Vantucky

All,

Really sorry about the long post, I could not find any technical details in the FSM or by searching here.

I have a '98 Tacoma with the 2.7L 3RZ motor in it. It seems to be running a bit lean, exhaust is running hotter than normal, loss of power at higher RPM's. I think I'm hearing pinging as the RPM's get higher, but can't be certain, it may be in my head or other road noise etc.

Anyhow, I have a newish engine, new exhaust, including CAT and O2 sensors.

I have checked for intake leaks using a propane source, although I did not do an extremely thorough check as I could not get my torch nozzle into the back areas of the intake plenum to check those gaskets. I will need to get a flexible extension hose of something for it and check again. I also plan to get a stethoscope and listen at the joints.

I cleaned my MAF sensor yesterday and that made a noticeable difference in the power output, but its not where I feel it should be or even where it was after the rebuild. So I hooked up a cheapish OBDII scanner to it which reads live data from the sensors and my MAF sensor for the most part behaves like I think it should, increasing the amount of air it meters as RPM's go up etc, however, its all over the board and not consistent with RPM's or speed. For example, I can be cruising at highway speed holding the throttle and RPM's constant and the MAF readings will fluctuate sometimes 30% - 40% from its high point for that RPM and throttle reading.

My question is what are typical MAF readings and how do they fluctuate as the vehicle is driven. Can I check the operation of the MAF in any other way? The FSM seems to just say blow air into it and monitor the voltage drops.

Also, any other things I should be looking for? What else would cause a lean condition? Vacuum leak? Low fuel pressure? Would the vehicle start if the fuel pump was starting to go or if the fuel pressure regular was acting up?

Thanks Guys - Rick

MudHippy

You're over-thinking this.

1. Any details you need to know to test the functionality of the MAF sensor are found in the FSM. http://www.ncttora.com/fsm/2003/Repa.../mafm/insp.pdf

2. Specifications as far as what the signal output from it during engine operation should be don't exist. Nor do they need to. If it isn't working it will fail the tests in the FSM and should be replaced. If it does pass, then...yeah...it's working just fine. Don't try to outwit the FSM.

3. You have an OBDII scanner. If there's a problem, it's designed to detect the DTCs that would result from it. These systems are highly sophisticated, and are capable of monitoring nearly every aspect of engine operation. Including being able to detect vacuum leaks, lean condition, low fuel pressure, fuel pump malfunction, or misfire(through reading the output signal strengths/patterns from the various sensors, such as MAP, MAF, Purge Flow Sensor, O2 Sensor, Fuel Rail Pressure Sensor, Fuel Pump Circuit Monitoring Program, Knock Sensor, etc.). So, like I said, if there's a problem it will most likely be able to tell you exactly what/where that problem is. Don't try to outwit the OBDII.


Here's more info on Toyota MAF sensors: http://autoshop101.com/forms/h34.pdf

See what I mean? Other than telling you it needs to be clean to function properly, it's the same stuff as the FSM. And that's all you're going to get.

Vantucky

I find it hard to believe that if the MAF passes the voltage fluctuation test as described in the FSM, than that's all there is to it, but whatever.

I've not messed with the fuel system on these vehicles much, would a failing fuel pump or pressure regulator cause a lean condition? The truck starts and idles fine so I did not look at fuel or spark initially, but I guess I should test the coil packs and the fuel pressure. I had the injectors sonic cleaned and tested last summer so I am assuming they still operate as needed.

Any other ideas for what to look for that could cause the exhaust to run hotter than normal and the engine to lack power at higher RPM's or not want to rev very high?

MudHippy

You're imagining things.

No DTCs = you're chasing your tail = barking up the wrong tree = there's nothing wrong.

Don't let things that don't have a basis in reality get to you. I've seen men driven over the edge mentally trying to diagnose things that aren't even real issues. I'm telling you plain and simple. DON'T TRY OUTWITTING THE FSM OR THE OBDII!!! Toyota built the thing, TRUST ME, they know how it works WAY better than you or I do. YOU DO NOT KNOW BETTER THAN TOYOTA ABOUT A TOYOTA!!! RTFM!!!

Good luck!

That is all...

Vantucky

Let me see if I follow you...

If the OBD system does not set any DTC's then there can be nothing wrong with the vehicle AT ALL? As Toyota designed the vehicle so its as if the hand of GOD reached down and imbued mystical powers in the thing so that it would detect all possible malfunctions, even malfunctions of the malfunction detection systems, etc. etc. etc.?

And I have read the FSM if you'll read my first post I talk about it....

obscurotron

Vantucky, what makes you say the exhaust is hotter than normal and the motor is running lean? Do you have an EGT sensor installed or a wideband O2 sensor or some other telemetry? I think to get to the bottom of the problem, if there is one, requires a big picture approach - relying on individual tests of components may not reveal any one given problem. I'd liken it to tolerance stacking. Everything by itself may be within spec, but get enough things close enough to borderline, and downstream you'll have a problem.

In response to previous statements, a DTC is only going to flag if the sensor inputs or outputs go outside of certain operating limits. So he could have a problem (or the start of one) and not flag a P-code/DTC. Obviously Vantucky knows his rig better than any of us, since he wrenches on it.

Vantucky

Thanks obscurotron

I have noticed a reduced power output over the last few months and noticed that the engine did not want to rev as high as it did post rebuild. I did not take the time to dig into it as the truck ran ok and no codes were being flagged.

