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86-95 Trucks & 4Runners 2nd/3rd gen pickups, and 1st/2nd gen 4Runners with IFS

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Old 10-22-2010, 01:52 PM   #1
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Help....High NOx at 15 MPH on smog (Calif)

I'm being nickel-ed and Dime-ed to death....

1991 Pick-up extra cab 4x4 SR5 3.slow 120K

Can't pass Calif smog. High NOx at 15 MPH barely passing at 25 MPH. (Failed 5th test this morning after replacing 2 1/2 year old Catalytic Converter)

1st test........Failed (High NOx) on both 15 and 25. Was getting a code 21 and 52. But CEL would go off after warm up.

Replaced 02 sensor (first with Bosch) Truck ran crappy.....returned Bosch...replaced with Denso. Truck ran great. Code 21 gone. Still was getting code 52 (knock sensor) during warm up.
checked all vacuum tubes.

re-test.......Failed. No change in NOx readings.

Tested ERG......working fine. Still pulled it off and cleaned. Ran 2 bottles injector cleaner in half tank of gas. Then Seafoam with a full tank.
re-checked all vacuum tubes.

3rd re-test.........Failed. No change in NOx reading.

Pulled intakes....replaced Knock sensor wire. Scrubbed everything clean.
Replaced Spark plugs...(didn't look to bad...running a little lean)
Replaced Spark plug wires, Cap and rotor. New air filter. Set timing.
re-checked all vacuum tubes.

Just to be sure......I ran the tank down to 1 gallon of gas and put in a gallon
of De-naturalized Alcohol.

4 re-test..........Failed. NOx readings went up..... (from 1200 to 1700ppm)
need a 891ppm or lower to pass.

Replaced 2 1/2 year old Cat (which passed smog 2 years ago with flying colors) with new Magnaflow "Calif" Cat. and replace the muffler while they were at it. Drove it on the freeway at 75 mph for 40 miles before taking it to be tested to get the CAT nice and hot.

5th RE-test.....Failed. All readings were down.

15 MPH went from 1756 to 1374ppm (Failed)
25 MPH went from 1196 to 874ppm (just passed)

I'm at a end here.........Truck is running better than ever since I got it
10 years ago. No codes......everything running fine.

Any ideas? Anybody heard of getting a bad "New" O2 sensor???? It's not
throwing a code......but that the only thing I can think of.

Help!
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Old 10-22-2010, 02:02 PM   #2
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Sounds like your running lean. Have you replace the fuel filter? How does the truck drive? Does it have plenty of power? How did you test and verify the EGR was working correctly? When you set the timing, did you jump the Te and the Te1 connector?

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Old 10-22-2010, 02:02 PM   #3
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High NoX is caused by running too hot...

Run the good stuff for gas, 93 or 91. This should help run a little richer, lean is hot.

Run some seafoam into the cylinders , carbon deposits can cause hot spots.

Make sure you warm up the cat nicely, drive at least 20 min on the way to the smog test, steady rpms on the highway. Keep the engine running when you get to the smog shop.

Not sure if a new O2 sensor will help, the older the sensor gets the richer a vehicle will usually run. A new O2 is usually suggested when HC's are too high.
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Old 10-22-2010, 02:07 PM   #4
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move to a decent state
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Old 10-22-2010, 02:44 PM   #5
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nox is formed by high combustion chamber temps(above 2500 f).Look for bad fuel pressure regulator or disconnected vac line to same.Could also be poo poo converter.What does hc look like?Co?
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Old 10-22-2010, 03:22 PM   #6
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Haven't replace the fuel filter. But it's not that old. Maybe 2 years.

Tested the ERG while it was running with a vacuum. Kills the engine.

Truck is running great. Has way more power than when I started.. and more than
it ever had.

Set the timing just as the FSM says.............
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Old 10-22-2010, 03:23 PM   #7
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move to a decent state
If Only........
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Old 10-22-2010, 03:36 PM   #8
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nox is formed by high combustion chamber temps(above 2500 f).Look for bad fuel pressure regulator or disconnected vac line to same.Could also be poo poo converter.What does hc look like?Co?
I will check the fuel pressure reg. But all Vac hoses are good.


