Crank with no spark and wont start
Seasoned Member
Joined: Oct 2010
Posts: 315
Likes: 1
Model: Cherokee
Always check your grounds also, have you tried a new coil yet? I just read when it heats up the problems start? Bad electronics are affected by heat, so is running a bad O2 sensor. I have a van with a power steering leak, its gotten a CPS all gunked up and it made a world of difference just cleaning it up. Hadn't even noticed it was running so poorly, lol. Oil and water leaks can mess a lot of stuff up.
Thread Starter
Member
Joined: Nov 2012
Posts: 150
Likes: 5
Year: 1993
Model: Grand Cherokee (ZJ)
Engine: 5.2L v8
Might be alternator???
So I took the jeep for a test drive today and I noticed that the battery gauge drops pretty low when it's at a stop, so I drove it back home, I parked it and with the engine on I turn the heater, high beams, radio, and I was rolling the electric windows down, I noticed that the battery gauge dropped drastically, when I gave it gas everything got super bright and stuff so I'm going to get the alternator tested just for ****s and gigs
Member
Joined: Aug 2016
Posts: 233
Likes: 4
From: Maryland
Year: 1996
Model: Grand Cherokee
Engine: 4.0 I6
Sounds like your alternator is doing its job. I'd get the battery tested. Don't know the specifics, but I would imagine that maxing out the electric load would exceed the alternator's capacity at idle. During those periods your battery should be picking up the slack. Then, when there's less power draw or higher engine speed, the alternator has some to spare and charges your battery back up.
Old fart with a wrench
Joined: Nov 2010
Posts: 14,398
Likes: 741
From: Manlius, east of Syracuse, NY
Year: 2000 XJ Sport & WJ Laredo
Model: Grand Cherokee (WJ)
Engine: 4.0L
The way an electrical system is supposed to work is the battery supplies the bulk of the power and the alternator keeps the battery up to it's max capacity. When the battery gets old and can't supply the needed power, the alternator carries more of the load and gets overworked. An alternator usually only puts out around 10 amps at idle.
A fully charged good battery should show around 12.5 volts when you turn on the key. Anything less and either your alternator didn't recharge the battery fully or the battery needs to be replaced, OR you have a parasitic load when the engine is off.
These are just my own figures, but have stood me well over the years. I've gotten into the habit of shutting down all auxiliary systems; ie wipers, lights, heater, radio, etc, before turning off the engine and sitting letting it run of a minute or 2 before turning it off. Just a habit from driving pieces of **** for years, plus watching my dad shut down airplanes after flight. He's sit there letting the engine cool off a bit before shutting it down.
A fully charged good battery should show around 12.5 volts when you turn on the key. Anything less and either your alternator didn't recharge the battery fully or the battery needs to be replaced, OR you have a parasitic load when the engine is off.
These are just my own figures, but have stood me well over the years. I've gotten into the habit of shutting down all auxiliary systems; ie wipers, lights, heater, radio, etc, before turning off the engine and sitting letting it run of a minute or 2 before turning it off. Just a habit from driving pieces of **** for years, plus watching my dad shut down airplanes after flight. He's sit there letting the engine cool off a bit before shutting it down.
Newbie
Joined: Jul 2024
Posts: 2
Likes: 0
Crank no spark
Okay, here's a quick tutorial on how the system works;
Turn the key on to run, PCM wakes up and runs the fuel pump for 2 seconds to charge the fuel rails, then waits for a signal from the Crank Sensor that tells it the crank is turning.
When it gets this signal, the PCM energizes the ASD relay and the fuel pump relay. The ASD relay controls the ignition and fuel injector circuits. The ignition coil and injectors are constantly powered by 12v if the ASD relay is on and the ignition and injectors are grounded thru drivers in the PCM.
SO, check the coil primary wire for power while cranking the engine. Also check an injector for power the same way. These are 12VDC, so set your meter accordingly. I know you have no spark, but if you have no power to the injectors as well, the ASD relay isn't pulling in or the CPS isn't delivering a signal to the PCM.
If you DO have power to the injectors, chances are the problem lies with the ignition system, ie; coil and cam sensor.
That's about all I can think of for a quick diagnosis. Good luck.
Turn the key on to run, PCM wakes up and runs the fuel pump for 2 seconds to charge the fuel rails, then waits for a signal from the Crank Sensor that tells it the crank is turning.
When it gets this signal, the PCM energizes the ASD relay and the fuel pump relay. The ASD relay controls the ignition and fuel injector circuits. The ignition coil and injectors are constantly powered by 12v if the ASD relay is on and the ignition and injectors are grounded thru drivers in the PCM.
SO, check the coil primary wire for power while cranking the engine. Also check an injector for power the same way. These are 12VDC, so set your meter accordingly. I know you have no spark, but if you have no power to the injectors as well, the ASD relay isn't pulling in or the CPS isn't delivering a signal to the PCM.
If you DO have power to the injectors, chances are the problem lies with the ignition system, ie; coil and cam sensor.
That's about all I can think of for a quick diagnosis. Good luck.