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87 Pontiac revisited (bit long, but detailed)

Discussion in 'Electronic Repair' started by [email protected], Jan 2, 2007.

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  1. Guest


    Yup the same one. Still fails on NOx.

    We have basically checked everything. The EGR was tested by not only
    false triggering it by ground the solenoid wire, it was also removed to
    check for free flow when open and proper sealing when closed. This a 5
    wire type, so it has a position transducer so if the computer told it
    to actuate and it didn't, it would know.

    The IAC was checked the most functional way I can think of, turn key
    on, then unplug IAC, start engine. It will idle high, plug in IAC with
    engine running and RPM drops. It was A OK.

    Had a MAP sensor handy so just changed that. Put in a brand new O2
    (lambda) sensor.

    Now it achieves closed loop operation and after the codes were cleared
    has not set any new ones.

    Still fails on NOx !. So we put a new cat on it, and it STILL fails on
    NOx !

    I am starting to think the problem is caused by excessive cylinder
    imbalance. That either by partially clogged injectors or vacuum leaks
    one or two cylinders are running too lean.

    The way I explained it to my buddy is this : When you got a lean
    cylinder you get NOx and HC, on a rich cylinder you get HC and CO.
    Mixing these two in the exhaust does not make them go away.

    At least that is my reasoning at this point. There is really not much
    else I can think of. You ?

    I am leaning toward vacuum leaks because the car has good power and
    even though the idle is not perfectly smooth, it does not have a clear
    miss. Off idle or under load it smooths out perfectly.

    The other thing is that it does not read all that low on HC and CO. It
    doesn't fail, but I have seen alot better readings from cars that run
    this good. Especially with a new cat.

    In fact my Dad's car which has the 3.1 version of the same engine read
    better with a totally blown out cat. It was replaced because it got
    loud, not to make it pass, it had already passed.

    Now I do remember how they used to check for vacuum leaks, by spraying
    starting fluid on the suspected areas. Is it still done this way ?
    Should I disconnect the IAC while doing this ? That would seem logical.

    There is one other thing. Cars still jump time. If the cam lobe design
    is anything like what the norm used to be for a passenger car, jumping
    a tooth would actually increase real compression, and lower average
    vacuum. Given the conditions, I think it is a real possibility. IIRC,
    the system in this car does not use a cam sensor because it does not
    need it. Firing the injectors 3 by 3 and having 3 coils it simply
    doesn't need a cam sensor. Firing the coils 2 by 2 andf the injectors 3
    by 3 there are waste sparks as well as waste (kinda) injections.

    On a more advanced engine like a 3.8 it needs both cam and crank
    sensors because the injectors are fired seperately. These engines can
    detect an error in cam timing but not a 2.8/3.1. I remember my other
    buddy with one of the last 2.5 "brick shithouse" engines that jumped
    time. It would run, so he takes it in to Mr Badwrench and the machine
    that costs the national debt said to replace the engine.

    I looked at it and after much pondering told him "tear down for timing
    chain". Later he showed me the almost non existant tensioner and the
    chain with the burrs all over it. After a set of timing irons (my pet
    name for the chain and tensioner and maybe gears) he was back in

    To support that theory, the 2.8 has very little backpressure at idle. I
    mean even with the EGR tube open it is not all that loud. I took it off
    and pulled the plunger manually and I just didn't think there was
    enough coming out of it. That is, however, a subjective judgement.

    Since it is in closed loop without an EGR code, I can only assume the
    plunger is moving when told to by the computer. We are sure it is not
    clogged. We are also sure the EGR is not leaking.

    So what, in your opinion is the better way to go ? Spray for vacuum
    leaks, check cam timing or look seriously at the injectors being partly
    clogged. The idle sounds a but like a lean misfire, and the power is
    good and smooth under load. By my reasoning the idle is affected more
    than the power range. Doesn't this point to a vacuum leak more than
    injectors ?

    If someone is going to up and say "injectors", would injector cleaner
    be a good idea ? Normally I avoid it like the plague. When the engineer
    designs those injectors there is a paper that says what they are to
    inject, and there is one word there ; gasoline. I also shun injector
    cleaner because when the injector is really clogged, the cleaner will
    never get to it. However there is always an exception. These do fire,
    but perhaps flow is decreased in a couple of them.

    In a 3.8 I would take and ground each injector line from the computer
    and see how much it takes to flood any given cylinder, but they are
    wired together in two banks in the 2.8/3.1 so there is no easy way to
    do that. There are only two wires at the computer and you can't really
    get to the other end because they have the top plenum over the

    Anything helpful is greatly appreciated. This guy is just back to work
    and has to drive all over the place. He has to periodically go begging
    for license plates and/or like last time, sign the car over to get
    another temp tag. We let him use a spare set of plates for a few
    months, but we got rid of the car and it would have to be tested to
    renew them. With the new parts and the new cat, even if he could afford
    another car right now, that would waste everything we put into this
    one. He does construction labor and this being a station wagon, it is
    the perfect work car for him. It's a breeze to drive compared to a
    truck and on the rare occasion he has to carry a ladder it will work.
    It locks and his tools fit.

