Engine Fuse Keeps Blowing
 

So, my car random died one sunny afternoon after shifting from first gear. Got it towed home, and began investigating. After a couple of hours my searchs led me to the Engine fuse under the dash. It was toast. So I replaced it with another 15A and tried to start. That blew too, so I put a 30A just to see if it would start and it did for a while and then it blew as well. I did not smell and smoke or anything the fuse just keeps blowing. I've talked to a few people a few of which being mechanics and most of them said it could be my fuel pump dying. Anyone have any similar problems? Could it be my fuel pump? It's a walbro 255 and it's only about two years old.

It's best to replace a 15 amp fuse with another 15 amp fuse. Engaging in such experimentation will never solve the problem and enhances the chance of it making things worse. With that said, your engine fuse provides power with the key to "on" via a Black/White wire to your Main Relay, Alternator, and Circuit Opening Relay.

The wiring to the alternator is simple and the Black/White wire is plugged into the back of the alternator by way of a two wire plug that also houses a White/Black wire. Check the pic below to look at the alternator diagram provided, and make sure you don't have these wires mixed up.

Also, how long after startup does it take for the fuse to blow?

http://img256.imageshack.us/img256/4...rwiring.th.png

You could rule out the Main Relay as a cause to your problem by disconnecting both plugs from underneath the relay. Then take two small lengthed jumper wires and use one of the jumper wires to bridge the Black/Green wire to the Black/Yellow wire and the other jumper wire to bridge the White/Blue wire to the Black/White wire. In jumpering these wires, in addition to the removal of the two wire plug, it will fully bypass the relay. Then try to start the car and see what unfolds.

Well, with a 15 amp fuse in it just blows as soon as I turn the key. I only did the 30 amp once and it started for about 2 mins then blew. I'll check the alternator wiring but I had that professionally installed unless they were stupid and missed something. My car was running fine for about 4 months and just did this out of the blue, no previous problems with fuses.

Will try this as well and post back

You could also check the fuel pump to some degree as a cause for your problem by jumpering the fuel check connector in the engine bay and then turn the key to on and this will activate the fuel pump.

Does the fuse blow with the key in the "on" position as well or just the "start" position?

EDIT:

Also, to check for a short in the wiring you can remove the 15 amp fuse and use the voltmeter and connect both of the meters leads to both of the terminals in the fuse slot and if voltage is present then you likely have a short. No key is necessary for this test.

Fuel pump seems to be running like a champ. It's making the noise at least when I do that. As for voltage where the fuse is I checked and there's like 0.01 volts I don't know if that means a short or not. alternator wiring is fine I'm just going to check the main relay right now.

Also: Fuse blows when key is In "on" position not start position sorry.

When you're finshed checking the main relay, remember to remove both jumper wires or it will help to drain the battery a bit.

Earlier I suggested you jumper some wires related to the Main Relay and that was a bit of overkill for all that's really necessary is to disconnect the plug with two wires only.

Also, I read a post by "HAILERS" who was responding to a member with the same situation as yours and he suggested pulling the two wire plug off of the Main Relay, the two wire plug off of the Alternator and pull the plug off of the Circuit Opening Relay. Next, you would place a working engine fuse into the fuse box and then turn the ignition to on and observe if the fuse blows or not. Next, if the fuse doesn't blow then you would start to reconnect one of the three plugs that were disconnected and see if the fuse continues to blow and if not then reconnect a second plug while leaving the first plug reconnected alone and see what happens and if the fuse still holds reconnect the final plug. This method will allow you a better grasp of which item in the circuit is the troublemaker.

Lastly, has there by chance been a fuel cut switch added to your fuel pump circuit?

I will have to try that method, I havn't had time to finish the first test anyways so I will start over with that one.

And Yes, a fuel cut switch has been added to the circuit. It's just a basic toggle on/off switch if that matters.

Just eliminate each item fed by the ENGINE fuse one at a time.

