I have noticed my car dropping off power at high rpm. I had my car dyno'd and the power goes flat at 7000rpm and starts falling off over 8000. It is a 2005 8, 6spd manual, has all maintenance and recalls done. I have about 40,000miles.

Many people have suggested the coils have gone bad, and the dealership refuses to touch my car. Is there any way to tell they have gone bad on my own?

Thanks,
Juergen

 

get your hands on an inductive pick-up timing light. hook up the lead on each of your plug wires individually and pull the trigger. you should see a nice steady even strobe pulse. if it blacks out or looks uneven in any way you probably have a coil failure. that method works great for me so far.

test all through your rpm range and under load(while driving) if possible

 

Where the heck would you get one of those lights?

 

auto zone, advance.... sears. just about any auto parts store thats got more than just oil and filters in it

 

You can check your coils with a plain old multimeter. Just pull them and check the resistance over the prongs. Use this link for knowing which posts to check and the resistnaces

 

resistance checks are fine and good for finding a coil that is just open or shorted all the time. not really for one that is breaking up under load. load testing it with the timing light hooked up will show the actual spark coming out of the coil every time it fires

 

First, why would you go through all that trouble when you can just check a resistance or four. Second, I would bet my third ******** that more than one coil is bad, as it is exactly the right mileage for this to happen. For this, you dont need a induction lamp. Finally, as I understand these coils, you may see a flash from the lamp even when the coil is failing. Meaning, if you were not informed, you would conclude that the coils are fine, yet they were toast.

I stand by the Mazda Service Manual as for the correct way to check the coils.

 

you can believe what you choose... but ive worked on way too many electrical circuits where the resistances checked fine but a wiring problem still existed. thats why you load test the circuit to make sure it is operational and able to carry electrical loads. service manuals have their uses, procedural things, key programming, pin locations on connectors and giving parameters for dtc's. but as a solid diagnostic procedure that will yield a correct diagnosis everytime... they wont. ive seen way too many tech's follow the flowchart diag to a conclusion and its wrong. so ill stand by my methods that have worked so well for me for the past 7 years and continue to "fix it right the first time"

 

Get new plugs. You'll get your top end back. like me

 

Fine, fine, fine. you are right. When I check my new coils in 30k miles and the resistances check out, I will remember this and ask myself wheather or not I should go out and buy an inductive lamp.

But I will still check the resistances first, then consider the lamp.

 

Not that simple. I changed my plugs, but this didn't fix the issue until I changed the coils.

 

Agreed!
My car's coils 'tested fine, within spec' - yet all four looked 'melted' and were replaced after I kept bitching. With the new coils and a new cat, my car runs 60-100hp BETTER. Literally.

 

I have 2 sets of coils, old ones all 4 fails the resistance test, but give sparks anyway. Also I purchased a set of new coils, resistance test failed to all these 4 new ones as well, but the car works fine no problem at all.

 

damn, I threw out my old timing gun about a year ago. Didn't plan on driving any more "antiques"

 

Even the Mazda manual has a use for ignition timing lights; to verify that the base timing is correct. What made you think only antiques use inductive lights?

Juergen, might there be a reason that the dealer refuses to deal with the car? I am curious about that because the power loss issue may be caused by two things that were mentioned in a previous post. The ignition coils have been prone to failure. This places an additional stress on the catalytic converter, which causes cat failure. The failure then leads to a clogged cat and loss of power. If the engine gradually loses power at lower and lower rpms, you can be assured that the cat is bad. The exhaust/emissions systems are regulated by the federal government, wherever you are, and that is one area the dealer will pay attention to because they could suffer seriously if they refused to service an emissions problem. You may want to remind them of that liability they carry.

 

Well I have an RP midpipe with cat in the garage about to go on the car, so I will check my stock cat when I pull it off.

MY dealer refuses to diagnose and warranty the problem because I have the RB intake, exhaust, and guage pod. We don't have an equivalent to the Magnussen-Moss act in canada.

How do the coils come off? I unplugged the plug wires, and electrical connection, but the coild are mounted using a 9 or 10mm bolt is this correct?

Thanks again,
Juergen

 

yes, one 10mm

 

Your right- it's a good tool to have around, i was going to mention to some of the less aged forum members that u used to have to adjust the timing on all cars using a simple $40 timing gun. But Oh Well, those were the days .

 

Yep I agree you have to test the electrical circuit under load.

That's been my experience for over 20 years.

 

how to test coils under load ?

 

The timing light thing is somewhat useful, but a coil might still put out enough zap to trip the light and fire the plug, but at a significantly lower voltage than optimal.
A good coil might even fail the FSM test and a bad one might pass.
Really, the only good test for bad coils is to swap them out.

 

haha, that's optimistic... There is no cheap way, just buying a new one and butt-dynoing...

 

using scanner to check misfire monitor results - could indicate faulty coils ?

 

the most foolproof way would probably be to buy an oscilloscope and measure the coil output directly

 

bingo