Hello all. I just bought a 94 this past weekend, and am currently trying to iron out the issues. The main one is a weird engine/electrical load based misfire and rough idle. I notice it also takes a few cranks too many to start. When idling or coasting, turning the steering wheel makes the engine idle drop and be a bit rough, and electrical loads can cause the same issue. Electrical loads also seem to make the engine misfire or enter limp mode when the throttle is being pressed down. No CEL comes on while this is happening. I've attached a video of this. The clicking noise is me rolling up the window, which seems to be the most consistent way of making it happen (Also ignore the squeaking in the background, the passenger side wheel bearing is shot). The idle speed itself seems to be correct, it sits at about 1100 on high idle, drops to 800 once warmed up, and turning on AC raises idle to 1000. I've ordered an FSM but haven't gotten it yet, so any help would be appreciated.
Engine Load Based Rough Idle/Misfire (1 Viewer)
- Thread starter znbail
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- Thread starter
- #2
Small update since I've gotten a bit more info on my issue. I bought a ToyOBD1 scanner to see what the engine is doing. The O2 sensor reading seems to be all over the place, and when I replicate my problem, I can see the "open loop" indicator turn on, and the O2 sensor readout says "OX Feedback Inactive Rich". I'm still not getting a CEL that would indicate the O2 sensor is bad.
ppc
M Go Blue
@znbail ...
A narrow band O2 sensor used in 90's vintage operate in much differently than current vintage wide band sensors. The voltage output constantly sweeps from lean to rich back lean on a continuous basis the speed of that switching is determined by engine speed/load. If you watch an air/fuel gauge, at idle the sweep may be one or two seconds, jump on the gogo peddle it sweeps faster than you can count. Problem is there is a limit to the peaks and valleys of the air fuel ratio. The engine ecm detects values beyond it's programmed limits the computer goes into open loop and runs the engine without O2 sensor data and basically runs the mixture rich for the safety of the engine. Lean conditions otherwise would start melting pistons etc.
Based on your limited information, everything would appear normal.
FYI, most wide band gauges display afr as just a number which for lack of a better term is mathematically smoothing the raw data and converts to number that is more constant than the narrow band sweeps that don't get smoothed .
*** Edit ***. The sweeping is necessary for proper function of the catalytic convertors to control/limit emissions.
Disclaimer ==== This is the AFR/O2 Sensor for Dummies. There of course is much more involved but this provides the basic understanding. A lot of this information can be found in the FSM and other Toyota documentation but is generic for all similar vintage vehicles from other manufactures.
A narrow band O2 sensor used in 90's vintage operate in much differently than current vintage wide band sensors. The voltage output constantly sweeps from lean to rich back lean on a continuous basis the speed of that switching is determined by engine speed/load. If you watch an air/fuel gauge, at idle the sweep may be one or two seconds, jump on the gogo peddle it sweeps faster than you can count. Problem is there is a limit to the peaks and valleys of the air fuel ratio. The engine ecm detects values beyond it's programmed limits the computer goes into open loop and runs the engine without O2 sensor data and basically runs the mixture rich for the safety of the engine. Lean conditions otherwise would start melting pistons etc.
Based on your limited information, everything would appear normal.
FYI, most wide band gauges display afr as just a number which for lack of a better term is mathematically smoothing the raw data and converts to number that is more constant than the narrow band sweeps that don't get smoothed .
*** Edit ***. The sweeping is necessary for proper function of the catalytic convertors to control/limit emissions.
Disclaimer ==== This is the AFR/O2 Sensor for Dummies. There of course is much more involved but this provides the basic understanding. A lot of this information can be found in the FSM and other Toyota documentation but is generic for all similar vintage vehicles from other manufactures.
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- Thread starter
- #4
@ppc The narrowband part makes sense for sure. What doesn't is how I'm able to put the car in open loop on demand. This isn't from a change in temp, or load, or throttle position, or any other normal variable that would make sense to go into open loop for. Without fail, every time I replicate the issue the open loop indicator turns on, and then when I let go of the window switch and the car starts running fine again, the open loop indicator turns off.
