Help low off the line power
11-13-2013, 06:56 PM
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Help low off the line power
Don't know if anybody will see my thread kinda of a pia to wait 30 days but here I go. Just bought an auto rx8 I have many years experience as a tech but not a lot of rotary experience. I have done a lot of reading but many things I've read seems like kids just repeating something they have heard. Lots of posts about how underpowered the 4 ports are. Had a gen 1seven many many years ago and it had quite a bit more power than this 8 off the line. Lots of sea foam ideas and coil solutions. But this car doesn't idle poorly or run rough but power doesn't seem reasonable until 4000. Showing my age here but a k-car would stay with it until 40. I would like to hear from actual mechanics not people who have heard this or the dealer said they did this and it fixed it. The car has sat for quite sometime not turning I put new plugs in it and got it running. It starts a bit hard but this is winter now in Ohio. To me the coils are plausible however I don't see this sort of problem on a piston engine without a misfire. I would also like to convert to ls truck coils as they are know to be heavy duty. Looking for ideas from techs who have actually experiment the problem. I intend to run compression but have read lots of different opinions on rotary compression reading also. Lots of info out there going many different directions.
11-13-2013, 07:00 PM
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I'm not really sure what you are asking? The title implies you are looking for power upgrades, but the post seems to imply you are troubleshooting a problem?
The post doesn't seem to be very clear.
I'd also be curious how you would determine who is qualified to answer your question, considering dealer techs are usually wrong and members here are typically right even though they aren't techs.
The post doesn't seem to be very clear.
I'd also be curious how you would determine who is qualified to answer your question, considering dealer techs are usually wrong and members here are typically right even though they aren't techs.
11-14-2013, 06:48 AM
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Point of argument here to clarify. A dealer tech by all means is a great source of knowlegde and definitely usually accurate. However unless a customer knows somone at the dealer, in many cases what the service writer bills or tells a customer is not always accurate. I have worked as an independent and at a dealer. I have had many cases where my friends will go to the dealer and they will be told somthing that is completely inaccurate by a service writer for billing purposes. Yet when I go talk to my friends who are techs about the cars problems and send the customer back they get completely different treatment these were usually cases where the vehicle was under warrantly and the dealer didn't want to fix the issue. I believe I clearly stated I would like to hear from actual mechanics or indivials who have physically done work on these cars, not just what sombody told them! As again being chastized for putting help in my title description and not following rules here I didn't just post my title as just help it had what I wanted help with. I will read the Rules in more detail next time. Or sell the damn car, this seems like a very nice site with a bunch of bureaucracy The car is very slow off the line and doesn't make power till 5000 rpm. THAT IS THE ISSUE" LOW POWER ON ACCELERATION PLEASE HELP WITH"!!!!!!!!!!!!!!!!!!
Last edited by carman72; 11-14-2013 at 07:05 AM.
11-14-2013, 09:54 AM
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carman,
I didn't once make any comment about whether or not you followed the rules, I am simply trying to understand your question here.
I 100% agree with you about how unreliable information is from a dealer tech. One advantage of a public forum is that if someone tells you something incorrect, other people that know it's incorrect can jump in and make the correction, clarifying the issue. In the case of the RX-8, dealer techs are even more ignorant about the quirks, where as the collective knowledge of millions of miles of driving across a decade here ... we tend to know what the answers are going to be.
Now to your question:
Unfortunately, due to the nature of the rotary, it's still not clear what problem you are trying to solve. Even a 100% completely healthy RX-8 is very slow off the line thanks to basically no torque and 3,000lbs to move, and the engine doesn't start waking up until 4,000rpm, and doesn't really come alive until 5,000rpm. It's power band is from ~5,000rpm to ~8,500rpm, and it's healthy for the engine to be up there.
Take a look at a stock dyno for the torque curve, notice the very low torque at low rpm.
Now, there are still certainly mechanical failures which will make this even worse. For example, engine compression of a rotary increases as the rpm increases, so if the engine is borderline failing compression then it will be weaker at low RPM, but seem more "normal" at higher rpm.
A vacuum leak will cause problems at low RPM far more than high RPM.
