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More power with O2 sensor disconnected?

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Old 08-29-2010, 07:58 AM   #1
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More power with O2 sensor disconnected?

Honestly, sorry for all these posts.

I found the problem with my "lack of power" issue but I'm uncertain what it means: During warm up, and the ECU is in open loop, my truck runs fantastic. Once @ operating temperature the truck bogs a bit.

So, I checked the components which would cause problems after the ECU went into open loop:
TPS (Changed out and adjusted to spec)
ECT (Right on the dot when tested at cold and operating temp)
AFM (Static and dynamic tests good)
O2 Sensor (Tested good but replaced anyways with OEM style Denso)

After all this, the truck still did the same thing. So I disconnected the O2 sensor and it idles better and has much better acceleration. It does the same thing with the old and the new O2 sensor!

1) Do I have the right O2 sensor?
-Part # from Sparkplugs.com: 234-4052. This part # is the same for FRONT California and FRONT federal emissions. I only have 1 O2 sensor, so I must have a federal emissions truck, correct? (Even though Im in CA).

2) ECU going bad?

3) I think the truck is running lean. But, if it was running good with the O2 sensor attached and during warm up, wouldn't that say the injectors are able to increase fuel input and not be clogged?

4) Does the cold start injector run during the entire warm up process or in closed loop?

Last edited by BajaRunner; 08-29-2010 at 09:19 AM.
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Old 08-29-2010, 09:04 AM   #2
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Your truck won`t run properly with the 02 sensor disconnected. When your truck is cold its in open loop, once it warms up to normal temperature it goes into closed loop and it uses the 02 sensor to set the air fuel ratio, with out the 02 sensor your truck won`t run as well and your gas mileage will go way down. So don`t disconnect it.
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Old 08-29-2010, 09:16 AM   #3
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No I won't but...

Why would the truck run better with more power with it disconnected? I only did it as an experiment. My lean misfire goes away with it disconnected.

I'm assuming its related to another problem. What could that other problem be?

I think its overcompensating disconnecting it, and giving the engine more fuel, and increasing the fuel to air ratio...and the truck runs better. I'm wondering why!?

Last edited by BajaRunner; 08-29-2010 at 09:20 AM.
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Old 08-29-2010, 12:36 PM   #4
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Read this:
http://autoshop101.com/forms/h44.pdf

If your ECU was bad, it would never run well.

Cold start injector, normally, only operates for a few seconds upon cranking and only when the motor is cold.....below 64* on pre '89 and 104* for '89 on.

If the truck is running lean because of the injectors being clogged, depending on much they are clogged, in closed loop the ECU is able to correct for that by keeping the injectors open longer. Without the O2, and in open loop, the ECU has no idea it's running lean. But, since it's been modifying a/f for some time with an O2, it's learned a habit/set a pattern for injector duration. Given enough time, with the O2 disconnected and if the injectors are clogged, you'll see the power begin to decrease, again. You'll develop spark knock and the KS will retard you're timing more or less depending how much load the vehicle is under at any given point.

Your truck has more power because the O2 and ECU is correcting for an imbalance and probably has been for some time. It may not be the because of the injectors, but whatever it is it can't be major.

A normal running vehicle can run just fine without an O2 sensor/in open loop. The majority of a/f ratio is determined by TPS, AFM, RPM signal from distributor, and THW input...... which is pretty accurate in and of itself provided everything mechanical and electrical is functioning normally. Having said that, it's not ideal for the catalytic converter. So, over time, it may clog prematurely. But, there's a lot of factors involved that would determine that happening.

As well, the ECU is does not "go into open loop", per se. Open loop simply means the ECU is not monitoring it's output (via exhaust) and making adjustments to a/f accordingly. So, it only ever really "goes into" closed loop. Open loop can be said to be the ECU's basic fuel program while closed loop is a modification to that. That's not the entire picture, but I'm using this as an illustration.