    We are getting to our wit's end here. We have even considered some
    skullduggery, like running it on pure ethanol for the test, or even
    test driving a car with the same engine and real quick switching the
    enigines and returning it. We don't want to do either. When I was a kid
    we would consider stealing a car and popping the engine in it, but no
    more. I/we don't want to do anything like that. Getting caught is not
    the problem, we could get away with it, but we do not WANT to. It is
    immoral. Well the ethanol isn't but that doesn't help him when test
    time comes around next year. We are in our 40s and want to do things
    right. There is no good reason this thing cannot pass.

    Well there is, but we are having trouble finding out what that reason

    Anyway, don't you just love my posts ? I know how it is. As much as we
    tell people to be thorough and give details as to what you have already
    done/tested instead of "Da thing don't work", I seem to be at the
    opposite end of the spectrum. Sometimes at work I am called upon to
    help another tech, and sometimes I say this, they reply "checked it", I
    say that and they say "Replaced it". While that tells me they are doing
    something, it doesn't make it any easier.

    So as you read my post and are about to say "______" and the next
    paragraph tells that I already did, don't get discouraged, please.

    The other thing is that I think of time as money, not that I need pay.
    This is almost a personal challenge. Like I said the guy is just back
    to work, I bought the cat. I'll loan him the money for gaskets, but do
    we need the intake set or the timing case set ? Actually he has a 30
    day now, by the time it runs out he'll have a check, but I still do not
    want to steer him wrong.

    What, in a way, I really need are ways to definitively check these
    things without a teardown. Got any ? For example, can someone say that
    at a certain reading of the timing marks (if any) that a certain valve
    under the front valve cover should be fully open, like at the peak of
    the lobe ? Or is there a way to plug up the exhaust and pump air into
    the intake to detect leaks ?

    I am always looking for new ways to test what is seemingly untestable.
    Pros have a few tricks, some of which they'll give up, others maybe
    not. For example I have extreme shortcuts when it comes to fixing TVs.
    We need that to make money.

    I din't want to make this too long, but I have had to adapt to figure
    out how to find the fault in TVs that are almost impossible to service.
    The scope is the first thing for me. Dead set, got SMPS standby, put
    probe near transformer. see RF ? move on to main SMPS and turn on, run
    for a sec and shutdown ? Get to the flyback, but set to 10uS triggered.
    See a five fingered waveform ? Bam, throw in a fly and wipe it's ass
    and ship it. By wipe it's ass I mean give it a tuneup, clean the lenses
    etc. and touch up the convergence. Auto diagnosticians surely have the
    same shortcuts.

    For example what alot of people don't know is before you buy a high
    mileage car there is a test. Take the oil filler cap off and put a
    piece of paper over it. It should stick at idle. There should be vacuum
    there. If it is blowing out the engine has compromised sealing of
    compression to crankcase. Don't pay alot for it, it is worn out. I do
    this before even thinking of looking at the odometer. I know a few
    things having been around cars alot, but the pros know more. I even
    know about the brand new defective radiator caps, that thingy in the
    middle should be spring loaded to the rubber seal. In some cars this is
    very important, especially bigblocks, if you happen to still have one.

    Kinda what I am looking for is how to check what. On the other side of
    the screen I know you can't troubleshoot it from there. I seem to be at
    a loss for testing techniques at this point. If someone can just up and
    tell me what the problem is it would be great, but I don't really
    expect that. Also, better techniques will come in handy. As cars get
    more and more complex it ain't getting any easier.

    Anything you got is very appreciated. Give me your address and I will
    at least send you some beer, if you want it. This is just one of those
    important things to get done, and it has become somwhat personal. I
    can't let it win. If it only knew that if it wins it goes to the
    crusher :)

    Everybody have a good year. I await your wisdom. Now I am off to scan
    the recent posts to see if I can spead some around, in the spirit of
    "pay forward".

    Have a good one.

  2. To test for a vacuum leak, just run the engine at idle and spray all
    over with anything flammable-- WD-40 is probably the safest. I wouldnt
    spray starting fluid, it's a bit too quick to evaporate and mighty
    explosive and intoxicating too. The old VW Rabbits would get
    hardening of the injector grommets and leak like crazy-- five seconds
    of spraying and you knew for sure they were leaking as the idle would
    speed up whenever you sprayed.

    To test the injectors, pull the wires off them one at a time. No wire
    means no injection which should result in lots of engine vibration but
    the NOx should drop if the injector's been faulty.

