ok getting desperate and need help fast
 

ok so my 92 is doing something really odd. it is randomly blowing the main 80Amp underhood fuse. Here is what happens,,,driving along and everyting runs fine, stop at a red light and if I accelerate even with the slightest amount of force it will essentially skip and act like its about to choke, then it acts normally until I switch the car off, when I cut off the car the fuse pops. I have went though 6 fuses in 3 weeks, the battery terminals are snug and clean, the fuel pump is engaging normally, the NGK plugs only have about 10,000 miles on them, fuel filter is fairly new, the cap and rotor look decent, Ive had the timing checked, the injectors are crystal clear, the belts are all good and the ECU is not throwing out any codes, according to the ECU everything is normal. Experts fire away at this because I am at a loss.

RE: ok getting desperate and need help fast
 

This is a long shot but is your engine/battery grounded well? The only thing that even comes to mind is that your alternator is overcharging or something.... i'm no expert but I'm kinda at a loss as well... Is it injected or Carb?

RE: ok getting desperate and need help fast
 

its the standard fuel injected F22A1 16-valve 4-cylinder. the battery is fine it has not lost any kind of charge, I havent had the alternator tested yet. I was thinking either the ignitor or the main relay having something to do with it. while Im thinking about it whats the diff between the ignitor and the ignition coil and which one has the ignition wire running from it to the top of the distributor cap?

RE: ok getting desperate and need help fast
 

The coil runs has a wire that runs from it (looks like a spark plug wire) that goes to the center of the distributor cap, the igntion unit or ignitor is inside the distributor... I never considered it but I suppose a coil discharging may blow that fuse... I'm not certain, just trying to "brainstorm"

RE: ok getting desperate and need help fast
 

I had the same thought, because like I said its when I step on the gas to accelerate it will hop and miss almost like a misfire, but then its fine until I cut the car off thats when it pops that 80amp fuse.

RE: ok getting desperate and need help fast
 

If it does it consistently you could try putting a volt meter on the wires and seeing if it skyrockets when the car is shut off....

RE: ok getting desperate and need help fast
 

I once had a fuse on a microwave oven that kept blowing. After opening the system for the 3rd time, I looked closely at the fuse holder and noticed some indication of heat. The fuse/holder contact was slighlty loose, apparently causing enough resistance to generate heat and partially melt the fuse. After a number of cycles it would fail.

Check your fuseholder very carefully for good contact and/or secure connections. Heat damages a fuse by softening the solder connections causing the fuse to fail below specification load.

good luck

RE: ok getting desperate and need help fast
 

thats the thing, the fuse4 is secure because its held in with 2 small phillips head screws. and its not really consistent either. since I posted this, it hasnt blown another fuse. It may blow one the next time I drive or it may be another 4 months before it does this again..totally random

RE: ok getting desperate and need help fast
 

One other longshot - doesn't sound like it's your problem, but an easy thing to check. If you alternator belt is slipping, sometimes the regulator will boost the alternator's output during the time the belt is slipping to compensate for the lower output. Then when the belt catches and drives the alternator to full rotation again, the boosted output can show up as a much higher voltage. Higher voltage leads to higher current, all things being equal, so that *could* be blowing your fuse.So, unlikely as it may be, check your alternator belt.

Rod

RE: ok getting desperate and need help fast
 

alrighty, checked the alternator, the alternator belt and they are both fine, cleaned all of my electrical connections, nothing looks like its grounding out anywhere... It Blew another one saturday night, I went out with some freinds at a restaraunt, the car sat for about an hour and a half, I came out started it, it was night so I turned on my headlights, drove it to the exit and all fine, I step on the gas to pull out and the entire car lights and all cut out for about a half second then came back to life, I drove it normally until I got home, the fuse blew yet again when I shut the car off..