HC is barely registering.....AVG is 56 .......Mine was 3

CO are at 00.0

CO as at 00.3 before new Cat.
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Old 10-22-2010, 04:23 PM   #9
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Check EGR vacuum control solenoid (vacuum switching valve, VSV) seems every toyota for EGR problem. Check for exhaust pressure when running at hose connected to bottom of EGR vacuum modulator. Make sure vacuum on two hoses leaving throttle plate when off idle and routed to modulator correctly. Make sure ignition timing not over advanced, or kick it back 6 degrees.
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Old 10-22-2010, 04:38 PM   #10
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High NOx generally points to the EGR system. While mixture, cat, O2 sensor, plugs can all have a small effect, I don't think they would be the cause of the high numbers you're getting.

I assume you put external (hand-pump) vacuum on the egr valve at idle, and that killed the engine. That's a pretty good test of the egr valve to the intake, but it doesn't sound like you've checked whether you are getting vacuum to the egr valve through the modulator.

One quick and dirty test is to drive the vehicle, and immediately check the temperature of the egr inlet tube. I'm told that it should be "warm," but not hot. (If yours is cool, the system is not opening the egr valve.)

Another more reliable but still easy test (easier than replacing the o2 sensor or removing the intake manifold, anyway), is to put a vacuum gage on the egr vacuum line, and watch it as you open the throttle with the engine warmed up.

It sounds like you've successfully completed half of the test of the EGR system. I'd look at the other half.
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Old 10-22-2010, 04:42 PM   #11
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You're running really lean, which causes high combustion temps & high nox.

You've got a new Denso O2 sensor, so you're fine there.

There are three other main suspects for the lean running - could be a combination of them.

Clogged injectors - if you didn't use Red Line SI-1 Complete Fuel System Cleaner or CRC's "Guaranteed to Pass - Emissions Test Formula", then your so-called injector cleaner didn't have polyether amine and was probably not effective. Run a bottle of the Red Line through the tank for best results. CRC's product is okay, but has less PEA. If you want to be absolutely certain, send the injectors to witchhunter.com (but it sure is a pain to get at them).

Vacuum leak - Many - perhaps most - of our trucks now have cracks in the rubber portion of the air hose going from air meter to throttle body. Check entire hose carefully, and also check thoroughly for vacuum leaks elsewhere, using unlit propane torch or starting ether and listening for an increase in rpm. Don't forget around injector o-rings and brake booster in addition to all intake/plenum/throttle body joints and vac hoses/VSVs. Maybe tighten plenum and throttle body mount bolts a little (not too much on either).

VAFM - if the air meter is out of range, it can cause lean mixture. Since there can be corrosion or resistance in the connection between the air meter & ecu, recommend checking VS voltage directly on the ecu terminals. That way you're directly reading what the ecu is seeing. Read between VS (positive test lead) and E2 (neg) terminals, using backprobe adapters on your multimeter test leads. If you don't have the adapters, push needles into the connectors and hold test leads against them. DC volts should be:
  • Ignition on, not running, air vane fully closed: 4.0 - 5.5 V
  • Ignition on, not running, air vane fully open: .2 - .5 V
  • motor idling: 2.3 - 2.8 V
  • 3000 rpm: .3 - 1.0 V

Also check that VC to E2 is 4.5 - 5.5 V when ignition on, not running. If VS is off and VC is okay, there is probably a problem with the air meter. If both VC and VS are bad, you may have a bad connection.

See MFI System - Troubleshooting section for ecu terminal map and more info: http://personal.utulsa.edu/~nathan-b...86troubles.pdf

Also would be a good idea to check the temp readings on THA - best to check the resistance directly on the VAFM terminals. See the VAFM chapter: http://personal.utulsa.edu/~nathan-b...92volumeai.pdf

Some people have had luck adjusting the spring on the air meter to change VS volts when motor is running. If the spring is loosened, the vane will open further and ecu will inject more fuel. But it will only work if VAFM rheostat is in good shape. Search the forum for details. Otherwise you may need a new one.

