Hi Guys-
First post!
I've been lurking here for years, but I've finally had enough of the problems with my truck, so I joined. I can't seem to find my exact issue, so here goes....

I have a 94 Toyota 4x4 manual with 3vze / 3.0. I put this motor in it back in 2020. Previous to that, it had sat for about 2 years while I was building my log cabin and didn't have time to replace the motor.
When I installed the new motor, I paid a guy over at Midas to modify the exhaust so the passenger side ported down under the vehicle and attached there instead of up on the engine on the driver side (which is why I think I had to replace the motor in the first place - burnt / broken valves in the back corner next to the exhaust).

Anyway, after I got it all put back together, it was running like a top. I think I had some issues with the EGR (can't remember what they were), but I found that LCEngineering had a kit to cap off the ports and remove the EGR, since I couldn't find a new one online. So I did that. Then I was getting literally 22 MPG running on 31" tires. It ran like this for a year. I could go up "car killer mountain" in 5th gear! (It's a long hill in the local area that a lot of people break down on). Then the rear diff went out, so I found a used 4runner that had slightly different gearing and the ABS wiring (I didn't use that) and stuck that on there. About 2 months after I got that replaced, I was driving down the highway - on flat ground - and the stupid thing all the sudden just decided it couldn't get up to speed. I downshifted into 4th, but could just barely get it to go 55. If I came up on a hill to climb - forget it - I was chugging along at 30 mph, max, struggling the whole time.

Ok, so it threw some codes at the time (this is going back 2 years now) - like the o2 sensor and other stuff. So here's what I've done - hope I don't leave anything out - if you think of something, just ask - I've probably replaced it:

- fuel pump
- fuel tank: I took it off and found it had rust in it, so I had it professionally cleaned and then they poly'd it or something to stop the rust.
- replaced fuel lines and fuel filter.
- replaced spark plugs, wiring, distributor
- replaced injectors
- O2 sensor
- Fuel pressure regulator
- AFM (I had tried the AFM for the 22re and opened the black box and adjusted the spring in there to try and make it work for a 3vze because there were no AFM's for a 3Vze available for a while, but I've since put the correct AFM on there)
- TPS (I initially used an aftermarket unit, and then was reading on here that they suck, so I bought a Denso unit and adjusted it with feeler gauges as someone described on this forum)
- I checked the ECU - it looks absolutely perfect - no rust, no dust, no corrosion.
- I ran it with the cold start injector unplugged for a while - thinking maybe it wasn't shutting off once the engine was warmed up, but that didn't help. But I could revisit this, if someone makes a good case for it.

There's probably other stuff I've replaced. Someone suggested adding some better grounds to the body and the engine, so I did that as well.

So right now, today, I get about 9 mpg. If I try to accelerate in 3rd gear, I can see black smoke pouring out of the exhaust. There's always a fuel smell up front somewhere while idling, but no evidence of leaking that I can find. After my most recent purchase (the AFM), the engine light went out for about a week or two, but it's back.

It idles fine, starting when cold is great. Starting after it's been running takes a bit more effort.

Acceleration goes like this:
1st: kinda sluggish
2nd: kinda sluggish, but I can feel the power kick in around 25 mph
3rd: feels like it's stalling until I get up to about 40, kicks out black/gray smoke, then the power kicks in again around 45 and it accelerates quickly
4th: fine
5th: if I put it in fifth around 50 mph when it's not quite ready, the engine light kicks in.

I know I need to adjust the timing one more time with the new AFM in there evening out the idle now (before it was pretty rough, and hard to get the timing right). And I'll try and pull the latest code and stick in a comment.

So here's where I'm leaning at this point: It's running too rich (obviously) - but why?
- maybe it's the EFI relay?
- or the COR?
- maybe I should replace all the engine wiring?
- or something else?

the ol' 94 in front of the cabin....

 

what's the most recent ecu code? after resetting the ecu

 

Ok, I just realized I never reset the ecu after installing the AFM. Here are the codes prior to resetting it:

ECU codes (6/9/24)
14 - Ignition signal --NO "IGF" signal to ECU, Igniter / Igniter Circuit, Igniter and Ignition Coil / Circuit
21 - Oxygen Sensor Signal / Oxygen Sensor Heater Signal, Open or Short in Oxygen Sensor or Oxygen Sensor Signal
31 - Manifold and / or Airflow Meter Sensor Signal Circuit, Airflow Meter / Circuit, Manifold Pressure Sensor / Circuit ECU
41 - Throttle Position Sensor Signal -- Open or Short in TPS Signal, TPS Sensor, TPS Signal / Circuit ECU
42 - Vehicle Speed Sensor Signal Circuit - No SPD. Signal for Several Seconds, While Vehicle is Operated Under Heavy Load (TPS / MAP / AIRFLOW INPUTS), Speed Sensor / Circuit ECU

Wow. maybe my wiring harness or ECU needs to be replaced, because all of these things on the list have been replaced in the last 2 years.....

