no power to the diagnostic check connector

[taka21]

Hey everyone im having an interesting issue. The engine cranks all day but wont start. when i jumper fp to B+ the fuel pump does not turn on (upon further inspection B+ actually has no voltage in the check connector). when i jumped power from the battery to the B+ the engine runs fine.
im getting power to both sides of the EFI fuse and im also getting power to the Main EFI relay. the CEL does not illuminate with the key in the on position and i replaced the bulb to make sure it wasn't just burned out. i replaced the EFI relay with a known good one but that didn't help either.
btw the car is an 86.5
my question is what am i missing????, any help would be greatly appreciated.
Thanks

 

[suprra_girl]

Do 2 pins in the isc have 12v with ign on?
In the big square yellow or gray connector where the ecu is check pin 9 does that have 12v?
Does the 2 b/r at the ecu in the end plug have 12v?

For you to have power on both sides of efi fuse it seems all before that circuit is fine, are you sure you swapped in a good relay? Pull up your engine bay relay block and check the b/r in the bottom of it (I'd be inclined to do this before dropping the glovebox)
I have the feeling that your main efi relay is not working for whatever reason, do you have power going in and out of the main efi relay? if so check the ground side of the relay, I think it ends up at the ground point beside the battery, also check E2 in the check connector to ground.

If your cel isn't illuminating it suggests that your 7.5a gauge fuse is out, if it is out then you have no tails, dash lights, power windows/seats, defog and heater etc

Have fun figuring it out

 

[Dirgle]

Check your 7.5A IGN fuse. Located behind the driver side kick panel.

 

[suprra_girl]

You're a good bouncing board Dirgle is ^ in regards to the cel? I see in the expanded diagrams that the cel goes to the ign fuse but in the efi section it goes to gauge fuse.
You will have to forgive me when it comes to the electrical side, I'm self taught through experience so I'm still learning all the ins n outs xD

 

[jetjock]

A lack of power on B+ and no MIL jives with the main relay being off. What Dirgle is getting at is without power to the ECU's IGSW (IGnition SWitch) input (how the box knows the key has been turned on) the ECU won't energize the main relay.

 

[suprra_girl]

Oooh, that'll be useful to remember in future, cheers jetjock

 

[jetjock]

My pleasure...

 

[taka21]

Ok so I got the car running I found that the ign fuse was not making proper contact in the junction box due to corrosion. I cleaned it up and bent the ends of the fuse in opposite directions to ensure contact and the car started right up. Thanks everyone for the help and input.

Sent from my HTCONE using Tapatalk 2

 

[Dirgle]

You're a good bouncing board Dirgle is ^ in regards to the cel? I see in the expanded diagrams that the cel goes to the ign fuse but in the efi section it goes to gauge fuse.
You will have to forgive me when it comes to the electrical side, I'm self taught through experience so I'm still learning all the ins n outs xD

Lol sorry that was a pretty short answer. The MIL being out was kind of the give away. While the MIL is indeed powered by the 7.5A GAUGE fuse. The ground is switched by the TCCS, allowing the light to function. That Diagnostic circuit, that the MIL light is apart of, is powered by the IGSW input instead of the ECU's +B line so that diagnostics can encompass the EFI main relay. In a sense placing that circuit at the very bottom of the totem pole, one of the first systems to be initialized when you turn the key, before anything externally to the ECU, including the EFI main relay. The fact that it didn't come on when the key was turned, and the bulb was checked, indicated that the 7.5A IGN fuse was the best place to start.

A lack of power on B+ and no MIL jives with the main relay being off. What Dirgle is getting at is without power to the ECU's IGSW (IGnition SWitch) input (how the box knows the key has been turned on) the ECU won't energize the main relay.

Yeah it looked like the best place to start. What did surprise me is that it started and ran by shunting power to the +B line. I didn't realize the IGSW was that independent of the TCCS circuits that are running the engine, that having it off wouldn't affect base operation. One of these days I'll pick up an extra ECU to open up and see just how the modules are laid out. Toyota has been one of the best at providing schematics for outside the TCCS. But get understandably vague about the interaction of some of the internals.

Ok so I got the car running I found that the ign fuse was not making proper contact in the junction box due to corrosion. I cleaned it up and bent the ends of the fuse in opposite directions to ensure contact and the car started right up. Thanks everyone for the help and input.

Sent from my HTCONE using Tapatalk 2

Glad to see you got it going. One more MKIII back on the road.

 

[jetjock]

That was a good call. From playing with the box on my simulator over the years all it cares about is B+. IGSW is for M-Rel control only. In fact I've used the shunting trick myself a few times. It's a quick way to verify Vc isn't pulled to ground because if it is the box will be paralyzed.

 

[suprra_girl]

Sooo, you two would be the ones to ask about mrel operation then?
Mine is near broken and I'm not sure why, I had a fancy ecu fella check over my ecu and he said it was fine but my mrel has really really bad voltage drop :/

I could never figure out why so I decided that I'm going to get studying on ecu electronics coz I really hate it when I can't figure it out, it quite bugs me lol

 

[Dirgle]

Love to do what I can to help. Might start a new thread though, since the OP resolved his issue. Make it easier for people with similar problem to search for it. I'll follow you over there. When you start it, list where you did your voltage drop tests, what the voltage drop you're seeing is. And any symptoms you believe relevant. Also since I'm in Denmark at the moment, i'll reply when I can be our time differences are pretty extreme.

 

[suprra_girl]

Will do cheers xD

 

[14u2c]

looks like the same problem I'm having. I will check and get back.