Bosch Auto Part Advice From Eau Claire Diesel

Eau Claire Diesel has been a trusted name in the auto parts industry since 1978. As the only Bosch service dealer within 100 miles, we specialize in fuel injection component repairs. Our locally owned business prides itself on having factory-trained technicians who are here to help you. Learn more about troubleshooting your Bosch equipment below, and contact us with any questions you come across!

Starts Hard

Verify the air cleaner is clean; just because it looks clean doesn't mean it flows the correct amount of air. If in doubt, replace it. Blowing out air filters does not work because the element usually gets more packed with debris than what you get out.

Verify the cranking speed is sufficient. If proper cranking speed is not achieved, then the injection pump will not supply adequate fuel to start.

Start by cleaning and charging the battery/s; if the battery is good, check the starter voltage drop. If this is good, replace the starter. We can supply most machines with an OSGR (offset gear reduction starter) to increase cranking speed and less battery draw.

Verify the fuel is fresh and the supply is good, check the lift pump if it has one, and check for fuel suction leaks. Install a clear fuel line from the fuel filter to the inlet on the injection pump. Monitor it for air bubbles, and if bubbles are present, you have a suction or vacuum leak in the supply hose. Keep moving the clear hose closer to the tank until the problem area is found and no air bubbles are present.

Verify and/or change the fuel filters. Do not assume because you just put a new filter on recently that it is good. If you have fuel contamination issues, the filter will be plugged up and need to be replaced. The tank should be cleaned or replaced, as well as all the supply lines. Supply issues can be found with the above testing procedure. You can also install a vacuum T in the fuel supply line and monitor the vacuum from the tank to the filter and filter to the pump.

Verify the overflow valve is not sticking open. Usually, when these stick open, you will not hear a squeaking sound when hand priming. If they open too early, then the galley where the plungers and barrels are will return too much fuel back to the filter/tank, and it will not have enough fuel in the galley to complete a full pumping stroke. You will usually see the supply pump peak pressure drop if this overflow valve is bad.

Starts Hard Hot

See the above "starts hard" information. If you can verify it all, then the injection pump may be weak. When fuel is hot, it becomes thin; when this happens, worn plungers and barrels leak off pressure more easily and do not supply the injector the full amount of pressure until the engine RPM is sufficient for the pumping head to have enough RPM to make the pressure the injectors require. It will then run.

Injector Rebuilt and Now Starts Hard

This may be the same issue as above's "starts hard hot" troubleshooting. The pumping head in the tractor may be getting weak and not able to supply enough injection pressure to fire reset or rebuilt injectors.

Low Power

Verify the fuel is fresh and the supply is good, check the lift pump if it has one, and check for fuel suction leaks. Install a clear fuel line from the fuel filter to the inlet on the injection pump and monitor it for air bubbles. If bubbles are present, you have a suction or vacuum leak in the supply hose. Keep moving the clear hose closer to the tank until the problem area is found and no air bubbles are present.

Verify and/or change the fuel filters. Do not assume because you just put a new filter on recently that it is good. If you have fuel contamination issues, the filter will be plugged up and need to be replaced. The tank should be cleaned or replaced, as well as all the supply lines. Supply issues can be found with the above testing procedure.

If all of the above checks out, verify that your compression is good. Good compression ranges vary between engines, but you typically want to see 400 pounds of compression and above for a well-running diesel engine. See the manual for your engine for the suggested rebuild tolerances.

If your compression is good, then the pump may have worn plungers and barrels or leaking delivery valve gaskets.

White Smoke

White smoke that burns your eyes is usually a sign of fuel supply and/or early injection timing, restricted airflow, and/or low compression. Verify the air filter is new. 

On some P-pumps, we have seen the gear slip on the pump shaft, and the timing becomes late. Reset the timing of the engine and pump by pulling the gear off the pump and reinstalling it with timing pins in the engine and brake. Clean the gear and shaft of the pump and reinstall the pump gear and torque to spec.

Try advancing the pump on high-hour machines, then perform the same process as above. Lock the engine pins and pop the gear loose. Mark the crankshaft balancer by timing finger and back the motor up the width of the factory timing line, then retest. Keep doing so until the engine starts to run correctly. If the problem doesn't change, then verify the supply and fuel quality; if they are good, test the compression. If that is good, the injection pump is weak.

Black Smoke

Black smoke may occur if the air filter is pluggled, the exhaust is plugged, the turbo is not sufficient for the amount of fuel, and/or the fuel pump fuel setting is set too high for the engine. Properly set the pump and turbo size, and there will be little to no black smoke under the full load.

Some P-pumps have an aneroid above the governor housing. Check to make sure this supply line from the engine intake isn't leaking or broken. This uses the turbo boost to push down the aneroid diaphragm and let the fuel rack in the pump move further to supply more fuel to the injectors. If all is good, verify the fittings of the tube/line are not plugged with debris, and check turbo boost pressure. If there is no boost pressure, check the turbo for issues, such as intake restriction, back pressure too high, and more.

Contact Us

Reach out to Eau Claire Diesel for more information about troubleshooting your Bosch P-pump and other auto parts. Our team is ready to assist you with expert advice and quality service.

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