I'm going to go reset it now, drive it to church, and see what codes I get. Again - these are the codes before resetting the ECU, but after adding a new AFM.

 

wow, it might have been easier to list the codes that didn't get tripped, lol reminds me of that tom cruise movie: "dea, atf, fbi... you hit the trifecta; guns, drugs, money laundering... the state of arkansas is gonna rip the bark right off of you boy"

 

Nice place. log homes are more work to maintain than most realize. Well done.

 

thanks guys.
Ok, drove it to church after clearing the codes - and the codes came back - I think the list above might have been for the 22re, so I found what I think is correct for my truck: https://www.troublecodes.net/toyota/...-94-t100-3-0l/

here are my current codes:
14 Ignition reference signal -no signal Wiring, ignition module, ECM
21 Heated oxygen sensor (H02S)-front –circuit Wiring, H02S, ECM21
31 Volume air flow (VAF) sensor-circuit Wiring, VAF sensor, ECM
41 Throttle position (TP) sensor -circuit Wiring, TP sensor, ECM
42 Vehicle speed sensor (VSS) -circuit Wiring, VSS, ECM

The vehicle speed sensor is an interesting one - I've seen where my speedometer cable just sits at 0 after I pull out from a gas station sometimes, and then after a minute or so, it'll kick in and show my speed. I don't know where that sensor is located, so that's one I haven't replaced.

If I'm going to try to determine whether it's wiring or the ECU, should I just check for ohms on the wiring and 5 v on the ECU pins, or is there something more I should do?
---------------------------------
and the text of the chart, in case they take it down:

Trouble code Fault location Probable cause
12 Engine speed (RPM) sensor-circuit Wiring, RPM sensor, ECM
13 Engine speed (RPM) sensor -above 1000 rpm Wiring, RPM sensor, ECM
14 Ignition reference signal -no signal Wiring, ignition module, ECM
16 Transmission control signal -malfunction ECM
21 Heated oxygen sensor (H02S)-front –circuit Wiring, H02S, ECM
22 Engine coolant temperature (ECT) sensor circuit Wiring, ECT sensor, ECM
24 lntake air temperature (lAT) sensor-circuit Wiring, lAT sensor, ECM
25 Mixture control -continuously lean Wiring, injector, H02S, ECT/VAF sensor, intake/fuel/ignition system, ECM
26 Mixture control -continuously rich Wiring, injector, fuel system, cold start injector, H02S, ECT/VAF sensor, ECM
27 Heated oxygen sensor (H02S) -rear-circuit Wiring, H02S, ECM
31 Volume air flow (VAF) sensor-circuit Wiring, VAF sensor, ECM
32 Volume air flow (VAF) sensor-circuit Wiring, VAF sensor, ECM
35 Barometric pressure (BARO) sensor-circuit ECM
41 Throttle position (TP) sensor -circuit Wiring, TP sensor, ECM
42 Vehicle speed sensor (VSS) -circuit Wiring, VSS, ECM
43 Starter signal -circuit Wiring, ignition switch, engine control relay, ECM
51 Switch signal -A/C switch ON during diagnosis Wiring, A/C switch, A/C amplifier, ECM
51 Switch signal -closed throttle position (CTP) switch OFF during diagnosis Wiring, CTP switch, ECM
51 Switch signal -park/neutral position (PNP) switch not in P or N during diagnosis Wiring, PNP switch, ECM
52 Knock sensor (KS) -circuit Wiring, KS, ECM
53 Knock control -malfunction ECM
71 Exhaust gas recirculation (EGR) system malfunction Hose leak/blockage, wiring, EGRT sensor, EGR solenoid, ECM

 

ehhh - not that bad. we went with a low-maintenance design invented by Skip Ellsworth, and now taught as a class by www.lhba.com -we have huge roof overhangs (like 8' on the gables and 4' on the eaves), working on finishing up a wrap around porch to keep the 1st floor logs out of the sun and rain. Other than that, stain it every 5-8 years, re-roof it every 30, and you're golden.

The best thing about this particular style: no settling. I don't have any screw jacks or false headers or anything. folks say "that's not possible", but I have friends living in theirs for 30 years, no problems.

