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Old 06-06-2013, 01:45 AM   #1
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Default Need help - 91' NA Starts/Idles fine, but no power on acceleration.

Hi everyone,

I just picked up my second miata (91’ NA) today with 259000 miles on it. The car starts and idles extremely smooth and great, no smoking on startup, quiet. However, there are several issues that I could use some advice in diagnosing:

Situation

-Previous owner advertised the miata as having a spun bearing. However, after seeing videos of miatas with spun bearings, it doesn’t really sound like that. It has more of a supercharger type whine to it coming from the firewall side of the engine.
-He also mentioned that the engine was rebuilt at some point. The engine bay looks clean and everything appears to be wired up very well.
-Owner said that the car ran and drove fine throughout the 3 weeks he owned it, however yesterday when he dumped the clutch at around 2000-2500, the whirring sound and loss of power began to occur. He assumed he spun a bearing based on the sound it made. It’s important to mention that he’s an 18 year old kid that has no experience with Miatas.

Symptoms

-When it comes to acceleration, it has a very large loss in power to the point where you can only get to about 40 mph initially, then quickly digress down to 30mph, then 15mph, then hardly even moving. The previous owner attempted to deliver it 9 miles to me but only made it about halfway before the car was barely getting going from the stoplight. The car had to get towed to my apartment complex, and when it arrived about 20 minutes later, the car was able to drive slowly (~15 mph) up my garage with relative ease. He said it was much worse at the time they decided to stop, but for whatever reason improved while it was off for 20 minutes.
-Another thing I noticed is that when the car hits about 2000 rpm, you can hear a whirring noise coming from what sounds like the firewall side of the engine. It gets a bit louder as the car loses power.
-You can also hear rattling, but upon inspecting underneath the car I noticed that the cat is bolted up very loosely to the catback on only one side of the flange so it could possibly be that.
-Clutch pedal feels like a brake pedal with rotors that need replacing – it pulsates.

Theories/Diagnosing

Based off what I’ve read, first things to do are:
-Change spark plug wires/spark plugs. The wires on top of the block are black – were those the OEM spark plug wire colors?
-Change fuel filter
-Check cat to see if its clogged – not sure how to do that
-Check timing belt/tensioner/idler pulley for overtightening.

Anything else you guys would recommend? Thoughts as to what it could possibly be? I have a 97 NA so I’m not used to working with OBD-I and the AFM on the earlier NAs, so I’m not too sure what other things I should be checking. I'd be more than happy to try and get pictures/videos if needed.

Thanks everyone for your time!

-Kris
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Old 06-06-2013, 10:17 PM   #2
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Pulsating clutch pedal?!?

Began with a clutch dump?

Time to check the flywheel and clutch. Sounds like something is seriously wrong there and it probably slips like crazy as it heats up.
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Old 06-06-2013, 10:45 PM   #3
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Quote:
Originally Posted by hornetball View Post
Pulsating clutch pedal?!?

Began with a clutch dump?

Time to check the flywheel and clutch. Sounds like something is seriously wrong there and it probably slips like crazy as it heats up.
That's what I thought at first too, and it probably does need replacing sooner than later. But if the acceleration problem were really the clutch, the RPMs would be climbing while the car's actual speed wouldn't. Or at the very least, a higher rate that's unproportional to the car's increase in speed.

In this case, the car itself simply feels dead & lethargic as you accelerate up to 2-3k RPMs. Once it passes about 2k RPM you hear a whistling/squealing noise coming from the front of the car that's proportional to the car's RPMs.

Before doing anything too invasive, I think I might first see if the cat is clogged and the exhaust backpressure is what is causing the noise. If you take a look at the video below, the sound I'm getting isn't nearly as bad as this guys (in fact, the car sounds completely normal at idle). But once I start accelerating and as the car warms up, you hear a similar squeal.


ALSO..I forgot to mention that at the time the car started acting up, apart from the squealing noise he also heard rattling that wasn't there before the incident. I can hear the rattling myself as well and it sounds like a heat shield, which is also one of the reasons why I wanted to check the cat first.
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Old 06-06-2013, 11:37 PM   #4
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The whine is most likely a throw out bearing that's going bad, or has gone bad.

The loss of power is most likely an improperly timed engine. Before tearing the front of the engine apart to look at the timing belt, check the CAS to make sure it's snug, then check the timing with a timing light.

Fix the timing first, then move on to a clutch job.
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Old 06-07-2013, 12:30 AM   #5
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Here's a video of the noise. Turns out it was more of a squeal than a whine. If you listen to the video with the bad catalytic converter above and the video I just took, it sounds almost exactly the same. Sorry its dark, but video was taken by the headers and the back of the block near the coilpack.


I can check the timing too sometime this weekend. Correct me if I'm wrong, but couldn't a clogged catalytic converter throw off the timing since the exhaust gases aren't being relieved from the system?
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