Longbed 90

I need some help here, and with respect, before you advise me to use the search feature, I have. Dozens of times. I've already followed most of the advice, but I haven't found the combination of problems I'm facing.

Here's the deal:

90 4Runner failing CA emissions for the third time due to high NO and HC. I can give you the specs if you like.

My idle is a bit high when cold, then a bit low when hot, fine when warm.

I'm getting poor fuel economy: 12 MPG no matter how I drive. I do have 31s on it, but I used to get 18 on the highway.

I just did a head rebuild due to a leaking gasket on #5, following Tod at engnbldr.com's advice, all the way down to using break in oil.

I've replaced in the last year or two, defeating multiple codes, the following:
TPS (yes, adjusted correctly from this forum)
VAFM
Starter
O2 sensor (Denso)
plugs & wires (two or three sets)
Fan (OEM)
Fan clutch (Aisin)
Timing belt
Timing idlers (both Aisin)
Coolant flush (multiple times)
VSV (used from pick a part, but solved an old problem
Rotor & Cap
3 new valves on head rebuild, along with entirely new gasket/bolt set
T-stat (several)
Rad cap
Radiator
ECT sender (new)
ECT sensor (pulled from pick a part, alleviated some idle trouble)

There's probably more I'm forgetting, and it is currently not throwing any codes.

According to the FSM here,

personal.utulsa.edu/~nathan-buchanan/93fsm/engine/63troubles.pdf

It's recommending ECT sensor, VAFM, Injectors, Cold Start Injector for both my running symptoms.

I'm ready to spend some more money, but I want to do so logically. Am I running rich or lean? Should I even mess with the Cat?

Help! Tearing my hair out (what little I have left).

I'm overdue on registration due to failed smog, so I need to get this fixed, and increase my mileage too. I wouldn't mind a bit.

Whatever help you can give me would be gold. Thanks in advance.

scope103

I can give you the answer, if you like.

Start here: http://www.cygnusx1.net/Media/Supra/...taTech/h56.pdf

Everything is connected to everything else, which is why we (actually, you) need all the numbers. Include the limits; even within CA the limits are different depending on where you live.

High NO is ALMOST always an EGR issue. That's what it does. That's ALL it does. Work your way through the diagnostics. http://personal.utulsa.edu/~nathan-b...77exhaustg.pdf

The cat has a small effect on NO, so I can't rule it out. (Note that your CO reading will help you think about what's going on with HC.)

RJR

- Actual emissions numbers would be helpful.
- Any CEL codes?
- High HC implies rich, high NO implies high exhaust temps and possibly lean

I don't see catalytic converter in your list of replaced parts. With both NO and HC out of spec, I'd be looking there.

With the engine warmed up and running 1500 rpm or so, connect TE1 and E1 of the diag connector. Check the voltage on the Vf pin. It should be switching back and forth between 0 and 5 volts about once per second. If it's stuck at either 0 or 5V, you have faulty closed loop operation, possibly due to a problem with the O2 sensor or another sensor.(5V implies rich operation, 0V implies lean). If the signal is switching properly, the most likely problem causing the excess emissions is a bad catalytic converter.

Longbed 90

Hey, thanks for the fast responses.

One last thing I forgot, I have a leaking exhaust manifold on the LH (driver's side) only SINCE the head rebuild. Oddly, it didn't fail me entirely on the last test. It was not present on the first two. Obviously, I'm going to replace it as soon as I can find one. Neither Rock Auto nor Yotashop stock the LH side.

Anyway, here are my emissions specs...

1st attempt (before head rebuild)
15 MPH HC Max 118 Meas 154 CO Max .47 Meas .25 NO Max 699 Meas 103
25MPH HC Max 98 Meas 76 CO Max .61 Meas .25 NO Max 601 Meas 90

2nd attempt, (before head rebuild, after ECT sensor and sender swap)
15 MPH HC Max 118 Meas 155 CO Max .47 Meas .28 NO Max 699 Meas 59
25 MPH HC Max 98 Meas 91 CO Max .61 Meas .33 NO Max 601 Meas 73

3rd attempt (after head rebuild)
15 MPH HC Max 118 Meas 190 CO Max .47 Meas .02 NO Max 699 Meas 1031
25 MPH HC Max 98 Meas 98 CO Max .61 Meas .01 NO Max 601 Meas 330

As you can see, I continue to fail the 15MPH and fail the 25MPH. First two because of high HC, third due to higher HC, and WAY higher NO.