Ignition failure isn't really a cause for a low RPM power loss symptom. Ignition failure typically will cause either idle problems or high RPM stumbling.
If you are at full throttle, the O2 sensor and fuel trims are ignored, so those shouldn't be the cause of the problem.
E-shaft sensor (crankshaft sensor) fouled or failure could manifest at any RPM, but it typically will prevent higher RPM usage at all, so that doesn't sound like your problem here.
Catalytic converter failure causes top end power problems, not low.
Primary fuel injector problems could cause low end power loss, either through too much fuel (leaking injector) or too little (not firing or clogged). The secondaries come on at higher RPM, which would help offset the problem.
What are your low RPM AFRs like? It's reported through the CAN BUS, so you should be able to get it with any OBD2 tool that sees live data. Same with your MAF airflow and fuel trims, which can be used to diagnose a vacuum leak.
If all of that checks out, it's likely that either A) there isn't actually a problem and you are just unfamiliar with the rotary, or B) The engine needs a compression test because it's failing.
I didn't once make any comment about whether or not you followed the rules, I am simply trying to understand your question here.
I 100% agree with you about how unreliable information is from a dealer tech. One advantage of a public forum is that if someone tells you something incorrect, other people that know it's incorrect can jump in and make the correction, clarifying the issue. In the case of the RX-8, dealer techs are even more ignorant about the quirks, where as the collective knowledge of millions of miles of driving across a decade here ... we tend to know what the answers are going to be.
Now to your question:
The car is very slow off the line and doesn't make power till 5000 rpm. THAT IS THE ISSUE" LOW POWER ON ACCELERATION PLEASE HELP WITH"!!!!!!!!!!!!!!!!!!
Take a look at a stock dyno for the torque curve, notice the very low torque at low rpm.
Now, there are still certainly mechanical failures which will make this even worse. For example, engine compression of a rotary increases as the rpm increases, so if the engine is borderline failing compression then it will be weaker at low RPM, but seem more "normal" at higher rpm.
A vacuum leak will cause problems at low RPM far more than high RPM.
Ignition failure isn't really a cause for a low RPM power loss symptom. Ignition failure typically will cause either idle problems or high RPM stumbling.
If you are at full throttle, the O2 sensor and fuel trims are ignored, so those shouldn't be the cause of the problem.
E-shaft sensor (crankshaft sensor) fouled or failure could manifest at any RPM, but it typically will prevent higher RPM usage at all, so that doesn't sound like your problem here.
Catalytic converter failure causes top end power problems, not low.
Primary fuel injector problems could cause low end power loss, either through too much fuel (leaking injector) or too little (not firing or clogged). The secondaries come on at higher RPM, which would help offset the problem.
What are your low RPM AFRs like? It's reported through the CAN BUS, so you should be able to get it with any OBD2 tool that sees live data. Same with your MAF airflow and fuel trims, which can be used to diagnose a vacuum leak.
If all of that checks out, it's likely that either A) there isn't actually a problem and you are just unfamiliar with the rotary, or B) The engine needs a compression test because it's failing.
11-14-2013, 10:46 AM
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Yes all of this is agreed. I don't feel it is an igniton or an exhaust flow problem. Car idles fine has no codes. I will look at fuel trim. Car does start hard. I will run compression but not feeling thats the issue car runs smooth. Just very very sluggish off the line, possible its nature. As I said 20 years ago I occasional drove an 85 rx7 it was much more powerful than this car, and yes I understand lighter. At this point I need to test drive other lower mileage cars to see what their performance is like. Many on this forum are stating bad coils could cause this issue, but it goes against most of what I know on a piston engine. There are some on the forum that state that if one of the coils fail you may not notice misfire, however power loss will be possible being that there are leading and trailing coils? Many have stated they have had this similar issue and replaced the coils. However no one seems to have any specs for ohming good or bad coils. They just say at certain mileage they are bad and replace them.
Last edited by carman72; 11-14-2013 at 10:53 AM.
11-14-2013, 11:08 AM
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Correct, there is a lot of conventional piston wisdom diagnosis points that you have to set aside for this car.
