Lmtv bogging down and stalling

[MOCO111]

I have had an issue (mainly in cold weather) where my 1995 M1093 (CAT 3116) will bog down and stall out, once it stalls it will start a few times but then it sounds like the starter won’t engage. I was stranded on the side of the road once before but got it to start by tapping the solenoid on the side of the engine. Could it be just the fuel shut off solenoid and if so has anyone changed one?

 

[Ronmar]

Fuel solenoid should be an on/off response just like when you turn off the switch.

Bogging sounds like fuel supply/air. You need to connect a pressure gauge to the T on the inlet to the secondary fuel filter(between filter and governor) and measure the primary fuel pressure. Should be 20@ idle and 60@ higher RPM. You can see one in one of my youtube videos(rronmar) on the fuel system. Once you take out the pulsations from the pump(restrict the line to the gauge) the pressure should be steady. If it sags while running this is probably air pockets passing thru the lift pump.

You can also run the return line into a bucket or put in a length of clear hose and look for excessive air in the returned fuel.

 

[MOCO111]

Fuel solenoid should be an on/off response just like when you turn off the switch.

Bogging sounds like fuel supply/air. You need to connect a pressure gauge to the T on the inlet to the secondary fuel filter(between filter and governor) and measure the primary fuel pressure. Should be 20@ idle and 60@ higher RPM. You can see one in one of my youtube videos(rronmar) on the fuel system. Once you take out the pulsations from the pump(restrict the line to the gauge) the pressure should be steady. If it sags while running this is probably air pockets passing thru the lift pump.

You can also run the return line into a bucket or put in a length of clear hose and look for excessive air in the returned fuel.

Update fuel solenoid is now clicking loudly and repeatedly when truck power supply is on before starting attempt.

 

[Ronmar]

Cool! Pulsing in a relay/solenoid circuit is usually a weak/high resistance connection In the circuit. A weak connection will pass full voltage until the load draws current. Then the restriction/ resistance will cause the voltage to drop(like a kink in a hose). Because of the way coils draw and employ current with a slight delay, a weak connection can set up a timing loop that causes the coil to pulse.

i dont have access to schematics right now to point you thru the circuit, but if you have a volt meter you can determine if the coil of the solenoid is the issue or if it is something in the circuit.

disconnect and Measure the voltage at the solenoid coil wires and determine which terminal is receiving the +24 and which is ground. You have +24 and ground available Right at the starter so you can use a jumper wire to power the solenoid directly. If it doesnt pulse with power jumped to it directly, solenoid is ok, circuit is suspect. This of course is assuming you are getting 25.0V or greater from the batteries…

Troubleshooting the circuit involves checking voltage along the path to determine where
It is loosing voltage when under load. If I recall correctly the solenoid circuit also powers the heater in the primary filter water separator bowl.

 

[MOCO111]

Cool! Pulsing in a relay/solenoid circuit is usually a weak/high resistance connection In the circuit. A weak connection will pass full voltage until the load draws current. Then the restriction/ resistance will cause the voltage to drop(like a kink in a hose). Because of the way coils draw and employ current with a slight delay, a weak connection can set up a timing loop that causes the coil to pulse.

i dont have access to schematics right now to point you thru the circuit, but if you have a volt meter you can determine if the coil of the solenoid is the issue or if it is something in the circuit.

disconnect and Measure the voltage at the solenoid coil wires and determine which terminal is receiving the +24 and which is ground. You have +24 and ground available Right at the starter so you can use a jumper wire to power the solenoid directly. If it doesnt pulse with power jumped to it directly, solenoid is ok, circuit is suspect. This of course is assuming you are getting 25.0V or greater from the batteries…

Troubleshooting the circuit involves checking voltage along the path to determine where
It is loosing voltage when under load. If I recall correctly the solenoid circuit also powers the heater in the primary filter water separator bowl.

Awesome! Thank you for your help. I’m fairly new to these vehicles. I’ve had mine for about 2 years but all it came with was the basic operations manual . I’ve got a link to the service manuals and I’ve tried to locate a solution in them but I figured I’d learn more from those who’ve worked on them and encountered the odd problems.

 

[Ronmar]

There should be a schematic in the back of each of the 5 service manuals.