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looking for emissions ideas

Discussion in '80-Series Tech' started by semlin, Mar 6, 2004.

  1. semlin

    semlin discouraged user

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    OK, so I can't pass emission but I am closer. Fixing the EGR has cut my NOX result nearly in half. I am now only failing with 1.8 times the passing level of NOX instead of 4x. :-[

    My HC and CO results remain pretty much the same (my CO was actually slightly higher this time). I am passing at 80% of acceptable levels, but I am at 4 times the average passing vehicle emissions for these two.

    At least now I have three sets of emission test results including the diagnostic trace reports which show the second by second emission outputs. I have looked at the results and I am hoping someone here might be able to correlate an anomoly to some part of the truck's system that is faulty.

    My HC and CO results have dropped across the board after each test except for 10 seconds in the test where the driver accelerates from about 70 kmh to 85 kmh (40 to 55 mph) after having accelrated from 35-70kmh (20-40 mph) in the previous 10 seconds.

    On each of the three tests there is a sudden huge identical steep spike off in both CO and HC for 10 seconds, which then drops off to nothing just as suddenly even though the vehicle maintains and even increases speed a little for another 40 seconds in the test. During the spike, the HC and CO emissions go off the chart and are roughly 8 times higher than immediately before and after.

    Except for this spike I would have average or below average HC and CO results.

    I have checked and this is a point when driving where the tranny will kickdown, run up to nearly 3000 rpm and then drop back down very quickly to 2000rpm. One thing I can think of is that the tranny might be slipping for a second allowing the motor to rev freely. I do feel an engine surge just then and the tach does flutter a little.

    I would have speculated that it was a brief delay before the EGR system activates at 2500 rpm, but I got exactly the same result when I know the the EGR system was not working.

    Can anyone think of another system that may be causing this problem? Hopefully one that might explain my NOX issue?





    There are a couple of
     
  2. landtank

    landtank SILVER Star

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    have you thought about a possible problem with the TPS. Possibly a flat spot in it that confusses the ECM.
     
  3. ppc

    ppc M Go Blue

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    I think that landtank is making a good suggestion with the TPS. I would also put a meter on the fuel pump circuit to see if in anyway the voltage supplied to the fuel pump correlates to the sudden huge spike. Those are the two things that might seem to be related to a sudden change.
     
  4. RavenTai

    RavenTai

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    are you flooring it to make this acceleration? can you still meet to requirements with a smaller throttle opening? at WOT (wide open throttle) the ECM gos out of closed loop and the mixture goes rich this would certainly cause emissions problems

    and like above if the TPS was giving a WOT signal when it should not it would again go into a rich state

    give this a read has a nice description of the relationship between fuel metering and exhaust emissions

    http://www.autoshop101.com/forms/h64.pdf
     
  5. landtoy80

    landtoy80

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    Have you done the new air filter, plugs, wires, cap rotor, oil change, ethanol gas and a can of "emission pass in a can"?
     
  6. Riley

    Riley

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    Simon - I was thinking this last time you repaired part of the system and then went for the test right away.......Consider that you have significantly repaired some major pieces of the EGR system (those hoses were totally plugged).

    Might the Emissions computer need to relearn that the freaking thing is working now and thus operating very different from before (i.e. it needs some drive cycles to relearn the new system ?)?

    Just thought. Might it be an idea to pull the power for 30min ?? or so to force the computer to start "relearning"? Then give it some good long drive cycles to get it's "head" straight.

    Of course I don't know what I'm talking about - but (in the first IH8MUD semester) when it was discussed about the system throwing codes, we learned that it takes some drive cycles for the computer to relearn, I have no idea if that applies to the EGR sub-system. Perhaps someone else does.

    I understand you need this fixed asap and waiting a few days to run the test sucks.. but consider that you might have already fixed this sucker and just need the computer to forget how plugged the system was (it was compensating somehow???).

    Anybody know about the computer learning verses EGR?

    edit - I know this is a long shot but thought I'd mention it.

