Yanmar “death rattle”
Not necessarily specific to Yanmar, I have seen this on a number of engines where improper idle speed and throttle cable adjustments caused a “death rattle” when returning from mid-upper RPM range. Problem occurs when the idle speed screw is set to low and the throttle cable is being used to set the idle speed-Improper procedure.
Using a digital tachometer and reflective tape on the crankshaft pulley, start and run your engine until warm, stop engine and disconnect the throttle cable. Take a reading using your digital tachometer, should be between 650-850 RPM, if not readjust.
Raise and lower your engine RPM by flipping the throttle arm on the engine, set it pop back naturally, do this several times to make sure the throttle lever is seating against the idle stop screw. Recheck your idle speed several times when the engine idle speed levels out.
If the idle speed is incorrect, readjust and repeat step 3 and recheck idle speed. Continue until idle speed remains within limits in step 1.
Move your shifter until the throttle lever is in the neutral if single lever/dual function lever or to the idle position.
Readjust your throttle cable at the engine, recheck idle speed after reattaching the throttle cable, if it stays constant you have a good fix.
Most Yanmar engines are supplied with a spring-loaded terminal which attaches to the end of the throttle cable and inturn attaches to the throttle arm on the engine. If used, insure the throttle cable terminal is adjusted so the spring pressure of the terminal is the only pressure used to push the throttle arm to the idle position. Allowing the cable to fully compress the terminal and forcibly push against the throttle arm will eventually damage the throttle arm and associated internal components.
In addition to the information emailed to me off site, please check your battery voltage using an analog multi-meter, digital units react to slowly to be effective. With a fully charged battery 13V across the terminals.
1, Check your battery voltage at the battery terminal and record your results, should be 13V.
2. Check the battery voltage at the starter where the battery cable attaches. Should get 12.5-13V.
3. With the meter set on the Ohm setting check between your ground terminal on the battery and to the block near where the ground cable attaches to your engine, should be zero ohms. If not remove the cable and clean terminal lug and block where attached, recheck results, if still showing high ohms replace the cable. Yanmars have had a lot of grounding problems associated with paint coupled with corrosion and in some cases related to where the ground cable is attached to the engine.
4. Check your Yanmar manual and relocate the ground cable to the spot above and aft of the starter as specified in the manual.
5. Check Ohms between the bell housing and the base of the starter, should be zero ohms, if not remove the starter and clean the starter base and bell housing, do not grease or paint this surface. Wire brush and 3M scrubber pads work great.
6. Check voltage at the battery while someone else attempts to start your engine, If your battery voltage drops below 10.5 volts, replace your battery. If your voltage is 10.5 or higher see step 4
7. Check voltage at the starter as described in step 2 while some one else attempts to start your engine. Again should be above 10.5 volts, If step 5 stays above 10.5 volts and step 6 goes below 10.5 replace clean terminal and recheck, if clean already, replace the cable.
If all above checks ok:
Using a remote starter switch, remove the ignition wire from the starter solenoid, attach one lead of the remote starter to the solenoid ignition terminal and the other lead to the starter positive post. With the remote starter switch, attempt to rotate your engine sever times, if all goes well your starter is ok.
More often than not, the problem is in the control panel start button or ignition switch, these will have to be ohm checked with the DC power shut off. Should be zero ohms when testing these circuits.
Believe it or not Yanmar and most engine manufacturer control panels are not warrantied once you take possession, are not water proof! Unless a wire is cut in the harness or water has created corrosion in the terminals at the back of the panel or at the connector plug at the port aft rear of the engine, Yanmar harness seldom have any problems, larger wires/conductors are never needed.
To set up the idle properly, disconnect the throttle cable. Run and warm the engine to full operating temperature.
Good luck on your projects
Marty Chin, BCC Shamrock
Bay Marine Diesel