More starting trouble when hot than when cold is one of the only symptoms that is unique to low compression (one exception below). Every other symptom of ignition failure is shared by at least 1 other failure method, and several of the symptoms are shared by several failure methods.
Regarding coils:
Keep in mind that the average piston engine waste spark coil is firing once for every revolution of the crankshaft. A coil on plug setup is firing once for every other revolution of the crankshaft. So a waste spark ignition piston engine car with a 6,000rpm red line is firing 6,000 times per minute, and probably lives it's life with an average of 3,000 times per minute. A coil on plug ignition setup on the same engine drops this to 3,000 times per minute at peak, 1,500 times per minute on the average cruise.
By comparison, each coil on the RX-8 fires3 times for every revolution of the driveshaft, for a peak rate of 27,000 times per minute at redline. The rotary even cruises at higher RPM, so the average cruise is still firing at around 12,000 times per minute. So from the firing rate alone, you can see one of the core reasons why our ignition doesn't last long. It would last longer with better coils, but even better coils are firing significantly more than on a piston engine.
Mazda does have an ohm test to test the coils, but frankly, it is completely worthless. A coil that is causing misfires can still pass the official ohm test. This has been proven multiple times. The reason is because the ohm test doesn't test the igniter, which is what fails in the coils. The better two methods to test coils is with a timing light and/or a coil tester like this:
The majority of owners simply have no inclination or ability to test coils however, and when symptoms show up we recommend replacing them all to make sure they get the bad one. Replacing 1 is still an option, though you have to keep in mind that the others are probably nearing failure anyway, so you can save a fair amount of labor by replacing them all at once. You are also minimizing the chance of cascading cat/O2/engine failure by replacing them all, rather than running that gauntlet 4 times as often by replacing the coils one at a time.
The original coil revision typically had it's first failure in the range of 30,000 miles. More recent coils probably last longer, but there is zero conclusive evidence to back this up yet. Considering how cheap coils are (~$30-35 each), and how expensive the cost of cascading failures is ($1,300 for a cat, $4,000+ for an engine, $250 for the front O2 sensor), it is simply a best practice to replace them all every 30k, even if you haven't had a failure yet. It's similar to waiting to replace tires when the tread gets low rather than waiting to replace them one at a time when they blow from running on cords.
Regarding the misfires:
The ECU doesn't always recognize misfires, and even if it does, it may not throw a CEL (Solid or flashing) for the misfire. The mode 6 test results show the stored misfire count however, for the misfires the ECU detected. I've seen misfire counts in the thousands from members that didn't yet know that the ignition was failing.
More starting trouble when hot than when cold is one of the only symptoms that is unique to low compression (one exception below). Every other symptom of ignition failure is shared by at least 1 other failure method, and several of the symptoms are shared by several failure methods.
Regarding coils:
Keep in mind that the average piston engine waste spark coil is firing once for every revolution of the crankshaft. A coil on plug setup is firing once for every other revolution of the crankshaft. So a waste spark ignition piston engine car with a 6,000rpm red line is firing 6,000 times per minute, and probably lives it's life with an average of 3,000 times per minute. A coil on plug ignition setup on the same engine drops this to 3,000 times per minute at peak, 1,500 times per minute on the average cruise.
By comparison, each coil on the RX-8 fires3 times for every revolution of the driveshaft, for a peak rate of 27,000 times per minute at redline. The rotary even cruises at higher RPM, so the average cruise is still firing at around 12,000 times per minute. So from the firing rate alone, you can see one of the core reasons why our ignition doesn't last long. It would last longer with better coils, but even better coils are firing significantly more than on a piston engine.
Mazda does have an ohm test to test the coils, but frankly, it is completely worthless. A coil that is causing misfires can still pass the official ohm test. This has been proven multiple times. The reason is because the ohm test doesn't test the igniter, which is what fails in the coils. The better two methods to test coils is with a timing light and/or a coil tester like this:
The majority of owners simply have no inclination or ability to test coils however, and when symptoms show up we recommend replacing them all to make sure they get the bad one. Replacing 1 is still an option, though you have to keep in mind that the others are probably nearing failure anyway, so you can save a fair amount of labor by replacing them all at once. You are also minimizing the chance of cascading cat/O2/engine failure by replacing them all, rather than running that gauntlet 4 times as often by replacing the coils one at a time.
