TJ Magna won't crank.

[Brendotec]

Hi there,

I have a TJ 3.5 Auto that won't crank half the time. When you turn the key to start, you hear the fuel pump going and that's it. It has a new starter motor in it already and I have had to bridge the 12V to the solenoid to get it to start so I could drive it. Even pulled the new starter and had it bench tested by an auto elec near work, as it's not my only car. I thought it might be the Park/Neutral switch on the trans so I put another one on. But the problem is still occurring. Any further ideas to look at would be much appreciated.

Thanks

Brendotec

[AQUAR]

"I have had to bridge the 12V to the solenoid to get it to start so I could drive it."

Doesn't that tell you there is a failure of the solenoid to switch on to the heavy duty contacts?
Maybe these contacts are bend a bit due to working fatigue.

[Brendotec]

"I have had to bridge the 12V to the solenoid to get it to start so I could drive it."

Doesn't that tell you there is a failure of the solenoid to switch on to the heavy duty contacts?
Maybe these contacts are bend a bit due to working fatigue.

Took a break from the starter problem while I replaced the heater core O-rings/pipes. Pretty easy job, much cleaner than the usual mechanic activities.

Starter is new, as I said originally. I did pull the starter out 6 months ago for the auto electrician to check out and it was perfect. Car hasn't been driven for 4 months. Anyway... I grabbed the wiring diagram and tested the start circuit from the ignition switch, thru the park switch, to the starter. Battery voltage is present all way, but still doesn't activate the starter. So I suspected high internal resistance in the starter circuit causing not enough power to activate the starter solenoid.

So, I used the 12v from the start circuit to power up a relay, which I fitted between the park switch and the starter motor. This gives uninterrupted battery voltage that by-passes the ignition switch and park switch. I have done this before on older cars and works a treat. Hopefully this helps out someone someday

[AQUAR]

Confusing when you mix terminology to describe a problem.
To me a basic starting system comprises the starter motor, a solenoid and an ignition switch.
Bridging the solenoid with 12 volts to start the engine isn't the same as supplying it via a relay that in turn is powered via the ignition switch.


I have an old Sigma and that was unable to deliver the voltage/current via the deteriorated contact in the ignition switch.
A relay is a good and long lasting solution for that.