95 FZJ80 won't start

[Roop]

Good afternoon mudders. I don't post much, but I do read a lot. I've been searching these forums for a couple months now and haven't been able to come up with the solution to my problem. Perhaps one of you can help me out.

What I have is a 1995 FZJ80, standard North American market vehicle, with no modifications to the powerplant, drivetrain, etc. 245,000 mi. I have owned the truck since 2020 and have put about the last 30k miles on it.

I purchased it knowing it had issues with the egr, which occasionally caused it to buck or surge, most noticeably when going up a slight grade at freeway speeds (65mph+). Since this was only a minor nuisance, I ignored it, along with the CEL which accompanied it. It ran like this for almost 4 years.

In June of this year it experienced a particularly bad episode while out on forest service roads in Idaho, and I barely managed to get it back to the highway before it quit altogether. Initially I assumed it had run out of gas, but it had half a tank. Oddly, the CEL turned OFF and would not illuminate when the ignition was cycled. I checked all the fuses, which seemed fine but I observed that the EFI MAIN relay was extremely hot. I spent several hours on the side of the road fiddling with it before I ultimately called for a tow. I took it home and figured I would try changing out the fuel pump and filter, which failed to fix the problem. After swapping out the EFI MAIN relay and going around pulling various connectors I did get it to run, but after a 5 minute drive up a forest road behind the place, it died and had to coast back to it's parking spot. Since that time I have not had time to work on it, as I am a firefighter and we've had a pretty busy summer here. I started fiddling with it yesterday and was able to get the fuel pump to cycle on, but after it sputters it quits, taking the CEL out with it and keeping the fuel pump from cycling on until I apparently get the right combo of relays/fuses/connectors pulled.

I have considered the MAF sensor, but the only one I could find was over $500, so I have been exploring cheaper items. I bought a code reader, but it shows no codes stored, possibly because I keep unplugging the battery, or possibly because it's 1995 toyota OBD 1.5ish... My next step is the fuel pressure regulator, but I can't see how that would affect the ECU and keep the fuel pump from running. Somewhere in the system is a sensor that is telling the computer to shut down the whole thing. What sensor or relay is that? Is my ECU failing? I thought it might be the Circuit Opening Relay, but it appears this vehicle lacks that component- it's built into the ECU. Anyone out there have any ideas? Thanks all. Roop.

 

[Kernal]

Could you make a list of the details how the symptoms started and what you have tested, tweaked (?fiddling meaning), and replaced so far?
Was any work (repairs, service, cleaning, or "fiddling") performed just before the symptoms started?

There is one known issue that has caused the FZJ80 engine to run rough then dying, a short in the main engine harness close to the EGR valve, this occurs when the harness bundle on the firewall droops down and gets too close to the hot EGR pipe which can melt the insulation on the wires inside the harness.
If those wires have become damaged over the years even slight movement of the harness has been known to cause an intermittent short(s).

Either way, list more history before and after the symptoms started and wait for more better advice from others.

 

[Roop]

By "fiddling" I mean that I have been pulling fuses and relays out trying to get it to show the CEL and run the fuel pump. Sorry, I have ADHD so I don't tend to document this kind of thing but generally just sort of spitball until something works. The symptoms leading up to it quitting on me were that it was doing it's usual surging, then doing it a little more, then it just quit while going downhill. it went from surging for a few seconds every 10 minutes to not running at all over the course of maybe, 30 minutes? I haven't done any sort of service to it in months, and the last substantial work was rebuilding the front axle last year, and a brake job over the winter. When I hit the correct combination of fuses, relays or connectors and I do get the fuel pump to work, it stutters with an accompaniment of clicking from either the EFI MAIN relay or some other relay under the dash that I haven't been able to pin down. After a moment it gives up and I have to start over finding a way to get it to turn back on. It cranks and sputters, so that rules out air and spark, but it won't maintain the power to the fuel pump. Something is telling the ECM to shut down the fuel and it puts itself into some kind of apparent safety mode. I did get it to run when I replaced the fuel pump the day after it happened but it only lasted a few minutes, though it did idle for almost an hour before I tried to drive it that day. I got it to sputter a couple times yesterday and this morning, but couldn't get it to catch before the fuel pump circuit was interrupted.

One other notable issue that it has had in the past: when driving in the wet or splashing through puddles etc, it has died completely, but it's always started up afterwards. I suspect the MAF sensor or wire harness has gotten water in it when that happens. This has contributed to my suspicion that it has something to do with that sensor. Part of my "fiddling" includes removing the wire harness connector from the MAF sensor. I have no idea if this does anything, but I hope it confuses the computer enough to put it into default or "limp" mode.