EDIT: Should mention that if there is a vacuum leak, then air is bypassing the air meter and the meter is only reading a portion of the air getting into the cyls, and therefore it will read low and cause the ecu to inject too little fuel. But that's not the fault of the air meter. The solution is to be sure to seal up all vacuum leaks before bothering to test the air meter.

EGR - As mentioned by other posters, it's your motor's main tool in the fight against Nox. How did you test it? Is the iron EGR tube good and hot where it goes into the plenum when motor at op temp and rpm around 2500? Have you removed and cleaned the EGR tubes? Have you removed the filter in the EGR modulator and blown it out with compressed air per the fsm? http://personal.utulsa.edu/~nathan-b...77exhaustg.pdf
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Old 10-22-2010, 06:13 PM   #12
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Since your truck is running "very well," a too-lean condition is not likely. But you can test for it directly. On the diagnostic connector, Jumper TE1 to E1, read the voltage (to E1) on Vf1. That's the amplified O2 sensor, and it should swing back and forth from about 0.5 volts to 5 volts 8 times in 10 seconds. If it is doing that, then whether or not you have a vacuum leak or a bad vafm the ECM has successfully compensated for it. If the leak is so bad that it has leaned out the mixture beyond what the ECM can compensate, then the O2 sensor won't swing. (And I would expect it to run poorly, but looking at the O2 sensor readings is diagnostic.)

If you do have a vacuum leak or a bad vafm or whatever, fixing them is a good idea, but they are probably not the cause of your NOx issue.

(You could have one bad injector that is causing one cylinder to run very lean, increasing NOx. The O2 sensor only sees the "average" exhaust. But your truck would probably be missing on that cylinder. So I would do the easy tests to look for the obvious suspects before going on to the harder stuff.)

As you've found out, while most of the electronics in the truck is to make it run well, the EGR system's primary function is to keep all of us from dying of lung cancer. So you can have high NOx and a beautifully running vehicle.

Tracking down leaks and corroded connectors is always a good idea, but I would rule out a problem with the EGR system first. That's the most likely cause, and the easiest to diagnose.
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Old 10-23-2010, 02:34 PM   #13
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I do believe I found the problem................I'm a idiot!

While running a ERG diagnose. I'm pretty sure I found the problem. After replacing the knock sensor wire, and cleaning the intakes after my 3rd failed test. In my haste to put
everything back together. I forgot something.........a single bolt.

Click the image to open in full size.

Ran propane over it.....and what to you know......a leak. torqued a new bolt on it.
Finished checking the rest on the ERG system. Everything seems good. I will take it
in first thing Monday. I think it should pass now.

Thanks everybody for your input. and sorry I'm an idiot!

I will update after the test.
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Old 10-24-2010, 12:48 AM   #14
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And something no one mentioned was ignition timing. Even a couple degrees advance can raise comb temps substantially.

but aren't you now eligible to go through the referee program and get waivers and costs paid by the state?

well not every one can wait 8 weeks for there daily driver to get the damn waiver. eerrrrrrrrrrrrrrrr

oh by the way your going to have to smog any truck over 15 years old every year now
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Old 10-24-2010, 01:32 PM   #15
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Proof? Now? Since when?
Search and yee shall find. He is probably referring to AB 859.
http://www.leginfo.ca.gov/cgi-bin/po...B&author=jones Out of committee but not yet voted on. So not law (yet).

I own an older-than-15yrs truck, but I also breathe California air almost every day. Passing smog checks are not difficult, unless you forget bolts when you reassemble the engine, or (better yet) deliberately start ripping off pieces of the engine.

For me, it would increase my cost of ownership from $50 every-two-years to $50 every year. But you don't have to read this forum for too long to notice that there are a lot of ill-maintained trucks that provide far more than their share of pollution. So fix 'em or get rid of 'em, okay?

