Engine running crappy, multiple CEL's, simple though elusive fix
Thread Starter
Honorary Member
Joined: May 2001
Posts: 2,121
Likes: 3
From: Indian Land SC
Engine running crappy, multiple CEL's, simple though elusive fix
Just thought I'd share this in case anyone else has a similar problem.
Background - last Nov. the car broke a plug (internally) which scratched the cylinder wall and broke an exhaust valve in #1. Cylinder damage was barely detectable so I had a complete valve job done and the out of town dealer put it back together. This is an SC car with 100k miles and a bad secondary O2 sensor heater, so it shows a CEL all the time.
The real problem - The car ran fine for 2k miles after the valve job and then started occassionally hesitating on light off-idle accelleration. Ran perfect all other times.
Then it started misfiring some at idle and off-idle, but again ran great at WOT or steady-state Interstate cruising. At this point I jumped out the Service Check Lead to see if any new codes were logged and got a blink code of 1 (no longs, 1 short) which translates to "high or low voltage on primary O2 sensor". So I check the sensor voltage and sure enough it's 3.7 volts which is way high.
So I buy a new sensor, install it, reset the ECM, and the car still runs like crap. But at least the O2 voltage is back in range, though it is low (never above .5 volts). Hmmmm. So I check for blink codes again and nothing new shows up.
The car's condition quickly degenerates into serious misfire and poor running. At 3500-4000 rpm, steady state, it runs fine, but any other condition it barely runs. I mean, I can't keep up with traffic pulling away from a red light. At idle it alternates between misfiring and knocking.
Now, the CEL indicates 7-3, misfire on #3. So I swap plugs (#3 & #2) and swap coils (#3 with #4), hoping the misfire moves to another cylinder and points to the problem. I reset the ECM and drive it some more. The next CEL is 7-4, misfire on #4. "AH-HA!", I exclaim, "It must be the coil that is bad." This is where I should have stopped, bought a coil, and lived happily ever after.
But to prove it to myself I decide to swap the coils from #4 and #1, expecting the problem to move to #1. Guess what? I get a misfire code on #2, not #1 as I expected. I keep driving it and eventually get a misfire code on #1, but it's accompanied by a misfire code on #3. And the car is really hard to drive now, worse than it was with the busted exhaust valve two months ago, so I give up playing backyard mechanic and take it to the dealer.
They call me later that day and report they've found the problem - a bad coil on (you guessed it) #1 cylinder. $85 (1 hour labor) for the troubleshooting, $95 for the coil, and $85 to install it. Not bad, at least they diagnosed it correctly in only one hour, but if I had a little more faith in myself I would have saved $170.
So the lessons learned are as follows:
1. Trust my own ability
2. One bad coil can REALLY mess with how this car runs.
PS - A while back I installed a dash switch to jump out the Service Check Lead, which is very handy. The interesting part is that the blink codes operate while the car is running. If I'm driving with no CEL, then see the CEL come ON, I can press the switch and it blinks out the code while I'm driving. I was surprised it worked this way because the book tells you to jump out the Service Check Lead with the ignition OFF, then turn the ignition ON to get the code.
.
Background - last Nov. the car broke a plug (internally) which scratched the cylinder wall and broke an exhaust valve in #1. Cylinder damage was barely detectable so I had a complete valve job done and the out of town dealer put it back together. This is an SC car with 100k miles and a bad secondary O2 sensor heater, so it shows a CEL all the time.
The real problem - The car ran fine for 2k miles after the valve job and then started occassionally hesitating on light off-idle accelleration. Ran perfect all other times.
Then it started misfiring some at idle and off-idle, but again ran great at WOT or steady-state Interstate cruising. At this point I jumped out the Service Check Lead to see if any new codes were logged and got a blink code of 1 (no longs, 1 short) which translates to "high or low voltage on primary O2 sensor". So I check the sensor voltage and sure enough it's 3.7 volts which is way high.
So I buy a new sensor, install it, reset the ECM, and the car still runs like crap. But at least the O2 voltage is back in range, though it is low (never above .5 volts). Hmmmm. So I check for blink codes again and nothing new shows up.
The car's condition quickly degenerates into serious misfire and poor running. At 3500-4000 rpm, steady state, it runs fine, but any other condition it barely runs. I mean, I can't keep up with traffic pulling away from a red light. At idle it alternates between misfiring and knocking.
Now, the CEL indicates 7-3, misfire on #3. So I swap plugs (#3 & #2) and swap coils (#3 with #4), hoping the misfire moves to another cylinder and points to the problem. I reset the ECM and drive it some more. The next CEL is 7-4, misfire on #4. "AH-HA!", I exclaim, "It must be the coil that is bad." This is where I should have stopped, bought a coil, and lived happily ever after.
But to prove it to myself I decide to swap the coils from #4 and #1, expecting the problem to move to #1. Guess what? I get a misfire code on #2, not #1 as I expected. I keep driving it and eventually get a misfire code on #1, but it's accompanied by a misfire code on #3. And the car is really hard to drive now, worse than it was with the busted exhaust valve two months ago, so I give up playing backyard mechanic and take it to the dealer.
They call me later that day and report they've found the problem - a bad coil on (you guessed it) #1 cylinder. $85 (1 hour labor) for the troubleshooting, $95 for the coil, and $85 to install it. Not bad, at least they diagnosed it correctly in only one hour, but if I had a little more faith in myself I would have saved $170.
So the lessons learned are as follows:
1. Trust my own ability
2. One bad coil can REALLY mess with how this car runs.
PS - A while back I installed a dash switch to jump out the Service Check Lead, which is very handy. The interesting part is that the blink codes operate while the car is running. If I'm driving with no CEL, then see the CEL come ON, I can press the switch and it blinks out the code while I'm driving. I was surprised it worked this way because the book tells you to jump out the Service Check Lead with the ignition OFF, then turn the ignition ON to get the code.
.
Joined: Jan 2001
Posts: 3,290
Likes: 14
From: Atlanta
Looks like your not alone, check this link:
http://forums.s2ki.com/forums/showthread.p...threadid=173990
http://forums.s2ki.com/forums/showthread.p...threadid=173990
Thread Starter
Honorary Member
Joined: May 2001
Posts: 2,121
Likes: 3
From: Indian Land SC
In the interest of further educating of my fellow S2k members, I have added another page to the now-nearly-famous Modifry S2000 Web Site.
I have posted clear (to me at 11PM on 4 hours sleep) instructions for putting the ECM into diagnostic mode so you can read the 'blink codes'. I also posted a list of the blink codes I have compiled so far. Go here for all the gory details.
Anybody have a bigger list of blink codes?
.
I have posted clear (to me at 11PM on 4 hours sleep) instructions for putting the ECM into diagnostic mode so you can read the 'blink codes'. I also posted a list of the blink codes I have compiled so far. Go here for all the gory details.
Anybody have a bigger list of blink codes?
.
