bad software/ECU ground

[Previologist]

Yeeeeeaaars ago i had this problem where my 97 would start and die immediately. To make a long story short and because I neither remember nor understand the details, someone on another forum thought it had lost a software ground. He had me try cutting a wire on a harness under the dash, over the brake pedal area, and run it directly to ground with a cheapie toggle switch. Bingo. I've been driving it that way for many years.

The only drawback is the fuel pump will run when it shouldn't, but that's what the toggle is for. I have never actually used it though and its worked great for at least 10 years and i haven't killed the fuel pump yet.

This was meant to be a temporary fix but since it works I've never pursued a permanent fix, or seen a need to.

 

[brillo_76]

Do you know which wire you cut and grounded? Maybe it was part of the immobilization system..

 

[BajaRunner96]

Been having the same issue with my 96 2.7 but I realized that if I unplug the TPS sensor it would maintain but idle surge to 1500 rpms and became a gas guzzler.

 

[Previologist]

Do you know which wire you cut and grounded? Maybe it was part of the immobilization system..

I never noticed anyone had replied to this before now. I will get a picture tomorrow.

 

[brillo_76]

No biggie....

 

[Previologist]

Looks like I grounded a green wire off the relay above the driver side kick panel. I guess it's some sort of light relay, 98987-02012

I don't really remember, its been so long. Maybe i added that green wire too, dunno.

But it worked. Without it, the truck will crank but won't run for more than a second. I've never been motivated to pursue it further because it works.

 

[brillo_76]

Interesting...

 

[Previologist]

Lol...

 

[negusm]

Looks like I grounded a green wire off the relay above the driver side kick panel. I guess it's some sort of light relay, 98987-02012

From the Circuit Diagram that looks like the COR (Circuit Open Relay). It's probably bad. But weird that it works intermittently like that.

 

[Sparky 97Runner]

Yeeeeeaaars ago i had this problem where my 97 would start and die immediately. To make a long story short and because I neither remember nor understand the details, someone on another forum thought it had lost a software ground. He had me try cutting a wire on a harness under the dash, over the brake pedal area, and run it directly to ground with a cheapie toggle switch. Bingo. I've been driving it that way for many years.

The only drawback is the fuel pump will run when it shouldn't, but that's what the toggle is for. I have never actually used it though and its worked great for at least 10 years and i haven't killed the fuel pump yet.

This was meant to be a temporary fix but since it works I've never pursued a permanent fix, or seen a need to.

That's pretty interesting that your ECU lost a ground like that. Good troubleshooting from the guy on the other forum though. I take it that's a maintained toggle switch? Here's the schematic for the 97 4Runner. You can see the green/yellow wire coming from the ECU feeding the circuit opening relay.

 

[Sparky 97Runner]

Also, make sure the ECU grounding point on the driver side of the intake manifold is connected good and clean.

 

[Previologist]

From the Circuit Diagram that looks like the COR (Circuit Open Relay). It's probably bad. But weird that it works intermittently like that.

Not sure what you mean by intermittently. But I agree its probably the COR, from your post on the other forum and this one I dug up after reading that..

Making a cor (circuit-opening relay) test relay

It seems mine is an easier way to get the same effect as the "test circuit" although I can't take credit for the idea.

 

[Previologist]

Also, make sure the ECU grounding point on the driver side of the intake manifold is connected good and clean.

The one hidden under that thick oil and dirt layer? Maybe I'll find it when I do the valve cover gaskets next spring.

I'm not sure what you mean by "maintained" toggle switch.

 

[Sparky 97Runner]

The one hidden under that thick oil and dirt layer? Maybe I'll find it when I do the valve cover gaskets next spring.

This one here.

 

[Sparky 97Runner]

I'm not sure what you mean by "maintained" toggle switch.

Maintained vs momentary. In your case maintained switch maintains its position until you push or pull it to the other position. A momentary switch would only maintain its position until you stop pushing the switch.

 

[Previologist]

Maintained vs momentary. In your case maintained switch maintains its position until you push or pull it to the other position. A momentary switch would only maintain its position until you stop pushing the switch.

Ah. Yes that's a maintained toggle switch.