FJ80 no spark problem

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Hey everyone, I mostly lurk here from time to time, and search for tech whenever I work on my 80. I just replaced my alternator this past monday and started to have an overcharge problem. At any rpm over 2000 all of the idiot lights would come on and the volts would climb to 16-18 volts. Yesterday I figured that the regulator must be faulty and made arrangements for another replacement. The cables all check out ok, and the battery is weak but ok. This morning the battery was completely dead, it started fine with a jump. On the way to pick up the new alternator, I hit a bump, all of the lights came on (dash) and 10 seconds later it died completely. It cranks and cranks, fuel pressure is good, but no spark at the coil. The fuses are all visibly ok, but one fusible link at the positive terminal was shot. I replaced it and still no spark. I can't get to my manual without a ride, and am wondering if there is something else I can check? I hope that I didn't fry the ecm, unfortunately my volt meter is at the shop with my manuals. Ugh. Any ideas? Thanks in advance, and need to get it fixed to drop the little one off in the am. Seth
 
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Some more info on the truck would be nice. Year/motor would be helpful.

Did you replace the alternator with OEM or ???

You said, "I hit a bump, all of the lights came on (dash) and 10 seconds later it died completely". That sure sounds like a bad connection to me. I'd go back over EVERYTHING you touched.

You said, "one fusible link at the positive terminal was shot". Did you check the others with a meter? Did you check the EFI fuse under the bonnet?
 
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I just helped a friend of mine a few minutes ago with a similar problem. Check the distributor leads and the lead from the coil. U may have one of them hanging loose.

Note: there is a design flaw in the pre-1993 LC80 series. The wiring for the EFI relay is under gauged [too small] and will sometimes over heat and blow the EFI fuse. Blowing this fuse stops the critter. Rewiring is the only recourse. Do a search for this problem.
 
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Sorry I forgot the important stuff. It's a 92 fj80 with 175k, and no it's not a dealer alternator, but it is a ND replacement. I have a good relationship with the rebuilder who is local. I have checked all connections that I touched, and all of the grounds, battery connections etc. I'm about to fire up the unimog to pick up my voltmeter, but that will be a slow trip. I don't have too much experience working on this, mostly as it is so reliable, so any ideas as to where to check are welcome. The fact that everything happened as I hit that big pothole may be coincidental, that was just when I glanced down. I assume that the efi fuse next to the engine would blow before the ecm, right? Please? Thanks, Seth
 
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I would still be looking for something mechanical at this point, ie. the seating of relays in the contacts, fuses, etc. Let's make sure you're all put together correctly first. Without a DMM or meter of some kind it will be difficult. I'll throw some stuff out at you to check when you can. I'm assuming the truck will crank but not fire.

With the key in the ON position, the CHECK ENGINE light should be on. If no CE light, then EFI circuit faulty. Check fusible links and associated connectors. If fusible links good, then check EFI fuse/relay. You can jump out pins 2/4 on the EFI relay socket to eliminate the possibility of a bad relay. If EFI fuse/relay good, then you will see +12 on pin 8 (B+) of check connector. At this point the EFI circuit is functional and the problem is elsewhere.

You should have spark at this point.
 
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Thank you for the response. No water crossings or acts of god, it all started after installing the new alternator. Before that everything was fine, I just knew that the battery was getting tired. I checked all of the fusible links and they are now all good, only one was fried. The efi relay has been upgraded with a heavy duty bosch unit. I can hear it click but can't test it for voltage yet. It's getting dark and I need new batteries for the multimeter, so I will check more in the am and post back. Thanks for the suggestions, Seth
 
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If you check out my website under the "woe and strife" section, you'll see that there is a drop in replacement from Toyota for the EFI relay. It's from a Camry. You can also download the schematics for a 1991 FJ80 in pdf format.

I re-read your original post and I'm a bit concerned about the "overcharge problem" that you mentioned. While I would assume that the ECU would have a voltage regulator of some sort, I'm not certain about that. But at this point it's all specuation until you get in and turn the key and start checking stuff.
 
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Ok, I just ran a few checks. All three fusible links are passing 12volts, and the relay and 50a efi fuse check out, but no check engine light. There is voltage at the coil, and at the pin (b+) at the diagnostic plug. From here I imagine that the overcharging damaged the ecm, coil, or distributor pick up. Is there any way for me to figure out which without just throwing parts at it? Thanks for your help so far. If it ends up being the ecm what are my options for finding a replacement? Seth:confused:
 
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Seth,
You keep mentioning the ECM. It is very rare for one of these to go bad. I know the FSM mentions the ECM in just about every electrical test but it is usually the last thing in every test; and Mr T suggests replacement only after all the other tests are good.