Just one man's opinion.
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Old 10-24-2010, 03:56 PM   #16
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Search and yee shall find. He is probably referring to AB 859.
http://www.leginfo.ca.gov/cgi-bin/po...B&author=jones Out of committee but not yet voted on. So not law (yet).

I own an older-than-15yrs truck, but I also breathe California air almost every day. Passing smog checks are not difficult, unless you forget bolts when you reassemble the engine, or (better yet) deliberately start ripping off pieces of the engine.

For me, it would increase my cost of ownership from $50 every-two-years to $50 every year. But you don't have to read this forum for too long to notice that there are a lot of ill-maintained trucks that provide far more than their share of pollution. So fix 'em or get rid of 'em, okay?

Just one man's opinion.
yes that is what i was refering to

i always keep my rig looking good and running good as possible. this is the first time i ever had a hard time passing so i will fix it, with that said there is a punk kid that drives a 85 pick up with out a bed no flat bed just some getto lights and a locked rear axle. people like that give these older toyota 4x4 a bad rep.

to stay on topic i have a simular problem getting my truck to pass smog. so i need to do the "caps" progam but it takes 6-8 weeks to get the ball rolling. . . so i will fix the problem but i have to drive my wifes jeep untill i can get a temp sticker.
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Old 10-25-2010, 03:44 PM   #17
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Failed

After finding the bolt, and fixing the leak, and running the full EGR test. I still failed.

HC was 0.00
CO was 0.00

NOx

15 MPH went from 1374ppm to 1247 (Failed) Max allowed is 721
25 MPH went from 874ppm to 676 (passed) Max allowed is 891

Still something not right. Like I said before. Truck is running great. Not missing. No
lag when you punch it.

The only thing I haven't tested is the EGR temp sensor. Will get a pot of oil going.
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Old 10-25-2010, 05:29 PM   #18
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Even with a new cat, I doubt you would get zero HC and zero CO unless the motor was running lean. It is possible for the motor to run well, even if it is on the lean side. But you'll be in danger of burning exhaust valves, and stressing your head gasket, not to mention the problem of passing emissions.

After running a few hundred miles, a look at the spark plugs would verify lean running, but I think the emissions results have already confirmed it.

But by all means, make sure the EGR system is working. The temp sensor doesn't have any effect whatsoever on EGR operation - it just squeals on the system to the computer (of CA trucks) so the computer can throw a code. But if you make sure the sensor is working right, that will help confirm that the valve is operating. Did you check that the EGR tubes were all clear?

Did you run a bottle of a PEA injector cleaner through the tank?

Is fuel pressure up to spec?
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Old 10-25-2010, 05:30 PM   #19
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O.K.

I'm not getting ANY Ohms reading off my EGR temp sensor. Nothing! Now, could this
be the route to all my problems with the high NOx readings? And if so....why haven't I been getting a Code 71?
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Old 10-25-2010, 06:08 PM   #20
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By "not any" ohms I assume you mean "open" (infinite ohms), not "shorted" (0 ohms).

Again, do the easy stuff first. Unplug the temp sensor, and run the truck at 2500 rpm for at least 5 minutes. (code 71 means an open in the temp circuit, among other things). If that doesn't throw a code, then you've got problems in the direction of the ecm (like a shorted wire). It that throws the code, you might want to re-do your ohmmeter check.

You said you ran the "full EGR test." From what I understand, that means you tracked the vacuum (with a gauge) all the way through the system, at all the specified rpms and temperatures. If that's the case, and you definitely got the rpm drop when the EGR valve opened (clogged EGR passages inside the plenum seem to be commonly reported; everything else could be "working" but you'll have very high NOx), then you need to look elsewhere.

I'm still not convinced that you're running lean, with all due respect to SBWalker, because your HC is so low. (Check out the technical articles at www.autoshop101.com for some background, but remember that a little bit of knowledge can be dangerous.) But checking the O2 sensor output not only goes a long way towards diagnosing that, it's easy (as in, easier than pulling the plugs).

It sounds like you've got a tricky problem here, so you'll need to be very systematic. Fortunately, you've covered a lot of ground already, and kept good notes.

Good luck!
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