All right, I have a Honda Civic 91, and it will not start unless the check engine light turns off. This can take up to 30 minutes of time sometimes. There always is a click before it turns off. I have already replaced the Main Relay. Two days ago after a lot of rain, the car exhibited some not usual noises as I waited for the check engine light to turn off (this is when I tried to start the car). After about an hour I finally was able to start it. 15 minutes into the drive the check engine light turned on and the car idled to a stop. I was able to restart it right away after pulling over. This happened twice. Since then the check engine light is taking longer to turn off, and now I haven't been able to get it off in over a day now. Please help, I need this car to drive to school and I can't afford to get rid of it.

Diagnosis and Recommendation:

I suspect your ECM (computer) is bad. I'm more than 90% certain of this. When it's failing, the Check Engine Light will not go out and the car won't start. Presently, you are experiencing intermittent failure--shortly, it won't work at all. It's not uncommon on older Hondas for this to happen. This is the most difficult problem for Honda owners to diagnose and solve. Without positive proof, most people will not suspect, let alone replace, their computer. Many Hondas have gone to the salvage yard, due to the inability to properly diagnose this problem. Do not continue driving your Civic, without fixing this problem. It's a major safety risk that could threaten your life.

Perform the K-Test below:

K-Test: Remove the MAP Sensor connector and turn the ignition switch to ON (Position II). Using a multimeter, check for 5 volts going between the MAP Sensor connector's reference wire (+) and ground. As you look at the connector, this is the socket on the right. Really press the black test lead into a cleaned main ECM ground on the thermostat housing. If the voltage is low, it's probably indicating ECM failure. Most failed ECMs will record a fraction of a volt. To me, the K-Test is simple, elegant, and accurate.

For around $260, you can replace it with a remanufactured Cardone ECM from O'Reilly Auto Parts, which comes with a lifetime warranty. Honda wants around $1,000, with only a 1-year warranty. You might find one on EBay for around $120.

Here's how to replace it yourself:

https://www.askmehelpdesk.com/cars-t...tml#post235038

If the K-Test confirms the ECM is bad, remove it from the car. It will have a clearly marked part number sticker on it. Then, buy a replacement for that exact part number. You could have your car back on the road in less than 1 hour and save yourself $1,400+. It's unbelievable what they charge for ECM diagnostic and repair service. In many cases, they still don't get it right.

Should you prefer, perform the tests, outlined in Sections A and B, below:

https://www.askmehelpdesk.com/cars-t...das-46563.html

Here is a partial list of other people, who have used the K-Test to identify failing ECMs:

https://www.askmehelpdesk.com/cars-t...ht=k-test+poll

K-Test Poll results are offered for reassurance and hope.

The unusual noises you heard were from the main relay. This happens when the ECM is failing. The ECM controls the main relay, through grounding Terminal 8, and when it's failing the relay goes berserk. There is a remote chance that the only problem is the main ECM ground (3-wire brass connector), located on the thermostat housing, needs cleaning with #240 abrasive cloth. This is only a possibility, if the ECM passes the K-Test.

Here's what the ECM looks like and costs at Advance Auto Parts:

While we find your parts, please enter your ZIP Code at PartsAmerica.com

The recommended preventive maintenance items below will help your Civic get you through school and beyond:

https://www.askmehelpdesk.com/cars-t...tml#post219991

A well-maintained Civic will go 350,000 miles.