Diagnosing Engine “No Starts”

The underlying causes of “no start” conditions can be either electrical or mechanical.  In order to start and run, an otherwise operational diesel engine needs fuel and air.  When the ignition key is “turned on,” one thing that happens is an electrical fuel valve called a “fuel solenoid” opens to allow fuel to flow to the injection pump.  No fuel, no start.  If the engine cranks but does not start, think of the humble fuel solenoid as a possible cause.

At it’s most basic, the ignition key or push-button operates the starter solenoid, and the starter solenoid picks, energizing the starter motor. If the engine does not crank (turn over) when the key is operated or the start push-button is pushed, the underlying problem is probably electrical.

In practice, there may be a dozen or more electrical connections in the starter solenoid pick circuit, depending upon how the engine manufacturer designed the circuit.  For example, Sanctuary is fit with a Cummins 4B engine.  On that engine, the starter solenoid circuit originates at the battery, goes to the “start” connection on a key operated ignition switch, goes on to the neutral safety switch (located in the transmission housing; prevents the engine from starting if the transmission is in gear), goes on in turn to the coil of a “secondary relay” and finally returns to ground.  Within this circuit, there are several intermediate connections on a terminal strip in the engine room and at the various switches and the relay.  So, there are many points of possible corrosion or wiring breaks that all must be viable in order to pick the secondary relay.  When that secondary relay picks, it’s the normally open points of that relay that actually put B+ battery power to the starter solenoid.  If that relay is picking when the key switch or “start” button is operated, probably everything in the pick circuit is OK (like that pesky neutral safety switch).  If the electrical connections at the secondary relay are OK, then the secondary relay itself becomes suspect (bad/worn/burned normally open points internal to the relay).

A starter motor pulls many hundreds of amps from the batteries (mine pulls 500 amps locked rotor and it’s a rather small starter motor).  When the starter motor is energized, the very high discharge current causes the battery terminal voltage to instantly fall off.  If battery terminal voltage falls off enough, the solenoid will drop out.  As soon as the solenoid drops, the battery voltage recovers enough to re-pick the solenoid.  This starts the next pick/drop out cycle.  This is called “chatter,” and it almost always means battery circuit problems.  Commonly, the problem is low battery charge.  The cause can be a battery that isn’t fully charged, or a bad battery, or bad connections, or a mechanically locked starter motor rotor.  Locked rotor could be a starter motor problem, or it could be that the engine itself is mechanically bound up.

RUNNING ENGINES ARE POTENTIALLY VERY DANGEROUS.  ONLY PROCEED FROM HERE IF YOU ARE COMFORTABLE AND EXPERIENCED WORKING ON RUNNING ENGINES.  ELSE, FOR YOUR PERSONAL SAFETY, CALL A MECHANIC.

MAKE SURE THAT YOUR CLOTHING AND BODY PARTS ARE WELL CLEAR OF ANY MOVING PARTS AND BELTS WHEN WORKING AROUND THE ENGINE.  DO NOT WEAR RINGS, WATCHES, JEWELERY OR ANY LOOSE CLOTHING.  NO LONG HAIR EITHER.  TEE SHIRTS ARE BEST; NO SLEEVES.  A SHIRT SLEEVE CAUGHT IN A SERPENTINE BELT WILL SPOIL YOUR WHOLE DAY.  FINGERS, HANDS AND ARMS ARE VERY DIFFICULT AND VERY EXPENSIVE TO REPLACE, TO SAY NOTHING OF EYES.  ALWAYS WEAR HEARING PROTECTION!  YOU’RE ALMOST DEAF ANYWAY; YOU MIGHT AS WELL SAVE WHAT LITTLE HEARING YOU STILL HAVE!  ANY OF THE FOLLOWING TESTS MAY CAUSE THE ENGINE TO START!

First, check that the timing pin on the engine is not engaged.  If it is engaged, starting the engine will shear that pin, and that could cause many thousands of dollars in engine damage.  That pin being engaged would only happen if a mechanic had been working on the engine to locate top dead center to do valve adjustments or to install the injection pump, but check it anyway!

If the engine has not been started in several months, suspect that the oil has drained from the cylinder walls and the internal parts (usually piston rings) may be bound to the cylinder walls.  To clear that, bar the engine over (make sure the fuel solenoid is “off” while baring the engine over, or it could start and damage you, the boat hull, the bar, and anything else nearby) and then remove the bar and try normally starting the engine again.

IF YOU CAN’T BAR THE ENGINE OVER, STOP.  CALL A MECHANIC.

The following procedure requires self-confidence, and is not for the timid of heart.  I learned this test as a kid working on my first car.  It is simple and very quick to complete.  Think carefully through each step, and execute with confidence.  Turn the key on (to open the fuel solenoid) and then take a big (fat, old, sacrificial) screwdriver, and us the metal shaft of the screwdriver to jumper across the battery cable connection at the solenoid to the strap buss that runs into the starter motor from the other large solenoid connection.  These connections on the started solenoid are the two large bolts on the starter solenoid.  Jupering across these two bolts will activate the starter motor by bypassing the solenoid.  B+ battery power will through the metal screwdriver shank to operate the starter motor.  Yes, it’ll spark.  Don’t be timid here.  Stick that baby in there firmly, and expect the engine to immediately turn over and start.  Don’t let the jumper touch the frame of the starter motor or the engine’s block, of course.  That will also spark!  If the engine turns over and starts, then you might assume the solenoid or the solenoid pick circuit is the cause of the no start.

If the engine doesn’t turn over with the solenoid jumpered, that is to say, if absolutely nothing happens, suspect the starter motor itself is bad.  One possible trick is to mechanically jar the starter motor’s internal brush rack.  If the motor has seen many cycles, the brushes will be worn, and eventually will be worn to the point that they do not make contact.  There may still be a few start cycles in that old motor, though.  Hit it with a hammer.  Yes, that’s right, hit it with a hammer.  Not so hard you hurt it, but several times, firmly.  That will jar the brush rack, and may allow the brushes to make contact again.  Perform the screwdriver jumper test again.  Again, expect that motor to immediately start. If this does work, you are definitely on borrowed time.  It wil only work a couple of times before the brushes will be so worn they won’t make contact.  Act immediately to get the starter motor rebuilt.

If the engine does turn over, but only very slowly, then suspect  battery terminal connections or the starter motor terminal connection, and also suspect the return connections at the engine block ground that connects the engine block back to the negative terminal of the battery.   If all connections are all in good condition, then consider low battery state-of-charge.

I once experienced an unusual starter motor failure that could result in a “no start” symptom.  The strap buss that runs from the starter solenoid to the brush rack inside the starter motor body broke inside the starter motor.  To check that, take a piece of wood (***not metal***) like a wooden hammer handle, and push the strap firmly downward into the starter motor body.  AS PREVIOUSLY DISCUSSED, MAKE ABSOLUTELY SURE YOUR BODY AND CLOTHING IS CLEAR OF ANY MOVING PARTS OF THE ENGINE!  While holding that strap down, have an assistant operate the key to start the engine. If it starts, you’ll have to pull the starter and take it to a shop to have the buss bar brazed.

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