Hello,

Not sure if anyone is still active in this forum, but I have ran into some issues with my 4runner that I can't seem to figure out and hopefully someone can point me in the right direction.
I have a 1992 4runner with the 22re, with an EGR delete, LCE header and SAS.

I live in CO and take it often into the mountains, it's also my daily driver.

So about a month ago, driving up to the mountains my EFI fuse kept blowing. I noticed one of the EGR connections looked like it was damaged, so I taped it up with electrical tape, replaced the fuse and that solved the issue. Notice: after this incident, starting the truck would require quite a bit of cranking where's before it would fire right up.

I then drove it for another 3 weeks or so, and then out of a sudden going to work my car died again with a blown EFI fuse. This time, I could not find any open wires, and replacing fuses did not help (I blew through all 4 extra 15a fuses I had) every time I started the truck the fuse would blow. Having to get to work, and without any other fuses, I used my last 25A fuse and was able to start the 4runner.

Immediately, the engine ran extremely rough. Looked like it was running off of 1 or 2 cylinders only (very rough idle , hesitation and shaking a lot) and black smoke (with high gasoline smell) and extreme lack of power. In addition, the check engine light came on for the first time owning the truck, and the codes are; 22, 24, 31, 41.
I then started to try and diagnose what's causing it, so far I've done the following.
* Checked all grounds.
* Replaced the fuel pump (figured it could be causing the initial EFI blown fuse after the first incident then drove it for 3 weeks no problems)
* Replaced the spark plugs (old ones were extremely fouled with carbon on all cylinders & got a SLIGHT increase in performance but engine still running rough)
* Heard injectors clicking (using a screwdriver while engine running)
* Checked for spark on all spark plugs (All showed spark)
* Jumping TE1 & E1 did not affect idle
* Checked resistance on MAF per 4crawler's write up and it was in spec.
* Checked for leaks in the intake system by spraying starter fluid (couldnt find any leaks however when sprayed fluid into intake system on purpose, the engine would lower rpms and almost die instead of increase RPMS)
* Replaced the coolant temp sensor (didn't get the code to disappear)
* Visually inspected o2 sensor's wiring for heat damage (didn't find anything & re-tapped it)
* Checked resistance on TPS (while still in the truck on closed and full throttle positions) and it was in spec.
* Removed the cable going to the starter and heard the Circuit Open Relay click.
* Jumped Fp & b+ and heard fuel pump turn on when keys was turned on
* Visually inspected the wiring harness for damage (Couldn't take a really good look underneath the intake but didn't see any damage)
* Currently the TPS is unplugged and I think the engine has a little more power (but not nearly the power it should have)

My next steps are to remove the throttle body, inspect and clean it as well as conduct the full diagnosis on the TPS (using feeler gauges, etc.) to see if it's in spec. If it checks, the next idea is to pull the wiring harness and visually inspect all wires for damage.

Does anyone have any other suggestions on what should be done next? Or maybe I am missing something? Should I conduct any other tests on the ECU side?

Any direction would be greatly appreciated.
Many thanks,
Nick

 

Well, the EFI fuse feeds most of the VSV's, the AFM, the ECU, 1 pair of injectors, #s 1&2, and the O2 sensors. Sounds like a short, or partial short, meaning very low resistance, in one of those circuits. IF I were a betting man, I would check the resistance of the O2 sensors first. AND look for damaged wiring. You already found some on the (removed) EGR system, there easily could be more. Insulation worn thin, or having a hole worn in it, something like that. The coolant sensor ma have corrosion on the threads. Make sure they are clean. Do NOT use a steel wire brush to clean them. Use the brass type. And be gentle, so you don't damage the aluminum threads. Do NOT apply any sort of anti seize, teflon tape, or anything else to the threads.

