Intermittent no start
 

56 Merc, new battery and new starter

Sometimes I will intermittently get no noise at all when turning the key. My fuel pump is wired with the key on and I hear it pumping every time even with the random no starts. If I try again right away the car will start.

Maybe ignition switch or body ground? I just don’t want it to get worse and not start one day and I’m stranded
Thanks for any thoughts

Re: Intermittent no start
 

Check and clean all electrical connections, including the ones at the starter switch. Possibly a bad starter switch

Re: Intermittent no start
 

Do check the battery to engine and engine to body Ground cables for clean & tight connections. Also the body ground of the starter solenoid. For some reason they're easily forgotten.
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Re: Intermittent no start
 

The neutral safety switch might need adjusting.

Re: Intermittent no start
 

Listen to see if you can hear/feel the solenoid when the key is in the start position.

Re: Intermittent no start
 

Are you describing engine NO-CRANK (does it crank) or NO-START?

Is the electric fuel pump a primer or transfer install (via mechanical pump)?

Re: Intermittent no start
 

Checked all connections and all seem good, they’re all fairly new. I’ll check the starter solenoid next along with the neutral safety switch. Thanks for the ideas

Re: Intermittent no start
 

It’s a no crank, electric pump is a primer. I only mentioned that because the ignition does turn on the fuel pump, thinking maybe that rules out ignition but I don’t know

Re: Intermittent no start
 

With a TEST LIGHT, check for current at the COIL (+)/RESISTOR when the key is turned to RUN.

Then TEST LIGHT on the "S" pin on the starter solenoid when key turned to START.

How is the pump wired, continuous run on IGN SW on RUN?

Re: Intermittent no start
 

Test light shows hot a coil terminal with key turned to run, also shows hot on starter solenoid in start position, yet right now the car is also starting normally. I’ll try and test these again next time I get a no crank, it’s just so random it can be once and not again for days or 5 times in a row.

The fuel pump is wired from a relay to a toggle switch, to the ignition switch on continuous run. The car is also running very rough and is breaking up on acceleration, I changed out coil but no luck. Not sure if it’s related

Re: Intermittent no start
 

I checked the neutral switch on the steering column, I found a wire that was jumping two wires together, I’m guessing this is to bypass the safety switch since I just found out the car starts in all gears. So while not a good thing, it’s prob not the problem with the no crank. I feel like it’s something electrical failing that is also causing rough idle and acceleration break up

Re: Intermittent no start
 

Once someone butchers a wiring harness, anything could have happened.

You can by-pass the IGN-START SYSTEM by running a jumper between the starter solenoid and coil and then jumping the solenoid. But it bypasses the NSS, so you have to be on your guard.