    Riley
     
  7. turbocruiser

    turbocruiser SILVER Star

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    Not sure how similar they are but I had a flat spot on the TPS on my 4Runner and it caused a really rough running engine only in the rpm range or in the throttle pedal range where the flat spot was. It was so rough running and occurred so low in rpms that it was impossible to drive the vehicle until I replaced it. Replacing it by the way requires about four hands - one to hold the position of the TPS, one to hold a feeler gauge, one to hold a multimeter and one to hold the driver that you use to tighten the TPS down in the correct position. It is a real PITA to coordinate all that especially considering one of the two hands I always have available was holding a :beer: and stubbornly unwilling to release that :beer: ! That article that raventai posted was super informative and one thing it stated was that a marginally degraded O2 sensor could cause these symptoms. Have you replaced either of the O2 sensors? Also, I'm sure this seems redundant to the advice already but the cat must be hot to really combust the remaining "fuel" in the exhaust. I guess I never thought of it in the past but really we all have two internal combustion inventions in all our vehicles - one is the engine, the other is the cat! Lastly, some chemical tricks ... to clean the system super well, try BG 44K; a friend recently failed an emissions test miserably, ran this, and easily passed, plus his truck (86 4Runner) ran super well afterwards. Also, another chemical trick ... methyl hydrate, one half liter, full fuel tank with highest octane fuel available, run it about a hundred miles and then prior to testing run the vehicle hard for an hour, guaranteed to pass. :-X
     
  8. semlin

    semlin discouraged user

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    Thanks for the suggestions guys

    I don't get to drive it during the test but they might be flooring it even though it is not necessary. Good point. Of course, this means my cruise has to be floored at this stage of the test when the "Average" cruisers do not. Maybe my kickdown needs adjusting.

    The TPS flat spot idea is also interesting as is the 02 sensor issue. I was hoping getting the EGR going would do the trick but...

    Riley, I don't think the ECU has to relearn the EGR system is working or at least the FSM does not mention it. The EGR system is basically mechanical.

    I have a bottle of metyhyl hydrate in the back of my truck right now ;). desperation is setting in as I get taken off the road on Wednesday if I don't pass, but I still want to figure out what the problem is.
     
  9. landtank

    landtank SILVER Star

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    You can check the TPS with a volt/ohm meter. The best would be an analog or sweep meter. What you look for is a smooth variation in resistance between pin 1 and 3 on the TPS sensor. That is of course if I'm reading the schematic right.

    Pin 1 is grounded through the ECM so you would also have continuity between that pin and the frame.

    Pin 2 is closed throttle position. With the throttle closed you should have continuity between pin 2 and pin 3, but only then!

    Pin 3 is the signal line to the ECM.

    Pin 4 is 5vdc
     
  10. Beowulf

    Beowulf

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    Rick,
    (slight thread hi-jack)
    I have an old Simpson VOM that I never use since I got the Fluke. I was planning to sell it on eBay but they don't bring much so it just sits in the bottom of the tool box. I guess your suggestion would be to keep it for these type of tests? Are there other (emissions) tests where the old analog VOM is better to use?
    -B-
     
  11. landtank

    landtank SILVER Star

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    B, it's more of a device test that it is good at. I wish I had one. A good example is a simple switch such as on the t-case. At one end of the scale you have open and at the other is closed. With a sweep meter you can see a pitted contact because as the switch is actuated there would be a studder in the motion of the needle going from open to closed, indicating a pit. With the TPS it's a variable resistor that is being checked so as you move the TPS through it's range, if there is a studder than that is a bad spot. Digital meters don't give you that visual as they update the values periodically so by nature it is jumpy. Typically switches and VRs don't fail completely but gradually and the sweep meter is the best tool to evaluate them. It's been in the back of my mind for a while that some of the working in of the diffs when these trucks are bought is partly due to the fact that a dorment switch goes bad faster than one used occasionally. That's why quickly clicking a switch repeatedly can bring them back to life as that action cleans the contacts.

    sorry if that more than you wanted, but I'd hold on to that meter and try using it the next time you think you have a bad switch. It works very well.