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Thread: 90 sc running pig rich need help

  1. #1
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    90 sc running pig rich need help

    I have a 1990 3.8l sc and it is running pig rich at idle and almost seems lean at wot. Had a breakout box and checked the mass airflow was reading a bit hight, replaced, no change. Coolant temp sensor for computer readings were ok, replaced anyways, no change. I scoped the cam and crank sigs and have a nice square wave on both. Changed plugs because by now they were black as sin still no help. Changed coil pack even though i had good looking spark still no help. Have put 12 gals of 93 octane in it and it is still running rich. Also checked computer power grounds ect all checked out fine. Fuel pressure is dead on. Fuel pressure regulator is not leaking and has vac at idle. I know alot of reasons for a car to run lean but not many more for a rich condition in open loop and closed loop. Any advice would be verry helpfull.

  2. #2
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    You didn't mention 02 sensor waveform. That would have been my first check.
    Quote Originally Posted by Miller View Post
    Ya thats why i tape mine down. People think its bc i dont have a moonroof seal (which is true) but its really to keep my roof from ripping off .
    Email me here.

  3. #3
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    In open loop o2 has no effect

  4. #4
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    Quote Originally Posted by Ninja38 View Post
    In open loop o2 has no effect
    Not exactly true. If it learns bad data in closed loop, it will be applied to open loop as well. You can verify this by disconnecting the battery to clear memory.
    Quote Originally Posted by Miller View Post
    Ya thats why i tape mine down. People think its bc i dont have a moonroof seal (which is true) but its really to keep my roof from ripping off .
    Email me here.

  5. #5
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    Have all ready done a battery reset, still no change. Will a bad computer do this? Also does anyone know what the octane adjust plug is for?

  6. #6
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    O2s are probably shot anyway i would replace them.
    MEMBER #2488 best rwhp 504 485 torque
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  7. #7
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    Did it always run this way or did it start doing this at some point? If it started at some point, go back over that happened or what you did. Give us a little more detailed background on how it got to the point of running rich.
    Quote Originally Posted by Miller View Post
    Ya thats why i tape mine down. People think its bc i dont have a moonroof seal (which is true) but its really to keep my roof from ripping off .
    Email me here.

  8. #8
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    No it had been sitting for about a year, would only start with starting fluid. So i drained all the gas, put 12 gallons of 93 in it. Still running verry rich at idle, cuts out and falls on its face under load and rpm. Got a breakout box and started checking sensors. As i said the mass was a little high, but other than that i could not find anything else out of spec. Got out the scope and did both cam and crank. Both looked nice and clean. O2s are pegged as you can imagine. I would have to check but the injectors were in spec at around i want to say 3.6 ms, all the readings ect are at work but was in spec (all this according to alldata) The one thing we could not check is the baro sensor as in this year depending on who you ask it also acts like a map but i do not know. Also had to change plugs and oil as both were loaded up with gas. Being i dont get a chance to work on it i always disconnect the battery as the battery is pretty ~~~~ but i use a jump box when i do start it and all voltages are good.

  9. #9
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    Quote Originally Posted by Ninja38 View Post
    No it had been sitting for about a year, would only start with starting fluid. So i drained all the gas, put 12 gallons of 93 in it. Still running verry rich at idle, cuts out and falls on its face under load and rpm. Got a breakout box and started checking sensors. As i said the mass was a little high, but other than that i could not find anything else out of spec. Got out the scope and did both cam and crank. Both looked nice and clean. O2s are pegged as you can imagine. I would have to check but the injectors were in spec at around i want to say 3.6 ms, all the readings ect are at work but was in spec (all this according to alldata) The one thing we could not check is the baro sensor as in this year depending on who you ask it also acts like a map but i do not know. Also had to change plugs and oil as both were loaded up with gas. Being i dont get a chance to work on it i always disconnect the battery as the battery is pretty ~~~~ but i use a jump box when i do start it and all voltages are good.

    When i took my care to the shootout last year i thought my 02s were ok too but when we looked at them they were switching very slowly. Its just a pretty safe bet to start there. Then again i would do whatever xr7dave tells you to do, he knows a little bit more about this than most of us or well, pretty much all of us lol.
    MEMBER #2488 best rwhp 504 485 torque
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  10. #10
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    well i disconected them and still running into the same problem, if im correct it should go to a factory baseline once it sets the o2 code. and they are not switching just staying rich as the car is just dumping fuel.
    Last edited by Ninja38; 05-20-2017 at 02:02 PM.

  11. #11
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    like i said this is not an easy one, alot of reasons to run lean but not many to run rich.

  12. #12
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    Quote Originally Posted by davec73 View Post
    when we looked at them they were switching very slowly.
    Happen to recall what brand they were, and what brand you replaced them with?

  13. #13
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    Something I've not seen yet, and probably a silly question.

    Are these the factory fuel injectors, or have they ever been replaced with a larger set?

    RwP

  14. #14
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    as far i know it is a stock engine

  15. #15
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    Does it hold fuel pressure after you shut it off? I rarely see problems with injectors on these even after sitting for years with old gas in them, but one has to wonder if maybe you have sticking injectors. I assume the engine runs smooth, not like it's misfiring or anything like that?

    How high is the MAF voltage over spec? I think normally a stock SC will see around 1v at idle but I have not checked that in a long time.

    If the 02's are working (you did say they read high all the time) then the most likely cause of a rich condition will be an artificially high MAF signal voltage or injector malfunction.

    BAP does not affect AFR, the fuel command comes pretty much directly from MAF signal modified by ECT. It's really pretty much that simple.

    The 02's come into play when the EEC tries to close loop, but that takes around 1 minute to 3 minutes or sometimes more depending on a variety of conditions. When the EEC attempts to go closed loop it will first look for a high 02 signal. You indicated that this exists, so then the next thing the EEC will do is begin to remove fuel until the 02's drop and then will begin it's switching routine. So if it's rich on startup, the first reaction you can observe is when the 02 begins to drop. This will be kind of hard to observe because you don't know exactly when it's going to happen. After a fixed amount of time with the trims maxed out (25%), if a lean condition doesn't result during that time, the EEC will "give up" and not attempt to correct again until there is a key cycle. So what I'm getting at is if in your observations you do not detect this happening, you may miss the event entirely and it may never (to your knowledge) even appear try to go into closed loop.

    I did notice that you said it seemed lean at WOT, which is puzzling. How did you determine this? Did 02 sensor voltage drop under boost? I know you said you checked fuel pressure, but I wonder if you could have a fuel deliver problem. Does pressure drop under boost? It should rise # for # under boost. So basically 48-52psi depending on rpm (at WOT). It would be pretty typical for you to have a bad fuel pump after sitting, etc., but that doesn't explain your rich idle condition. It may be you have two separate problems going.

    Oh, did you say whether you ever verified TPS voltage and sensor output? It's a quick check with the BO box and will eliminate that as a contributing issue.
    Quote Originally Posted by Miller View Post
    Ya thats why i tape mine down. People think its bc i dont have a moonroof seal (which is true) but its really to keep my roof from ripping off .
    Email me here.

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