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I am hoping scope103 or RJR will see this and chime in. I understand the basics of closed loop vs. open loop but bear with me as electrical stuff is not my thing.
1, VF1 voltage with E1 and TE1 jumpered. At idle I get 5v, at 2500 it jumps around and appears to be working but it’s a bit all over. I realize that my meter though it updates 3 times per second it may not be seeing the exact voltage changes.
2, VF1 voltage without jumpering TE1. At idle I get 1.085v. At 2500 it drops to 52mv and doesn’t move.
3, OX1 voltage. At idle I get .775v. At 2500 I get about .78-.79v. At 2000 rpm the voltage will actually move around and drop considerably. Once again my meter is only showing me when it jumps down from the .7**v to something lower, I have no idea what the really number is.
I have read and re-read the above mentioned post and I am still a bit confused, so here are my questions.
Does an output voltage of .78-.79 reading on OX1 mean the mixture IS rich or does it mean it’s telling the ECM to richen the mixture?
Does 52mv reading on VF1 un-jumpered mean I am running lean?
Is 5v at idle normal at VF1 when TE1 is jumpered?
Am I doing any of this right?
Open for all thoughts and comments. Here is a link to a video I made for reference.
- IMPORTANT: Closed loop mode only works when the engine is warmed up! (Coolant temperature above 140 degF). Also only when throttle is off idle and not wide open.
Just to summarize (all of this applies only to closed loop mode operation.)
- The O2 sensor output cycles from 0V (lean mixture) to +1 volt (rich mixture). It has a very narrow range in between. In closed loop mode the ECU will adjust mixture so the O2 sensor switches from 0 to +1 volt and back about once/second. As my previous post states, it's a very high output impedance, so you can't look at it directly with a simple analog meter. Most digital meters are fine, but the slow response time of the cheap ones makes the switching hard to see.
- With TE1 grounded and the throttle at idle (TPS idle switch closed), VF1 will show 0V if there are diagnostic codes present, +5 volts if no codes.
- With TE1 grounded and the throttle off idle, VF1 is a buffered, amplified version of the O2 sensor and switches between 0V and +5V when in closed loop mode.
- With TE1 open, VF1 reports the ECU fuel trim correction. 2.5 volts means it's nicely centered up. < 2.5 volts means the ECU is leaning out the mixture slightly. If > 2.5 volts, it's driving it richer. If the voltage is stuck at either 0V or +5V, the ECU has run out of control range and will possibly be throwing a code soon.
WIth respect to your measurements above.
1 and 3 are really saying the same thing. They are both observing the O2 sensor, one buffered, one direct. Both are showing that the O2 sensor appears to be working, but generally is showing a mixture biased toward rich. An output of near 1 volt (.78) from the O2 sensor indicates a rich mixture. The ECU will try to make it more lean.
2 indicates your ECU is working pretty hard to keep the mixture lean enough, which agrees with your O2 sensor observations. 52mv (effectively 0V) means the ECU wants the mixture to be even leaner but has run out of range.
Bottom line, something is making your mixture overly rich.
Other things to consider:
- Are you seeing any CEL codes?
- Have you put in aftermarket injectors?
- Have you checked out the VAFM for smooth electrical operation?
- How old is the O2 sensor?
- How's the fuel pressure? Too high can cause rich operation.
Scope103 put together the diagram below. It's a useful summary of how the diag port works.
RJR, thank you for going thru that again and being specific to my readings. That helps a lot.
Regarding your questions:
- Are you seeing any CEL codes?
No codes at this time
- Have you put in aftermarket injectors?
I installed the flamethrowers when I rebuilt the engine a year ago.
- Have you checked out the VAFM for smooth electrical operation?
I have not, I think I only did some basic test that was in the FSM, If I remember correctly is was just a resistance check.
- How old is the O2 sensor?
Replaced last week.
- How's the fuel pressure? Too high can cause rich operation.
I have not checked this lately. I installed a brand new Toyota regulator at the time of the rebuild because the old one was off.
A little more background. 93 3VZE, full head port, bowls, runners, everything matched. Doug Thorley headers, flowmaster muffler. Otherwise completely stock.
A couple other things to mention. I had been running around with the AFM 3 clicks rich, it seemed to run much better there and mileage was 16-18 which is normal for my commute. A month or so ago what started this was a poor idle and terrible fuel mileage, the thing started to surge at idle, then we had a bunch of rain. I blasted thru some big puddles and then the next day the thing started started stalling at idle. I adjusted the AFM back to stock and replaced the o2 sensor and have run about a half a tank of gas. I don't have any stalling anymore and the idle is perfect. I can tell the mileage is much closer to what is was before. I will do an actual check when I fill up next. I just thought I would include this in case it could be related.
It sounds like you're on the right track. If the ECU isn't throwing a code, it means it is able to get the mixture correct under normal closed loop operation. You can probably get the trim voltage centered better if you adjust the AFM more in the lean direction, but it probably won't affect running or mileage much. My guess is your root problem a month ago was a bad O2 sensor and/or compromised wiring because of the rain and a poorly sealed connector. Because the O2 sensor has such a high output impedance, it doesn't take much moisture in the connections to degrade its output.
So I found this nifty little gadget that will read and log OBD1 data in real time. It connects to the data port to read data then transmits it through Bluetooth to an app. Its really a cool little tool. You can also export the data into a spread sheet for further analysis. I included below a snap shot of a few lines from the spreadsheet.
I found that this logger confirmed what we had determined by looking at the voltage. I adjusted the AFM 3,6, then 9 clicks lean. I will probably go back a bit. Once it seems to look good I will go back and see if the actual voltage output confirms what I am seeing in the app and logs.
Anyway its just a really cool tool to help analyze what is going on in our OBD1 toyotas.
I bought it here. https://zf-scantools.com/index.php?rt=index/home His name is Jean-Francois Breton. He is located in Canada. Very nice, helpful guy. It took less than a week to receive and it was plug and play.
It really is cool. I like that I can drive around and see what is going on on my phone or tablet.
Off topic but how do you like running the 33x10.5s on your 94 with the 4:56 gears. I am thinking of going this route on my next set of tires and I have the same gearing. Any pics you can share with me?
I like the 33's. I could notice a little bit of a performance hit when I first made the change, but the 3vze was never a hot-rod anyway, so I got used to it pretty quick. I like the extra clearance and diameter off-road a lot. That to me is more noticeable than the performance degradation. I wouldn't go back. I had a little bit of rubbing in the rear wheel wells when the rear tires were completely stuffed, but that was because the bumpstops were rotted off. I replaced those and it's been fine. Plus, the rubbing was just on the plastic fender liner, so no real damage occurring.
I don't have any "driveway pictures." Here are a couple of pics from a trip we made to the Maze in Canyonlands a year ago.
The Maze is awesome, and was sort of a "bucket list" trip for me. Remote with jaw-dropping scenery. A friend ('06 4runner) and I went with our two adult sons, so it was special. About 160 miles of gravel, 80 miles or so in low-range, saw three other vehicles and about 10 other people in a week. Definitely worth doing. A stock 2nd gen would be adequate for the roads, although having the front locker and the 33" tires made things easier. With open diffs you might have to try a couple of lines and/or stack some rocks in certain places.
04-12-2017, 09:06 AM
