Power issues since botched water crossing

Good course of action you have planned. I suspect you do know what you are doing based on your posts. I do have to ask though just in case that you know what oscilloscope pattern to look for, or if you don't have that, what voltage values to look for right?

 

o-scopes make it so easy to spot abnormalities especially if it is great under normal conditions and then poor under acceleration

 

Good move. My GF's 4runner was acting up. I suspected fuel pump. She goes ahead and fills the tank . Fuel pump went out 10 miles after filling up the tank. I've been postponing that nightmare for 3 weeks now.

 

Page ES155 in the FSM has standard voltage values, which is in the section for troubleshooting P0171/0174 codes.

Im not sure whether my OBD reader will support an Oscilloscope view or not, but it will show sensor output values. If it does have an oscope view, I have never personally used one to troubleshoot.

Im on my way home now, I'll give it a shot...

Thanks for your help.

 

Good! Keep us updated.

 

Ok, here is what I know.

Fuel system in closed loop, warm engine.

MAF at Idle=4.1 g/s
MAF at 2500 rpm=15g/s

Took truck for a drive. It seems as though it is running better. I was able to get it to stutter, but it was more difficult to replicate today than before.

A/F b1s1= 3.25-5v
A/F b2s1= 3.25-5v
O2 b1s1=0.0-0.7v
O2 b2s2=0.0-0.7v

All sensors change in unison while driving (including during stuttering) depending on throttle position/load.


Unfortunately, the FSM troubleshooting guide involves using a control in their Intelligent Tester that changes to fuel trim level to see how the sensors react.

I was unable to use an oscope view

02 b1s1 Pin 1-2 = 14.4ohm
Pin 1-4 = o/l

O2b2s2 Pin 1-2 = 13.4ohm
Pin 1-4 = o/l

A/F resistance will have to wait until the exhaust cools down. They don't look that easy to get too.

Fuel Pump Resistor Pin1-2= .5-.6ohm (which is below the FSM spec of .71-.75)

What does this pump resistor do? It is the only thing out of spec have found thus far.

 

I am certainly no expert at this, but if A/F and O2 sensors are all always reporting the same as their opposite bank, it would be unlikely that they are all bad. Both O2 sensors would have been submerged, but only 1 AF sensor would have been in the water. (and maybe not even, high water mark would be close)

This fuel pump resistor has me wondering though.

 

If things are improving it may be possible that sensors, connections, and seals are drying up from what water may have entered them. I wouldn't condemn that resistor yet.

As far as your A/F sensors are concerned, that doesn't look right. The voltages appear way too high even at their start. Like they are stuck rich. Then again. I do not know what their initial values are supposed to be and what their allowed tolerances should be. Does anyone here have access to an FSM on what the acceptable voltages should be? I'll search around a bit and get back to you on that, in the mean time try to find the acceptable low and high values as well. The rears appear to be ok and those are more to make sure that the catalyst is converting the emissions correctly. They are more reference sensors which "talk" to the A/F sensors. The PCM then measures the difference between the A/F sensors then looks at the values of the oxygen sensors and determines weather or not the catalyst is within correct threshold limits.

EDIT: The more I look at it, the more those AFR sensors seem to be stuck super high rich. Which would indicate that they are telling your PCM that you are dumping out fuel, which is in turn causing your PCM to compensate for that and intake additional air to try and correct the issue. Hence the P0171, P0174 code.

 

The fuel pump speed is controlled at two levels (high speed or low speed) by engine condition (starting,light load, heavy load). When the engine starts the fuel pump relay closes and positive battery voltage is applied directly to the fuel pump. The fuel pump operates at high speed.

During idling or under light loads power is supplied to the fuel pump via the fuel pump resistor. The fuel pump operates at low speed. Another thing to check would be the fuel pump relay contacts to see of they are good. You may not be getting full voltage to the fuel pump.

 

This is a good tip also OP. Check the fuel pump relay contacts and make sure they don't look fried up and burnt. If they are, that would be telling of issues within the fuel system.

 

OP, we got a problem here. It appears that your AFR sensors should only achieve a maximum of 4.00 volts at the most. You are achieving 5 volts, which is telling me that your truck is running too lean under certain conditions. Optimum running voltage is 3.30 volts (14.7 a/f ratio), which explains to me why you are running normally most of the time until higher rpms, or WOT possibly.

