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Humphrey
03-04-2000, 07:26 PM
My car has been idling rough lately and so I decided to change both the spark plugs and wires. Now it seems to be choking/knocking at a low acceleration (as if there were an insufficient level of voltage to fire the spark plugs). It seems to me that the distributor cap and/or ignition coil is faulty. I知 am wondering how to troubleshoot this problem.<p>Thank you. <br>

Grant
03-04-2000, 09:05 PM
<i>: My car has been idling rough lately and so I decided to change both the spark plugs and wires. Now it seems to be choking/knocking at a low acceleration (as if there were an insufficient level of voltage to fire the spark plugs). It seems to me that the distributor cap and/or ignition coil is faulty. I知 am wondering how to troubleshoot this problem.<p>: Thank you. <p>Are you sure you did not cross one of the plug wires? If not then did you open the gap too wide on the plugs? If the gap is to wide then the plugs may have a hard time "sparking" across the gap. Did you change any thing else? Cap? Rotor? What type plug wires did you use? Some high resistant plug wires will not work well. How old is the coil? How bad was it running before you made the changes. Let us know! <p></i>

Humphrey
03-04-2000, 10:38 PM
<i><br>Here're the specs:<br><ul><br><li>Gap setting - .030"<br><li>Spark Plug Wire Set - Champion (PowerPath)<br></ul><p>As for the distributor cap, I did try to remove the 8mm screws holding the cap but never removed it.<p>Yes. The coil seems to be very old.<br></i>

Grant
03-05-2000, 10:00 AM
<i>: <br>: Here're the specs:<br>: <ul><br>: <li>Gap setting - .030"<br>: <li>Spark Plug Wire Set - Champion (PowerPath)<br>: </ul><p>: As for the distributor cap, I did try to remove the 8mm screws holding the cap but never removed it.<p>: Yes. The coil seems to be very old.<p></i><p>You may have an unrelated problem but I doubt it. I suggest that it is related to your working on the wires, plugs, etc. What else did you unplug or remove to get at the plugs and the wires. Did you remove the air cleaner/ air flow meter assembly to get at the plugs? If so did you disconnect the plug to the air flow meter? What about the plug to the idle speed actuator? If so be sure that these plugs are clean and attached correctly. Be sure to check that everything is connected correctly i.e spark plug wires, coil wire to cap and attachements to spark plugs and is making good contact. Assuming all the above is correct then I would look at the spark plug wires. Is the Champion Power Point wires carbon fiber or is it wire wound wire centers? Did you save your old wires? If all else fails re-install old wires to see if the problem goes away. Coil. This is harder to check. Sometimes a cold coil will not work very well until it gets warmed up. If the coil is not producing a good voltage output and you changed the plug wires to a high resitance type wire the spark plug may not be getting a good voltage (or good current). At idle the input voltage to the primary side of the coil is lowest and the makes the problem worse. I would suggest not doing anything to the coil until you confirm the perforamce of the spark plug wires. Let us know what happens.

Bob
03-05-2000, 05:14 PM
<i>: My car has been idling rough lately and so I decided to change both the spark plugs and wires. Now it seems to be choking/knocking at a low acceleration (as if there were an insufficient level of voltage to fire the spark plugs). It seems to me that the distributor cap and/or ignition coil is faulty. I知 am wondering how to troubleshoot this problem.<p>: Thank you. <br>----------------------------------------------<br>Though it's a PITA, you might end up replacing the old parts, then verify taht the car is running as previous to your changes. Then replace one group of parts at a time to see when the problem appears.<p>The problem is that sometimes it is TWO things together that cause a proble. I once had a 380SL that ran crappy only under load. I changed plugs (pulling one wire at a time showed no bad or misfiring cylinders)-no help. I checked the wires with an ohmmeter, no problem. I checked the cap and rotor, no problem. I was down to suspecting the fuel injection system. Come to find out, there was one plug wire and one bad terminal on the dist cap that when paired would cause the problem, but either alone would as well (only under load remember), so changing all the plug wires OR the cap wouldn't remove the problem-ONLY by changing BOTH would the problem disappear completely. Drove me nuts for awhile.<p>Good luck. Do check the rotor-sometimes these will cross-fire and fire two plugs at once, but not show a carbon track.<p>Bob<p></i>