Hope this helps, I can give CO2 and O2 for the first and third tests, but I can't read them on the 2nd.

scope103

First, you had decent (not great, but decent, and passing) NOx levels before the head rebuild, and then it fell apart. My money says you reassembled the EGR system incorrectly, and it's just not working the way it used to. Use the manual cited and check through that.

Your CO is pretty good; low CO coupled with high HC can indicate a LEAN condition. It's worth doing the test RJR suggested just to look for that (but it's probably not your problem; if the O2 sensor signal isn't flipping, the ECU SHOULD throw a code).

Another, more subtle, problem is the leaking exhaust manifold. If that leak allows air INTO the exhaust stream, it makes the O2 sensor think you're too lean and it tries to (incorrectly) richen it up. That will definitely give you high HC, but you should get high CO along with that. This situation won't throw a code; you're just tricking the O2 sensor.

So which one is it? Your O2 should be very close to zero; if it's up in the 5-6% range you're definitely on the "lean" side (what did we say about "all" the numbers being important?) But this isn't Gospel; something is wrong with your NOx, which can start dragging the other numbers around. First things first.

Janos01

It is also possible that you have a bad injector that is spraying too much fuel. Is your truck running rich at all?

Longbed 90

RJR, I ran the test you recommended, and it came back constant 0.11, indicating lean. And no CEL or stored codes.

Scope, I printed everything you linked and will begin on that this weekend, EGR system first. Here are my stats for CO2 and O2, respectively:

1st test
15MPH 14.35 0.39
25MPH 14.60 0.05

2nd test
15MPH 13.11 2.13
25MPH 13.60 1.43

Again, indicating lean, right?

Janos, the smog tech suggested a rich condition, and I was on the verge of replacing all six injectors, and/or looking into the cold start system. Just wanted to get as much information as I could first.

Anyone have any good leads on a new LH exhaust manifold? I'm coming up dry.

millball

The fact that the O2 sensor test showed lean when in fact your engine is running rich, is a major clue.
The ECU sees what it thinks is a lean condition being reported, so it dumps more fuel.

Fix your exhaust leak and make the EGR right. It may be that you'll need another O2sensor too, but wait till the other issues are resolved to see what happens.

scope103

A constant .11v on the O2 sensor should throw code 25. http://personal.utulsa.edu/~nathan-b...85diagnosi.pdf Make sure you're "racing" the engine (about 2,000 rpm) for a minute or so before you take the reading; the O2 sensor doesn't work if it isn't hot enough.

Otherwise, I'm with millball.

Longbed 90

Ok, so that Vf pin is the O2 diagnostic port?

And Millball, the rich condition you mentioned, is your conclusion derived from high HC on emissions? Other symptoms like poor fuel economy and shoddy idle?

It has a new(ish) Denso O2 in it and no code 25. A year or so ago, I was running simultaneous 25 and 26 (continuously lean and rich codes) and the new sensor cleared those. Am I then looking at a 25 year old crappy cat that has now ruined my new O2?

millball

All of the above.

You also need to determine whether the system is going into closed loop, or not.

Open loop operation usually results in richer than optimal conditions.

Longbed 90

And sorry, but that's determined by?

scope103

Here's the FSM for the test of the O2 sensor: http://personal.utulsa.edu/~nathan-b...01heatedox.pdf

Vf1 is the "conditioned" O2 sensor signal, swinging all the way from 0 to 5v. The actual O2 sensor (which you can measure at the Ox1 terminal) is more like 0.1 to 0.9 http://www.cygnusx1.net/Media/Supra/...taTech/h24.pdf . As millball mentioned, "open loop" is usually rich, but you should only be in open loop for a few seconds (and the smog test procedure requires the engine to be run long enough to assure that). The way to TELL you're in closed loop is the swinging of the O2 sensor voltage (either Ox1 or Vf1).