In addition to rebuilding the long block, I had a brand new header and custom exhaust installed after I rebuilt the engine last summer. The header was LCE's stainless steel baby and the exhaust tubing was made from aluminized steel. A few weeks ago while doing an oil change I noticed that the exhaust gasket between the header and the CAT had failed, so I took the truck back to the exhaust shop and had them replace the gasket. He noted that the plating had started to burn off the exhaust tubing and the header itself. I asked him if that was normal wear for the type of tubing he installed and he said no, it only occurs where the engine is running hotter than normal.

I know that a lean condition will cause your exhaust to run too hot and so I started looking at what could cause a lean condition. As it made sense that the engine was running lean given the symptoms of a hot exhaust, general reduced power output and not reving as normal.

I noted above that after cleaning the MAF sensor and making sure that all the joints in the intake tubing were wrenched down good, the truck does definitely have more power and rev's better. Although I don't feel like its where it was after the rebuild 10K miles ago.

I have not done any scientific tests or installed an EGT sensor to actually measure the exhaust temp. Although my EGR temp sensor is new as it went out about August time last year. I guess if the exhaust temp was actually too high and the EGR system was open that should throw a code, although I'm not positive about that.

I also have not tested the ignition or fuel systems like I said although I think I'd have other symptoms if that were an issue.

I also am thinking of doing a compression test, possibly a leak down test too, just to see what kinda shape the motor is in now that its all broke in and so that I can have a baseline for future reference if needed.

Thanks for your help. Any ideas on what to look for or think about would be great.

obscurotron

Can you get an OBDII scanner (not just a code puller, but an actual scanner that can monitor in real-time) and look at your long-term and short-term fuel trim? If you really suspect a lean issue, those two numbers right there should tell you in a clean nanosecond if something is amiss. Even if they are within specs so as to not flag a lean or rich DTC, if they are consistently showing a tendency towards a lean condition, there is a good clue. At the same time, you should be able to watch the o2 sensor output waveform. That right there will confirm whether or not you are barking up the right tree.

This tool (the BR-3) worked for me:

http://www.obddiagnostics.com/ (no affiliation).

Presuming the O2 sensor is good, that device right there is going to tell you if you are in fact running lean. It's not cheap, but for $100 or so it's a good tool to have in the stable.

It beats the hell out of playing the guessing game (I'm getting too old for that crap with my cars!!) we all know and love.

Vantucky

FYI for whoever might read this later.

I found MAF specs in the FSM, for the 3RZ motor they are 2.6 - 3.7 gm/sec at idle and 9.2 - 13.3 gm/sec at 2,500 rpm without load.

sebastianholmes

your timing too high?

Vantucky

The timing is controlled by the ECU on these vehicles and mine is within spec. (i.e. 7 - 13 degrees advance at idle.)

sebastianholmes

oh my bad, everything i read just sounded like timing that was advanced way too much

BigBallsMcFalls

probably the new bank 1 sensor 1 is inappropriate for the vehicle

that can cause lean out

verify it is exactly the OEM sensor required.

Vantucky

I think I finally figured it out. Turns out my thermostat was either opening too soon or not closing fast enough. The dash gauge read normal, but the ECT was fluctuating between 175 and 179 while driving after warmed up. This was causing the ECU to flip between open and closed loop modes. This caused the lack of power at the top end that I noticed.

So I popped in a new t-stat and the ECT is running around 185 again like it should. Truck drives like it did a few months back.

I am still a bit troubled, I always thought that a hot exhaust was indicative of a lean condition, but when the ECU enters open loop, it richens up the mixture. Maybe by flipping back and forth between open and closed loop it was flipping between rich and lean more than normal and that caused the hot exhaust. I'm not rally sure. Hopefully there are not other tuning issues to work out. Truck runs good again so that a nice sign.

Now however, I'm getting a PO420 code thats pending. It has not popped the CEL yet, but I'm sure it will eventually. It's pending in the ECU and went pending again right after I reset it. I'm afraid the CAT may have suffered some by running in open loop so much. I know a rich AF mixture will ruin a CAT. Can a rich A/F mixture also ruin the O2 sensors?

And regarding the O2 sensors, mine are factory Toyota replacements. They are freaking expensive, but I have a hard time putting anything else in there...

TheDurk

I can't help with the rest, but the Denso aftermarket sensors that you can get on Amazon and elsewhere for much less are the EXACT SAME sensor that you get from the dealer. Go here: http://www.densoaftermarket.com/catalog/ to get the right Denso number. Use 'Cross-reference' and the Toyota number. They (and URD) have the wrong number in the vehicle search for the rear sensor on early 3G auto V6 4Runners. Cross-reference gets it right. Don't know about Tacos.

I'd sure try a new rear sensor before I'd get a new cat, excess fuel can't be good for these.

Vantucky

Thanks for the tip on the DENSO brand, if thats who Toyota sources their O2 sensors from thats good enough for me.

Also, does anyone know what the Toyota Parts Warranty is on O2 sensors and what I would need to do to get the dealer to take it back on warranty?

BigBallsMcFalls

yes running rich can dirty up the sensors

rich = cooler exhaust = cats don't get hot enough = soot on the 02

DailyDrive

MudHippy, you should not take all advice online too seriously, just selectively, while applying own logic. But, without any further ado, here is a graph of my properly working MAF.

This is RPM and g/s reading from the MAF, overlayed on the same plane, while driving for about 5-10 minutes. As you can see, there is absolutely no wild readings or unexplained deviations. The MAF displays pretty much the same as the RPM, as logic suggests it would.