Will not start

First thing is to check all of the fuses. Then get a wiring diagram and check which circuits are directly fed from the battery. Next see what you are missing, spark or fuel. It could have easily damaged the PCM and more. The problem is that every vehicle acts a bit different to a reversed polarity issue. So you have to start at the battery and work backwards. Usually anything that gets power through a relay or the ignition switch will be okay if the switch was off.

To start with, there is going to be a pile of blown fuses. Check in the under-hood fuse box, and the one inside. A large one that is bolted in the under-hood fuse box is for the generator. Expect that one to be blown for sure.

You have to be more specific. By "does not start", do you mean the starter does not crank the engine, or the engine cranks fine but it does not run?

On some cars that large fuse is just for the generator's output circuit and nothing else. On other cars, the manufacturer may use the generator's output terminal for a convenient tie point for other circuits, rather than running them all the way back to the fuse box. In that case all those other circuits will also be dead.

I am pretty sure you are going to find a lot of other smaller blown fuses. All computer modules have diodes in them between the grounds and the twelve volt feeds. Those are one-way valves for electrical current flow. They are in there backward so they are turned off. It is like they are not even there. That is, until the battery or jumper cables are connected backward. That puts the diodes "forward-biased" and they act like a dead short. That causes the fuses to blow, thereby protecting the modules from further damage. Most of the time a new fuse is all that is needed, but on occasion there will be a computer that is damaged.

The mid 1990's is right about when the insane engineers started involving the Engine Computers with the neutral safety switch function. You may want to try jumping the starter solenoid to crank the engine. That might at least tell you if the rest of the Engine computer is working.

Spark and fuel, but it does not run? That is surprising. Be aware if you are leaving the fresh air tube off the throttle body when you crank the engine, none of the incoming air will go through the mass air flow sensor. The air will not get measured, so the Engine Computer will not calculate any fuel to go with it. The engine should still run for a couple of seconds on the fuel you put in there, but it will stall after that is used up.

Besides air and fuel, you need compression and correct valve timing. Those two things should not have changed from reversed polarity. Hold the throttle open a little during cranking. The Engine Computer is going to have to relearn some things since the battery was disconnected. It my not be ready to provide the small amount of throttle opening for starting.

I am going to have to think about this some more.

Very doubtful. First of all, forget the sensors. Computers do not send signals to them. The computers may provide the supply voltage to run the sensors, but then the sensors provide data to the computers. There are only a few sensors that can prevent a cranking engine from running. The rest just have a small effect on engine performance. With reversed polarity, no computer is going to turn on, so most sensors won't get their computer-supplied voltage.

While it is possible for a computer to be damaged from reverse polarity, remember there's a diode in them to force the fuse to blow. Most of the time the fuse blows before any further damage can occur, but those diodes are very small and can't handle much current. It is possible for one to short from the excessive current, then actually crack open from the heat. At that point it is no longer in the circuit. Reverse polarity for a second time, or for an extended amount of time, can damage the computer's circuitry and fail to blow the fuse. The point is, it's impossible to know without taking the computer apart to assess the damage.

You need to connect a scanner to view live data. That will let you see what the Engine Computer is seeing from the sensors, and will help you identify if a required signal is missing.

Sorry for butting in Steve. Don't know why I didn't see your replies before I started typing.

No sweat, repeat question, I got one you got the other. Plus your answer is more complete.

Yes this is a interference motor and it will hit valves when the timing belts goes. Sorry.

Please let us know what happens.

Best, Ken

Try resetting security system see our link for this. if not listed here look online.

https://www.2carpros.com/articles/how-to-reset-a-security-system

Hi AH TRA KMENGSLOT,

Here is a link to an informative article from this site with step by step instructions and pictures and a video on what to check for when your vehicle cranks, but will not start.

https://www.2carpros.com/articles/car-cranks-but-wont-start

If you need any further help please come back to the site as we are always happy to help.

Thank you for visiting 2CarPros.

Kindest regards,

Renee
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