RE: ok getting desperate and need help fast
 

Looking at the charging circuit diagram, the sole load path that could blow only the No. 15, 80A fuse and no others is the B+ wire from underhood fuse box to alternator. I see several possibilities; 1) an intermittent short somewhere in the B+ wire from underhood fuse box to alternator 2) the battery has an intermittent internal short that somehow causes a high current demand spike on shutdown and blows the fuse w/ high current from the alternator, instead of from the battery. If you have a spare battery, you might try substituting for a while to see if this cures the problem, 3) an intermittent short in alternator field winding, voltage regulator, or rectifier causing Fuse 15 to blow. Possibility 1) may be more likely, but will require opening into the wiring harness to inspect the B+ wire. Try inspecting all the B+ wire you can access first.

This is one of those problems that may require simply substituting parts until you eliminate the fault. I have found that used parts offer a reasonable cost way to do this.

good luck

RE: ok getting desperate and need help fast
 

that is a GREAT help thank you Texas.

RE: ok getting desperate and need help fast
 

Wow. This is a very informative thread. Be sure to keep us updated! Especially if you figure out what the problem was!

RE: ok getting desperate and need help fast
 

well I checked the visible parts of the B+ wire and everything is still intact, IE no charred areas or exposed wire, but I know that there can be a short with all the sheilding still in place. the Battery is only 5 months old, it is a SuperStart Maintenance free battery from O'reilly, the Battery that was previously in there was an AutoCraft Silver from Advance, but that one was in there when I bought the car. will keep you guys updated. just out of curiosity how much would a complete new B+ wire be? and is that something I can get at a parts store.

RE: ok getting desperate and need help fast
 

Just a reminder - while you are working on electrical stuff under the hood make sure you ALWAYS take off any rings you are wearing. If you get the ring between a hot wire and ground it'll take your finger right off.

A continuity checker is a useful tool for checking for shorts. For instance, if you can disconnect both ends of the B+ wire and connect one end to the checker and the other probe on the checker to ground, try to manipulate the wire at various places along its length. Gently bending or stretching, shaking etc. If you get any reading on the checker - like around 0..3 ohms - you have a short.

Having said that, considering that your problem only happens when you shut off the engine, it doesn't sound like a mechanical problem. Alternator or regulator sounds more likely.

Rod

RE: ok getting desperate and need help fast
 

i am not doubting you...but how will it take your finger off? i am having trouble visualizing that.

RE: ok getting desperate and need help fast
 

Just wondering, could the engine shudder/shake at shutdown cause something in the alternator - fuse box circuit to vibrate and short over? I would be curious to take a look at the wiring in the fuse box to see if any are actually able to contact another.

RE: ok getting desperate and need help fast
 

smaglik: i am not doubting you...but how will it take your finger off? i am having trouble visualizing that.

--------------------------------------------

Depends on which wire you come in contact with - but a gold ring (for instance) between B+ and ground will conduct current real well and become red hot very quickly - faster than you can react. The temperature is what does you in and if the ring makes it tored hot, that'senough to take off the finger... so I'm told. A pal of mine *almost* lost his finger that way. Had to take antibiotics, though because the skin under his ring became badly blistered and got infected.

RE: ok getting desperate and need help fast
 

well I dont wear any rings so that wont be a concern, also when I work on any car I have a pair of Craftsman Mechanics gloves that I wear. Not sure about the engine shutter considering theres something going on while the car is running that causes the fuse to blow when I shut it off, I know when its going to blow before I cut the car off because from a dead stop when i start to go the whole car will cut out for about a half second then come back to life, then it will run fine until I shut it off and thats when the fuse pops. Its been running fine here recently again and its been raining the past couple of days so I havent been able to check the rest of the wire, but when it stops I'll give that wire test a try.

RE: ok getting desperate and need help fast
 

bought a new battery yesterday. got a sear die hard, pulled out of sears parking lot and it did the same thing, had to replace another fuse when I got to the house, so short in the battery eliminated as a possible cause.

