no power to the main relay

[orangesky]

I got a great deal on an 89T that the previous owner was unable to repair. I have ambitious goals for the car but need to make it run first .

All of the vehicle accessories work, the car cranks but doesn't have fuel or spark. The 7mgte has no power going to the ECU.

All the fuses under the hood check out OK and I swapped my other fuses in there just in case there were maybe some small cracks I couldn't see. All the fuses in the driver kick panel are also OK.

On the ECU I verified that "Batt" and "IGSW" both have power. Also, "E01" and "E02" had ground. However, "+B" and "+B1" did not have power.

The main relay does not have power going to it, nor did any of the terminals it plugs into. The 15A EFI and 30A AM2 fuses both have power.

If I run a wire straight from the battery to the Main Relay wire (brown-red), the ECU has power and the car starts. I swapped the Main Relay with one from my other mk3 and that didn't fix the problem.

I checked the wire that connects from the battery to the fusebox (white) and there is no fusible link within it nor any signs of damage.

Thoughts?

 

[jetjock]

http://www.cygnusx1.net/Supra/Library/TEWD/MK3/manual.aspx?S=Main&P=47

If the ECU has ground and Batt power, once power is applied to IGSW M-Rel will have power. M-Rel is what energizes the main relay.

If the EFI fuse has power (in your case it must because Batt has power) but that power is not present at the main relay socket (but bringing power to the socket works) you must have a problem in J/B 2 (the fuse box):

http://www.cygnusx1.net/Supra/Librar...px?S=Main&P=19

Be sure to check M-Rel though because without it power can't be passed to +B and +B1 even after you get power from the EFI fuse to the relay...

 

[3p141592654]

JJ is right of course, the only way you can have power at the BATT terminal of the ECU and no power on pin 4 of the Main relay is a fault in J/B 2 Inner Circuit.

http://www.cygnusx1.net/Supra/Library/TEWD/MK3/manual.aspx?S=Main&P=19

That would be a very unusual failure. I would triple check that there is no voltage present on pin 4 of the main relay before I pulled that J/B out. Also, I would check for continuity from the EFI fuse to the main relay pin 4 and (2F) pin 5. Those should all be connected together.

 

[jetjock]

Ugh. I meant J/B 2 but linked to J/B 1. Corrected. Thanks 3...

 

[orangesky]

Part of the goal of this car is to put a 2jz in it, is it worth it to continue troubleshooting this? I'm afraid the problem will follow me with the new engine in there, but I don't want to spend much more time on it... Will this fusebox be used with the 2jz?

 

[jetjock]

I suppose it all depends on how long until you put the 2J in. It's a simple problem though and therefore should be simple to fix even if it did follow. In fact I suspect it's even simpler than I'm making it out to be.

Btw (and also speaking for my esteemed colleague) you're welcome...