The original coil revision typically had it's first failure in the range of 30,000 miles. More recent coils probably last longer, but there is zero conclusive evidence to back this up yet. Considering how cheap coils are (~$30-35 each), and how expensive the cost of cascading failures is ($1,300 for a cat, $4,000+ for an engine, $250 for the front O2 sensor), it is simply a best practice to replace them all every 30k, even if you haven't had a failure yet. It's similar to waiting to replace tires when the tread gets low rather than waiting to replace them one at a time when they blow from running on cords.
Regarding the misfires:
The ECU doesn't always recognize misfires, and even if it does, it may not throw a CEL (Solid or flashing) for the misfire. The mode 6 test results show the stored misfire count however, for the misfires the ECU detected. I've seen misfire counts in the thousands from members that didn't yet know that the ignition was failing.
11-14-2013, 11:43 AM
#8
By comparison, each coil on the RX-8 fires3 times for every revolution of the driveshaft, for a peak rate of 27,000 times per minute at redline. The rotary even cruises at higher RPM, so the average cruise is still firing at around 12,000 times per minute. So from the firing rate alone, you can see one of the core reasons why our ignition doesn't last long. It would last longer with better coils, but even better coils are firing significantly more than on a piston engine.
And BAH-ZING-GHA
Yes I'm getting a room
11-15-2013, 10:16 AM
#9
Driving my unreliable rx8
By comparison, each coil on the RX-8 fires3 times for every revolution of the driveshaft, for a peak rate of 27,000 times per minute at redline. The rotary even cruises at higher RPM, so the average cruise is still firing at around 12,000 times per minute. So from the firing rate alone, you can see one of the core reasons why our ignition doesn't last long. It would last longer with better coils, but even better coils are firing significantly more than on a piston engine.
11-15-2013, 10:31 AM
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Yes, you are right. I was thinking "But the coil still fires on each of the 3 faces", but I just watched the animation again, and I see that my numbers are incorrect. Thanks for pointing this out.
So the correct math is actually the same coil firing rate as a waste-spark piston ignition system, at 1 spark per revolution. The other point of the rotary living at a higher RPM average is still a key factor, just not to the degree I originally stated.
Gravey, it makes all the difference. Watch the e-shaft vs the face against the spark plugs:
So the correct math is actually the same coil firing rate as a waste-spark piston ignition system, at 1 spark per revolution. The other point of the rotary living at a higher RPM average is still a key factor, just not to the degree I originally stated.
Gravey, it makes all the difference. Watch the e-shaft vs the face against the spark plugs:
11-16-2013, 06:12 AM
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Ok so a normal waste spark system fires twice for ever rotation of the crankshaft(tdc compression and tdc exhaust) the rotary according to the video appears the same. Other than high revs minute why are they failing? Motorcycles have coils and are running 9000 all day long no coil failures in this proportion. Is there any data on the ls coils and how they hold up? They are know to be robust and in the ls racing world truck coils do great.
11-16-2013, 08:01 AM
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Top dead center compression to top dead center exhaust is 1 rotation, not half a rotation.
Heat is another problem carman. Limited airflow around the coils which are set against a very hot engine. Motorcycles have significantly more airflow and significant lower average mileage.
The BHR ignition is the primary upgrade that people go to, for which there really isn't any data about how long they hold up, because other than a less than 1% random failure rate, they appear to hold up for longer than anyone has had them. They are priced accordingly of course, and the "break even" point on cost is approximately 100,000 miles. They are better all around though, with a far more stable spark.
Heat is another problem carman. Limited airflow around the coils which are set against a very hot engine. Motorcycles have significantly more airflow and significant lower average mileage.
The BHR ignition is the primary upgrade that people go to, for which there really isn't any data about how long they hold up, because other than a less than 1% random failure rate, they appear to hold up for longer than anyone has had them. They are priced accordingly of course, and the "break even" point on cost is approximately 100,000 miles. They are better all around though, with a far more stable spark.
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