Bad Ecu Relay

[billison]

is it common for these to just go out? When to
Move the car and no prime. Tested the fuel pump relay and it wasn’t getting power from
The ecu. Checked the ecu relay and I have Power at #2 and #4 and a ground on 1, and if I jump 4 or 3 it primes. Plus the relay was warm. I assume these are the signs of a bad ecu relay..

My car is pretty torn apart so everything gets banged up pretty good and it was a deep pressure washing 2 weeks ago for paining purposes ( no interior).

Like I said, all signs point to a bad relay, didn’t know if I should look at other stuff too

 

[imp]

Buy a new relay for 10 bucks, plug it in in place of the old one, and find out. Not rocket science. imp

 

[billison]

That’s the plan. But I didn’t know if something would cause it to short or something.

 

[a91what]

The ecu grounds the relay, so if checking to ground you will get no reading. I chased my tail around for a bit untill I figured this one out..... Lol.

 

[billison]

The ecu grounds the relay, so if checking to ground you will get no reading. I chased my tail around for a bit untill I figured this one out..... Lol.

What cha mean?

Like if the ecu is out you won’t find ground?

 

[a91what]

Ecu does not supply 12v. The relay gets 12v from a fuse then the ecu supplies ground to one side of the coil to trigger the relay.

 

[jrichker]

What cha mean?

Like if the ecu is out you won’t find ground?

No computer plugged in and functioning properly, the fuel pump relay doesn't work...

Automobile computers use current sink technology. They do not source power to any relay, solenoid or actuator like the IAC, fuel pump relay, or fuel injectors. Instead the computer provides a ground path for the positive battery voltage to get back to the battery negative terminal. That flow of power from positive to negative is what provides the energy to make the IAC, fuel pump relay, or fuel injectors work. No ground provided by the computer, then the actuators and relays don't operate.

One side of the any relay/actuator/solenoid in the engine compartment will be connected to a red wire that has 12-14 volts anytime the ignition switch is in the run position. The other side will have 12-14 volts when the relay/actuator/solenoid isn't turned on. Once the computer turns on the clamp side, the voltage on the computer side of the wire will drop down to 1 volt or less.


The picture shows the common ground point for the battery , computer, & extra 3G alternator ground wire as described above in paragraph 2. A screwdriver points to the bolt that is the common ground point.

The battery common ground is a 10 gauge pigtail with the computer ground attached to it.
Picture courtesy timewarped1972

Correct negative battery ground cable.

The computer's main power ground (the one that comes from the battery ground wire) uses pins 40 & 60 for all the things it controls internally: it comes off the ground pigtail on the battery ground wire.
This is a must have ground for the computer to operate properly.
Due to its proximity to the battery, it may become corroded by acid fumes from the battery.
In 86-90 model cars, it is a black cylinder about 2 1/2" long by 1" diameter with a black/lt green wire.
In 91-95 model cars it is a black cylinder about 2 1/2" long by 1" diameter with a black/white wire.
You'll find it up next to the starter solenoid where the wire goes into the wiring harness.

 

[a91what]

 

[billison]

I follow now.

 

[billison]

Tossed a new one in. 20 friggin dollars. But she fired right up. It looked like the original unit. I’m gonna just assume it got beat up when I was cleaning the floorboards.

 

[jrichker]

I am glad to hear that you got it working good.

It seems like $20 is a lot to pay when the innards are the same as a $5 relay. The main difference is the plastic case that the actual working parts of the relay fits in. It is just like everything else: if you want to play, you have to pay first.

 

[billison]

Yup. I leaned how to trouble shoot 2 relays so it’s cheap school.