Cummins ISF3.8 intake and turbocharging system check

The air supply system of engines with a selective catalytic reduction (SCR) system consists of the following components:

air filter;
intake air duct;
turbocharger;
charge air pipe;
charge air cooler;
intake system heater.

Fig. 1. Diagram of the intake and turbocharging system.

Checking the intake system resistance

Install a vacuum or water manometer in the intake air duct.
The manometer adapter must be installed perpendicular to the air flow on a straight section of the duct, at a distance of one duct diameter from the turbocharger.

Note: on many automotive engines, the intake system resistance can be measured by removing the mechanical clogging indicator and fitting a vacuum or water manometer in its place.

Fig. 2. Installing the manometer in the intake air duct.

Set the engine to the operating mode with maximum fuel delivery, maximum load and rated speed.
Read the manometer readings. Maximum intake system resistance: 635 mm of water column.

Fig. 3. Reading the manometer readings.

If the resistance exceeds the norm:

replace or clean the air filter;
check the intake air duct for damage.

Turbocharging system

Preliminary checks

Check the hose connecting the compressor and the charge air cooler for ruptures.

Note: the use of low-quality hoses may cause them to rupture when the maximum boost pressure is reached (for example, when driving on a motorway at a speed close to the maximum, when driving uphill or when overtaking). Drivers of early-production GAZ «Valdai» vehicles are particularly affected by this fault.

In addition, the hose of these vehicles has a complex shape and is not always available on the market. As a compromise solution, dealers propose reducing the boost pressure, but at the cost of power. Some owners solved the problem radically by fitting a homemade metal adapter to the hose to reduce its diameter, which made it possible to install a stronger hose having the same dimensions at both ends.

Caution! Driving with a ruptured hose causes dirty air to be drawn in, which will lead to rapid failure of the turbine and the cylinder-piston group.

Remove the intake air duct and the intake air hose from the turbocharger.

Fig. 5. Removal of the intake air duct from the turbocharger.
Check the compressor blades for damage. Replace the turbocharger if damage is found.
If the compressor wheel is damaged, check the intake air duct and the filter element for damage.

Fig. 6. Checking the compressor wheel.
Eliminate all damage before starting the engine.
Remove the outlet hose from the turbocharger outlet union.
Check the turbine wheel for damage.

Fig. 7. Checking the turbine wheel.
Check the turbocharger wastegate control mechanism.
Check the lever pin. Replace the turbocharger if the lever pin is worn beyond the permissible limit.

Fig. 8. Checking the wastegate control mechanism.
Check the valve and its seat for cracks or erosion.

Fig. 9. Checking the valve and its seat.
Replace the turbocharger if necessary.
Move the lever by hand to check the freedom of rotation of its shaft. Check for excessive play between the shaft and the bush. Replace the turbocharger if the shaft and bush are damaged or seized.

Fig. 10. Checking the freedom of rotation of the lever shaft.
Check the turbocharger wastegate actuator.
Check the axial play of the turbocharger shaft.
- Install a dial indicator on the turbocharger shaft.
- Push the shaft in.
- Set the indicator to zero.
Fig. 11. Installing the indicator for the axial play check.
Move the shaft towards the indicator probe and determine the axial play. Axial play: 0.001–0.076 mm.

Fig. 12. Measuring the axial play of the turbocharger shaft.
Check the radial play of the turbocharger shaft bearing.
- Gently press the compressor wheel against the housing and measure the play with a feeler gauge.
Fig. 13. Measuring the radial play (first position).
Record the play value.

Fig. 14. Recording the measured play.
Keeping the feeler gauge in the same position, move the compressor wheel away from the housing and measure the play between them again.
Subtract the smaller play value from the larger one. The result obtained is the bearing radial play. Radial play: 0.396–0.602 mm.
Repeat these operations for the turbine wheel.
Replace the turbocharger if the bearing radial play does not meet the norm.
Check the turbocharger compressor inlet and outlet hoses for oil.

If oil is found in both channels, check for an oil source before the turbocharger.

Note:

The presence of oil traces at the compressor inlet is permitted for engines with a closed crankcase ventilation system, in which the crankcase cavity communicates with the intake air duct.
After a turbocharger failure or in other cases where oil or foreign particles enter the charge air system, it must be checked and cleaned.

Fig. 15. Checking the compressor hoses for oil.

If deposits and/or oil streaks are found only in the outlet hose, install the intake air duct and the charge air cooler pipes to check the intake system resistance.
Check the intake system resistance. If there is no resistance in the inlet channel, replace the turbocharger.

Fig. 16. Checking the intake system resistance.

Leak test

Add fluorescent dye (No. 3376891) to the engine oil at the rate of one dose per 38 litres of oil.
Note: the fluorescent dye is supplied in 118 ml plastic bottles.
Let the engine run at low idle for 10 min.

Fig. 17. Adding fluorescent dye to the oil.
Stop the engine.
Allow the turbocharger to cool.
Remove the exhaust pipe from the turbocharger outlet union.
Remove the exhaust system outlet hose.

Fig. 18. Removal of the exhaust pipe from the turbocharger.
Using a high-intensity heat radiation lamp, check the turbine outlet hose for oil. A dark blue glow indicates fuel in the oil, and a yellow one indicates an oil leak.

Fig. 19. Checking the turbine outlet hose by the fluorescent method.
If oil is found in the turbine housing, remove the oil return line and check whether it is blocked. If a blockage is found, clear it.
Install the return line with new O-rings on the cylinder block.

Fig. 20. Checking the oil return line.
If the return line is not blocked, remove the turbocharger.
Using a high-intensity heat radiation lamp, check the turbine outlet hose for oil. A yellow glow indicates an oil leak from the engine.

In the case of a yellow glow, the turbocharger can be refitted and continue to be used. A thin layer of oil on the housing and turbine wheel need not be removed, as it will burn off by itself during engine operation. All oily deposits in the turbine housing must be removed before installation with a clean cloth.

If no yellow glow is found at the turbine inlet, replace the turbocharger.

Fig. 21. Checking the turbocharger for oil leaks.
Install the exhaust manifold outlet hose.
Install the exhaust pipe on the turbocharger outlet union.
Install the intake pipe on the turbocharger compressor inlet channel.

The above materials cover the inspection of the air supply system of Cummins ISF3.8 engines with a selective catalytic reduction system: checking the intake system resistance, preliminary checks of the turbocharging system, and leak testing of the turbocharger by the fluorescent method. The material is intended for diagnostics, fault-finding and repair of the air supply system.