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Misfire, out of ideas

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  • Misfire, out of ideas

    I hope someone has some ideas, because I'm clean out of them.

    A week ago, I drove my 96 SL2 to work. Ran great, just as it has since I got it. It was a rainy day, like many the car has sat through. When I left the parking lot, and ever since then, the engine had NO power at more than 10-15% throttle. Ran smooth at idle and very low throttle, but very rough at anything above that, causing the SES light to flash after running that way for more than a few seconds.

    Replaced spark plugs and spark plug wires. No change. Cleaned the EGR valve in case it was sticking (had that problem on my 95 SC2), but it didn't stick, and didn't fix the problem.

    I suspected that maybe something electrical had gotten wet and shorted out, as it was wet for a couple of days after the problem started. But the weather dried out, and the problem hasn't gone away.

    Plugged in my OBD-II software, drove around a bit while a friend watched the laptop. Had a "P0300 Random/Multiple Cylinder Misfire Detected" error. While driving, we watched it add a "P0131 Oxy Sensor Circuit Lo Voltage (bank1, Sensor1)" error. That's the O2 sensor in the header/exhaust manifold.

    Replaced the O2 sensor. Didn't fix the poor running problem, but after clearing the codes the P0131 never came back, so I probably avoided a future problem that hadn't gotten bad yet.

    Using the OBD-II software to monitor the engine in real time, we determined that the throttle position sensor and MAP sensor were working OK. Also determined that the catalytic converter is functioning properly, as the voltage of O2 sensor #2 is significantly lower than #1 (after replacing #1).

    I had the idea of disconnecting the exhaust between the header and the cat to see if maybe a clogged cat was causing all this trouble, but the header is welded to the cat, so this wasn't possible.

    Removed the MSD coils. Cleaned all the contacts, put dielectric grease on all contact surfaces, reassembled. No change.

    Replaced the fuel filter. (What a PITA that was). No change.

    Installed an additional ground wire between the body and the engine. No change.

    Filled the tank with premium (the 10.0:1 compression requires it) and added injector cleaner / octane booster. No change.

    Cleaned the throttle body. No change.

    During this whole process, which has taken place over the past week, I disconnected the battery overnight to reset the computer a few times. No change any of those times.

    As you can see, I've tried a LOT of different things, and nothing I've tried has fixed it. I've run out of ideas. Can anybody help? I'd give up and take it to the shop at this point, except I can't afford to until I get paid at the end of this week. [img]{SMILIES_PATH}/evil.gif[/img]
    - Justin<br />91 Sentra SE-R, &quot;The Millenium Falcon&quot;<br />91 Miata, &quot;The Otter&quot;<br />ex 95 SC2 (Locutus), 96 SL2 (Silverstreak), 96 SL2 (Apollo), 94 SW2 (Ninja Wagon)

  • #2
    well, at least it got you to do a shit ton of maintence on it. honestly I have no idea, but since everyone always blames the crank sensor, I point my finger at that.


    • #3
      whats your fuel pressure?
      sigpic-VOLVO 745T 175K MBC ...
      - 9 BOLT Aluminum Intake 3rd gen sedan... Beige... 160K

      You're so crazy! enough in a way that i'll probably say you destroyed me!
      ~The Used


      • #4
        Is your valve cover gasket leaking oil into the spark plug gallies? Happened to me causing similar problems to my 97 sl2.


        • #5
          wow you can write alot!
          Just baught a Big Mac, Throw some Cheese on that bitch...
          <br />
          <br />**i*14: i actually shot a bird for sitting over my car
          <br />
          <br />tool:
          <br />One who lacks the mental capacity to know he is being used
          <br />
          <br />[quote author="Schizzo97SC2"]what have we learned boys and girls? SOHC's are not fast. ever.[/quote]


          • #6
            Originally posted by djgeo05
            wow you can write alot!
            he just pressed enter twice after every sintence so it looks alot bigger
            [quote author="triman54 on, May 16 2008, 04:02 PM"] A Saturn is like a box of chocolates... [/quote]<br /><br />2007 Central Florida Region East Coast Champion STS<br />2007 CFR West Coast Champion STS<br /><br />


            • #7
              i know that this is almost two odvious and can be over looked but is the spark plug boot pushed all the way onto the spark plug. you heard the click? secondly get rid of the msd coils. i had an ass load of problems with those things. i put oem ones and and problem gone. ohh and the msd were not even a week old.

              secondly look athe the electod on the coil and see if there is excessive wear there. kinda makes a loose connection when you connect the spark plug wire to it.

              and you are sure you have all the spark plug wires in the correct order right.
              2007 chevy classic 2500hd 4x4 duramax
              1996 383 lt1 auto trans am
              1995 sl1. single cam of fury
              1995 jeep wrangler lifted 4x4 4.0
              1995 ford explorer 4x4


              • #8
                And the winner is... COILS!!!!

                I live with the current owner of my first (of three) Saturns, a 95 SC2. I asked her nicely if I could borrow her coils to pop on my car and see what happened. She's a good sport, and agreed. I have NO idea how old those coils are - I never replaced them, and I bought that SC2 in 99. But I put them on, and my SL2 ran great once again! Then I was nice and put the coils back on her car for her. [img]{SMILIES_PATH}/icon_twisted.gif[/img]

                So this is for sl2racer:

                - Justin<br />91 Sentra SE-R, &quot;The Millenium Falcon&quot;<br />91 Miata, &quot;The Otter&quot;<br />ex 95 SC2 (Locutus), 96 SL2 (Silverstreak), 96 SL2 (Apollo), 94 SW2 (Ninja Wagon)


                • #9
                  Yep MSD coils on OBD2=teh not good. I kept telling Josh to dump the MSD's for stockers and after an incedent on the innerstate heading back from the track, he finally listened.
                  -6S Resident Mechanical Forensics member #001.
                  1995 SC2 Turbo 3.6L DOHC, 6sp manual, Ford 8.8 rearend running on MS3x.
                  1998 F-250 5.4L triton...stock.


                  • #10
                    Just curious, why are MSDs not good specifically on OBD-II cars? I did notice different wiring harnesses on the 95 SC2 I borrowed coils from to test on my car.

                    I bought and installed some stock replacement coils today. Working just fine now. [img]{SMILIES_PATH}/smile.gif[/img]
                    - Justin<br />91 Sentra SE-R, &quot;The Millenium Falcon&quot;<br />91 Miata, &quot;The Otter&quot;<br />ex 95 SC2 (Locutus), 96 SL2 (Silverstreak), 96 SL2 (Apollo), 94 SW2 (Ninja Wagon)


                    • #11
                      The squentail injection uses the resistance in the cuiruit (going from the coil to the plug, threw the head, back threw the coupled plug and back to the coil pack) to determine the posistion of the crank so that the PCM can calculated the when to spray the fuel injector AND to modifiy spark timing on the next combustion even. If the resistance changes out of the "known working pernamenters" the comupter thinks the crank is in another spot.

                      As the piston moves up and the compression goes up, it gets harder (more resistance) to fire the with platiunum plugs, the PCM pulls timging until it starts to misfire from having to retarded timing.

                      WIth the reduced secondary resistance of the MSD coils, the PCM thinks its firing too retarded and starts to advacne the timing a bit....until it just starts to knock on acceleration....then the knock sensor sees it and pulls timign out.

                      You have to remember that your a/f ratios will be crazy too.
                      -6S Resident Mechanical Forensics member #001.
                      1995 SC2 Turbo 3.6L DOHC, 6sp manual, Ford 8.8 rearend running on MS3x.
                      1998 F-250 5.4L triton...stock.


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