I'm betting one of the two O2 sensors, though. That's just a WAG though.
Pat☺

 

I had an EFI blowing fuse problem and it was due to the wire harness that ran under the truck bed had come off it's attachment and had been bouncing off the exhaust. After that had burned through a few wires insulation, the next bounce would short out on the exhaust pipe and blow the EFI fuse. It was consistent but fairly random at blowing the fuse. You said you looked at the O2 sensors, I imagine you already inspected the harnesses under the bed.

-jim

 

Thanks Pat and Jim

So yesterday I pulled the throttle body and inspected the TPS outside the vehicle and it passed diagnosis. I also double checked the o2 sensor wiring and didnt see any damage to the wires. I havent been able to check resistance on the o2 sensor (couldnt find the diagnosis procedure online. If someone has it quickly it would be greatly appreciated!) but I will be doing that as well.

I guess next steps is to pull the entire harness out and inspect for damage....

@Jim, do you mean the harness that went to your o2 sensor, or the harness going to your fuel tank? That is the one harness I have not really looked into. Would a short on the fuel pump or its connections cause an EFI fuse to blow?

 

It was the harness going to the O2 sensors - seems to be fairly common.

EFI fuse is inline with the EFI Main relay -> Circuit Opening Relay -> Fuel pump.

-jim

 

Alright, quick update for y'all! Hoping someone can point me in the right direction...

So this weekend I pulled the whole harness and visually inspected for any broken wires. Fixed some connections where the wiring had cracked from old plastic... The main one was the #1 injector which visibly had a lack of plastic so now that's all fixed up.

I also replaced the coolant temp sensor and thermostat while I had the upper intake off.

Put everything back together and all the engine codes are still present and the check engine light on. The engine seems to be running a little less rich, but still rich. Interestingly enough now I have an extra code 51. As of now it's showing; 22, 24,31,41,51.

So now I'm at a loss of ideas on what to do next. I'm thinking about replacing the TPS & MAF but I hate to throw money at them since they passed diagnosis when tested with a multimeter... Does anyone have any other recommendations? Should I be looking at a faulty ECU/ECM? Should I replace the o2 sensor before the TPS or MAF? What other relays should I inspect? Any ideas would be greatly appreciated!

Many thanks,
Nick

 

running rich makes me think of the cold start injector, but all those codes... Kind of wonder if using that 25A fuse could have overloaded a circuit in the ECU?

https://www.yotatech.com/forums/f116.../#post51818333

But I would do the testing before opening it up.


-jim

 

Thanks Jim, I also suspect a faulty ECU. Unfortunately the link you posted is no longer available. Do you have any other resources for the FSM ECU diagnosis process?

 

Hope this helps

 

Thank you!! I will go through this as soon as possible. Appreciate the help and will update as soon as possible!!

 

Quick question. Am I measuring the connectors or the ECU pins itself?

 

It looks like the connectors should be plugged into the ECM and then checked from the backside of the connector?

 

That is correct, yes.
Pat☺

 

Happy Labor day!

So yesterday I was able to start the diagnosis on the ECU... my findings are quite interesting. I hope some of y'all can explain to me why the previous owner would've messed with the ECU himself??? Also, if someone can help me find a good source to purchase a new ECU, or someone who can fix these?

After conducting the first voltage test (+B - E1) & (+B1 - E1) I got readings of 2.3V where the standard voltage should be 9-14. So I decided to open the ECU and dig further. What I found is posted below in the pictures. Someone jumped terminals with wire, looks like they pushed two of the (resistors?) out of place to do their shenanigans... I assume that my 25Amp fuse probably blew the last of the shenanigans life and that is probably the cause of all my engine codes, hard startup, rough idle, etc...

Interestingly enough, the 4runner will start and run (rough) with the damaged ECU, so I should be able to drive it to work and back until I find a replacement.

If someone can help me or point me in the right direction to find a new ECU that would be amazing! I have the following info that I was able to retrieve from the front panel.
Toyota Engine Control
*1756000781z* 6-080 HE
89661-35630
10P 18P 14P

The damaged resistors inside the ECU are numbered (C0002 & C0004) not sure if this helps.

