Tell me why it won't spark!

[jetjock]

It's a simply circuit so it shouldn't be very difficult. Here's a tip: instead of the fuse use a 12 volt light bulb in place of the fuse. The bulb will limit the current. When you find the short the bulb will either go out or dim. That way you won't burn through fuses.

Btw, fuses exist to protect wiring, not loads. It's the reason they're placed as close to the power source as possible.

 

[IHI-RHC7]

Here's a breakdown of the load on the IGN fuse.

It looks like the 1I-4 pin is not used in our cars, but the wiring is ran anyway.
The two terminals that could cause a short circuit are 1I-6 and 1G-9
1I-6 goes directly to the ECU through one other harness to harness connector. 1G-9 is routed to a wire-wire connector, to the combination meter, to a second wire-wire connector and then to a third wire to wire connector before connecting to the alternator.
A particularly easy fix possibility is that you could have blown the diode in the combination meter and shorted out the battery warning light. This is not probable, but a possibility.
It is more likely that the TCCS is shorted internally due to the reversed current. The easiest way to check this would be to disconnect the T plug from the ecu and crank with a bulb in place of a fuse, like JJ suggests. If the bulb burns bright while cranking, it would seem you are still shorted, if it is dim or off altogether, the TCCS is the culprit. Remember that the car won't start with the T- plug disconnected from the TCCS, but it will help you troubleshoot.

 

[the1andonly0032]

Just to add I guess if anyone knows what this is someone has suggested that it could be the coil condenser but i really have no clue what a coil condenser is so drop a note on that too if ya will

 

[bigaaron]

Just to add I guess if anyone knows what this is someone has suggested that it could be the coil condenser but i really have no clue what a coil condenser is so drop a note on that too if ya will

A condenser is basically a capacitor used for noise filtering.

 

[the1andonly0032]

alright next thing to test is the ecu w/ crossed fingers how would I go about testing that? just unplug it and then turn the key and if the fuse doesnt blow then its the ecu that's bad...im guessing...next question where is the ecu..again i was guessing thats it would be like passenger kick panel and after I took the panel off the right side and the glove box out and everything I found a lot of wires and a big nasty plastic covering sort of thing....Is my ecu under that or somewhere else? Help and tell me where ECU is please.

 

[supraturbo510]

i had this same problem last sunday all i did was change my coil pack with a extra one i had laying around and it started up

 

[bigaaron]

alright next thing to test is the ecu w/ crossed fingers how would I go about testing that? just unplug it and then turn the key and if the fuse doesnt blow then its the ecu that's bad...im guessing...next question where is the ecu..again i was guessing thats it would be like passenger kick panel and after I took the panel off the right side and the glove box out and everything I found a lot of wires and a big nasty plastic covering sort of thing....Is my ecu under that or somewhere else? Help and tell me where ECU is please.

Yes, that is a good idea. The ecu is directly above the glove box.

 

[the1andonly0032]

alright GOOD NEWS kinda.... when the ecu was all unplugged i turned the key and FUSE didnt blow! I then stuck one plug in at a time and found which plug causes it to blow and it was the A terminals on this website http://www.plxdevices.com/ECUDatabase/Toyota/TOY_Supra_87_88.pdf but i doubt you can fix that right? i have to buy a new ECU altogether? and also if i have to do that does anyone have one for a manual 7m-gte with ac

 

[bigaaron]

ecu is possibly dead

I told you that over a month ago. :biglaugh:

 

[jdub]

Based on that "A" plug diagram...How does the wiring going to the injectors look?

 

[jetjock]

I was going to say something similiar. According to that pinout the A connector has only grounds and injector outputs (also grounds). And looking at my schematics I don't see any relation of that connector to the 7.5 IGN fuse. I see no way for a fault in the ecu A circuit to cause excessive current to flow through that fuse. Something doesn't jive, at least from a theoretical standpoint. Better not chuck that ecu yet.

 

[bigaaron]

It is when you ground the ecu through that plug that the fuse blows. Remember, the power was hooked up with reverse polarity and the injectors are not pulsed until he cranks the car. Just try a new ecu already. :biglaugh:
BTW, you can use a auto or manual ecu as long as it has the correct connectors, pre 89 or 89+.

 

[shaeff]

just for reference sake, as i skimmed this thread and didn't see it, if the 7.5A IGN fuse in the driver's kick panel is blown, the check engine light will NOT function. i learned that the hard way.

time for bed! (damn night job!)

-shaeff

 

[the1andonly0032]

Alright this is pissing me off....I got a brand new ECU and put it in and turned the key and it STILL wont spark! but the IGN fuse and none of the other fuses blow but it still won't spark.....