tmac35235

89 jeep cherokee 4.0 was running great. Cold weather killed my battery. So went to jump it off and hooked the battery cables up wrong for a split second and now i have no spark. Any ideas?

Bustedback

Check your fuses and fusible links

TwoXJS

I was in the same boat as you before. Hooked them up wrong and didn't realize it until it was too late. Ended up frying the computer from trying to turn it over. Believe it or not, the starter was turning BACKWARDS! Yeah, no joke....Then the computer caught on fire. Lucky we had a fire extinguisher right next to us. I would do what Busted said, check fuses and links first.

cruiser54

Yep. They're connected to this relay.

RTorrez1

I don't believe it! Because it is not possible! If it's hooked up backwards it can cause damage but it will never run backwards.

BlueRidgeMark

Way back when, White Freightliners used to come from the factory either positive or negative ground. Roll of the dice which one you got when you bought a truck.

Why? Back when the company started, they ordered their first batch of starter motors and didn't specify which way they should be wired. So, some came one way, and some came another way. They just put some juice to them, found out which way they spun, and sorted them that way.

I guess I can understand the first order being that way, but they did this nonsense for several decades before they finally wised up. Stayed that way up into the late '70s or early '80s, IIRC.

It made things fun when installing two-way radios in them. Always had to check the polarity, and if they were positive ground, time for a DC-DC inverter. Oh, well, that just added to the profits.


All that to say, a DC motor will spin either way, depending on the polarity applied. So, a starter motor spinning backwards? Maybe...

But I'm with you on this, RT, that story does have something of an aroma about it.

TwoXJS

I didn't believe it could either, but we heard the motor spinning when the key was turned. The gear wasnt engaging the flywheel though

tmac35235

Who ever had the jeep before me rewired a lot of the main power cables and removed the fuse links. I believe it killed the relay your talking about in the picture. I hope that fixes it.
Thanks for your input.

DFlintstone

Look again....that start relay is near the battery. One of the large posts should have a fan or about 5 wires coming off it. See if any look burnt.

Just no spark? Got dash lights and/or gauges? Do you hear the fuel pump run a couple seconds when you first turn it on?

If you don't have a digital meter, get one. Even the Harbor Freight cheap-o meter is fine. Less than $5 (I use them allot to keep my better ones safe).

Your Jeep is pretty tough, even the ECU. Cruiser would know better than me but I might suspect the ICU (Ign. Unit) before the ECU. Even though the reversed cables wouldn't harm it, I'd take the 90 seconds to check the CPS anyway. It's the heartbeat, nothing will work without that.

I'd check ground resistance, See Cruisers stuff. Engine to body, both of those to battery negative, and the sensor ground circuit.

If the CPS is up to snuff and the grounds are good that narrows it down. Radi mentioned a way to check the trigger wire from the ECU to the ICU that I didn't fully understand. That may end up on your list!

OH! And welcome to the forum!

tmac35235

Thanks Flinstone for the help.
I replaced the cam and crank position censer just 2 months before I crossed my battery cables and the jeep was running fine up until I crossed the cables. Doesn't both cps's report back to the ECU? Also the cam position censer is just a solid state coil right? I am not sure how to check it.