Wiring Harness, ECU, and Continuity

[Tae361]

I'm in a bit of a bind in finding out why I keep blowing my EFI fuse and have narrowed it down to some sort after going over EVERY mechanical part wired to the harness and EVERY ground point atleast 10+ times.

I was wondering if there is an easier way of testing the continuity of each wire that runs through the harness between the relay and the ECU without hacking up the harness and individually inspecting each wire. I know that my multimeter wont reach from the ECU clips to the yellow connector before the wires enter the fuse box to the EFI fuse and relay.

One thing I dont understand when checking the ECU in the TSRM is how it says-

HINT: Perform all voltage measurements with the connectors connected.


How am I supposed to fit the anode and cathode into the ECU pins with the connectors connected??

 

[deabionni]

How am I supposed to fit the anode and cathode into the ECU pins with the connectors connected??

Get to the wires from the back side of the connector. If your meter has probes that come to a point, then you can follow the wire through the back of the connector to make contact with the pin while the ECU is still connected.

To test the harness itself for continuity, I found it easiest to unplug the ECU & related connectors under the dash; and pull the harness through the firewall. Once done, you can check the entire harness with a multi-meter while it's all in the engine bay.

 

[Tae361]

Get to the wires from the back side of the connector. If your meter has probes that come to a point, then you can follow the wire through the back of the connector to make contact with the pin while the ECU is still connected.

My meter does have probes that come to the point but they are pretty thick. As for both checking the ECU and harness could I attach wire to the probes so I can connect one anode in the engine part of the harness and use the cathode to test the wire from inside the car, I really don't want to pull the harness through the firewall that would be the last resort. For the ECU I'd hook wires up to both the anode and cathode and slip them in behind the connector on the ECU. I dunno if that may screw up my voltage readings though.

 

[Tae361]

So I was able to test every wire I could find attached to a connector for continuity at the ECU and every wire tested out perfect. I decided to detach the connector to the fuse box for all of the 15A fuses and found some corrosion on the pin for the Black-Red wire going to my 15A EFI fuse. Could this be a reason it is blowing?

I was unable to test my ECU since my battery was dead and I will let it charge tonight. I will be out there testing the ECU tomorrow for anymore possible information to consult you guys with.

 

[jetjock]

Anode and cathode?

Testing must be done with things connected because the ECU deals with voltage, not resistance. You can buy a set of back probes for peanuts. As for making the meter leads reach during continuity checks you can always extend them. That's what a noob would do. A pro would just short to the chassis and use that as the extension.

There are several techniques that can be employed for blowing fuses. Current limiting by using a light bulb or a power supply, resistance to ground checks, circuit isolation, current tracing, on and on. Or you could just keep putting bigger fuses in. I wouldn't recommend doing that though

 

[HommerSimpson]

when you say blow ? you mean you put new one in and turn key on it blows ? turn over and it blows ? cranks up and runs for a minut and blows ? or last for hrs ? days or weeks ?

 

[Kckazdude]

Easiest way I have ever found to test a harness.

http://www.napaonline.com/NOLPPSE/(S(cewsf1452aqklr55iuryzz55))/Detail.aspx?R=BK_7001084_0006398698

 

[Tae361]

when you say blow ? you mean you put new one in and turn key on it blows ? turn over and it blows ? cranks up and runs for a minut and blows ? or last for hrs ? days or weeks ?

I turn the key and it blows.

Testing must be done with things connected because the ECU deals with voltage, not resistance. You can buy a set of back probes for peanuts. As for making the meter leads reach during continuity checks you can always extend them. That's what a noob would do. A pro would just short to the chassis and use that as the extension.

There are several techniques that can be employed for blowing fuses. Current limiting by using a light bulb or a power supply, resistance to ground checks, circuit isolation, current tracing, on and on. Or you could just keep putting bigger fuses in. I wouldn't recommend doing that though

I did what noobs do and extend the lead using fresh wire, from now on I will just short to the chassis.

I did find out that the probes are small enough to stick into the connectors from behind so I don't have a problem with that, and I plan on testing the ECU when my battery is charged so I can have the proper voltage running through it, otherwise it would be useless without the battery connected I know.

With the techniques for blowing fuses, you want me to test the amount of current that is running through the fuse? Since its obviously higher than 15A which is why the fuse is blowing- What information would this provide me to find the reason why there is so much current flowing through this fuse? Would this show me that there is too little resistance in the circuit?

By I = V/R
R would have to equal 0.8ohms or less for the fuse to blow.

EDIT: I also found that the same Black-Red wire that goes to the EFI fuse also goes to the fuel pump resistor.

 

[Tae361]

So I finally got a chance to go to my car today and test out a few culprits I found from researching quite a bit on these forums. Apparently the first thing I checked which I would have never thought of doing seemed to shed some light on the situation.

I disconnected my ECU and turned on the ignition and my 15A EFI fuse did not blow. I then plugged it back in and the fuse blew. I also double a triple checked my 02 sensor as well as my A/F ratio's splicing into the 02 sensor harness and everything is good, just alittle grease.

This ECU was working fine before the swap but I guess when I cris-crossed wires I shorted it out. I see the ECU on the wiring diagram as its own entity so it could cause a short at the fuse.. Does this sound plausible?