I ran the FSM test on the oxygen sensors last night, and one of them failed the test, so I ordered a pair to replace both.
I ran the FSM test on the oxygen sensors last night, and one of them failed the test, so I ordered a pair to replace both.
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ppc
M Go Blue
I don't understand how getting a open loop condition "at will". What are you doing for that to happen? That where you're very unclear there. The window switch/motor is going to be a high current draw, lowers the voltage in your vehicl the Toyocom unit probably resets based upon some type of voltage spike or drop.
- Thread starter
- #6
I can get an open loop condition at will because it happens every time I press the window switch, without fail. Some other electrical loads like the turn signals do it too, but oddly enough headlights don't seem to cause it. I've test driven around the block multiple times to confirm this, and every time I press the window switch, the RPMs drop and throttle is unresponsive as shown in the video. I've confirmed the ECU is entering open loop mode when this happens. If it was an issue with the scanner, I would think it would drop communications or other readouts would also act up, but that and the O2 readout saying "Ox feedback inactive" are the only readouts that seem affected by what's happening. I've driven around without turning anything electrical on for 20-30 minutes to get a baseline, and neither of those two things occured during the normal drive.
ppc
M Go Blue
You previously stated the window switch usage removed/reset to normal not that it also caused it. That is a critical piece of info. Be precise and complete when you post.
You surely are not the only one as of late but I'm getting reluctant to help people because I spend a lot and time and effort to respond.
The Toyocom device and associated software is created by a hobbyist. Very smart guy but the product is not fool proof but very good at the price point like you might expect from Hewlett Packard or NASA.
Your voltage fluctuations are very common with the 80 Series. Poor grounds, week battery, failing voltage regulator internal to the alternator.
Use the forum search function or google to search those for those threads.
I think your Toyocom hardware and software are working as designed.
- Thread starter
- #8
I feel like I state pretty clearly here that rolling up the window is what's causing my issue, and releasing the switch is what makes it go away.
Alternator and battery are both new. There are no other forums from what I can find that have even close to what I'm seeing.
ppc
M Go Blue
In this forum, searching using the correct terms will be many threads. It will develop your search techniques. Start with "dimming lights" or similar.
Again...Your voltage fluctuations are very common with the 80 Series. Poor grounds, week battery, failing voltage regulator internal to the alternator.
Use the forum search function or google to search those for those threads.
Again...Your voltage fluctuations are very common with the 80 Series. Poor grounds, week battery, failing voltage regulator internal to the alternator.
Use the forum search function or google to search those for those threads.
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Malleus
Far west of Siegen
First, you don't have to wait for a service manual. They're in the Resources section for free download, both the engine/chassis service manual and the electrical wiring diagram, as well as the Wire Harness Repair Manual. I'd recommend downloading all three and familiarizing yourself with the terminology used in them. Using common language always helps communication.
Second, the search function - on this site - works far less reliably than google + "IH8MUD", IME.
Finally, there is a description of the diagnosis of engine problem, in the fuel (SFI) system section. I'd recommend you start there, even if you don't think your problem is a "fuel system" problem, because this is where the diagnostics for the engine controls are described. This section begins on page EG-217 and contains all the ECU/ECM values you need to verify while the engine is running. The troubleshooting section begins on page EG-231. If you use the pdf copy from the Resources section, these are bookmarked for you, as well as other helpful areas of interest (but you have to use Acrobat to use them).
Second, the search function - on this site - works far less reliably than google + "IH8MUD", IME.
Finally, there is a description of the diagnosis of engine problem, in the fuel (SFI) system section. I'd recommend you start there, even if you don't think your problem is a "fuel system" problem, because this is where the diagnostics for the engine controls are described. This section begins on page EG-217 and contains all the ECU/ECM values you need to verify while the engine is running. The troubleshooting section begins on page EG-231. If you use the pdf copy from the Resources section, these are bookmarked for you, as well as other helpful areas of interest (but you have to use Acrobat to use them).
