Hi, y'all.
I have a 1993 civic coupe with a d16z6 engine. I've only had the car for half a year or thereabouts, so I don't know a lot about its history. However, I don't think the engine is original.
Anyway, here is my problem. The car will start right up and drive fine for the first 5 or ten minutes. After the engine is warmed up, it idles rough( I've even stalled it a couple times now), and has poor acceleration. It acts as if the fuel gets cut off when I put my foot in it. If I should happen to turn it off or stall it, it won't start again until I've let it cool down for forty-five minutes to an hour. I pulled the injectors out of the intake manifold and watched them as someone turned the engine over. When the engine is warm, the injectors do not squirt near as much fuel as when it has had a chance to cool down. A small stream comes out but not near as much as should come out. I replaced the injectors themselves, so I know that is not the issue.
So here's my question. What would cause the injectors to get poor signal when the engine is warm but work fine when the engine is cool? Faulty sensor or wires somewhere? I'd appreciate any input or guidance on how to diagnose this issue.
Also, I can hear the fuel pump priming as normal and I have good fuel pressure at the injectors, so I believe the main relay is not the issue. According to my understanding the injectors and pump are related to the main relay. My logic is that if the pump is working fine the main relay is probably not the culprit. Please correct me if I'm in error.
Thanks in advance!
Kaleb

 

Does unplugging the O2 sensor prevent the problem?

 

I'm not sure. I could give it a shot. How might that be causing my problem?

 

The ECU uses the signal from the O2 sensor to determine the fuel trim. A bad O2 sensor can make the engine run lean.

 

Alright, should I try taking it on a short drive with the oxygen sensor unplugged?

 

Yep

 

Alright, I think that's it. Thanks for the advice. The issue didn't show up while driving it with the oxygen sensor unplugged. Plugged it back in and the issue came back. Apparently the previous owner spliced the o2 sensor pigtail for some reason. The solder job was awful. I cleaned it up, so we'll see if that fixes it. If not, I'll get a new sensor. Again, thanks for the help.
Kaleb

 

👍

 

So, I got a chance to take the car on a couple longer drives yesterday and today. The problem reoccurred both with the repaired o2 sensor pigtial unplugged and plugged in. Could it possibly still be the O2 sensor? Any other sensors that commonly go out on these Hondas?
One thing puzzled me. I didn't get a check engine light when I unplugged the O2 sensor. Is that normal?

 

Does engine still run properly with the O2 sensor unplugged? Post pictures of the repaired wires. It is also possible that the O2 sensor is bad.

Does the cluster CEL work?

 

Engine ran properly with o2 sensor unplugged. I'll try to get pictures up tomorrow evening. I believe the light works. I've checked for codes before. I didn't verify that this time, though.

 

I should clarify, the engine ran fine without the sensor it was cold. Once it had plenty of time to warm up, the stalling when I give it gas and poor idling come back.

 

I should clarify, the engine ran fine without the sensor it was cold. Once it had plenty of time to warm up, the stalling when I give it gas and poor idling come back.

 

Unplugging the O2 sensor and running the engine should throw an O2 sensor code.

Turn key from Off to ON(II). The CEL should turn on and then off after 2 seconds.

If the CEL works, then check for stored codes in ECU.

 

Alright, I'll check that out as soon as I get a chance. Does the computer use any other sensors to calculate how much fuel to put into the engine?

 

Many, but only the O2 sensor signal is used by the ECU after the engine warms up.

If the CEL works fine and no unexpected codes are thrown, check whether unplugging both the O2 sensor and ECT (engine coolant temp) sensor prevents the problem.

 

Awesome, thanks! I'll check it out.

 

Alright, CEL bulb was burnt out. I replaced it and got codes 6, 41, and 43. My hanes book say those mean coolant temperature, oxygen sensor heater, and fuel supply system oxygen sensor, respectively. I had already run the car with the ECT sensor unplugged at this point. On a test drive with both the ECT and O2 sensors unplugged, the conditions occured like normal after about eight minutes of driving. However, my temperature gauge showed normal temperature. Does the computer have another method of measuring engine temperature? Did I unplug the wrong sensor? I unplugged the one directly below the distributor. On the test drive, the engine was idling around 1,300 or 1,400 rpm as opposed to 900 to 1,000 like normal when it had had time to warm up.
I'm thinking replace the oxygen sensor at this point. I'll be in town this afternoon and could pick one up. Does anyone have a better idea?

 

1) There are two temp sensors under the distributor - a one wire sensor and a two-wire sensor. You want to unplug the two-wire sensor. The one-wire sensor is for the cluster gauge.

2) Clear the three CEL codes from the ECU by removing the hood Back Up fuse for 5 minutes.

3) Reinstall fuse; reconnect all sensors; and drive the car until engine is warmed up.

4) Jump service connector to see which CEL codes return.

5) Post the codes that return.

 

Alright, I replaced the oxygen sensor. I figured a soldered oxygen sensor pigtail is a problem waiting to happen, even if its not causing the problem I have.
So, I cleared the ECU, replaced that sensor, plugged in all the sensors, and took it on a test drive. The hesitation and backfiring when I step on the throttle occur like normal. However, I believe the symptoms were slightly less severe. No CEL for the entire drive. When I got back, there were no codes. When I got it back it idled rough, about the same as before changing the oxygen sensor.
What next?

 

When engine is cold or only after warmed up?

Have you checked the ignition timing with a timing gun?

Unplug the 2-wire ECT sensor under the distributor and take for drive. Problem still evident?

 

Hey, just wanted to give a quick update for anyone else experiencing a similar issue. I took the car into a shop and they diagnosed my issue. They eventually found parts broken and/or missing in the distributor. I replaced the distributor and set the timing and the engine has been running great for several weeks now. Thanks ya'll for the help.