Humphrey
03-05-2000, 07:41 PM
While in the troubleshooting stage I decided to begin by checking the spark plug wires for proper installation and the spark plugs for any unusual deposit. The installation was fine, but the spark plugs were soaked in gasoline with a carbon deposit. The fuel pump? Then, as I progressed in checking the distributor cap, I noticed excessive burn contacts.<p>For the reinstallation of the cap, I made sure that the points of contact were all cleaned.<p><B>Note:</B> No other parts had to be removed for the removal and installation of these 2 pieces.<br>

Callan
03-05-2000, 09:15 PM
You need to know what your secondary voltage is at the plugs, and what the level of spark output from the coil is on the primary side. Unless you have a new test coil and cap and rotor to bypass this route, you might want to pay a shop for a quick look at the ignition system. <p>If all checks out, even with your old parts in place, then it's off to looking at the air flow meter, loose grounds at the cylinder head, or a test control unit for poor fuel metering. Too much fuel on your car is usually caused by a bad connection to the above items, low voltage to the Motronic control unit or a poor ground, bad fuel pressure regulator, or a bad Motronic unit.<br>Did the spark plug wire set have new coil wire with it, or did you reuse the old one?<p>I've been burned more than once by an interm. open coil wire. Very trick to always catch, as it happens more under load, and that's not easy to duplicate in a shop setting.<p>The injector grounds are those mass of brown wires at the left rear of the cyl. head. ,under the intake boot. Any crud or loose connection here can play havoc with fuel metering. <p>Don't rule out a bad or missing pin on the flywheel face for the reference sensor. Even warped flywheel teeth that give a weird reading to the Motronic unit can cause spark and fuel problems. Garbage in gets you garbage out[but you already knew this]<p>Just try to seperate if the problem is spark or fuel first, then troubleshooting will get easier.<br>Always here to help.

Humphrey
03-06-2000, 11:03 PM
The spark plug set did come with the coil wire.<p>I'm taking the car to shop this Wednesday so they can check the ignition system.

Humprey
03-07-2000, 08:25 PM
With the spark plugs cleaned completely I had no problem starting the car. However, I noticed a lot of smoke on start up with a slight miss.<p>I知 thinking that this is more of a fuel problem than an electrical problem since each plug was tested for spark and no. If this is a fuel problem, could the COLD START VALVE and/or FUEL INJECTOR be causing this? The engine has high fuel consumption. <br>

Humprey
03-07-2000, 08:26 PM
With the spark plugs cleaned completely I had no problem starting the car. However, I noticed a lot of smoke on start up with a slight miss.<p>I知 thinking that this is more of a fuel problem than an electrical problem since each plug was tested for spark and no. If this is a fuel problem, could the COLD START VALVE and/or FUEL INJECTOR be causing this? The engine has high fuel consumption. <br>

Callan
03-09-2000, 07:23 PM
If you see white smoke, not a lot, and the outside temp is lower than say 50 degrees, then it's just moisture in the exhaust and water vapor from the comsumed air. <p>Continuous black smoke or alot when you accelerate is not good. This is the way to kill a working cat. conv. Have the fuel pressure checked, should be at 30psi or so[2.6 to 2.8 BAR is OK too]. Make sure the idle contact of the throttle switch is clicking closed when you open and then shut the throttle. If the contacts are staying open, you'll get a rough idle, black smoke from a too rich mixture, and a slightly weird idle on a 3.3 or 3.5 liter BMW.<p>You won't get much of an idle surge like you would with the smaller M-20 engines, so it's an easy thing to miss. It's also easier to adjust the throttle switch if needed. <br>Pull the intake boot off the air flow meter and make sure that the inner flap hasn't warped from a backfire or engine heat. It can stick in a slightly open "from normal idle" position and you end up with a too rich mixture again. I have successfully filed the outer casing[where the flap is hitting inside, not the flap itself] of air flow meters for this to buy an owner some time, but the only real cure would be another air flow meter.<p>Lastly, the shop that you were going to use for a scope check, do they have a decent exhaust gas anyl? If so, you can unscrew one of the two 12mm port bolts on top of either manifold to "sample" how rich or lean the engine is running.<br>Anything under 3% is usually not a bad air flow meter or Control unit. These two parts usually give you a very rich CO mixture like almost off the scale at 10% CO when they are really failing.<p>1.5 to 2.0% isn't that dire, but needs to be corrected. You'll also need to know how high the Hydrocarbons are as well. Low to normal CO but high HC is usually injector troubles.<p>Let us know what you find.


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