Pull the two wire plug off the Main Relay and put the key to ON and wait. If the fuse does not blow that isn't it.

Pull the plug off the Circuit Opening Relay and put the key to ON and wait. IF the fuse does not blow it isn't that item.

Prior to the above Circuit Opening Relay check, pull the fuel pumps elect plug apart and go to ON with the key and at the same time jumper the fuel pump check connector. IF the fuse does not blow it isn't the fuel pump.

Pull the small plug off the alternator. Key to ON and wait. IF the fuse does not blow that isn't the problem.

IF this was an automatic you'd pull the plug off the Lock Up Relay and key to ON and wait. IF the fuse does not blow that isn't the problem.

That's all the ENGINE fuse does in life. I'd suspect the home made fuel cut switch that is on your car is the real problem.

Most of this is just a repeat of things said previously in this thread.

Look at the series four wiring. Look at the top of each wiring page. Where ever you see the line 1 with a splice going to it with the numbers 1 with (1) next to it, that item is fed by the ENGINE fuse and those are the only items you need to look at.

Thanks for the info everyone. I have a whole day tomorrow to do some testing. And will find out for sure what it is. The switch has been good to me for a longggg while never had any problems but No reason to rule that out like you said it could be the real problem. BTW I did make sure the switch was installed properly (Meaning it was helped put in by a professional) so it's not like I just connected some random wires hahaha Anyways I now have all info I need to finish off this problem. Thanks again.

lol found a couple problems alll started by one stupid thing....Well, my main relay was dead, i replaced it and bought a bunch of new 15a fuses, but....batt was dead so got a boost. Car started up like a champ but as soon as jumpers were disconnected the engine died after 30 secs or so. Batt wasn't being charged. Looked behind the alt only to see this little spade connector hanging there....which probably caussed all my problems to begin with....haha needless to say, tightened the connector and triple checked the rest of my e-bay. Thanks for the help guys, appreciate it!

Happy endings are good. Now for a late night horror flick. Let the blood letting begin!

Hi, all I'm having the same problem but when I unplug, the circuit relay, main relay, and alternator, and turn the key to the on position my 15 amp engine fuse blows. Any ideas?

Must be a grounded out wire or two wires melted together or something.

I'd try looking under your dash and see if you discover some melted wiring.

Installing higher amp fuse will just allow the wiring too heat up more before the fuse blows and possibly burn up whatever is getting fried even more.

Check your fuel pump mine kept blowing do to a bad pump

If the car was ever an automatic it then would have wiring for the Lock Up Relay in addition to the items you mentioned.

Its a manual, a s4 with a jdm swapped t2 engine, the passenger side harness is used/new. I unplugged the fuel pump and the fuse is still blowing. Man I hate electrical. Anyone have any other ideas to isolate the short?

You need to do a series of ohm tests to isolate the troubled section of wiring which is likely going to result in the B/W wire, powered by the Engine fuse, being grounded out.

if you have a CAI filter, check to be sure it isn't resting on the 2 step fuel pump relay wiring behind the headlight. also check your pump switch wiring to be sure it isn't grounding out on the chassis.

I've isolated the short to somewhere in the 19 pin/wire harness connected to the ecu (middle of the three plugs, the left two of the three plugs are newly installed and run on the passenger side). Next step is finding which one. To do the ohm test I just put my multimeter to ground and positive lead to said wire in question?

You ohm a wire by placing a meter lead on one point of the wire, thus the Red meter lead is placed at one point of the wire for example and the other meter lead to another point along the length of the wire and when set to ohms the multimeter will tell you something about the segment of wire located between the two meter leads. A low ohm reading indicates little resistance, which is something that does not occur if the wire is grounding out.

So the wires should have no resistance? If they have some or infinite they are open/shorted? That being said are the black white wires power wires? With the power and key on and fuse out, because it will blow, with the emission harness i believe the short is in unplugged from the ecu, the black white wires at the plugs are showing ground versus power. I'm using a logic probe. Does that mean they are being affected?