untrackable misfire!!
04-03-2007, 09:07 PM
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untrackable misfire!! ok, i'm getting a p0300 code and a flashing SES light. we hooked my car up to my buddy's Digital Horsepower tuner (unlocked for his V6) to do some data capture. it would only let me monitor 6 cylinders, but i found that i'm getting about 200 misfires on cylinder 5 every 20 seconds or so. so, thinking i had found the source of the problem, i changed the plugs on that side and swapped the 1 and 5 coil packs. took it for a drive, NO CHANGE!! however, i did find that this is only happening in the 1200-1500 rpm range with a load on the engine (doesn't do it sitting still in neutral). above that, the misfire count went to zero. i need to get this fixed, it driving my crazy!! any help would be awesome. thanks in advance.
--Bill
--Bill
04-04-2007, 01:42 AM
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or you can get a tethoscope or however you spell it and try to hold it to each primary off of the header...you will generally hear alot more noise coming from the missing cylinder do to just moving parts and no ignition...
04-04-2007, 06:08 AM
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the part the confuses me and makes me think it's sensor is the fact that it runs perfectly above that rpm range. i figured that ruled out mechanical failure in the valve train...i could be wrong though. so Blur, you think i should start with moving all the coils around and examining the the harness?
04-04-2007, 08:30 PM
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Fuel injector, spark plug, spark plug wire, coil. Those are the starting places. Watch it run at night and see if there is a slight arcing around that cylinder.
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04-04-2007, 10:18 PM
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Originally Posted by squall01
the part the confuses me and makes me think it's sensor is the fact that it runs perfectly above that rpm range. i figured that ruled out mechanical failure in the valve train...i could be wrong though. so Blur, you think i should start with moving all the coils around and examining the the harness?
I've seen in other engines(5.3L)where a valve spring broke and the compression and leakdown test passed. Had a misfire below 1500 RPM and went away above that.
04-08-2007, 06:42 PM
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+1 for the valve springs. I had the same problem in the same rpm range the car ran fine no noise. I pulled the valve covers and found the no 3 and no 7 exhaust springs broken.
04-09-2007, 07:57 PM
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You need to monitor the misfire counter logs for all 8 cylinders.
The cam crank relationship is timed if ouyt of synch they set a seprate code.
If it is flashing it is a current trackable misfire, you should be able to look at the logs & narrow it down.
The cam crank relationship is timed if ouyt of synch they set a seprate code.
If it is flashing it is a current trackable misfire, you should be able to look at the logs & narrow it down.
04-09-2007, 10:31 PM
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My 96 SS used to come up with the misfire which was always P0300 when I checked it after a while. I got a scanner and traced it to P0302 when it was actually occuring and then it changed to the P0300 which made it look like random misfire. I changed the plugs, wires, moved injectors around, did coil and ICM and never got rid of it. But even when it would pop up, the car was running smooth as glass so I think it was a false code. The guy I sold the car to still gets the code once in a while and he said the car never skips a beat so I think it's an ECU issue or maybe faulty wiring somewhere.
04-10-2007, 06:07 AM
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Originally Posted by wrencher
You need to monitor the misfire counter logs for all 8 cylinders.
The cam crank relationship is timed if ouyt of synch they set a seprate code.
If it is flashing it is a current trackable misfire, you should be able to look at the logs & narrow it down.
The cam crank relationship is timed if ouyt of synch they set a seprate code.
If it is flashing it is a current trackable misfire, you should be able to look at the logs & narrow it down.
04-10-2007, 10:18 AM
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does anyone know if the computers read the cylinder numbers the same on the v6 and the v8. for example, cylinder 5 on a v6 is still the 3rd one back on the driver's side on the v8.
04-11-2007, 07:45 PM
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i'm thinking about checking the injector. what is the best way to do this? also, is there a way to tell if it's a valve spring without pulling the valve cover?
Last edited by squall01; 04-12-2007 at 08:15 PM.
05-04-2007, 06:53 PM
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well...here is an update. so far, we have swapped the coils around, injectors, plugs, wires...everything...still cylinder five. the code is now actually showing p0305. so it's something wrong with that cylinder. what should be my next step? pull the valve covers?