91 honda civic EF engine check light on because of Speedo?

I recently purchased a 1991 EF 4-speed. I have put around 400 miles on it. Really amazed by the gas mileage. I got 33MPG, mainly highway. It may seem to be nothing to Honda veteran, but I'm really impressed for what this old machine can do.

I put on a new muffler, old one is rusty and leaking. I adjusted throttle cable, it was too tight which led to high and fluctuating idle… I also cleaned the throttle body… It runs fantastic…

The problems…

1. It has loud noise from valve train (maybe?)… Is it normal for Honda? Maybe just the valve clearance? Or distributor?

2. While I was driving along highway, the ECL on and I notice that the Speedo quit working. (It was working when I purchased it)… Is the ECL related to the speedo? I have seen some vehicles with no speedo but still would not trigger ECL… I drove about 100miles on highway after this problem occurred… Not a lot of feel in power loss, water temp remain the same… Will Autozone be able to read the code, considering this is an old vehicle with OBD-I (I guess) ?

Yes if the speedometer is quit working. Guessing the code is 17. This will help you to retrieve the code on any Honda OBD 1 vehicle: Let us know what code you have,

and the code definition:
http://www.decepticonracing.com/articles/honda-engine-codes-88-91-civic.php

Most likely it will be the VSS (Vehicle Speed Sensor) that is at fault. The VSS is cable driven and connect to the speedometer head unit behind the dash cluster. The cluster has to be send out for repair if the head unit is defected. From 92 and newer Civic models has an electrical VSS. Yours is cable driven and A/T VSS is differ from M/T.

The VSS: The speed sensor is located on the top of the transmission, stand near the driver fender and look down into the engine bay near the rear of the engine. That is where it is located.

Years ago, I used to buy just a VSS rebuild kit at the dealer, but now, I replace the whole thing due to car in the same era getting older and the driven gear has worn out. Here is how to check:

The cable, unless it broke in half or snap out of the VSS (Make the needle quit working) most of the time the needle is bouncing because the cable is dried out, some remove it to lubricate but I prefer to replace it:
How to replace the VSS: This is for an electrical VSS, cable driven VSS is the same procedure:

The speedometer head: Just send the whole cluster out to this address. This is the link:
www.speedometer.org

A tread for you to read: A minor detail that people has missed when work with the cable:
http://www.civicforums.com/forums/184-1st-5th-gen/319450-1991-civic-vehicle-speed-sensor-code-17-problem.html

About the "loud" noise, it could be in the timing belt area. How many miles on the engine? Have an inspection on the belt and let me know. I can send the information, video how to replace it if you need it.

Valves train do not make loud noise but it is good to have the valve adjustment if it's ticking, the valves could be too tight and may "recess" onto the valve seats and you'll have major problem. Hope I have given to you enough information to see what you looking at. HTH.

Edit: If you need more information e mail me. HTH

Pretty sure your 91 should be obd-0. Autozone wouldn't be able to use a scanner on it.