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Those pictures are EXACTLY what was needed, thank you!
Looking at what's going on, whoever worked on it before didn't know nearly as much as they obviously thought they did. First, obvious problem, they put one of the diodes in backwards. They should both be oriented in the same direction. IE: the stripe should be at the same end on both diodes, and one of them is reversed. Probably the origin of the short to ground. If you look at the back, the run from the diode goes to ground, and when they put the diode in backward, it let the current flow straight to ground. The run burned open, as you can see. Apparently, it took the two capacitors with it. Looks like he tried to repair the run, and put a wire on to make sure the caps were still in the circuit.
I could go on with what the person that worked on it last did wrong (boy did he). I won't. It's just a ruined ECU after he got done with it. A paper weight. Useless for what it's supposed to do. It could be repaired, but it'll take a lot of work. New diodes, caps, run repairs, and so on. Sheesh!!! And, just between thee and me me, I HATE, DESPISE, cold joins, and there were several. All the ones whoever did were cruddy, cold, no good, solder joins. Shoddy workmanship!
Yes, using the higher value fuse did damage, I wager, but the way the ECU was ruined by the PO, you didn't do much more than he did. I would put the correct value fuse back in, and see what's downstream of the ECU. I'll see if I have a schematic that shows the circuit entire. That way you can check for problems downstream of the ECU. I would wager there's no problems, though. It looks like the PO was the cause of the troubles.
You can check the "far" side of the EFI fuse for a short to ground with the ECU out of the truck. Just measure fuse to ground, with the fuse out of it socket. You can determine the "far" side of the fuse by pulling the fuse out, turn the key on, and read both sides of the fuse for voltage. With the fuse out, one side will have voltage on it, the other won't. The side without voltage on it is the "far" side of the fuse. Turn the key off, and pull BOTH leads off the battery. Wait a minute or two to allow any caps to drain down. Even small amounts of electricity in a circuit will blow a multimeter's ohms side. Read the far side of the fuse to ground, and it should have a high, or even infinite, resistance, to ground. I'd wager, after seeing the ECU in detail, that it was your problem.
If I were you, and I'm not, but if I were, I would put the new ECU in, put the right size fuse in the EFI slot, and try it out. Start the truck up. I'd wager it'll work fine.
Pat, once again thank you so much for your guidance. It's been an absolute pleasure having someone experienced like you help a newb out. I feel like I owe you a couple beers!!!
Went ahead and conducted the test you mentioned on the EFI fuse.
Far side was reading 32 mV and the other side read 12.32V. Once battery was disconnected, far side to ground checked out as infinite (O.L.)
Excited to slap this ECU on tonight and give you guys updates tomorrow!
Swapped the ECU and she's running better than ever! I can't believe I figured this out and probably saved so much money instead of buying new o2 sensors, TPS, MAF etc.... I really couldn't do it without everyone's help, so once again thank you! I'm replacing spark plugs, checking the timing and giving her an oil change ASAP.
Also figured I'd take the opportunity of this thread to ask a couple more questions. I've got a few things to work on, maybe y'all have a good direction to start?
1. Once warmed up, my idle still sits at 870-900rpm even if the idle screw is bottomed out (the o-ring looks ok). Should I be looking at my Idle control valve? (maybe it needs a new gasket? Carbon built up preventing it to close once warm? Vacuum or air leaks could cause this?)
Note: During the ecu issue, I backed the screw out enough to keep the engine running. With the screw bottomed out, the engine would almost stall at 300-400rpms. Now with the new ecu, and without adjusting the screw the cold start was around 2300rpms and once warmed up around 1600rpms. After the warm-up, I bottomed the screw, and the idle wouldn't drop below 870rpms?
2. Also my fuel line seems to be de-pressurizing once the 4runner sits for over a couple of hours. I need to crank it maybe 2-3 times before it starts. Once it starts, I can turn it off and start it back on immediately without any issues (even if cold). Am I possibly overlooking another system that could make it seem like it's a fuel line depressurization?
