CEL and Rough Idle at Stop
08-03-2012, 04:59 AM
#1
CEL and Rough Idle at Stop
Okay guys, I have a bit of a challenge for you, and anyone who can figure this out would be a tremendous help, because I can't find anything that exactly matches my case in the forums.
I drive a 2006, AT. The engine has 105k miles, and recently I've been having some trouble. One day while driving (at high RPM) my CEL came on and started flashing, and remained on. I assumed that meant misfire, as I've seen here in the forums before. A couple days later, I changed the spark plugs (which looked extremely fouled and carboned), the ignition coils, and the spark plug wires. The engine light is still on, and the only noticeable difference in the car is that it doesn't hesitate around 6300-6500 under WOT.
Now for part 2 of the issues. When coming to a stop at a stop light, the engine is very shaky, and the idle will drop for a second to maybe 550-600 and the car will shudder, and return to normal idle. Depending on how long I'm sitting at the light, it can do this once, or many times, and is scary because it acts like it's going to die. The problem appears to only happen when I have the A/C on. With it off, the car stops much, much more smoothly and the extreme bouncing idle doesn't happen. I don't want to think that it's compression loss, because the car accelerates fine, normal 8 sec 0-60 times, and starts up perfectly normal from hot! Hopefully someone can help me out, thanks for reading!
I drive a 2006, AT. The engine has 105k miles, and recently I've been having some trouble. One day while driving (at high RPM) my CEL came on and started flashing, and remained on. I assumed that meant misfire, as I've seen here in the forums before. A couple days later, I changed the spark plugs (which looked extremely fouled and carboned), the ignition coils, and the spark plug wires. The engine light is still on, and the only noticeable difference in the car is that it doesn't hesitate around 6300-6500 under WOT.
Now for part 2 of the issues. When coming to a stop at a stop light, the engine is very shaky, and the idle will drop for a second to maybe 550-600 and the car will shudder, and return to normal idle. Depending on how long I'm sitting at the light, it can do this once, or many times, and is scary because it acts like it's going to die. The problem appears to only happen when I have the A/C on. With it off, the car stops much, much more smoothly and the extreme bouncing idle doesn't happen. I don't want to think that it's compression loss, because the car accelerates fine, normal 8 sec 0-60 times, and starts up perfectly normal from hot! Hopefully someone can help me out, thanks for reading!
Last edited by RIWWP; 08-05-2012 at 08:40 AM. Reason: cleaned up the size change, the bolded text, and added some paragraph breaks
08-03-2012, 06:05 PM
#5
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https://www.rx8club.com/trouble-shoo...h-idle-236385/
for your rough idle i have the same problem but just on the idle part
for your rough idle i have the same problem but just on the idle part
08-05-2012, 08:47 AM
#6
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OP, I removed certain parts of your post. If you recall what you wrote before, you should be able to see what I removed. I highly recommend that you don't post that again. I also removed the universal bold and size change, as it was unnecessary. We can read the post better with the normal text.
Your flashing CEL is a misfire. Not 'might be', not 'maybe', not 'might be something else', a flashing CEL is ALWAYS a misfire.
Misfires can be caused by any of the following:
- 1 or more failing coils (~30,000 mile average lifespan)
- 1 or more failing plug wires (~30,000 mile average lifespan)
- 1 or more fouled or cooked spark plugs (if everything stays clean, they will get fouled when you lose a plug wire or coil, otherwise replacing them 15-20k is often of a benefit)
- vacuum leak
- compression loss
- cat failure
- e-shaft sensor fouling
- MAF failing
- aftermarket intake
- intake screens missing
- intake valving failing (any of the 4 valves)
- grounding problem at the engine block
- grounding problem at the battery
Of these, failing ignition is the most common culprit.
https://www.rx8club.com/rx-8-discuss...t-here-202454/
And moved to troubleshooting.
Your flashing CEL is a misfire. Not 'might be', not 'maybe', not 'might be something else', a flashing CEL is ALWAYS a misfire.
Misfires can be caused by any of the following:
- 1 or more failing coils (~30,000 mile average lifespan)
- 1 or more failing plug wires (~30,000 mile average lifespan)
- 1 or more fouled or cooked spark plugs (if everything stays clean, they will get fouled when you lose a plug wire or coil, otherwise replacing them 15-20k is often of a benefit)
- vacuum leak
- compression loss
- cat failure
- e-shaft sensor fouling
- MAF failing
- aftermarket intake
- intake screens missing
- intake valving failing (any of the 4 valves)
- grounding problem at the engine block
- grounding problem at the battery
Of these, failing ignition is the most common culprit.
https://www.rx8club.com/rx-8-discuss...t-here-202454/
Importance of Ignition Health:
************************ READ THIS!!!! ************************
One of the most often overlooked or ignored parts of RX-8 ownership is the health of the ignition system. This includes the ignition coils, spark plug wires, and spark plugs. They fail. Often. So often as to be critical parts of regular maintenance.
Before I detail why, check out the first post of this thread here: https://www.rx8club.com/series-i-trouble-shooting-95/impact-old-coils-wires-plugs-234383/ (owner's post here: https://www.rx8club.com/showpost.php...&postcount=189)
The owner's power dropped from 199whp to 172whp JUST from failing ignition. That's a 13.5% power loss!
Do I have your attention now? Good.
Mazda officially lists the plug wires and plugs as part of regular maintenance, but not the coils. Many dealers STILL don't know how easily the coils can fail. And they fail about the same time as the wires and plugs, which is about every 30,000 miles. Some can last longer, some shorter, and it's more related to your total RPMs than it is to your mileage. Highway cruising is easier on the coils than spending a day pounding around a race track.