Something is wrong, and I can't explain why you're not getting a code.

millball

I have understood that open and closed loop operation is partly determined by one of the coolant temp sensors.


If the ECU thinks that the engine is cold, open loop operation may continue indefinitely.

Not so???

Emissions testing of OBD-1 is sniff only. OBD-2 emissions testing (1996 and later) does read ECU conditions and readiness.

scope103

Hmm. Seems so. http://www.cygnusx1.net/Media/Supra/...taTech/h44.pdf (this document is for an OBD-2 vehicle, but I'm sure the concept is the same). But an open/short in the ECT circuit should throw code 22. It's hard to imagine how else the ECU could think the engine was cold when it was not. I'm not sure, but I don't think a stuck-open thermostat can cool the engine enough to put it into open loop mode.

But there are more mysteries here.

RJR

Make sure when you run that test that you have TE1 and E1 shorted in the diag port. If you don't, the VF pin will not show the O2 sensor, but rather the fuel trim voltage, which can be one of 5 steps between roughly 0 and 5 volts. Nominally it should be at 2.5 volts when in closed loop operation.

With TE1 open, .11 volts indicates either that the engine is running rich and the ECU is at its limits trying to fix that, or that the engine is running open loop (probably the case here.) As was said, a bad ECT sensor reading can cause the engine to remain in open loop, and I think a bad TPS can as well (idle switch stuck closed). I don't think OBD1 will throw a code just because the ECU doesn't see the engine ever warm up. Nor will the emissions test station catch this, because they can't read the OBD1 port. OBD1 is not a standard. Every make and possibly model of vehicle is different, both electrically and physically.

As others have said, you need to fix the exhaust leak and the EGR, but my guess is you will still have the problem you had before you rebuilt the head.

Longbed 90

Ok, so I pulled the O2 sensor and tested the resistance. It's coming back .01 (at the 20k setting) indicating, according to this:

http://personal.utulsa.edu/~nathan-b...01heatedox.pdf

a bad O2 sensor. Frustrating, because I replaced it a year or so ago. So, now the question is what ruined it?

Obviously a rich condition, given the soot, which explains the poor fuel economy. I have read that a bad cat can ruin a good O2 sensor. True?

I can throw it back in and run the hot test, but is it even worth the time?

Now what?

millball

If the O2 sensor in question is upstream of the cat, it is more likely that a bad O2 sensor can ruin the cat. A cat that is fed too much unburned fuel, gets hot, sometimes so hot that its ceramic matrix can be melted.

So, no, generally, a bad cat cannot wreck the O2 sensor

But, the opposite, maybe.

scope103

No, no. The test you ran is just of the heater. .01 on the 20K ohms scale is 10 ohms, and the spec is 5.1 to 6.3. What did you expect the meter to read on that scale?

If that's the only scale you have, you need a new meter. This is the one everyone mentions http://www.harborfreight.com/7-funct...ter-90899.html (because it's cheap -- in fact, HF often offers it for FREE with purchase!) It has a 200 ohm scale, so you'll be looking for 05.8. (But don't expect to get that close; the resistance of the leads alone is 1-2 ohms.)

So where does that leave you? You might have a bad heater (probably not, but I can't say for sure), and you should replace it if that's the case. But even a sensor with a dead heater will work when racing the engine, where the exhaust alone holds the temperature up. You can test the actual sensor part at the Ox1 port when running, looking for the 0.1 to 0.9v signal. (the 2000mv scale on the HF meter will do that; since it's a digital meter it's a little tricky to see the "flop" from 0.1 to 0.9)

Longbed 90

I know how to use a multimeter only on voltage. I'm still learning with ohms, so bear with me. Self taught here. That is the exact multimeter I'm using from hobo freight. Also, what is the 'mv' in 2000mv?

A bad heater? Is that a part of the O2 sensor? I'm getting into unknown territory here...

When I adjust my TPS, do I also use the 200 ohm scale? If not, which one?

Just ran the test on 200 and came back with 7.5. Out of spec.