06-06-2013, 12:45 AM
Join Date: Sep 2009
Location: Skokie, IL
Total Cats: 4
Need help - 91' NA Starts/Idles fine, but no power on acceleration.
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:
-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.
-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.
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!