    Is the engine hard to start after it's been sitting off for a few
    minutes? That might point to drippy injectors. A can of injector
    cleaner can't hurt to try.

    Good luck.
  3. webpa

    webpa Guest

    Been through all this with an '86 Fiero. Flushed, adjusted, then
    replaced EVERYTHING...every sensor, vacuum hose, valve, and
    no effect. In the end, it took a new catalytic converter...which cost
    all of US$86, installed. By Midas Mufflers. About 1/4 of what I'd
    spent on the other parts. So: Don't jump to conclusions.
  4. M Berger

    M Berger Guest

    That's less than the price of a decent catalytic converter,
    and Midas is usually very high on labor costs. In fact,
    our local Midas quotes $ 300 and up. I wonder what they
    really did to your car?
  5. webpa

    webpa Guest

    Replaced the converter and about one foot of pipe with a generic
    small-engine unit (parts cost ~US$50). I still have the old one.
    Engine then passed the emissions test with better-than-new-engine
    numbers for CO, NO, and HC. Has passed each subsequent test (4 of
    them) with the same results. Maybe I hit Midas on a slow day?
  6. Guest

    Thanks folks. I completely forgot about the injector seals.

    Will spray for leaks using WD40 with the IAC disconnected.

    Unfortunately it is impossible to disconnect each injector seperately.
    There is a plenum in the way. Even if the wires come out seperately, in
    this car they are hooked up three and three, I have really never
    examined the harness to see, but it doesn't matter, to make any
    injector specific test I believe a bunch of wires would have to be cut.

    Save that till after we get alot closer to the BFH. I would not want to
    sit there crimping wires back together. And believe me there is no way
    to get to the plugs right on them.

    I also thought of doing an RPM drop (or vacuum) check by disconnecting
    plug wires, but they made that a PITA too. Not real bad, but you need a
    screwdriver or something to ground the coil output during testing,
    otherwise the cylinder opposite from it in the firing order will lose
    firing voltage resulting in erroneous readings. This is because the
    three coils' secondaries are completely floating.

    As much as I like these late 80s early 90s EC management systems they
    do have some difficulties in troubleshooting at times. I like it when I
    am in a hurry and can just turn the key and drive even when it is 0
    degrees outside. My 87 hasn't stalled for years unless something else
    screwed up. Within about 40 seconds of running there are days it hit
    5,000 RPM to get on the freeway (I live real close).

    I think it is wonderful, the ECM system in these GMs. It is like having
    a competent engine engineer under your hood at all times, and he is
    busy. Constantly adjusting timing, even the setting of the weight
    springs in the distributor. Constant control over the choke, well the
    ersatz choke, and constantly adjusting not only the screws on your
    carb, but changing the jets while you drive down the road.

    Yes, it is wonderful. I think it is even more wonderful that Bosch did
    it without electronics. But when it screws up, people are alot less

    Anyway, in the responses thusfar I didn't see anyone take the wind of
    the timing chain idea into their sails. Kinda glad.

    Gonna go spray for those leaks and get back to you.

    Thanks again.

  7. Guest

    Also, cats are not as expensive as they used to be for regular cars.
    The one we put on was $36 brand new in the box.

    A place like Midas probably buys by the truckload, so they might pay
    say $25. If they charge you say $80 installed, they made $55 in about
    20 minutes. As long as there were no other complications, you would've
    been charged for them as well. The mechanic probably makes between $15
    and $25 an hour. This should be billing at 3X that. It might be more in
    this type of business because it can be high maintainence. Three X is
    just a rule of thumb though, high cielings cost energy in the winter at
    least, and mess with the bottom line.

    Last cat I had put in a car was $100 at the local muffler shop, but
    this was a couple of years ago. It seems there is a new manufacturer or
    something out there.

  8. Bob Urz

    Bob Urz Guest

    You would be hard pressed to get a muffler for that much money ($25).
    And a cat is full of rare metals (at least a real cat does)

    You might find some generic cats (usually Pre OBD2) after market for
    a more reasonable price. But they are generic with no ends (flanges)
    welded on and no ports for O2 sensors.

    Factory fit out of the box cats are usually in the hundreds of dollars

  9. Meat Plow

    Meat Plow Guest

    A direct fit Catco for an 87 Grand Prix is $109.00.
  10. Hi!
    I remember this.
    Hmm, maybe a move to where emissions testing isn't commonplace is in order?
    Yes, I believe it is. I also seem to remember hearing of carb cleaner being
    used this way...but both are rather volatile substances. WD40 isn't quite as
    volatile, but it is safer.
    Worth a check...what can it hurt since you've done just about everything
    else by now?