Second question first: There's nothing wrong. The FSM specs that the pressurization lasts a whopping 5 minutes. Therefore, anything over and above that is gravy. If you want to pressurize the line before you crank it over, turn the key to START without pushing in the clutch, or the Clutch Cancel switch. It won't crank over, but you'll hear the whine of the fuel pump. After a few seconds, the whine will change tone a bit. Not a lot, but enough to hear. Once it does, push the clutch pedal down, and VROOM! Awaaaayyyy we go, as Jackie Gleason used to say.
On your first question, yes, could very well be the Idle Air Control Valve. If it's staying open, even a small amount, it will adversely affect the idle as you descrie. They get old, and dirty, and it blocks the correct operation. There are a ton of videos on YT that describe how to take them apart, clean, and reinstall them. I suggest watching a couple before trying to work on it. Get yourself an impact screwdriver. You'll need it to take the IACV apart, I promise. You can either buy a new gasket from Toyota, or make it yourself. Not really all that complexly shaped. A little gasket materiel, a good sharp Xacto knife, and you're GTG.
Yes, vacuum lines can also affect the idle. Check them all for leaks. Or just replace them. All the same size. Just watch your routing. Use the sticker on the inside of the hood, upper left (passenger side) of the hood when it's open. Double check each one as you go. That includes the big tube from the AFM to the TB. It's prone to the corner pieces developing cracks. Flex them while looking in, and see if you can see any light.
Check for any codes, as well. Make sure they all clear when you pull the battery negative off fro a minute, and none appear afterward. They can actually be quite helpful.
I'm glad the new ECU did the trick.
Replace the distributor cap and rotor, as well as the plugs. It matters.
Have fun!
Pat☺
Now, it's an imperative that you take your truck off-road, and get it really dirty. Toyotas run better if you get them good and dirty off-road once in a while. I bet yours is way overdue by now.
The new ECU fixed all my electrical issues and I can't thank everyone enough, especially Pat, I probably would've never figured this out by myself!
I've taken it out and enjoyed the last bit of snow here in Colorado, which has been killer. Through the months I've replaced the whole top end and converted to a double chain setup from LCE after a head gasket failed on the #3 cylinder, added some rock sliders and some LEDs to help with the night driving (found a sweet switcher panel off Etsy that goes in place of the old ashtray), built a drawer system in the back, and had tint installed (progress pic below).
I love this 4runner, but unfortunately, I'm always chasing things that were either neglected by the previous owner or just plain old. Down the list of things, I am chasing a high idle which is driving me insane (it was there as well with the old ECU). I've tested and adjusted the TPS, adjusted timing, replaced the MAF sensor with a good working one from a buddy, tested vacuum lines for leaks, replaced the intake air tubing, replaced the IACV gasket, checked for any blockage on coolant hoses and fitting going to the IACV, and my idle will still hover at 1100. I've even tried screwing the idle screw valve completely shut and also taped the IACV port on the throttle body shut and the damn thing will still idle at 1100???
What else could be causing this? I always thought that if the IACV is functioning properly (or taped to act as if it was) and the idle screw was adjusted to the close position the engine would have to drop idle?
The engine has also always sputtered water-like substances from the exhaust and I feel like it is running rich since my MPG is pretty low.
Like with electrical issues, I am out of things to try and I hope one of you wizards knows what the hell is going on
ps; if yall want to see more of the mods I'm happy to upload them
No insult intended, but are you sure you're adjusting the Idle Adjust Screw, and not the larger, cover screw that is over it? Not that *I* ever did something like that<ahem>
Just checking.
Another thought: Did you check/replace the o-ring on the idle adjust screw? They get old and brittle, and drop pieces down into the air passages the screw adjusts. Make certain the air passages are good and clear. No pieces of o-ring, dirt, or other crud in them. Make sure the o-ring is still nice and rubery. If you put a new one on, put a little Vaseline, or silicon Dielectric Grease on the o-ring before you put the screw in. It keeps the rubber soft and flexible, making a good seal, and making the o-ring last much longer.
Sep 8, 2022 | 12:54 PM
