3.0 Rough, Code 12
#1
3.0 Rough, Code 12
So my '90 3vze (Auto trans) is having troubles.
Idle is stumbly, it takes a bit of cranking to get it to start when it's warm.
I have an air/fuel ratio meter mounted to the dash, so i know a bit more.
WHen i cold start it, it runs rich for about 5 minutes, and then idles normal, but it still chugs a bit. When i first step on the gas from a stop, the air spikes and i bog out for a second or two, and then it goes back to normal mixture, until the trans shifts into second, and then it goes to a rich mixture for about 5 minutes. After that, it's more or less normal, but you can still smell it's running rich in the exhaust.
I'm also being thrown code 12. I've been doing some researching on it, and i came up with
open or short in NE circuit
open or short in the STA circuit
or the ECM
Problem being i have no idea what either of those circuits are, where to find them, or how to test them (Electrical noobie). I tried digging, but nobody really explains it.
Any insight would be greatly appreciated.
Idle is stumbly, it takes a bit of cranking to get it to start when it's warm.
I have an air/fuel ratio meter mounted to the dash, so i know a bit more.
WHen i cold start it, it runs rich for about 5 minutes, and then idles normal, but it still chugs a bit. When i first step on the gas from a stop, the air spikes and i bog out for a second or two, and then it goes back to normal mixture, until the trans shifts into second, and then it goes to a rich mixture for about 5 minutes. After that, it's more or less normal, but you can still smell it's running rich in the exhaust.
I'm also being thrown code 12. I've been doing some researching on it, and i came up with
open or short in NE circuit
open or short in the STA circuit
or the ECM
Problem being i have no idea what either of those circuits are, where to find them, or how to test them (Electrical noobie). I tried digging, but nobody really explains it.
Any insight would be greatly appreciated.
#2
Registered User
Join Date: Mar 2009
Location: Georgia
Posts: 390
Likes: 0
Received 0 Likes
on
0 Posts
could be a bad distributor, giving a bad signal to ignitor. a lab scope is the only real way to check the signal that i know of. pull the distributor cap and see if there is any excessive play on the rotor shaft indicating worn bearings maybe.
#3
Registered User
First things first. These engines have a "Cold Start Injector" which sprays extra fuel to ensure the engine starts in "cold" conditions. When the ECT and the IAT both record temperatures under a specific threshold, it triggers the ECU to run the injector. If only one give the reading or if both are over the threshold, it does not run. So the fact that you are reading a rich condition until the engine warms up is completely normal. That means that your ECT, IAT and ECU are all functioning perfectly in those regards.
After warming up though, you should not be switching between lean and rich conditions. The O2 sensor should adjust in a fraction of a second, not over several seconds or minutes like you are describing. I am wondering, do you have a wide-band O2 sensor on? It is a universal one or specifically for these trucks? However, fixing the CEL light might clear up the whole deal and not worry about the O2.
A code 12 is:
• Open or short in NE, G circuit
• Distributor (it's broken)
• Open or short in STA circuit
• ECM
This page will help you understand what those circuits are:
http://personal.utulsa.edu/~nathan-b.../9systemci.pdf
So basically, either the wires NE or G are damaged or broken (visual check to confirm, use a voltmeter to check) or the wire STA is broken, or the distributor is shot, or the ECM (ECU computer) is shot. ECU's rarely go bad. Distributors are obvious when they are failing, they will be like what oldblue described, or just all rusty inside like mine was. Usually though when they fail, it's a total failure and you're dead in the water.
We can't tell you what is exactly causing the issue, you'll have to investigate. But there is a problem, and that CEL (and possibly the rough driving) will not go away until it is fixed.
After warming up though, you should not be switching between lean and rich conditions. The O2 sensor should adjust in a fraction of a second, not over several seconds or minutes like you are describing. I am wondering, do you have a wide-band O2 sensor on? It is a universal one or specifically for these trucks? However, fixing the CEL light might clear up the whole deal and not worry about the O2.