    It's worth a try. Get some injector cleaner and run it through the car. It
    might make a huge difference. Here's a little story you might want to take
    the time to read. I may have mentioned when you first posted about this car.
    But if not, read on:

    My dad bought a 1988 Buick LeSabre (3800 V6) for $100. It didn't look bad
    and rode well, if it ran long enough to get up to speed. When we started it
    had gas in the oil, many cylinders not firing and a service engine light
    that wouldn't go out. The previous owner had driven it until it would run
    reliably any longer. My dad drove it home, which was an adventure. We didn't
    have any better way at the time. No trailer we had was long enough, so it
    was followed with a "chase car" in case of problems. A mechanic said "junk
    it and cut your losses".

    Well...I don't think that way, and neither did anyone else involved. We
    started fixing problems...fresh oil and filter, new plugs, plug wires, and a
    spark module (as we still didn't have fire on at least one cylinder) were
    all installed and they made quite a difference. But something still wasn't
    quite right. The engine light was still on, and it didn't run like it
    should. It was hard to start as well.

    So one night, with only a little gas in the tank, we put in some
    Lucas-branded fuel injector cleaner. (Come to think of it, we might have
    actually put in more than one bottle, as this seemed serious and we were
    desperate.) The mix was way too strong, and we all kind of wondered what
    kind of abuse this might inflict on the fuel injection and pumping system.

    Now, it was about 11 o'clock at night when we started this car in the
    driveway with virtually no muffler left (the entire *top* of the muffler was
    gone) and let it rip. It bucked and snorted something awful at first.
    Finally, after about ten minutes, the cloud we were making subsided, and the
    car evened out nicely. Thankfully, our neighbors are into playing with cars
    as well.

    The engine light turned off in the strangest way. After the muffler had been
    replaced, the light was still on. It went out and never showed up again (nor
    did any codes) after we put the final little elbow piece on the back of the
    pipe leading off the muffler. Who knew the engine computer could be that

    After all that, the car ran fine for several thousand miles until the fuel
    pump failed. And that's where we've left it for now. Nobody (myself
    included) has had time to do any more than drop the tank off the car, as all
    the fuel line was so rusty that it fell apart.

    So that's the story. (As for the bit about the Lucas fuel injector seemed to work, and I've met Mr. Lucas himself. He's a
    genuinely nice guy who believes in the stuff he sells. No, I have no
    affiliation with the company or its products other than as a satisfied
    I get the feeling there may be a story to share it? I agree that
    isn't right, but it would be pretty funny. And if I'd done that, the new
    engine would act the same way!
    I tend to agree with that.
    Sure, it was an interesting read. I well remember the original post, and
    might have replied to it.
    Thanks for the info. That's an interesting idea...I'd never thought of that.
    No need. Hopefully something I've said might make for a path to the
    solution. If it does, so much the better. I'm no automotive expert by any
    means, but I'm not afraid of them either...having changed starters,
    flexplates/flywheels, fuel tanks, oil and other stuff.

  11. Roger Delkin

    Roger Delkin Guest

    wrote in message
    While reading the description of your problem, I was thinking, "clogged
    injector(s)." I had an '88 Pontiac Grand Am, different engine but the same
    basic fuel and ignition system. I kept the engine well maintained even
    though I didn't care so much for the suspension, body, interior. . .
    ANYway, the car ran pretty well until I loaned it to a friend, who
    apparently was buying the cheapest gasoline possible. When he brought the
    car back to me, it was stuttering, had to start, rough idle, but still had
    somewhat reasonable power. I ran a few diagnostics and found that the
    injectors were indeed firing (used an oscilloscope on the wires into the
    injectors). The problem was solved by removing, cleaning, and reinstalling
    the injectors (don't forget new seals). Note that the liquid injector
    cleaner may or may not fix your problem; you may have to R&R your injectors
    to really get them clean.

    I sold the car soon after with 246,000 miles on it, not bad considering I
    pretty much always drove it like I stole it. It was shipped down to Mexico
    and placed into service as a taxi. Really!

  12. I am dropping in without knowing much about what is going on here. I
    just wish to add this:

    It was thought for a while that I might have a leaking intake manifold
    gasket on a Y-code 307 V-8 in a 1989 Oldsmobile Custom Cruiser. I tried
    spraying WD-40 at the seams, to no avail. A trusted technician at the
    local Cadillac dealer said the stuff to use for that pupose is
    carburetor cleaner. That will ignite, causing the rpm's to bump up as
    it is sucked into the cylinders. I did as he suggested, and the rpm's
    did increase. It turns out that the manifold gasket was not at fault.
    Rather, there was a disintegrated thermal vacuum switch adjacent to the
    suspected bad spot in the gasket. Replacing that cost a few tens of
    dollars and a few minutes, not several hundred dollars and several
    hours. It was quite a relief.

    My vote is for carburetor cleaner.
  13. David Lesher

    David Lesher Guest

    Better is a propane torch. Not lit, just cracked open. When the
    leak such propane, the car runs far smoother.
  14. David Lesher

    David Lesher Guest
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