I have an engine miss that just won’t go away. I’ve tried all the reasonable things I can think of. The car is all original, no cuts to the wiring ever. Even the radio harness is intact. It’s a bone stock 1991 Civic LX 5 speed with 306,000 miles.

So so the symptom is this. Under any load, it misses like crazy between 2250-3250 rpm. It drives normally under this range, and if you can get it over, it will still fly at 80 and greater mph down the interstate. The tach dances like crazy during this. It did this a few times, stopped for a few days, and then it became a permanent feature.

Here is is what I’ve replaced:

Distributor, complete. The bearings were shot in the old one. This did not fix anything.
Spark plug wires and spark plugs. No change.
The main cylinder head ground strap. (Engine runs smoother at idle and low speeds, code 20 gone. No change in core symtoms

 

You mentioned the car drove better when you changed one of the ground straps, have you checked your other grounds (particularly thermostat housing).

It's possible for the motor to be running badly and no codes to be showing, as long as the sensors it reads are in range it'll show no problems.

Maybe also check your ignition timing, replace your fuel filter if it hasn't been done for a while and check your pressure regulator is working correctly (check the how to in the workshop manual).

Goodluck! Intermittent issues like this are such a pain. I had a similar intermittent mid range missfire that turned out to be an injector wire that was partially exposed and would occasionally earth on the fuel rail and cause it to hesitate. Took me years to find it.

 

Thanks for the reply. I'm continuing to focus on the grounding issue.

I have ordered a replacement battery-body-transmission ground as mine is in pretty poor shape. To the thermostat I guess this is the infamous 'g101' ground that handles the ECU and many other things? It is in place but pretty gross. While I wait for my ground cable I think I'll go ahead and pull the thermostat, might as well replace it while I'm in there to clean the ground and its mating surface.

Just checked out the pics of your 4-door. Very nice. I'm planning on getting mine resprayed soon and putting some 14" Honda alloys on it. Once upon a time I dreamed of a b-swap but at this point I want to keep this car factory throughout.

 

That fixed it. One of the bolts for the thermostat housing itself was loose, breaking the ground path. Strange that it never leaked coolant in that area.

 

Cheers, yeah there's definitely appeal in keeping these original now. It's getting harder and harder to come by an original example.

Awesome stuff, glad you found it.