The thing to note, in your situation, is if the gas mileage will go up or down with the O2 disconnected. If it goes up, then your engine is running too lean for some reason. If it goes down a bit and runs well enough, it would be normal. But, if it goes down considerably and the vehicle runs like poop, something's causing it to run rich. You will have to leave the O2 disconnected for a few tanks to really utilize this "method" in determining what's going on. This is because the ECU makes adjustments to it's basic program gradually. IOW's, right now, it has a particular habit that's been masking a symptom. Given enough time, and without the ECU being able to monitor and adjust, the real condition will reveal itself as the ECU is no longer able to make it's adjustments and will more or less "unlearn" it's habit of masking.

Of course, you could also just run a voltage feedback test at your diagnostic port the determine which side of the rich/lean spectrum the O2 keeps leaning towards. This is a better way to figure out what's going on.
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Old 08-30-2010, 11:14 AM   #5
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OK Thook, thanks for all the great information again. I feel pretty clear on how the ECU works and goes into a feedback loop from the AFM, TPS, O2 sensor, etc...

Like I said earlier, I can feel the truck pull and put out more power for the first 5 minutes of driving. Once its reached operating temp, It slows down a bit. I also noticed that disconnecting the O2 sensor makes it feel as if it was in that "warm up" stage and had more pull.

I've read how to test the O2 sensor through the diag port, but I dont know how to interpret the voltage readings to tell me if its running lean or rich?


I was hoping someone could just verify the Denso O2 sensor part # for me to make sure I got the right one. Attached is the OEM one I pulled out, and the "OEM replacement" Denso I bought:


And here is a weird wiring job the PO did. This harness sits right beneath the coil, on the drivers side in the engine bay. Notice the one wire is clipped completely from the harness and a bigger, red wire is behind it. Could this be something for the alarm system?


Also to note in the background the burnt ground. I tested voltage from positive terminal and it matches the battery voltage, but I'll be replacing that wire here soon.
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Old 08-30-2010, 11:58 AM   #6
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Untape that wiring harness and see if you can figure out what the po did and why he would have cut that wire, and see if you can put it back to the way it was stock. Also repair the burned wire and see if that helps anything.
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Old 08-30-2010, 07:22 PM   #7
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Well the burnt wire in the background is the same wire that was cut. Its a white with black strip. It runs from a ground, right behind the power steering bracket to a ground on the body. It is almost like a connecting wire from grounds? Could this be true? Anyways, the new red wire now takes its place.
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Old 08-30-2010, 09:27 PM   #8
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So the alternator has the "B" plug that goes to the battery, and a 4 wire harness.... does that 4 wire harness contain the "ground" for the alternator? I'm trying to figure where the white wire with black strip goes to the alternator or not.

I'm not sure that the PO wired it correctly.

When I turn on my turn signal, my volt gauge ticks down, I dont know if this is a normal issue. If not then it might have something to do with this wire job.

I've looked at the wiring diagrams, and its not really helping me. If anyone could explain how the wiring from the alternator is routed, I'd be stoked.
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Old 08-30-2010, 10:10 PM   #9
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Is you O2 connector for four wires or three? It's hard to tell in the pic.
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Old 08-31-2010, 06:48 AM   #10
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4 Wires!
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Old 08-31-2010, 07:19 PM   #11
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Anyways, the wiring is OK from the alternator and fixing it didn't help anything.

I'm still trying to figure out why the truck runs better when warming up/cold... are there any other logical reasons for this?

Idle is still not smooth, trying to time the truck, the timing mark jumps from 5 to 8 degrees... This is starting to get frustrating.
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Old 08-31-2010, 09:36 PM   #12
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Hmmm.........how do I put this? Until the engine warms up and the O2 sensor warms up, the O2 is not generating a voltage signal to the ECU. So, that little factor's out of the way in so far is how the ECU is controlling warm up enrichment. Once the engine does warm up, the ECU "shifts" in to trimming fuel to a more ideal ratio. Only then is the O2 signal utilized. However, as with many electrical components, if the voltage signal that's being utilized is funky, then adjustments made according to that will be funky. And, of course, the vehicle will run funky. I'm kinda surprised you didn't get a code with that wiring so screwed up

Anyway, seems to me you're not reading much on the autoshop site. Fair enough, I know it's a lot to read and cognize in a short amount of time. And, if I'm mistaken, I certainly don't mean any offense. It's just that if you would read it would explain most of the questions you have. Certainly you need to fix that wiring for several reasons, but as far as verifying the O2 part number, that's somewhere on the forum in several threads. Run an advanced search using "thook" under "posts by". I posted in one that came up fairly recently that has the part number.