Do me a favor and snap your pedal to wide open throttle real quick while monitoring the two air fuel ratio sensors. If you snap the throttle and the sensors go over 4.00 volts, you got a contaminated, bad set of AFR sensors in your truck bud.

This table shows acceptable AFR ranges for the sensors on Toyota's (Notice 4.00 volts is the ceiling which is acceptable to reach):

 

Here is the FSM for the P0171/74 codes. If I read it correct, the "Intelligent Tester" creates an artificial LEAN or RICH fuel situation by increasing or decreasing fuel volume inorder to see how the sensors react. Unfortunately I cannot replicate this, but it does state that in a LEAN scenario, the AF Sensors should read >3.35v, if fuel was RICH, it should read <3.0v.

 

You are correct. The acceptable voltages through Toyota for their air fuel ratio sensors are much higher then that of a standard oxygen sensor. Please refer to my updated post. That will have the information you need to properly test it without using an "intelligent tester"

That stutter you feel at higher RPM's is not good because if you were to reach levels of 5.00 volts while in high RPM's and you are running at that voltage, that would mean that you are running at a dangerous level of 24.2 air/fuel ratio (If 1.00 volts based on my calculations ramps up the air fuel ratio that much according to the jump from 3.00-4.00 volts on the chart, either way you are looking at being well over 20.0 air fuel ratio at higher RPM's) which is very lean! Running that lean creates insanely excessive heat on the engine, you could end up causing serious damage to the engine!

Our only concern right now is looking for oddities at higher RPM's, where you are having problems. If you can confirm the sensors are over exceeding 4.00V at wide open throttle snap tests, they are BAD.

 

I am almost certain that they both reached 5v at WOT.

I am definitely no expert at this, but could this just mean that the fuel mixture was actually physically VERY lean, beyond the sensors acceptable operating range?

I am certainly not saying it is impossible that the sensors are bad, infact it is logical, but BOTH AF sensors report the exact same voltages from different locations. Maybe I am over analyzing, but is it not strange that both sensors would fail exactly the same, with the exact same outputs?

 

I don't care where they are located. If water happened to get into both of them, regardless of how much and their sniffer sampled in water, no matter how minute, it will cause both of them to fail immediately and start to act erratically.

If they are indeed running at 5.00V at WOT, I would replace them at the expense of your entire engine. If it was my truck I would do it without question. Yes my wallet would hate me, but running that lean is SERIOUSLY dangerous to your internals bud!

Recheck those sensors at WOT to be sure if you want to be 100% positive about it. If they are bad, bit the bullet and do them. You gotta pay to play man.

 

You know, at this point I'd take it to the dealer and ask for a diag and quote.. see what they say and possibly get info to help if you still purse on your own.

 

Did you try dielectric grease on fuel pump connector.

 

Im definitely not concerned about the $$. If they are fouled, I'll replace them. As I'm sure your aware, the AF sensors "sniffer" are inside the exhaust pipe, O2 as well. Now I have never had a submerged truck before, but I have certainly had my O2 sensors below water in river crossings dozens of times.

Again, I am not arguing that they are good, merely that it is not conclusive.

Im trying to justify in my head why all 4 would be bad when they werent even all exposed to water in the first place. They are not reaponding "irratically" they are responding exactly the same as their counterpart, in perfect sync with one and other.

I would agree it is a good idea at this point to replace them anyway as a precautionary measure.

This is what I do, I lay awake at night and try to rationalize.

 

Not all 4 are bad. Your rears are in perfect operating range and condition and again, they are only used as reference sensors for the PCM to determine weather or not the catalyst is within its threshold limits.

Your fronts are the ones which are funky and are operating beyond their electrical limits and specifications and THAT my friend is what I am suggesting is bad. Only your upstream sensors (fronts) NOT your downstreams (rears)

Water finds it's way into some weird places and it could damn sure find its way through some exhaust gaskets very quickly.

Take my advice for what it's worth, but the proof is lying right there in your scan tool in the test you performed. Replace the 2 fronts, leave the rears be.

 

Ok... anyone have suggestions where to source 2xA/F sensors if the the dealer is $$$?