 

[azusa]

Have you checked the oxygen sensors and connectors? Disconnect the connectors on both oxygen sensors. Check wiring, making sure nothing is touching the exhaust pipes.

 

[AussieHJCruza]

If the CEL is not illuminated when the key is in the 'on' position, engine not running, the engine will not start. It will crank.

Fusible link, EFI relay etc. is where I'd be starting. First issue to chase is this not being illuminated.

What do you mean by fuel pump cycling?

 

[Roop]

When I bump the starter, the fuel pump is suppposed to run for about 5 seconds. When the CEL does not illuminate the fuel pump won't cycle on.

If the CEL is not illuminated when the key is in the 'on' position, engine not running, the engine will not start. It will crank.

Fusible link, EFI relay etc. is where I'd be starting. First issue to chase is this not being illuminated.

What do you mean by fuel pump cycling?

 

[60 toy ota]

Oddly, the CEL turned OFF and would not illuminate when the ignition was cycled.

I have considered the MAF sensor, but the only one I could find was over $500, so I have been exploring cheaper items. I bought a code reader, but it shows no codes stored, possibly because I keep unplugging the battery, or possibly because it's 1995 toyota OBD 1.5ish... My next step is the fuel pressure regulator, but I can't see how that would affect the ECU and keep the fuel pump from running. Somewhere in the system is a sensor that is telling the computer to shut down the whole thing. What sensor or relay is that?

CEL should be illuminated with key on engine off in all circumstances. If it's not lighting up you have a power issue (ok, maybe ground issue but that's far less likely) that is not designed into the system and you're going to chase a lot of dead ends suspecting parts that are not in line with the power source to the ECU, especially parts that are not related to the electrical system altogether. And this isn't an issue that would be stored in the codes. In other words, we know already the issue is somewhere between the fusible link and the ECU.

Something is telling the ECM to shut down the fuel and it puts itself into some kind of apparent safety mode......I hope it confuses the computer enough to put it into default or "limp" mode.

Again, There is no safety/limp mode on the 80. There is no kind of sensor or relay or signal that "tells" the ECU to shut anything down, the ECU is simply loosing power. The only thing that would cause this is a short or open circuit.

with an accompaniment of clicking from either the EFI MAIN relay or some other relay under the dash that I haven't been able to pin down.

A classic behavior of a possible short, but more likely open circuit. A short will almost always lead to a blown fuse, which it doesn't sound like you're getting.
This clicking is going to be your friend when it comes do diagnosing the issue. Intermittent problems are really hard to diagnose and you want some kind of an indicator that lets you know when it's acting up. your goal is to be able to "toggle" the issue on and off (think like finding a loose bulb in a strand of christmas lights). @Kernal sent you down a good path when he suggested you look at your harness.
With key on engine off, try to get the clicking to occur in a predictable/controllable fashion. Do this by testing/wiggling your suspect areas: Harness by the EGR pipe, battery connection, fusible link, EFI main relay, fuses, ground points, etc. Better yet, isolate the issue to one of the 4 relay pins on EFI main. Since you have sporadic clicking, we can assume for now that the load side of the relay is OK because the issue is upstream of that. That leaves signal voltage, load voltage, and grounds. You can easily check for each of these with a test light or multimeter. With the key on you should have constant power and constant ground on their respective pins.

 

[Roop]

Found it. Now, what is it and how do I fix it? It looks like this connector has been shorting right at the end for some time now.

 

[tarbe]

I had a similar issue years ago...turned out my charcoal canister was plugged and evidently creating a vacuum in my tank. Removing the gas cap allowed a start. I ended up replacing the charcoal canister.

 

[Kernal]

That's one of the Fusible wires of the Fusible link bundle, should be three of them coming off the positive battery post.
The fix is to buy a new Fusible link 90982-08264 (clean the battery posts and clamps while you're in there).

The nuts inside that small black junction box can sometimes be difficult to loosen by hand as there's isn't much to grip onto,
if you have a small impact that can zip those nuts off in half a second.

 

[Mark W]

Fusible link. Classic "first thing to check" problem once you are aware that it can be a problem.

Keep a spare one in the glove box.


Mark...

 

[60 toy ota]

And for my sanity, I need to point out that isn't a short, it's an open circuit. To be brief a short is an improper path of electrical flow, an open circuit is no flow at all.

 

[Roop]

Whelp, I got that thing swapped out last night and took the ol' Cruiser for a spin. She runs like a top now! I really wonder how long that bugger has been a problem, seems like it's got more power now!