The idle rpm and timing is going to be erratic until you get a solid O2 signal.
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Old 08-31-2010, 10:08 PM   #13
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You will need to untape the wiring harness until you find the missing wire that was cut from the plug, figure out why it was cut from the plug, fix it and put it back like it was stock. OR, does that red wire connect to the wire that was cut and then go to the 02 sensor ?. Im guessing your 02 sensor has three wires because it has a built in heater, if thats the case and the heater part of the 02 sensor isn`t working, then the 02 sensor might not be getting hot enough to function properly.
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Old 09-01-2010, 09:17 AM   #14
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Quote:
Originally Posted by myyota View Post
You will need to untape the wiring harness until you find the missing wire that was cut from the plug, figure out why it was cut from the plug, fix it and put it back like it was stock. OR, does that red wire connect to the wire that was cut and then go to the 02 sensor ?. Im guessing your 02 sensor has three wires because it has a built in heater, if thats the case and the heater part of the 02 sensor isn`t working, then the 02 sensor might not be getting hot enough to function properly.

That's why I asked him if his connector was for four or three wires. His has four. Two for the heater circuit and two for the sensor signal. And, that's why I'm surprised he didn't get any codes. If the heater or signal circuit's broken, the ECU should set a DTC. My guess is that's what the red wire was for; to make up for the one cut.
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Old 09-01-2010, 12:20 PM   #15
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Just to make clear, that 4 wire harness with the cut wire HAS NOTHING TO DO WITH THE O2 sensor!!! Its the harness for the alternator! I am fairly certain I have the wires hooked up correctly for the alternator, otherwise I doubt I'd be getting a charge.

Anyways -- As far the O2 sensor is concerned, wouldn't I throw either a Rich/Lean CEL or an O2 sensor CEL if something was way off?

I've truly read the autoshop 101 document you posted. I understand that for the most part.

From what I have gathered, the O2 sensor output and heater circuit are functioning properly. But like I've said, my torque, power etc is better during the warm up cycle and the ECU is not getting information from the O2 sensor, and when I disconnect it. The air flow meter seems to be functioning properly too.

I'm still unsure on what else to check.

Last edited by BajaRunner; 09-01-2010 at 12:21 PM.
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Old 09-01-2010, 01:26 PM   #16
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Another thing which I cannot find information on, is the optimum operating temperature of the 22re. When I measure the thermostat housing with a temperature reader (point and click style) it reads 235 F. The temp gauge reads exactly half in the dash. The temperature difference in the radiator is only about 20F. (Brand new radiator, cap, thermostat and water pump). I was wondering if its running too hot and causing the engine to run poorly.

I'm assuming since the temp gauge is at halfway, its probably running a tad too hot. I have a new NAPA thermostat but will try a Toyota one... Since all the coolant parts are new, it must have something to do with that.

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Old 09-01-2010, 02:37 PM   #17
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Baja when you replaced the Tstat with the new Rad did you put in a lower temp tstat? I have seen cars run like crap when people have done this.

Chris
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Old 09-01-2010, 03:02 PM   #18
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THanks for the reply!

No I put the stock temperature 185F one in NAPA gave me as a stock replacement. From what I have read, the NAPA ones aren't good as the OEM. I'm still concerned on what the operating temperature should be, and its possibly not running optimum temperature.
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Old 09-02-2010, 01:07 PM   #19
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Can anyone give me the temperature I should be reading at the thermostat housing?
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Old 09-02-2010, 07:08 PM   #20
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Not sure if the burnt oil is from the previous owner saying he had the head work because he was burning oil, or if its a current problem... Took some pictures...any ideas on what could cause this?

Found out that the PCV valve grommet that was less than 1 month old was torn... I'll be getting a new one tomorrow. Maybe its a cause of some problems. The burnt look is only on #3 and #4 exhaust.

Burnt oil on rocker arms...




Last edited by BajaRunner; 09-02-2010 at 07:10 PM.
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