Engine Performance problem
1994 Honda Civic 4 cyl Front Wheel Drive Manual 178000 miles
Thank you for your time. My Civic has 178K miles on it. When the engine is cold, especially in the mornings, it has plenty of power and response. On a hot afternoon, after sitting in the sun, it's a little less power. The main symptom is almost exactly 8 minutes into my drive, the idle goes down (from 800 to 550 roughly), the engine gets noisier (valve sounding, I think), and I lose a significant amount of power. The idle change is well past the FITV stage, and a good 5 minutes past the engine being brought up to operating temperature. Based on my fuel gauge being much higher (2/3 full) than it usually is after 160miles on this tank, I'm guessing it's running lean, or that the timing is off. If I stop the car, wait five minutes, and start it again, the problem persists. So, the power loss is clearly a matter of temperature. If I wait 3 hours, I have power again, for 8 minutes. I'm going to test the fuel pressure, check timing, and replace the oxygen sensor this weekend. I don't want to throw 20 parts at it, so I'm hoping you can help me prioritize things. Cooling system works great, timing belt/water pump are new, throttle body is clean, TPS tests perfectly. After turning off my car, CAT is 280 degrees before and 380 degrees aft. Vacuum stabalizes at 18 pretty responsively. My car doesn't have an EGR. Not likely main relay, because it seems more engine temp dependent, than cabin temp dependent. PCV is new. Oil is GTX 5W30 and is in good shape. Fuel pump primes. Coil meets Haynes resistance specs. Distributor is only two years old. Disconnecting MAP stalls engine. Spark plugs have gas carbon on ring, white ceramic looks great, tip looks a bit on the white side. The valves were adjusted recently. Air filter looks great.
Another note. The idle seems to stabalize at a different level every time. The RPMs drop, hang a little at 900, then continue to 700, or 800, or 600, depending on the mood of the car. I noticed that when the car has power this idle tends to settle more in the 800 or 900 and when it's lost power it settles in the 600 area.
The power loss can be described as similar to the loss you get when turning on the AC, only double that. It isn't jerking, or stalling, it just feels light on the pedal. An inch of accelerator movement, might only slightly, slowly, begin to think putting some torque on the wheels. Golf carts have more power.
So, I'm thinking Knock Sensor, replace all vacuum lines, Ignitor, Improper timing belt installation, ECT sensor, or Crank Sensor. As a novice, I'd love to have an expert help me. I have a feeling the symptom of having power when cold, but not when hot can narrow the sensor/timing troubleshooting down.
THANKS AGAIN for your time.
have the same problem?
Tuesday, April 21st, 2009 AT 12:20 PM