92 Civic - Sudden Bad Fuel Economy
 

My Car: 1992 Civic LX 1.5L
Engine: D15B7

About a week ago the coil failed on my civic so I installed a new one. Strangely, my car still wouldn't start after installing the new coil (plus rotor and distributor cap), but now some of the cylinders were firing. Turned out that some of the spark plugs were fouled up (it seems that I have a leak in the spark plug tube - I'll have to replace the seals) so I cleaned them up and reinstalled them. Finally it started but my MPG was terrible (around 15 MPG) plus I was getting code 43 "fuel supply system."

I've tested the 02 sensor and it seems to pass all of the tests in Haynes except for "12 Check for proper supply voltage to the heater. Measure the voltage between the yellow/black wire (+) and the black wire (-) on the oxygen sensor electrical connector. There should be battery voltage with the ignition key ON (engine not running). If there is no voltage, check the circuit between the main relay, the ECM and the sensor."

I checked the voltage from the yellow/black wire (which it turns out is only on the female side of the connector) and the black wire (there are two black wires on the oxygen sensor electrical connector in my car). I get no voltage (using either black wire), but I'm not really sure if I'm doing this test correctly. Any ideas?

If the heater isn't working could this cause poor MPG?

I've installed new spark plugs. MPG seems to have improved but I'm not sure if it's back to normal yet.

Any ideas what else could be killing my MPG?

I know that ignition timing could also be a culprit but I didn't touch adjustment bolt on the distributor.

One last question, if the rotor hit the distributor cap terminals could it mess up the ignition timing? I tried to bend the terminal on my old cap in to be closer to the rotor when I was troubleshooting the no start condition. It is possible that the old rotor hit a terminal on the old distributor cap. Possible?

Thanks for the help.

Re: 92 Civic - Sudden Bad Fuel Economy
 

If the rotor get damaged in any way it could cause most likely both throw timing off and also cause misfire. The fact of getting the terminal bent to meet the rotor sounds like a warped cap.

And as for voltage to the 02 is the voltage wire to ground on the volt setting . Sound like you were testing for continuity not voltage.

Re: 92 Civic - Sudden Bad Fuel Economy
 

When you say your plugs were fouled, was it a dry foul or wet foul.

The oil in the spark plug tubes won't seep into the cylinder to cause wet fouling. If it did then you'd have worse problems of gas escaping around the spark plug (air is thinner than fluid {water/oil}).

One of the first things I'd look at is a compression test... If your compression is too low it won't burn the fuel efficiently and cause fouling. If compression is good then I'd follow that with a leak down test. If those check out as being good then it's got to be ignition related. The O2 sensor can definitely cause poor MPG but if it's just the heater portion that's not working it wouldn't affect it that much. Would just mean it takes longer to get to operating temperature. If the sensor part wasn't working you'd get horrible gas mileage and also should throw a CEL.


Do you have any CEL's?

Re: 92 Civic - Sudden Bad Fuel Economy
 

So did the ignitor fail or did the ICM (Ignition Control Module) did? Also did you check if your spark plug wires were within spec? When was the last time you did any ignition maintenance?

Re: 92 Civic - Sudden Bad Fuel Economy
 

So it looks like I'm at 27 mpg now. My estimate was probably off before/new spark plugs probably made a bit of a difference. In terms of my spark plugs, they were badly corroded (plus there seems to be an oil leak in two of the spark plug wells). One of them was having trouble firing even outside of the engine. Thanks everyone for the suggestions. Much appreciated.

Re: 92 Civic - Sudden Bad Fuel Economy
 

The coil failed. Aren't the igniter and ICM outside of the coil? Haven't checked my spark plug wires but I'll do that as well. I did use a spark tester though which passed on all of the wires.

Re: 92 Civic - Sudden Bad Fuel Economy
 

Replace the plug wires and go from there.

Are any CEL codes thrown?

Re: 92 Civic - Sudden Bad Fuel Economy
 

No CELs. I did get a 43 "fuel supply system" but it's gone now.