RE: ok getting desperate and need help fast
 

You might try measuring resistance to ground of the B+ wire w/ the wire separated from alternator and fuse box. A good wire should always show infinite resistance or open circuit. If you wiggle, push, &pullthe harness around a brief short circuit occurs, the B+ wire must be replaced. I would suggest buying a separate equivalent wire and wire tying to existing harness rather than tear up the harness to extract the defective B+ wire.

good luck

RE: ok getting desperate and need help fast
 

where can you buy that B+ wire at?

RE: ok getting desperate and need help fast
 

I'm not sure what gauge wire, but match the original wire. Check shop manual for correct wire gauge or dimension and go to any automotive electrical shop for quality wire.

Did you find a short in the B+ wire?

good luck

RE: ok getting desperate and need help fast
 

I have been working a lot recently and havent had time to get in and try it out plus I dont have any kind of electrical wire tester so thats been hindering me as well.

RE: ok getting desperate and need help fast
 

One further test would be to disconnect and securely insulate the B+ wire at the Alternator. I would also disconnect the alternator plug connector. You would be running on the battery so don't try to go too far. If this fixes the problem, you know the fault must be the alternator. If problem still occurs, it pins the fault on the B+ wire itself (short in harness somewhere). As long as you don't run lights or AC, the battery should run the car for a couple of hrs easy.

good luck

RE: ok getting desperate and need help fast
 

interesting approach....Ive tried that on older chevys to see if the alternator or battery were going out but with cars that are injected and have ECMs I didnt want to try it for fear of messing something up. I'll give that a shot. Do you know if I can get this wire at an auto parts store or is it a dealership item??

RE: ok getting desperate and need help fast
 

You should be able to purchase B+ equivalent wire at any auto parts store. B+ provides charging current to the battery and supports load when alternator is working. When you remove the B+ wire and disconnect alternator, the battery must supply all current. I don't think you can damage the ECU, but can't be certain.

good luck

RE: ok getting desperate and need help fast
 

alrighty I'll give that a shot then.

RE: ok getting desperate and need help fast
 

chk the white/red wire that goes to the alternator, make sure it does not have a bare spot somewhere.. also there could be a bare wire under the under-hood fuse box,, and lastly could be a bad alternator itself
i'd look at the wiring harness first

sounds like something is moving just enough to make it touch ground and blow the fuse , if it was a true short it would blow the fuse instantly

RE: ok getting desperate and need help fast
 

thanks desert.

RE: ok getting desperate and need help fast
 

hopefully the problem has been solved, turns out it was not anything directly in the electrical system...I hadone of the metal A/C lines bumping up against the ground bolt on the alternator. Thanks all for the help.

RE: ok getting desperate and need help fast
 

MMM.. it is not the fix unless the a/c line was touching against a power source,,
the only way to blow a fuse is to give gound to a power wire or a power wire shorted to gound,,
a/c line has no power source,, ground bolt has no power source so fuse cannot blow ,,
was a/c line also touching alt hot wiring ?? if so yes fuse will blow. if a/c line was away from power wiring you will have the same issue again ..

RE: ok getting desperate and need help fast
 

Yeah. I don't think the alternatorhas a 'ground' bolt. It's grounded thru it's mounting brackets. So I assume he's talking about the big bolted hot wire on the alternator. It's supposed to have a rubber boot over the bolt, right?

RE: ok getting desperate and need help fast
 

hmm ok, I have a split wire going into the alternator.. one is the main plug that is covered by the rubber boot, and then there is another that is split off of that one that looks like a ground that is bolted to the front side of the alternator.

RE: ok getting desperate and need help fast
 

The multi-wire plug has control signals, warning light wire,field excitation, or whatever. The big wire on the front with a bolt is the HOT power lead that carries all the alternator's power over to the battery. It's supposed to have a rubber boot too.

RE: ok getting desperate and need help fast
 

aaaalrighty then, I'll set about putting a rubber boot on there. ok so thats what the metal A/C hose was hitting. that also corresponds to deserts explanation. sweet thanks guys.