[dhuze]

I have a 93 Jeep Cherokee that keeps blowing the 30amp engine control fuse as soon as the key is turned on. I can't find the problem. It's not the ignition switch or the Crankshaft possition sensor (CPS)


The problem happened while I was driving. all of the sudden I got a pop and no more engine running.

[SSearchVT]

My guess would be that the insulation has worn through on a positive lead - shorting the system out. Start checking the grommets at the firewall and work your way from there. If it's popping a 30 amp fuse - look at the big wires first.

You can save yourself a lot of pissing around with fuses if you go to the auto supply store and get a temporary breaker to put in place. It will pop to a resettable circuit instead of blowing the fuse.

[richw]

thats a lot of power so sounds like a dead short.

1 trick is run the 12v+ first through a headlight to act as a known load

then new fuse and hook it up its crude but there may be smake show where the break is

[dhuze]

Originally Posted by richw

thats a lot of power so sounds like a dead short.

1 trick is run the 12v+ first through a headlight to act as a known load

then new fuse and hook it up its crude but there may be smake show where the break is

I tried an 80 amp fuse for a few seconds to make a "smake" show, but it didnt work. I figured whatever was causing it needed to be replaced anyways. I also popped a 40 amp fuse. The parts store ran out of 30's. I looked around for worn insulation too, but no luck finding any. Chasing wires sucks especially on an old dirty engine.

[R1slowflyer]

check your grounds from the battery, the alternator, the engine.

if those are loose a good bump or even just a little time will open the system and cause the battery to die out then when it gets a good connection again pop goes a fuse from the surge.



always check your grounds first.

[dhuze]

I checked the grounds first. It blows the fuse in my multimeter so Finding the source just got a little harder.
I'm with Rich on the dead short issue. I just need to find out whats causing it.

[SSearchVT]

This is a bad idea - so do it at your own risk. Make a substitute for the fuse out of 12 or 14 gauge household wire then look for the smoke. Again - This is a bad idea - so do it at your own risk. Personally I would unhook the ECU first...

There should only be a few wires on the Engine control circuit - take a look at the schematic in a hatnes manual - and trace them one by one.

[R1slowflyer]

If your blowing fuses in your meter than there is a short. whats your meter rated for?

[richw]

If you put the headlight in series as a load you will stop blowing fuses even if its a dead short

[dhuze]

Originally Posted by SSearchVT

.............. Make a substitute for the fuse out of 12 or 14 gauge household wire then look for the smoke. Again - This is a bad idea - so do it at your own risk.............

Ha ha ha. That was already done It didn't help. I only left it hot maybe 10 seconds. Nothing.

Originally Posted by SSearchVT

...........

There should only be a few wires on the Engine control circuit - take a look at the schematic in a hatnes manual - and trace them one by one.

I worked on that too.

Finally I did it my way and feel I have it narrowed down. I took the relays out of the fuse block and replaced them one at a time. It blows when I put the relay in for the fuel pump.

My options now are:

1) check wires coming from fuel pump
2) replace relay
3) replace the fucking fuel pump


P.S. whoever chose the location for the CPS is a fucking asshole duche bag, who should have his balls cut off for acting like a female and not using logic in it's placement :

[banzairx7]

Come on guys, these are some of the worst recomendations to solve this I have ever heard of. You NEVER replace a blowing fuse with a larger fuse! That will only make the problem worse, if not catch the car on fire.

You need a wiring diagram first off. You'll get no where without it. From that you can figure out what exactly runs off that circuit. Disconnect things from that circuit one by one. Use the multimeter to see if the circuit is still grounded after you disconnect the latest part. There maybe connectors on the circuit also. Unplugging those will take out more branches of the circuit quicker and will speed up the exact item or location giving you trouble.

Do not put your multimeter across the two terminals of where the fuse goes. Thats why you blew out your meter. Just check the non powered side of the fuse to ground. If its grounded move on to the next item.

[dhuze]

Oh Bonzair. I figured a fire would really narrow down the search for the problem. I didn't cross both of the terminals where the fuse goes. I tested the ground using the battery negative and the fuse block without the possitive disconnected. One side is always hot.
I'm done for the night on this piece of shit. I have the problem narrowed down between the fuse block and somewhere under the dash. I better find a toasty mouse somewhere under it all.
You seem to know what you are talking about. Hows about you finish what I started? I just blow fuses until I'm broke. For all I know I'm chasing the wrong wires, but it only happens with the relay for the fuel pump in so I'm chasing those.

[dhuze]

Quick somebody say "check the O2 sensor."

I finally found the short after about 4 days of chasing wires. The exhaust had burned the casing away and was contacting the wire shorting it out. I had it narrowed down to the fuel system. Too bad the O2 sensor is at the end of the line. I almost didn't check it becuase I figured that couldnt short it out.

[Honclfibr]

Originally Posted by banzairx7

Do not put your multimeter across the two terminals of where the fuse goes. Thats why you blew out your meter. Just check the non powered side of the fuse to ground. If its grounded move on to the next item.

Incorrect, when measuring voltage or impedance your multimeter is a high impedance load and will not draw any significant amount of current. It can safely be connected across any terminal you're likely to find in a home/auto setting.

If you're blowing fuses you've probably got the leads hooked up to measure current. When measuring current your meter is inline and is a low impedance source. If you connect it between the fuse in this case it will complete the circuit and now your meter is the fuse. This is not good for your meter or for the circuit.

[ZX-12R]

Originally Posted by Honclfibr

It can safely be connected across any terminal you're likely to find in a home/auto setting.

Just watch out for the high voltage side of your coils and HID ballasts if you have them. You can test those with your tongue.

[dhuze]

Originally Posted by ZX-12R

Just watch out for the high voltage side of your coils and HID ballasts if you have them. You can test those with your tongue.

Years ago I tested a coil on my running engine by leaning on it. It sucked almost as bad as the hood I stood up into.