A code 12 is:
• Open or short in NE, G circuit
• Distributor (it's broken)
• Open or short in STA circuit
• ECM
This page will help you understand what those circuits are:
http://personal.utulsa.edu/~nathan-b.../9systemci.pdf
So basically, either the wires NE or G are damaged or broken (visual check to confirm, use a voltmeter to check) or the wire STA is broken, or the distributor is shot, or the ECM (ECU computer) is shot. ECU's rarely go bad. Distributors are obvious when they are failing, they will be like what oldblue described, or just all rusty inside like mine was. Usually though when they fail, it's a total failure and you're dead in the water.
We can't tell you what is exactly causing the issue, you'll have to investigate. But there is a problem, and that CEL (and possibly the rough driving) will not go away until it is fixed.
Last edited by Gamefreakgc; 11-06-2013 at 02:18 PM.
#4
First things first. These engines have a "Cold Start Injector" which sprays extra fuel to ensure the engine starts in "cold" conditions. When the ECT and the IAT both record temperatures under a specific threshold, it triggers the ECU to run the injector. If only one give the reading or if both are over the threshold, it does not run. So the fact that you are reading a rich condition until the engine warms up is completely normal. That means that your ECT, IAT and ECU are all functioning perfectly in those regards.
After warming up though, you should not be switching between lean and rich conditions. The O2 sensor should adjust in a fraction of a second, not over several seconds or minutes like you are describing. I am wondering, do you have a wide-band O2 sensor on? It is a universal one or specifically for these trucks? However, fixing the CEL light might clear up the whole deal and not worry about the O2.
A code 12 is:
• Open or short in NE, G circuit
• Distributor (it's broken)
• Open or short in STA circuit
• ECM
This page will help you understand what those circuits are:
http://personal.utulsa.edu/~nathan-b.../9systemci.pdf
So basically, either the wires NE or G are damaged or broken (visual check to confirm, use a voltmeter to check) or the wire STA is broken, or the distributor is shot, or the ECM (ECU computer) is shot. ECU's rarely go bad. Distributors are obvious when they are failing, they will be like what oldblue described, or just all rusty inside like mine was. Usually though when they fail, it's a total failure and you're dead in the water.
We can't tell you what is exactly causing the issue, you'll have to investigate. But there is a problem, and that CEL (and possibly the rough driving) will not go away until it is fixed.
After warming up though, you should not be switching between lean and rich conditions. The O2 sensor should adjust in a fraction of a second, not over several seconds or minutes like you are describing. I am wondering, do you have a wide-band O2 sensor on? It is a universal one or specifically for these trucks? However, fixing the CEL light might clear up the whole deal and not worry about the O2.
A code 12 is:
• Open or short in NE, G circuit
• Distributor (it's broken)
• Open or short in STA circuit
• ECM
This page will help you understand what those circuits are:
http://personal.utulsa.edu/~nathan-b.../9systemci.pdf
So basically, either the wires NE or G are damaged or broken (visual check to confirm, use a voltmeter to check) or the wire STA is broken, or the distributor is shot, or the ECM (ECU computer) is shot. ECU's rarely go bad. Distributors are obvious when they are failing, they will be like what oldblue described, or just all rusty inside like mine was. Usually though when they fail, it's a total failure and you're dead in the water.
We can't tell you what is exactly causing the issue, you'll have to investigate. But there is a problem, and that CEL (and possibly the rough driving) will not go away until it is fixed.
The o2 sensor is also new, so I doubt it's that
I'm gonna poke around and see what's up
#5
Registered User
http://personal.utulsa.edu/~nathan-b...85diagnosi.pdf
it is most likely a bad distributor.
here are the steps for the tests you will need to test.
http://personal.utulsa.edu/~nathan-b...86troubles.pdf
it is most likely a bad distributor.
here are the steps for the tests you will need to test.
http://personal.utulsa.edu/~nathan-b...86troubles.pdf
#6
http://personal.utulsa.edu/~nathan-b...85diagnosi.pdf
it is most likely a bad distributor.
here are the steps for the tests you will need to test.
http://personal.utulsa.edu/~nathan-b...86troubles.pdf
it is most likely a bad distributor.
here are the steps for the tests you will need to test.
http://personal.utulsa.edu/~nathan-b...86troubles.pdf
So it looks like i'm going to be tracing ALOT of wiring...