You guys have been amazing helping me diagnose my issues, as always very thankful to have this resource around, appreciate it a bunch!


Does anyone know why someone would do that?

Notice top right where someone jumped terminals?

Closer look at the damage...

 

I have NO earthly idea as to why someone would solder that chunk of wire in there like that, I honestly don't. Whatever, it was a BAD idea.

The two items that are actually diodes. The two labels you call out, CXXXX, indicate capacitors. The two caps at the wires inner end. They both LOOK OK, but that's not necessarily accurate. I believe, however, the diodes failed (burned open) before the cap did, protecting the caps. Probably when you put in the 25A fuse. The secret is to find what's shorted to ground, causing the excess current flow. It could be inside the ECU, or something further downstream, outside the ECU.

I believe, from the looks of the pictures, that the run on the circuit board that goes from the end of the diode to the caps burned open at sometime in the past, and that's why the wire was installed. To replace the run. Just WHY the run burned I don't know. Something IN the ECU, it appears, was bad, but just what I'm not sure.

Best bet, IMHO, is to see if there's a problem outside the ECU that's shorted to ground. Something that might have caused the short that ate the two diodes. If you just slap in a new (to you) ECU, and the problem is still there, you'll just fail the new ECU.

Sorry, a lot of rambling, and not a lot of help, I'm afraid. Wish I could do more...
Pat☺

 

Thanks Pat, The rambling helps more than you know!
I just ordered a new ECU from ebay, seems to be the same exact replacement part but now that you mention I probably won't slap it on quite yet until I'm more confident the short is resolved. As to an issue like this, do you have any suggestions on where to start looking? I've went through the whole engine harness, visually inspected, and re-tapped everything. I guess I can go towards the interior electrical (under dash) and fuel pump next?

I wonder if the codes for the capacitors could give me a direction on what systems failed?

 

Check what is connected to the pins those two diodes are on. Check that (those?) circuits. If they read OK, chances are it was something in the ECU that crumped on you. If you find a short to ground external to the ECU, track it down and repair it before you put in the new ECU, or it'll eat the new one, too.

Go back to OEM fuse rating, too. Don't use a higher amperage fuse or...well...you can see what troubles that can cause.

Good luck to ya!
Pat☺

 

Thanks again Pat!

Only problem figuring out which pins those diodes and capacitors are from is that they're to the left of the last pin, so they don't necessarily look to be connected to pins directly. At least that's what they look like for me...

 

Yeah. Just follow the runs from the diodes to the pins they connect to. You might have to pull the board, including the connectors, out of the metal case to do it. Not really all that hard. Just be careful not to break any wires or runs going to the connector.

This kind of thing was my career for my whole working life. Radar Tech, and Electric Shop Supervisor. This kind f thing is right in my wheelhouse, as the saying goes.
Good luck. If you get the board and connectors out of the case, take pictures of both sides of the board, especially focused on the diodes. Lets see if we can figure out what pins they go to

I bet that wire soldered in is because a run burned open on the board, but if that's not the case, you need to get rid of it. I hate bad repairs like that....

Pat☺

 

I'm really surprised this thing still fires up with such damage to the ECU... Today I was able to get it out of the case for better pictures. I hope Pat or someone here can point me in the right direction on which circuit caused this to go. Is it possible it was caused by the EFI fuse with higher rating than OEM? Maybe the owner did the same mistake I did and replaced with a higher fuse before having to do his shenanigans? Then I went ahead and ruined his shenanigans with my higher rated fuse? That's my initial thought, but who knows?!

Either way, the new ECU arrives tomorrow morning, and I would love to slap it on, but will wait for your guys opinion! Technically, the new ECU should be protected if I use the correct fuse ratings right? Unless there's a short elsewhere I guess? Any suggestions? I will have the weekend to go through any direction you guys might think of!