1UZ in 1976 FJ40. Check engine light wiring.

Effjay76

New Member
I have the engine in. I have wired everything up that needs to be wired. ECU, Igniters, injectors, fuel pump. etc. The engine runs great, idles and revs smoothly.

Engine is from 1992 sc400.

I have the check engine (W) (blue and yellow) wire from the ecu isolated, not connected to anything except the test light. I understand it should be producing a ground signal before starting even if there isn't any codes, but I cannot get anything from it. I have a test light connected to power and running to the W wire.

I currently have power running to everything once the ign switch comes on and maybe that's the problem. I haven't wired up the safety feature that shuts the fuel pump off when the engine isn't running, so the ecu thinks the engine is running as soon as it gets power? I'll change my relay wiring to activate this feature and see if that does it.

Any other ideas on what could be preventing the ecu from sending a ground to the CEL wire? Do I need to connect some other equipment to that wire?
 

gloverman

Well-Known Member
My two cents is either ecu not wired correctly or the ecu itself. Pretty common for these ecus to have issues internally these days. Not wiring the fuel pump ecu to the engine ecu should not affect the check light. Only the check light should be on that circuit.
 

Mx-400

New Member
I've been having the same issue. I'm currently on my 3rd 1uz in a swap and I've never been able to get diagnostic codes
 

gloverman

Well-Known Member
If you cant get diagnostic codes then something is wrong or done wrong. Every conversion I do I get comms with a scan tool, diagnostic codes an check light. I was working on another today that was wired years ago. It's now got an issue and found its way to my place. No check light , no way of checking fault codes so I will be sorting. I didnt need that stuff to find the delaminated front pulley but loom will come out and be repaired so allow communicaton.
 
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