Unless you know or suspect something that you haven't mentioned then keep looking to the areas that Jon has mentioned. Those things you touched when doing the alt replacement and those things related to getting juice to the system. FWIW, the fusible links are cheap so it is a good idea to keep a set in the truck for spares. If you are going to throw parts at it today then I would start with the fusible links; you've already said one was "bad" and that in itself is suspicious.

Trace down that circuit of the fusible link that failed because it is a "last resort" fuse. There should be a primary fuse that protects that same circuit. How does the ground strap look; the one to the block and the one to the body?

-B-
 
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Just checked out your site, nice! And nice truck also! I've had my mog at Paragon,(saw your pics) but haven't braved the 80 yet. I'm sure it would be fine but I try to keep it clean as it is my daily ride. I'm going to puzzle over the electric diagrams for a while unless someone else has a bright idea. Starting to realize I should have sprung for the oem alternator, but it isn't just around the corner like this one. Live and learn I guess. Seth
 
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Seth,
If you are going to throw parts at it today then I would start with the fusible links; you've already said one was "bad" and that in itself is suspicious.

Trace down that circuit of the fusible link that failed because it is a "last resort" fuse. There should be a primary fuse that protects that same circuit.

-B-

Good idea, that one was completely melted, almost missing entirely in fact. It was the one that goes from battery positive to the smaller of the two nut/bolt juctions. Thanks, Seth
 
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Ok, I just ran a few checks. All three fusible links are passing 12volts, and the relay and 50a efi fuse check out, but no check engine light. There is voltage at the coil, and at the pin (b+) at the diagnostic plug.


The 50a fuse is NOT the EFI fuse. It is the main fuse and feeds the neutral start switch. Look at the cover of the fusebox under the bonnet. You will see a 15A EFI fuse. But we've already established that it's good. You really need to go through EVERY SINGLE FUSE in this truck at this point. That includes ALL the fuses by the driver's left knee.

If the B+ terminal at the check connector is hot then the ECU is hot as well. The ECU fires the CE light by grounding a feed from the gauge fuse (10A).

Let me think about this for a while.

BTW, what voltage are you seeing when you say +12?
 
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Does the ecu recieve its ground through the bolted mounting or is there a wire that I can check? I'm checking that grounds and so far they all check out ok. Also, is there a method to see if a fire signal is being sent to either the coil or injectors? I've been back over evry plug that I touched. There is one that is shot, the two wire temp sensor ( below upper rad hose) disintegrtated when I touched it, but I'd be surprised if that would keep the ecu from firing at all, or throwing the check engine light on. Has anyone ever had the check bulb burn out. I searched and found mention of the drive indicator light failing but not he others. And it just started raining, hooray. Thanks, Seth
 
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ECU is grounded through pins 13;16;24;26 all terminating on the ground lug on the intake manifold (US driver's side).

The -IG signal from the igniter is what runs the tachometer and you can monitor that signal from the check connector, but you really need a scope for that. If your meter has a freq counter on it you could try that. Any reading at all would indicate that the igniter is putting out pulses. That means that the dissy coils are sending signal to the ECU and the ECU is sending signal to the igniter. The igniter in turn sends signal to the coil.

We really need to focus on the CE lamp and why it's not illuminated with the key in the ON position. I doubt it's the lamp itself, but stranger things have happened. If you have truly checked and re-checked all the fuses in the vehicle (with a meter NOT just by eye) then it's possible that the ECU is tanked from the over voltage condition, but I'm still holding back on that one.
 
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I gather that if I jump tg1 and e1 at the dignostic plug it should set the CE light, am I right about that? I've got a friend relaying info from the fsm over the phone, but hes a ways away. If I try that and still no light maybe then what. My meter will register any pulse if I set it on hold, so I will try that. Thanks again.
 
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I gather that if I jump tg1 and e1 at the dignostic plug it should set the CE light, am I right about that?

Jumping those 2 will display any diagnostic codes that the ECU has logged. However it is the ECU that illuminates the CE lamp by grounding pin 8. If the ECU is busted-broke you can jump all the pins you want and the CE lamp will not illuminate.

You have yet to confirm without doubt that you have gone though every fuse on the vehicle. I don't mind taking time to help you out but I need help from you.
 
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Thanks, I really am thankful for the helpful peolpe here. I have tested each fuse for continuity, and every plug that I can find. Everything is tight and clean, fuel pressure is good (not sure if that is operated by the ecu), cranking speed is good, voltage is around 12.2 volts. The battery is weak so I've been keeping it on a trickle 2 amp charge when not working on it. There may be an electrical drain somewhere, two mornings in a row the battery was stone dead. I knew it was weak, and figured that the overcharging may have been the final straw. In the am I'm going for the replacement alternator, and will try to guilt them into a battery and coil, if they can get one. I'm suposed to get my fsm back this weekend, I split mine with a friend as we would both rather spend money on more toys. Many thanks for your time and suggestions, I'll keep at it till its fixed, Seth
 

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