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Old 10-08-2011   #1
jvb6806
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Miata Misfire Diagnostic

i got a call to take a look at a miata with a random cyl misfire code, i assume P0300, but i will confirm when i get out there tomorrow. owner also says that the car doesn't seem to have the "pep" that it used to. i am not sure if the issue is temperature dependent. i have no idea if the light is flashing under load, but i assume they would have told me that.

it is a 99 10 anniversary edition. it is my understanding that the car was in the shop for some emission related issues in addition to the misfire. the emission codes were addressed and those codes are supposedly gone. my guess is a cat code due to the misfire. after throwing a few parts at the car (plugs, wires, fuel filter) the shop said it would be $700 to replace the ignition coil and that might not even be the problem.

i was doing a little reading and it looks like the 99 & 00 miata's had an issue with the coils. does that sound correct to you guys?

i am going to start with olming out the coil to see where that is at.

if that checks out i was going to move onto the Harmonic Balancer & check the wiring of the Crank Angle Sensor. I am bringing the scope it to make sure the signal is consistent when it is cold & warm. the miata uses a hall effect correct?

i don't have a low amp clamp to check the injector draw, i need to order one next week. i could check the signal to them but my guess is that is off it would be due to the cam angle sensor. does anyone know if the cam angle sensor is hall effect or inductive?

i am going to bring a fuel pressure tester but i am not sure if the miata has a schrader valve.

any other thoughts from the miata crowd? emanual...
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Originally Posted by MoeBawlz
i have an 18hp racecar

Last edited by jvb6806; 10-08-2011 at 11:57 PM.
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Old 10-09-2011   #2
marty
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I had to replace the coilpack on my 99, but I would look at the crank angle sensor first.

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Old 10-09-2011   #3
Agent XY
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If the part you need to replace is

18-10x its only 206.42 through the mazda speed program!
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Old 10-09-2011   #4
jvb6806
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Haha so your guess is the coil pack is dead? I am trying to diagnose instead of throwing parts at it. They have already thrown a fair amount of money into the car.
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Old 10-09-2011   #5
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I think you can only test so much from checking the resistance of the coils. You could just use a spark tester and go through the coils one by one. I have had a set of coils who resistances checked out fine but when put under load failed to spark properly.

I just posted the price as a reference to how ridiculous we already know the dealer is.

Good luck!
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Old 10-10-2011   #6
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fyi, my coil pack would only short when they were wet. the only symptoms i had to go by were that the car wouldn't run if it was raining outside.

how old are the spark plug wires, and are they OEM? OEM wires are supposedly shit on miatas. everyone replaces them with NGK wires.
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Old 10-10-2011   #7
Emanuel
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I'm pretty new to the Miata scene, but so far experienced a couple typical Miata issues on friends cars and the Miatas i worked on.

#1 issue: spark plugs and wires
#2 issue: loose crank pulley due to sloppy installation/messed up key way (originally only the '89/'90 cars, but it makes his comeback on 1.8's again for some reason)
#3 cracked coil pack, being sensitive to moisture.

Other than that there are occasional dirty MAF sensors, vacuum leaks, miss adjusted throttle bodies and bad O2 sensors, causing trouble. One often overlooked result of a bad O2 sensor could be a damaged/molten catalytic converter that reduces the airflow and cause low power.

Also watch out for cheap aftermarket replacement stuff. Except for the plug wires, OEM is better than almost any cheaper option.

hope that helps a little.

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Old 10-26-2011   #8
Emanuel
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So I'm experiencing an issue that seems to get slowly worse. At part throttle and low rpm (1500-1800) and especially from a stop, my car displays some slight hesitation, which is very annoying to me.
At autox, full throttle or in neutral everything is fine. Alex replaced the always problematic ignition wires and plugs in January, I can't believe that they are already bad. Of course it's possible. Everything I found online says ignition wires.

http://www.magnecor.com/magnecor1/truth.htm

I also have from the very beginning the what I call "waving" problem going on. Basically on normal driving and part throttle, the cars power out put is not linear and seems to come in waves. Again it isn't an issue under full load.
So I asked EddieX if I could borrow Dan's MAF from his 1996 Miata, but no change. It also doesn't matter if it is wet or dry outside.

I checked for Vacuum leaks and timing/ loose pulley issues, everything seems to be alright. We cleaned and adjusted the throttle body (that helped a little). No codes.

Any ideas? Aged O2 sensors maybe?

I wonder if I should contact a dyno tune place with experience and the right equipment to see if the can tell me what is wrong.

I'm a little bit at a loss, I never experienced something similar and my resurces are limited. It ruins the fun of driving my car, but I don't want to spend random money and replace things until it's fixed.

Does anybody have equipment to track the engine management under certain conditions?

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Old 10-26-2011   #9
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Quote:
Originally Posted by Emanuel View Post
So I'm experiencing an issue that seems to get slowly worse. At part throttle and low rpm (1500-1800) and especially from a stop, my car displays some slight hesitation, which is very annoying to me.
At autox, full throttle or in neutral everything is fine. Alex replaced the always problematic ignition wires and plugs in January, I can't believe that they are already bad. Of course it's possible. Everything I found online says ignition wires.

http://www.magnecor.com/magnecor1/truth.htm

I also have from the very beginning the what I call "waving" problem going on. Basically on normal driving and part throttle, the cars power out put is not linear and seems to come in waves. Again it isn't an issue under full load.
So I asked EddieX if I could borrow Dan's MAF from his 1996 Miata, but no change. It also doesn't matter if it is wet or dry outside.

I checked for Vacuum leaks and timing/ loose pulley issues, everything seems to be alright. We cleaned and adjusted the throttle body (that helped a little). No codes.

Any ideas? Aged O2 sensors maybe?

I wonder if I should contact a dyno tune place with experience and the right equipment to see if the can tell me what is wrong.

I'm a little bit at a loss, I never experienced something similar and my resurces are limited. It ruins the fun of driving my car, but I don't want to spend random money and replace things until it's fixed.

Does anybody have equipment to track the engine management under certain conditions?

Although I doubt it is the issue, a few guys on miata.net have had similar issues and claim they had bad coils. This activity is usually spawned by wet weather when it is the coils though so I am not sure. Good luck!

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Old 10-26-2011   #10
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Nathan you should have a set of 1.8 coils in your box o crap.
May be worth cecking them.

Cars I've had that have done surging have had a bad tps or bad iac. The miata has a more advanced ecu than those cars though so may be not a cause.
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