When coils fail, they don't suddenly shut off. They start producing weaker pulses scattered among strong ones. The rate of weak pulses slowly increases and pulses start getting dropped entirely, which is where misfires start. All of this means that you aren't burning all the fuel and aren't using all the air that the engine pulled in for that combustion, and it unburnt fuel and air gets dumped into the exhaust, where it happily ignites with the presence of plenty of heat. This saturates the cat in both fuel and heat, and will rapidly kill the cat (A $1,300 USD replacement). Continuing to drive on a failing cat will add other problems such as engine damage and vehicle fires. I am not exaggerating, this can happen with just a single cat failure!
Plug fouling and wire failure is largely the same result, since all 3 pieces are needed for a complete spark. Foul the plug and it doesn't matter if the coil and wire are good. Break down the wire and it doesn't matter if the coil and plug are good.
Symptoms of ignition failure include: Power Loss, mileage drop, unstable idle, bad idle, inability to idle, shaking at idle, unstable high rpm, misfiring, flashing CEL, coughing engine, glowing cat, flooding, inability to start, inability to pass an emissions sniffer test, and just about anything you can think of where a weak or missing spark causes problems.
And if one fails, it will cascade to the other trio on the same rotor. A plug that can't fire will start fouling the other. A coil that can't fire a plug starts wearing out rapidly (if you want to test this, just unplug a wire from a plug and run the engine for a while. The coil will rapidly fail. Not unique to rotary engines)
Why do coils fail so easily?
This is largely because Mazda opted for cheap coils because of RX-7 owner complaints about how expensive their coils were. The RX-7 coils lasted much longer though. So Mazda went cheap, and so we have to replace regularly. And you can't compare to piston engine coils. A piston engine with the same setup of 1 coil for 1 plug has an average RPM of about 2,500rpm and the coil is firing every other revolution, so the coil is firing about 1,250 pulses per minute. Our rotary has an average RPM of more like 4,000rpm, and each coil fires every revolution, so about 4,000 pulses per minute. That's a bit over 3 times more. Even a piston max RPM of about 6,000rpm vs our 9,000rpm makes the difference 3,000 pulses per minute vs 9,000 pulses per minute, or 3 times as fast.
If our coils would last about 3 times longer, you are talking an average of 90,000 miles.
So keep your ignition healthy!
************************ READ THIS!!!! ************************
One of the most often overlooked or ignored parts of RX-8 ownership is the health of the ignition system. This includes the ignition coils, spark plug wires, and spark plugs. They fail. Often. So often as to be critical parts of regular maintenance.
Before I detail why, check out the first post of this thread here: https://www.rx8club.com/series-i-trouble-shooting-95/impact-old-coils-wires-plugs-234383/ (owner's post here: https://www.rx8club.com/showpost.php...&postcount=189)
The owner's power dropped from 199whp to 172whp JUST from failing ignition. That's a 13.5% power loss!
Do I have your attention now? Good.
Mazda officially lists the plug wires and plugs as part of regular maintenance, but not the coils. Many dealers STILL don't know how easily the coils can fail. And they fail about the same time as the wires and plugs, which is about every 30,000 miles. Some can last longer, some shorter, and it's more related to your total RPMs than it is to your mileage. Highway cruising is easier on the coils than spending a day pounding around a race track.
When coils fail, they don't suddenly shut off. They start producing weaker pulses scattered among strong ones. The rate of weak pulses slowly increases and pulses start getting dropped entirely, which is where misfires start. All of this means that you aren't burning all the fuel and aren't using all the air that the engine pulled in for that combustion, and it unburnt fuel and air gets dumped into the exhaust, where it happily ignites with the presence of plenty of heat. This saturates the cat in both fuel and heat, and will rapidly kill the cat (A $1,300 USD replacement). Continuing to drive on a failing cat will add other problems such as engine damage and vehicle fires. I am not exaggerating, this can happen with just a single cat failure!
Plug fouling and wire failure is largely the same result, since all 3 pieces are needed for a complete spark. Foul the plug and it doesn't matter if the coil and wire are good. Break down the wire and it doesn't matter if the coil and plug are good.
Symptoms of ignition failure include: Power Loss, mileage drop, unstable idle, bad idle, inability to idle, shaking at idle, unstable high rpm, misfiring, flashing CEL, coughing engine, glowing cat, flooding, inability to start, inability to pass an emissions sniffer test, and just about anything you can think of where a weak or missing spark causes problems.
And if one fails, it will cascade to the other trio on the same rotor. A plug that can't fire will start fouling the other. A coil that can't fire a plug starts wearing out rapidly (if you want to test this, just unplug a wire from a plug and run the engine for a while. The coil will rapidly fail. Not unique to rotary engines)
Why do coils fail so easily?
This is largely because Mazda opted for cheap coils because of RX-7 owner complaints about how expensive their coils were. The RX-7 coils lasted much longer though. So Mazda went cheap, and so we have to replace regularly. And you can't compare to piston engine coils. A piston engine with the same setup of 1 coil for 1 plug has an average RPM of about 2,500rpm and the coil is firing every other revolution, so the coil is firing about 1,250 pulses per minute. Our rotary has an average RPM of more like 4,000rpm, and each coil fires every revolution, so about 4,000 pulses per minute. That's a bit over 3 times more. Even a piston max RPM of about 6,000rpm vs our 9,000rpm makes the difference 3,000 pulses per minute vs 9,000 pulses per minute, or 3 times as fast.
If our coils would last about 3 times longer, you are talking an average of 90,000 miles.
So keep your ignition healthy!
And moved to troubleshooting.
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