Resurrecting Someone Elses FJ80 Project (1 Viewer)

[jonheld]

Another thought, have you verified the 2 pick up coils in the distributor housing? The ECU uses those to adjust timing as well as a crank position sensor.
Have a look at this document:

General Tech - 3FE EFI Diagnostics

3FE EFI Diagnostics updated for 2020

forum.ih8mud.com

 

[jonheld]

I found 12v between IDL-E2 when at WOT rather than the expected 4-6v which would confirm the diagnostic code 41 from before.

The FSM specifies 4-6 volts between IDL and E2 with the throttle valve open, not WOT.

 

[IowaEngineer]

My garage has been unbearably hot over the last week with the heat wave we've been having, so my progress has slowed down. I also took a detour to rip out that alarm system I found when accessing the ECU. I don't think it was necessarily related to any of my issues, but it obviously was not installed with a high standard of workmanship and I'd rather just deal with OEM electrical until everything is operating properly.

I am now more convinced that my crank with no start problem is somehow a result of the ECU not commanding the injectors to fire. If I rig up a system to monitor current flowing through injector 1, I see nothing when I crank. If I bypass the ECU and manually short the low side of the front bank of injectors to ground I can hear them click, see ~1.5A of current through the bank of injectors, and the engine will then run (roughly) for a few seconds where it otherwise would not have. That convinces me that the fuel supply to the injectors is fine and the injectors themselves are electrically fine. It would also indicate that I have spark and that my timing is at least in the right ballpark.

I have verified that the three wires from the distributor pickup have continuity to the corresponding pins on the ECU. I checked the distributor pickup resistances and saw closer to 220Ω on both which is within the 140-1800Ω per the FSM. The gaps for both pickups are within specification.

 

[jonheld]

I am now more convinced that my crank with no start problem is somehow a result of the ECU not commanding the injectors to fire.

This just popped into my head. Please verify that you see +12 at the ECU connector E6 pin 6 with the key ON/RUN.
This is the IGN ON signal to the ECU that comes from the 7.5amp IGN fuse in the fuse box by the driver's left knee. Some alarms will tap into this black/light blue wire. It's possible that one of the vampire taps fractured this and on a 3FE will not prevent the CEL from illuminating like it does on later models.

Make sure you're seeing +12 at ECU connector E4 pin 2 when cranking the starter.

 

[IowaEngineer]

This just popped into my head. Please verify that you see +12 at the ECU connector E6 pin 6 with the key ON/RUN.
This is the IGN ON signal to the ECU that comes from the 7.5amp IGN fuse in the fuse box by the driver's left knee. Some alarms will tap into this black/light blue wire. It's possible that one of the vampire taps fractured this and on a 3FE will not prevent the CEL from illuminating like it does on later models.

Make sure you're seeing +12 at ECU connector E4 pin 2 when cranking the starter.

I pulled the fuse panel back out to double check. This installer did not tap the IGN wire, but I also made sure it stil had 12v at the ECU. Also made sure that I had 12v on E4 pin 2 while cranking.

Is it possible that a bad ECU ground could manifest like this? Maybe the low side drivers in the ECU to fire the injectors are activating, but there is a flawed path to ground for that circuit so the injectors can't actually fire?

 

[jonheld]

I pulled the fuse panel back out to double check. This installer did not tap the IGN wire, but I also made sure it stil had 12v at the ECU. Also made sure that I had 12v on E4 pin 2 while cranking.

Is it possible that a bad ECU ground could manifest like this? Maybe the low side drivers in the ECU to fire the injectors are activating, but there is a flawed path to ground for that circuit so the injectors can't actually fire?

Not likely. The ECU is grounded on 4 pins and each terminate at ground point EC on the manifold. This also provides the ground for the AFM and both O2 sensors.
ECU ground points are E4-13/24/26 and E5-16.
If the ECU had a bad ground, you wouldn't get a CEL because the ECU would be dead.

 

[IowaEngineer]

I'm at a loss and really don't have any more rational ideas to try.

I put the scope on all three of the distributor coil pickup lines at the ECU and could see reasonably clean square waves of varying freqeuncies on all of them when I cranked the engine over. As a shot in the dark I swapped the EFI relay for a backup because it was getting a bit warm and have read that heat can be an issue there, but saw no change.

In summary:

• Fuel supply is confirmed to be unobstructed from the pump all the way through to the fuel pressure regulator.
• Fuel injectos and wiring is confirmed to be good and will fire if manually shorted to ground at the ECU
• Spark/timing is confirmed to be good as it will run after manually shorting fuel injectors or adding starting fluid
  • Have also verified that I have spark from the coil and spark through to the plugs by making sure I can see it jump to the body from the high tension cords
• Distributor pickup coils and clearances all test within spec and show square wave forms at the ECU as would be expected. (It is possible that these square waves are somehow below the detection range of the ECU, but nothing about that is specified in the FSM)
  • I believe that the distributor is not 180° out as the engine will run when manually given fuel, and does not sound to be firing with valves open
• My no-start behavior does not change if I have the fuel pump diagnostic jumper installed or not, that should eliminate the VAF fuel switch as a suspect

Trouble shooting seems to have this narrowed down to the ECU either not commmanding the injectors to fire, or being electrically unable to command the injectors to fire. Without having a logic tree that documents the states that the ECU must see in order to command the injector to fire, I'm beginning to think I need to parts cannon a new ECU at this.

 

[jonheld]

I'm beginning to think I need to parts cannon a new ECU at this.

Quite frankly, I'm out of ideas as well. Although an ECU failure is extremely rare, it has happened before. You could try opening up the ECU case and look for questionable components. It is mostly made of discreet components from 1986.

 

[jonheld]

I don't have a 3FE ECU in front of me, but electrolytic caps dry out over time. If any of them look "puffy" or have the top "leaves" or sections separating, it should be replaced.

 

[jonheld]

I'm beginning to think I need to parts cannon a new ECU at this.

Grasping for straws here, but what is the Toyota part number on your current ECU? Is it possible that the PO swapped it for one out of an FJ62?

 

[IowaEngineer]

Grasping for straws here, but what is the Toyota part number on your current ECU? Is it possible that the PO swapped it for one out of an FJ62?

89661-60090. I have no reason to believe that the PO ever touched the ECU.

 

[IowaEngineer]

Looks like we have a winner.

Edit: I have not chased it upstream yet, but that blown resistor goes to pin 16 on E4 (EGR). I dont see a conflict on the wiring diagram where a fault on EGR would take out the injector circuit.

TWS and IGT are the resistors on either side of it, but neither of them appear to have real damage. There is some delamination around both of the pads for the EGR resistor, but doesnt seem to have broken any of the traces

 

[IowaEngineer]

I know it's a long shot, but would anyone happen to know or be able to test to see what that resistor should have been? It got so hot the ink burned off, and it's obviously too far gone to test. It's either R625 or R635 (board is also a bit scorched, so hard to make out) on the layout.

 

[jonheld]

I know it's a long shot, but would anyone happen to know or be able to test to see what that resistor should have been? It got so hot the ink burned off, and it's obviously too far gone to test. It's either R625 or R635 (board is also a bit scorched, so hard to make out) on the layout.

Without having the ECU schematic in front of me, I can't tell, however E4-16 is the ground path for the EGR VSV coil. If that coil is shorted internally, that pin would be getting +12 from the EFI MAIN Relay.