would require replacing the valve seals in the head and pretty much calls for a nice head rebuild to do so. You can try switching to a thicker oil to see if this fixes the problem.

Oil in intake piping

This is a common problem with All Trac/GT-four. There is not necessarily anything wrong with the car. The way the engine works is that the pressure and some oil vapor from the head goes into the intake piping to be burned during the combustion process. What happens however is that these vapors collect in the intake piping between the AFM and turbo to form puddles of oil. This is even more pronounced as you turn up boost as the turbo is literally sucking all the vapors out of the crankcase. The first thing you need to do is to clean the intake piping. Most people end up venting the crankcase vapors to air in order to help solve this problem. There are also filters and tanks that can be installed to catch the oil.

Another reason for oil in the intake is the front turbo oil seal. If this seal is leaking it will leak oil under boost onto the compressor and further shoot it into the intercooler. Symptoms of this problem are oil in the intercooler, and oil on the compressor blade. This is hard to determine because of the above problem. One way to find out is to clean the front intake piping where the oil is vented in. Then clean the turbo side of the intake system. Go for a few boosting runs then inspect. The oil will collect post-turbo much faster than it would collect in the turbo intake piping. If the intake side is relatively dry, and the intercooler side is oily, you most likely have bad turbo seals.

Check Engine Light On

The ECU has detected a problem, check the error codes in the ECU to find out what the problem is. If the check engine light came on while boosting or hard acceleration, then went back off, you may have experience overboost or engine knock. The car will go into a slow (limp) mode for a little bit, then return to normal performance. Do not continue to push the car until you have determined what the problem is.

Vibration from rear under light load

This is a rare problem, but can happen. If you notice a vibration from the center rear of the car under part throttle, it may be your driveshaft center bearing. This bearing keeps the driveshaft straight and if installed incorrectly or faulty, can cause excessive vibration. Have this checked.

If the vibration is constant and increases with rolling speed, check the rear wheel bearings.

Vibration/buzzing from front wheels

A common problem with our aging cars is the wheel bearings. You can almost bet on the wheel bearings going out sooner or later, so if you are experiencing these problems, have them replaced. You may not notice this right away, but eventually the noises from the wheels will increase. If you notice that the sound gets louder as you move faster (not necessarily acceleration), it's a sure bet on the wheel bearings. The bearings cannot be service, they are sealed units and must be replaced by a shop.

Clicking/Crunching While Turning

This can usually be diagnosed as the CV Axle joint. The boots that protect them tend to break or tear over time. Once this happens dirt and debris will enter the joints and created noise. The rebuild is easy and fairly cheap. Inspect your CV Axle boots. If any are damaged, cracked, or torn, have the axle rebuilt.

Noisy suspension on rough roads

You might notice on a bumpy road all sorts of clunk sounds. This is hard to diagnose since the All Trac has numerous suspension parts. Some of the most common problems are the A Arm bushings and the sway bar bushings in the front. The reason is that oil and power steering fluid leaks are common and drip their way to these bushings. The fluids will eat away at the bushings and actually cause it to fall apart. If you are noticing these noises check under the car the condition of all the bushings.

If the bushings check out, but you still have a clunk on bumps, check the top strut mounts. These often over looked suspension pieces can crack and fall apart over time. Another possibility would be the ball joints under the struts.

Bubbling coolant overflow tank (overheat)

The way the cooling system is designed allows excessive pressure from overheat to be released from the cooling system into an overflow tank. The radiator cap is set to open at a certain pressure to protect the rest of the cooling system. If the radiator cap is not working properly, it will open too early and allow the coolant to spill out into the overflow tank. The tank will overfill and spill coolant out to road. You may or may not overheat, but after the car cools the system will now be low on coolant and potentially cause problems. Suspect the radiator cap first if the overflow bottle is a little too active. If the radiator cap checks out, start looking for coolant leaks.


This is a tough question to answer. The cooling system can fail due to coolant leaks or insufficient flow. You need to check for leaks first. As mentioned above check the radiator cap for proper operation. The next logical step would be to check or replace the thermostat. If the car runs hot under certain conditions, but does not necessarily overheat, the cooling system is constricted. You may want to suspect your radiator and/or cooling system passages. A flush and pressure test of the cooling system may need to be done.

If the car overheats constantly, and the coolant level is constantly low, there are probably leaks. Leaks are hard to find sometimes because the water is hot when it leaks, as is the engine and the water can evaporate before being seen. Check all visible hoses. There is a cooling hose that is at the back of the engine which you cannot see. Since it is not visible it is rarely replace and can be the cause of problems. It is a rubber those that runs from the head to the block under the intake manifold. It is closer to the distributor side of the engine.If you have a question you would like answered, email us.