Any tips to make this easier on me? Lol
#7
So i traced the STA wire from the ECU side, and from the Starter until it joined up with the main bunch of wires from the ECU, and i didn't find anything. I didn't follow it back to the ECM because the stock harness hasn't been opened, and It didn't seem like something would go wrong in there.
I did find that though. THe distributor has 6 wires coming out of it, and 3 are spliced into one, which does to the connector, which has 4 wires coming from it.
Think that might have anything to do with it?
I did find that though. THe distributor has 6 wires coming out of it, and 3 are spliced into one, which does to the connector, which has 4 wires coming from it.
Think that might have anything to do with it?
Trending Topics
#9
Registered User
I should add that the 88-92 distributors are the same. From 93-95 they changed the plug. Find a replacement. Junkyard would be the cheapest. Take a voltmeter and test it per the FSM before you buy it. I wonder if that is even a Toyota distributor
#10
I'm not sure how to check the voltage on it though. I guess i'll keep researching.
#11
Registered User
in this picture you can see the plug on my 94 3vze distributor. the plug is a single row of 4. there are NO wires coming out of the distributor itself. the plug is molded into the body of the distributor. The only wires are on the harness side of the plug. This is why I wondered if that was even a Toyota distributor.
http://personal.utulsa.edu/~nathan-b...12onvehicl.pdf
In this link, the last page will tell you how to test the distributor.
#13
Rough Idle while in drive and foots on the brake
I have a 1994 toyota 4runner. as of just recently it started to rough idle when im in drive and foots on the brake. It comes and goes, sometimes idles rougher than other times. Usually when the cat has been warmed up and driven. when in park you cant tell anything is wrong except for a small possible hickup. I dont feel any power loss or hesitation when driving and no check engine light has come on. Any possible solutions would help, My funds are limited aswell. Thank you
#14
Registered User
https://www.yotatech.com/forums/f116...iagram-274913/
read this. the important stuff is in the middle. Mud Hippy is basically a 3vze Guru. pay attention to what he says.
read this. the important stuff is in the middle. Mud Hippy is basically a 3vze Guru. pay attention to what he says.
#15
Thanks for the help. It was a misfire in cyl 5. Compression is 75, and 120-140 on everything else.
Sounds like I have some work ahead of me. Would that be the reason I'm getting a code 12? Or should I still replace the distributor.
Sounds like I have some work ahead of me. Would that be the reason I'm getting a code 12? Or should I still replace the distributor.
#16
No, that shouldn't cause any codes.
You could also check the starter relay and COR to see if both of those are working properly. Since they're both part of the STA circuit. And not thoroughly covered in the basic troubleshooting procedures.
http://personal.utulsa.edu/~nathan-b.../2starterr.pdf
http://personal.utulsa.edu/~nathan-b...96circuito.pdf
And there's no reason to replace the distributor without verifying that there's actually problem with it. And/or without verifying that the code isn't caused by something other than it.
You could also check the starter relay and COR to see if both of those are working properly. Since they're both part of the STA circuit. And not thoroughly covered in the basic troubleshooting procedures.
http://personal.utulsa.edu/~nathan-b.../2starterr.pdf
http://personal.utulsa.edu/~nathan-b...96circuito.pdf
And there's no reason to replace the distributor without verifying that there's actually problem with it. And/or without verifying that the code isn't caused by something other than it.
Thread
Thread Starter
Forum
Replies
Last Post
montanatruck
86-95 Trucks & 4Runners
15
02-26-2017 07:07 AM
nframe
3.4 Swaps
3
08-16-2015 09:03 AM