CEL light may be blown

[SandiegoLC]

Hi All, is there a relatively easy way to get to the CEL light on the dash on a 91 Fj80 3FE. I think i may have a blown light. I chased down the EFI woes and everything checks OK but i still don't have CEL. No CEL = no spark. Been chasing this problem for a couple of weeks.
Thank you in advance.

 

[BILT4ME]

Hi All, is there a relatively easy way to get to the CEL light on the dash on a 91 Fj80 3FE. I think i may have a blown light. I chased down the EFI woes and everything checks OK but i still don't have CEL. No CEL = no spark. Been chasing this problem for a couple of weeks.
Thank you in advance.

Check your fusible links by the battery. May have one or more blown. Easy to replace, about $15.

 

[jonheld]

Hi All, is there a relatively easy way to get to the CEL light on the dash on a 91 Fj80 3FE. I think i may have a blown light. I chased down the EFI woes and everything checks OK but i still don't have CEL. No CEL = no spark. Been chasing this problem for a couple of weeks.
Thank you in advance.

This is a confusing post.
Does your engine start?
A replacement light bulb will not magically cure this.

 

[SandiegoLC]

I just wanted to make sure i check everything before replacing the ECU.
I have +12 on b+
+12 on brass
+12 on pin 2 and 3 of relay
replaced the fusible links, which were blown
Replaced the EFI relay
Replaced the fuse
checked both O2 sensors and wires-OK
i get continuity to pin 3 on the ECU
but still no CEL i just wanted to make sure that the light was working. I know replacing the bulb will not magically solve the problem.
Thank you!

 

[gnob]

Check to see if you have voltage at the CEL ECU pin.
If the light is not bad, you have an ECU issue.

 

[SandiegoLC]

Check to see if you have voltage at the CEL ECU pin.
If the light is not bad, you have an ECU issue.

Thank you. The light was good. i checked continuity at the dash and it was good.
Which is the CEL ECU pin?

 

[jonheld]

I just wanted to make sure i check everything before replacing the ECU.
I have +12 on b+
+12 on brass
+12 on pin 2 and 3 of relay
replaced the fusible links, which were blown
Replaced the EFI relay
Replaced the fuse
checked both O2 sensors and wires-OK
i get continuity to pin 3 on the ECU
but still no CEL i just wanted to make sure that the light was working. I know replacing the bulb will not magically solve the problem.
Thank you!

Does the engine run?

 

[SandiegoLC]

The engine turns over but it does not run. it was running perfectly before this issue.

 

[SandiegoLC]

Also no CEL if i bridge pins 2&4 on the efi relay bay. Thank you!

 

[jonheld]

The engine turns over but it does not run. it was running perfectly before this issue.

Please give some details.
Was this truck running one day and just stopped running?
Were you under the hood for something unrelated and then it wouldn't start?

 

[jonheld]

You also mentioned that the fusible links were blown. Which one of the 3 was blown? What was the cause?

 

[SandiegoLC]

Hi Jonheld,
the blue fusible link was blown. I have been checking to see if it had a bad ground or shorted out wire but i couldn't find anything in the harness. It all appears to be good as far as wiring. I checked the alternator for proper grounding and it all appears good, all the wires coming from the coil appear to be in good order, no frayed or damaged wires in the firewall, both o2 sensors are good and the wires are good as well, the CEL light was good, the printed circuit on the dash is good. i've not messed with the AFM/MAF.
At this point i dont know what else to check.
The truck just stopped running while i was on the freeway. The fusible link was blown and so was the fuse. The ECU does not appear to have any external damage such as a blown resistor or capacitor. I did check the resistor that a couple of people have posted before where it was physically damaged but it checked out fine at 2.3 OHMS +-5%.
I ordered a new to me ECU and should be getting it this week.
The cruiser has 296K on the clock, was hoping to get it to 300k. i've had the truck for about 15 years, im the second owner. it's not a daily driver but i take it out every couple of weeks to go camping and stuff, never had any issues aside from bad starter, alternator or battery.
The only thing i did recently, about 4 weeks, was to install new shocks and springs.
Thank you for any input.

 

[jonheld]

The fusible link was blown and so was the fuse.

"The fusible link was blown and so was the fuse"
I assume you mean the 15 amp EFI fuse.
With all parts back in place does the 15 amp EFI fuse continue to blow?
A failed ECU is extremely rare, but it has happened in the past.
Have you tried to simply unplug the connector on the AFM?
DO NOT REMOVE THE 2 PHILLIPS SCREWS ON THE SIDE OF THE CONNECTOR HOUSING.
There is a thin spring clip on the connector that gets lifted up to release the connector.
Simply check to see if the CEL illuminates with the key in the ON position without the AFM connected.

There is also a possible wire chafe point above the glovebox where the ECU harness passes through the firewall. That is also pretty rare, but has happened.

 

[SandiegoLC]

Yes, the 15 amp efi fuse was blown.
Once i put everything back together, the fuse is NOT blowing anymore. I disconnected the AFM as described but still no CEL.
I will double check the chafe point at the glove box.
Thank you, again for your input.

 

[SandiegoLC]

Again, thank you everyone for your input. The cruiser lives on!!
It turns out that the ECU was blown. Chased everything down, the only thing i can attribute it to was the fact that the fusible links were almost 30 years old. I think they just failed.
I did find that the red and gray wire to the starter was damaged and the wires were exposed. IDK if that had anything to do with issue.
i'll post back if anything changes.

thanks!!!

 

[BILT4ME]

Again, thank you everyone for your input. The cruiser lives on!!
It turns out that the ECU was blown. Chased everything down, the only thing i can attribute it to was the fact that the fusible links were almost 30 years old. I think they just failed.
I did find that the red and gray wire to the starter was damaged and the wires were exposed. IDK if that had anything to do with issue.
i'll post back if anything changes.

thanks!!!

So.... You replaced the ECU or you replaced the fusible links?

I'm confused.

 

[SandiegoLC]

replaced both. Started with fusible links, checked wiring, fuses, relays, sensors, and finally replaced the ECU after making sure all else was ok. The ECU was indeed blown.

 

[jonheld]

Again, thank you everyone for your input. The cruiser lives on!!
It turns out that the ECU was blown. Chased everything down, the only thing i can attribute it to was the fact that the fusible links were almost 30 years old. I think they just failed.
I did find that the red and gray wire to the starter was damaged and the wires were exposed. IDK if that had anything to do with issue.
i'll post back if anything changes.

thanks!!!

The fusible links are simply fuses. It is likely that a component shorted within the ECU and caused excessive draw.