Help identifying misfire conditon on 1998 Honda Civic DX

Question

I'm struggling to identify the cause of a misfire condition in my 1998 Honda Civic. It has D16Y7 engine with 185,000 miles on it.

The spark plugs, wires, distributor cap, rotor, and ignition coil were all replaced a year ago when a different misfire condition developed. It has run perfectly even since.

Last week under heavy load (going up a hill on the highway) the engine started losing power and the check engine light started flashing. The codes were

• P0300 - random misfire
• P0301 - misfire cylinder 1
• P0303 - misfire cylinder 3

Naturally, I checked the ignition components first, since they have been problematic in the past.

The spark plugs looked good. Golden brown in color.

Plug wires were good. Resistance within specification and rubber in good condition.

Cap and rotor were clean inside and little wear on the contacts.

Ignition coil was within manufacturer specification.

I turned to the service manual, which provided a troubleshooting chart for DTCs P0300 in combination with any of P0301-P0304. It had different directions for the type of misfire (high rpm, low rpm, etc). I cleared the codes and took the car for a test drive until the check engine light came on again. The misfire seems to occur at low rpm and high load. The codes were again:

• P0300 - random misfire
• P0301 - misfire cylinder 1
• P0303 - misfire cylinder 3

Following this guide, it indicated that the next thing to check was the fuel pressure. I don't have a fuel pressure gauge, but I went ahead and replaced the fuel filter. Next it said to check the ICM (ignition control module or ignitor). The service manual provides no way to test the functionality of this component. It only has a procedure for testing the inputs to the modules and says to replace it if the inputs are normal. Finally, it said to check the valve clearances. I did this and all the valves were within specification.

I'm stumped as to what can be causing this misfire. The fact that cylinder 1 and 3 misfire DTCs came back after clearing the computer makes me think that it is a cylinder specific problem. I don't want to blindly replace components in the hopes that it will fix the problem. What other tests can I do to rule out spark plugs, wires, ICM, or what other problem might cause this to happen?

Answer 1

With that many miles, consider a compression check before going any further, especially since the misfire happens at highway speeds.

Answer 2

It's probably your distributor. Was the replacement aftermarket? If so, I'd bet money it's your distributor.

You would remove the rotor cap and check for corrosion of the contacts and rotor. You said you have done this.

The easiest test is to find a known good distributor (if you live near Dallas, I know someone with several cough me cough)

On these cars, I can't explain why but aftermarket distributors don't work and don't last.

From there (using a known good distributor), you want to work backwards, get a spark plug tester, and test you get a consistent strong spark at each cylinder. You likely won't and can use that information to troubleshoot. The only components in the ignition remaining are the plugs, wires, and timing (from the ECU).