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I have a 1990 Mazda mx5 NA6 and over the past two weeks I've noticed that there is hardly any power whatsoever from a stand still. At the lights it takes about 20 seconds at full throttle to get to 3000rpm in first, even worse up a slight incline. However, downhill, the car takes off fine. Also, once I get a run up, the car runs okay, although it could probably run a little bit better due to a few flat spots here and there.

I've replaced the plugs, leads and rear coolant temp sensor with no avail. It seems like it may have the symptoms of a SNC failure from research, but to me, it doesn't seem like the pulley is wobbling.

Is there anything else that could be the cause of the problem? The car is quite difficult to drive at the moment.

CAS or TPS.

I currently have a tps issue that gives me a milder version of your symptoms.
Other than CAS and TPS, could it be ECU?


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Clutch slipping

Is there any way to check to see if it is CAS or TPS issue before I go and buy parts that I wouldn't need?

I don't think my clutch is slipping

Na6 has a small amount of adjustability in the tps. Mark it's position against the tb first, then you could try loosening the 2 bolts (7mm socket), rotate a little, tighten bolts and see if improved. Sorry, I only know the trial by error way.

Re CAS, I'm not sure how to test, maybe resistance or try another CAS.

Clutch, load up in third or forth gear and go up a hill. If she revs fast all if a sudden your clutch is stuffed.

I'm no expert but just wanted to help if I could.


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doubtfull of slipping clutch. if it was slipping is would take 20 milliseconds to hit 3000rpm, not 20 seconds.

does it have a werid exhaust/combustion sounds?

I'll put my money on worn crank shaft keyway AKA SNC failure (which can happen to any B6 or BP engine).
It doesn't have to visibly wobble to be worn.

It has a slight burble when idling.

The only way to be sure of a SNC failure and worn key way would be to open it up, correct?

Thanks heaps for the help so far guys by the way, just want to get the car back to where it was asap. It's doing my head in haha

Yep, you'd need to be able to inspect the keyway.
Try pulling the #1 plug and use a skewer or screwdriver (rest it on top of the piston) to set the engine to TDC. Then check where the crankshaft pulley timing mark is indicating. If it is not at the TDC mark (and not 180 degrees out) then that would be an indication.

jerdes wrote:It has a slight burble when idling.
The only way to be sure of a SNC failure and worn key way would be to open it up, correct?

My old NA6 had a strange hum at idle the morning of the day that it stopped due to SNC failure, but I had to drive a few hundred kms to Sydney that day for a meeting so just had to go.

Removing the crank pulley should allow you to see the condition of the crank nose.

But before doing anything, connecting up & aiming a ignition timing light at the crank pully & engine block ignition timing reference pointer should also highlight pulley movement or wobble if present.

93_Clubman wrote:But before doing anything, connecting up & aiming a ignition timing light at the crank pully & engine block ignition timing reference pointer should also highlight pulley movement or wobble if present.

Good suggestion - but also remember to short the GND and TEN (timing lock) pins on the diag connector. This will tell the ECU to lock timing at 10 deg to ensure the timing doesn't change (as it should) when you rev. This way you'll see if the timing mark changes because of worn crank pulley (and this would be the reason why it is running poorly)

I hope for your sake that it is not a snc issue. Please let us know how you go.


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So I've just checked the timing. TDC is set properly and when the car is running my timing light shows that it is set at 14 degrees.

I'm going to try and disconnect my cat converter and see if that makes a difference at all.

Just removed the cat converter to have a look and it's perfectly in tact. So that crosses that off the list.

Is it still a high chance of SNC failure even though the crankshaft pulley lined up perfectly when at TDC. If so, I have no choice but to pull it apart and have a closer look.

Anyone have any recommendations on the best place to source the necessary parts for the task?