I milled this 8x8x13 post the other day for a carport:

 

well all of those codes at the same time is a big discouraging... you could follow the toyota fsm procedure for troubleshooting each item separately.

the problem with ohming out wiring is that it might only take a few strands of wire to pass, but actual use may require more strands to be reliable... given your location, and the fact that the vehicle sat for long periods of time(?), i'd be inclined to inspect the wiring for rats chewing on it... had that happen to my wife's honda in yosemite valley, it was only parked for a couple of weeks but the critters chewed up some stuff.

when the wiring(or grounds) is messed up it can create all kinds of havoc that is impossible to troubleshoot, i had that happen with corroded connections in the wiring to the injectors on my 22re: https://forum.ih8mud.com/threads/a-2...-i-had.311436/

what happened there is that toyota went in and hacked up the harness after the fact, so that the actual wiring doesn't match the schematic in their own manual... i doubt that you have that issue on your late-model 3.0, but i'm wondering of the engine harness is damaged.

 

First, here's the FSM on trouble codes. https://web.archive.org/web/20141031...26diagnosi.pdf It's more descriptive than the ones you have. (But Kudos to you for posting what you found the codes meant, rather than making the rest of us look them up for you.)

What you're missing is code 26: Air-Fuel Rich Malfunction. I'd start by checking the conditioned output of the O2 sensor: https://web.archive.org/web/20150306...42oxygense.pdf You already have code 21, so it's possible the O2 sensor circuit isn't working at all.

Persistent lack of IGF (code 14) is supposed to shut off the ignition (to prevent a fire), so i doubt that's your long-term problem. Lack of VSS could be an issue, but if your speedometer is showing a reasonable number you probably have an intermittent failure of the electronic VSS at the back of the transfer case (it will only get worse, but probably isn't your current problem). Given your codes, you should probably use your multimeter to test your TPS and VAF; that's one side of the equation, but wiring is more difficult to test.

It's not the COR or EFI relay.

Try to get away from thinking "No, it's not the X circuit, I replaced X a few years ago." Your truck isn't a pile of Legos. Using a trouble code to tell you to replace a specific component works every now and then, but it isn't any substitute for actual diagnosis of the problem.

 

I'm afraid you're going to be right. An ECU is much easier to replace than a rats nest.

Ok, so I searched for "wiring harness" on ebay - all I can find is used ones, which makes sense for a 30 year old vehicle. So maybe I should just focus on replacing the connectors for the codes the engine threw?

Or maybe I try to buy all the connectors singly and then run new wiring for each? I've never done this extensive of a wiring job on a vehicle before. My buddy did one on his 1973 bronco when he swapped in a v8 from a mountaineer, but I'm not that kind of a mechanical wiring god, so....

Thanks for the response, though.

 

I talked to a buddy today that's been a mechanic for 50 years -
he is saying that since it sat for 2 years, maybe rats got the wiring, but he suggested against checking wiring for each sensor with a code. Instead he thinks I should check the wiring where the engine bay wiring goes through the firewall and down to the ECM / ECU. says there's probably a place where they plug into each other - not at the ECM, but before it. I'm looking up behind the glovebox and I think I can see some plugs up in there, but I'm going to have to take out part of the dash to get to it.

Anyway, his theory is that maybe it got wet in that area (I DID see some corrosion on the COR when I looked there). So he says to take some vinegar and clean up all the contacts and wiring, and then spray some dielectric grease in there and put it all back together and see if that makes a difference.

so I'll report back when I get that done...

thanks guys!

 

crap.

there are no "plugs" in the firewall: it goes straight from the ECU plugs, right out through the firewall and to all the sensors. The ECU plug ends look great - nice shiny copper/gold connectors.

so I gotta do this the hard way.....

 

Are you absolutely certain you don't have the IH-1 and other connections that connect the engine harness to cowl harness and body harness and ECU? It is a 94, even if not a 4runner.
And on the 4R's, those connectors are "inside" or hidden by the ECM. And ECM connectors are attached to 'bottom' side, helps keep moisture out. I'd check those connectors first, before struggling with the engine harness.

Good luck.

 

Thanks!

Yes, the plugs come around and plug into the bottom of the ECU.

But check them for what? the connectors look extremely clean - the copper is shiny, even. Maybe you mean "inside the plugs"? how would I check that?

 

Guess I'm way in over my head here. But it looks like you've nearly replaced every physical device (and I'm guessing also checked timing, valve clearance, and compression) yet still get mysterious intermittent and random fails?

