Random Misfire with no codes
10-15-2006, 06:55 PM
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Random Misfire with no codes I have been getting random misfires under normal driving conditions. Mostly crusing, lugging and loafing. The engine does not misfire at high rpm or under hard acceloration. The problem does not seem to be temp related. Fuel pump and filter have been replaced. However it seems to behave like it's starving for fuel. Any thoughts?
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10-17-2006, 08:16 PM
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Originally Posted by wm_sorg
I have been getting random misfires under normal driving conditions. Mostly crusing, lugging and loafing. The engine does not misfire at high rpm or under hard acceloration. The problem does not seem to be temp related. Fuel pump and filter have been replaced. However it seems to behave like it's starving for fuel. Any thoughts?
10-17-2006, 08:23 PM
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Sounds like something spark related. Thats what my car used to do when the plugs were going out after 80K miles. It would stumble under any throttle application at low RPM's, but in the higher RPMs the issue wasn't there. Basically I think the spark wasn't strong enough to ignite the rich mixture under a load at lower RPMs.
I'd replace the plugs and wires first off. Use either stock AC Delco wires or Granatelli zero resistance wires (thats what I used and they are excellent). For plugs I used AC Delco Iridiums, I think they are the best for our engines, and have virtually no gap erosion even after 100K miles.
If the misfire is still there after you change the plugs and wires, I'd suspect a bad coil or a fuel issue.
I'd replace the plugs and wires first off. Use either stock AC Delco wires or Granatelli zero resistance wires (thats what I used and they are excellent). For plugs I used AC Delco Iridiums, I think they are the best for our engines, and have virtually no gap erosion even after 100K miles.
If the misfire is still there after you change the plugs and wires, I'd suspect a bad coil or a fuel issue.
10-17-2006, 08:48 PM
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Unfortunately no log files. I am looking into a software solution. The car has a mild cam with tune a4 with yank SS3600. The problem literally developed overnight. Car ran great. Parked it and next day less than a mile from home it started. Seems to stumble under cruise. If I open the throttle it somewhat helps clear it past the dead spot. The dead spot is random. If I get VCM software will it help me diagnose even though PCM does not detect fault?
10-24-2007, 05:51 PM
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You can have a random-seeming miss when something is the
"tip of the iceberg" and you're just barely tickling the problem.
Like one weak cylinder (injector lean, maybe) and then the
proportional fueling as it wanders around, stumbles when it's
swinging lean and that cylinder is up to bat. Or something.
Hard to diagnose these cars without the tools because there
are so many wheels within wheels. Not like carbs where it all
came through the same big hole pretty much.
Ignition problems usually manifest worst / first at high load.
I'd be inclined to chase a light-load, closed loop miss through
the fuel delivery and air metering paths first.
"tip of the iceberg" and you're just barely tickling the problem.
Like one weak cylinder (injector lean, maybe) and then the
proportional fueling as it wanders around, stumbles when it's
swinging lean and that cylinder is up to bat. Or something.
Hard to diagnose these cars without the tools because there
are so many wheels within wheels. Not like carbs where it all
came through the same big hole pretty much.
Ignition problems usually manifest worst / first at high load.
I'd be inclined to chase a light-load, closed loop miss through
the fuel delivery and air metering paths first.
10-25-2007, 12:46 PM
#16
Efilive has a scan tool that is only 250 bucks. It allows you to do cly balance tests and allows you to see all the enhanced perameters on your car. You can watch each cyl individually and see exactly what cly has the issue. That problem is usually a 10 minute issue to figure out exactly what is wrong.
10-25-2007, 09:11 PM
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well i tried a diff maf , im goin to try a new set of injectors tomorrow. how would u know if the regulator is leakin it back into the manifold. plus i put new o2 in today all so ...most time if it does die it you do have to give it gas to get it to fire back up. it did the same thing on my old motor and i put a new 408 stoker in it bout 3 months ago and same thing so .....
