check engine light - again!

[Landshark]

a few months ago my check engine light came on and the car briefly ran rough. my buddy scanned it and it was "misfire - #1 cylinder." the dealer replaced all the spark plugs and the #1 coil pack.
now its back - car ran rough for less than a minute, check engine light came on and......."misfire - #1 cylinder"!!!!!
does anybody know what might cause this other than plug or coil pack? the ignitor module? what sensors might cause this, if any?

thanks for any help!!!

[Beav]

Ignition misfire awareness is only found in OBDII vehicles. #1 misfire would set a P0301 code. Generally the computer is right when determining which cylinder misfired, but I've had a couple that weren't 100% correct. A misfire condition has to occur on two consecutive drive cycles in order to set a code.

The crankshaft sensor 'sees' each tooth on the crankshaft reluctor and 'notices' sudden accelerations/decelerations between teeth. Such abnormalities indicate power variances, and a deceleration occurring instead of an acceleration indicates a misfire. The main reason for this feature is to prevent catalytic convertor damage caused by excess fuel coming from the misfiring cylinder.

A misfire can be caused by any of the normal deficiencies - a bad plug, coil, injector, vacuum leak, EGR malfunction and, of course, a loose wire. A bad ignitor would normally cause random misfires (P0300 - random misfire) or a no-start condition. A bad computer rarely singles out one cylinder. Vacuum leaks are constant and an EGR problem would more than likely affect more than one cylinder. My suggestion would be to check the connections for the #1 coil and injector. If o.k. check the resistance of the injector, it should be around 10-13 ohms (although most cars run @ 12-16, 10-13 is Subie spec.) If that's o.k. I'd pull the coil and plug and see how they look. If you can't see any problems change the coil and plug with another cylinder, clear the code and watch for the check engine light to return. If it comes back on it should be the same code if injector (or something more of a PITA like a bad wire) or the code for the cylinder with the original #1 coil and plug, indicating a problem with the (drum roll please...) coil or plug.

Good luck!

[Landshark]

thanks, Beav - that was very informative. this one might be hard to find - its been fine for a few months since the plugs and coil were replaced, then it happened a week or two ago, then tonight. AAARRRRGH!!!

[Ron Mummert]

Originally posted by Beav
Ignition misfire awareness is only found in OBDII vehicles. #1 misfire would set a P0301 code. Generally the computer is right when determining which cylinder misfired, but I've had a couple that weren't 100% correct. A misfire condition has to occur on two consecutive drive cycles in order to set a code.

The crankshaft sensor 'sees' each tooth on the crankshaft reluctor and 'notices' sudden accelerations/decelerations between teeth. Such abnormalities indicate power variances, and a deceleration occurring instead of an acceleration indicates a misfire. The main reason for this feature is to prevent catalytic convertor damage caused by excess fuel coming from the misfiring cylinder.

A misfire can be caused by any of the normal deficiencies - a bad plug, coil, injector, vacuum leak, EGR malfunction and, of course, a loose wire. A bad ignitor would normally cause random misfires (P0300 - random misfire) or a no-start condition. A bad computer rarely singles out one cylinder. Vacuum leaks are constant and an EGR problem would more than likely affect more than one cylinder. My suggestion would be to check the connections for the #1 coil and injector. If o.k. check the resistance of the injector, it should be around 10-13 ohms (although most cars run @ 12-16, 10-13 is Subie spec.) If that's o.k. I'd pull the coil and plug and see how they look. If you can't see any problems change the coil and plug with another cylinder, clear the code and watch for the check engine light to return. If it comes back on it should be the same code if injector (or something more of a PITA like a bad wire) or the code for the cylinder with the original #1 coil and plug, indicating a problem with the (drum roll please...) coil or plug.

Good luck!

Judas, Beav. How the crap did my '70 Olds make it to over 230K WITHOUT any computer intervention? I mean not even an Atari was deemed attachable to this primitive V-8. Yes - every 10K demanded a "tune-up". Plugs, points, rotor, & plug wires occasionally. A whoppin' thirty bucks at most. Beam me back, Scotty!

Ron. (Why did I survive to see the 21st century?)

Ron,
Remember the bionic mouse? Were you "taken"?

[Beav]

Originally posted by Ron Mummert




Judas, Beav. How the crap did my '70 Olds make it to over 230K WITHOUT any computer intervention? I mean not even an Atari was deemed attachable to this primitive V-8. Yes - every 10K demanded a "tune-up". Plugs, points, rotor, & plug wires occasionally. A whoppin' thirty bucks at most. Beam me back, Scotty!

Ron. (Why did I survive to see the 21st century?)

This is only a small part of what the computer does. But take it a bit farther on just this one item, the computer also has to be 'smart' enough to know that the idjit driving the car isn't just playing with the gas pedal. Think of how small an increment of time is measured to determine if a misfire occured on one cylinder, let's say at 3000 rpm....

They wouldn't build them this way if we hadn't wanted to pay for them. Clean air has a price. I remember a cartoon years ago that showed a car driving the coast highway. Instead of a smoke cloud coming from the tailpipe there was a spot of clear air. I think it was about eight years ago Saab or Volvo demonstrated their technology in London. The demo vehicle was actually producing cleaner air at the tailpipe than what was going into the engine. Of course it was probably dripping plutonium from the transmission...