So that's why I'd check the harness (and what I would have bet you have what electric wire diagrams say connet those various harnesses). I had to build a custom harness (put a 99 5vz into a 95 body) that I sort of spliced together for the end result. Those IH-1 and various harness connectors did not in themselves have corrorded contacts 'cuz they're all (on my 94, 95 and that 99) tucked up under the dash in various locations. Thiis kind of .. decentralization(?) is why an EWD is essential imho. If there was an issue you could (luck out in my case) and find it by doing an ohm/stress/bendy test. And especially the 'sensor' connectors that are in engine bay (part of engine harness) and underneath (trans is spliced into engine harness) are usually quite suspect. And the loom of wire on top of motor? Totally freakin baked and brittle.

Spent a 'small eternal' amount of time as a tech at a Big Evil Red Oil services company. I had two main t-shooting rules to start. 1) check the wiring and connectors. 2) Check them again.
I apperently developed a reputation (yes, as a PITA) for condemning engine wire harnesses. Like good half a dozen. They were 'customer' isssues, and BER wasn't responsible. Got to the point where the yard would have me come back in to work with the Cat guy to diagnose them. I once rigged up a crappy 60 ohm resistor to use as the engine harness terminating resistor; went days off, crew went to next well. Left instructions that cat needed to replace harness. 8 months later, thought that pump had been sent back to reclamation. Nope. New well. There it is. My crappy little (seriosly a 60 ohm resistor ELECTRICAL TAPED TO THE WIRE LOOM) had failed.

Long diatribe but my worthless experience is that its most likely a comm issue before the actual device.

 

One thing to keep in mind, codes tend to have a cascading effect. And what I mean by that is a component fails and sets a code. But the condition created by that failed component throws another sensor out of parameters, and it throws a code. And so on and so on. When the root problem is fixed the other sensors fall back into parameter and quit setting codes. So some of your codes are most likely not an issue.
Yes, the ecu is on the list. But if you look at a troubleshooting chart where each code lists possible failures ECu is in every single one. You’ll also notice it’s dead last in each list. ECU failure is rare. Water getting inside will do it, or a human accidentally back feeding power through the unit will testing can also do it. Other than that, it’s remarkably durable. You can pull the lid on the ECU and give it a smell and visual check. If it looks good odds are it is.

 

Ok, got the carport done, so now I have a dry place to work.

Sorry it took so long to get back to this. Here's what I've done now:
- unplugged all the wiring from the ECU, un-wound all the protective coverings and pushed it up into the engine bay so I can test it all easier. Just doing continuity tests on all the components that threw codes. I noticed right away that my TPS plug housing is just not working at all - it doesn't lock in place. I bought a replacement along with the new TPS several months ago, so I spliced the new plug in.

Just going down the list to see what I see as far as continuity goes. If I find something, this is an easy-ish fix, I hope.

One thing:
going through the codes - the speed sensor - this is interesting because I noticed for the past two years - maybe two or three times - I'll pull out of a parking lot and the speedometer is just sitting there at 0. Then suddenly, it'll spring into action and show 40 mph or whatever. so I guess that could be the wiring is shot. or the sensor. I'll test and see what I find.

 

Ok, I found this post: https://www.yotatech.com/forums/f116.../#post52453076

so there are 2 speed sensors?

My rig:
1994 Toyota v6 3.0 4wd manual transmission. According to that post I linked above, I have 2 speed sensors.

I did a continuity test on both:
1st one (has 2 wires, nearest the front of the truck on the transmission) - super greasy, looks like it has some kind of magnetic connection - just pads (?), not a plug - maybe I'm testing it wrong, but I can't get continuity from these pads back to the ECU or anywhere in the system. Does anyone have a part number on this one? or what is it called on Ebay, exactly?

2nd one (has 3 wires, near the back of the transmission, right where the rear drive shaft connects): all 3 wires go to some random plug with 16 connections - it does NOT connect to the ECU, as far as I can tell. Is this the one that feeds the dashboard needle? Ebay has a bunch of these for $14, but I don't think this is my problem.

anyway, thanks for any ideas.

*** update ****
Searching around on RockAuto and ebay - it looks like the only "2 connector" speed sensor is for an automatic transmission - is this the right part number: 8941135010 ? even though it's for an automatic? (and mine is a manual).

 

Looks like the right part #. Check out the link for the online parts catalog. Click on 89411C. A popup will come up with the 10 digit part #. Still available thru toyota for $100 online price.


https://www.japan-parts.eu/toyota/us...mission#89411C

 

I like Lakeland Toyota's site: https://parts.lakelandtoyota.com/p/t...941135010.html Put in the part number, and ask "what does this fit." So you've found the right part.

That only addresses one code. How are you doing looking for the cause of the others?