97 Nissan Pickup ECU circuit problem

[djellum]

Hey,

 

97 nissan pickup, KA24 4 cyl, Manual 4x4

 

so I drove my truck to a friends house, stopped at a gas station on the way back.  turned off the truck at the pump and it dieseled for about 10 seconds and wont start.  will crank fine but doesn't even attempt to fire up or even sputter.  when you turned the key there was no check engine light that would normally come on to tell you that it is functioning.  Had it towed home.

 

checked this morning and the engine control fuse was blown.  replaced it and now I sometimes get a check engine light when the key is on accessory and sometimes not.  

 

when I dont its the same as before, cranks with no attempt to start.  when it comes on then I hear a clicking on the right side of the motor compartment and it cranks with no attempt to start and the check engine light blinks rapidly.  

 

there are some relays on that side where the clicking is, fuel pump relay for sure.  Fuse hasnt blown again yet, but can a bad relay feed back into and blow the fuse?  also can the fuel pump relay affect the power that gets to the ECU?

 

speculation aside, what would be the prefered diagnosis method for this.  I assumed that no check engine light was a sign of a power issue to the ECU, and the fuse supports that.  what connections/relays/fuses are there that can rob an ECU of its power?  I'll also check the grounds on the ECU.

 

Any other help or ideas are appreciated 

[mikaleda]

I really know very little about Nissan, but what I would guess is a grounding problem to the ecu is a likely culprit. Another thing to check for might be main grounding off of the battery itself and maybe check power at the fuse/relay box.

Edited February 25, 2013 by mikaleda

[djellum]

Heres a copy of the wiring diagram.

 

Checked battery ground and its good.  Checked the fuseable links, they are fine, the fuse on the left is the one in the cabin that I replaced so its good.  Distributor spins but no spark.  Leaves EGI relay, ignition, ECU, and grounds on ECU, and possibly the fuel relay but until I have spark im not going to worry about it.  Lots of noise from the relay box, clicks and buzz for whatever that is worth.  

 

Looking for grounds on the ECU now, and I may just throw the $9 at a new EGI relay, though i know that usually is just wasting $9 I am kind of hopeful on it.  the truck doesn't leak or have any rust and due to the sudden nature of it I really lean towards failed electrical component (though why it failed is another matter)

 

heres the diagram if it helps anyone.