1994 Dodge Spirit poor gas mileage

Hi luclin. Welcome to the forum. What have you tried so far? Surely the Check Engine light must be on. Have you read the diagnostic codes? Do you know how? If you've had them read, what are they? There are a number of things that can cause too much fuel. The most common would probably be the MAP sensor or a cracked vacuum hose going to it. Holler back after you've checked the codes.

Cardiodoc

Readings from the oxygen sensor will only cause the Engine Computer to add or subtract fuel from the calculated value by 10 percent. That calculated value is determined mostly by the MAP sensor. As long as its signal voltage is between.5 and 4.5 volts, the computer will believe it and not set a fault code related to it. A cracked vacuum hose will mimic low vacuum which means hard acceleration and the need for more fuel. Fuel pressure regulators leaking fuel into the intake are real common on GM products but almost unheard of on Chryslers. Other than that, the MAP sensor is the only thing that can cause that much fuel to be dumped in.

With that much fuel, some will be washing down the cylinder walls and getting into the oil. It would be smart to change the oil as soon as this problem is solved.

Caradiodoc

Boy, I was confused there for a moment. I just answered a similar question yesterday for a Caravan. Thought I was getting "old-timer's disease" when I read "Spirit" in my e-mail notification. :)

With as much fuel that's being dumped into the engine, something is more seriously wrong than the O2 sensor. Look into the throttle body while the engine is running. You should see a nice cone-shaped spray of fuel. If you see large droplets of raw fuel, something is wrong with the pressure regulator or its o-ring. Look for raw fuel on top of the regulator too. If the spring-loaded diaphragm is leaking, (which I've never encountered or heard of), fuel will run through the air bleed hole on top of the unit.

Did this problem start all of a sudden or did it gradually get worse over time? Is it possible someone installed an incorrect fuel pump in the tank? Normal fuel pressure is around 14 psi for throttle body fuel injection systems but multiport systems can run over 45 psi. If fuel pressure is too high, the regulator will be overwhelmed and not be able to pass the extra fuel back to the tank fast enough. Also look for a restricted fuel return line from the throttle body to the tank. That will cause pressure to go too high. Excessive fuel pressure means too much fuel entering the engine.

I believe you are going to find a mechanical issue causing this much extra fuel, not an electrical problem. Watch the spray from the injector nozzle while a helper turns off the engine. The spray should stop instantly. If it continues to dribble with the engine stopped, the injector is leaking and is unable to control fuel delivery properly. They normally give such little trouble, a good used one from a salvage yard would be a satisfactory replacement.

Caradiodoc

Hey, how about that? I just replied to your new post. Here's the copy / paste version:

0.2 volts on the ground wire, 5.0 volts on the supply wire, and 0.5 to 4.5 volts on the signal wire. The signal voltage when you turn on the ignition switch but before cranking the engine is stored in memory as the barometric pressure. The higher the engine vacuum, the lower the voltage will be.

5.0 volts on the signal wire means the ground wire is open. 0 volts means the feed wire is open. If you measure 0.5 to 4.5 volts at the sensor but a scanner that displays live data shows 5.0 volts, that means the signal wire is open. Anything outside of 0.5 to 4.5 volts will trigger a fault code. For a broken signal wire, a high value "pull-up" resistor in the computer insures the voltage won't float around a normal value. Rather, that insures it will go to a voltage that will set a fault code.

Caradiodoc

Black / light blue is ground for all of the sensors. Violet / white is the 5 volt feed to all of them. MAP signal wire is dark green / red. It's in the middle of the three wires in the plug.

Caradiodoc

Don't have the proper service manual at hand. There should be a sticker with that listed. Look under the center of the hood or on the radiator core support near the hood latch. On the right side it will list the spark plug number and gap. The timing will be there too.

To set the base timing by turning the distributor, you must eliminate the electronic advance done by the Engine computer. By far the easiest way to put it in base timing mode is to unplug the coolant temperature sensor. That will turn on the Check Engine light and set a diagnostic fault code, and you can adjust the timing. If the Check Engine light does not go out when you reconnect the sensor, it will after you cycle the ignition switch off and restart the engine. The code will erase automatically after you start the engine 50 times.

There are two coolant temperature sensors near the thermostat housing. You want the one with two wires. It's for the Engine Computer. The other one has a single wire, usually purple. It's for the dash gauge.

Caradiodoc

I want to say 10 degrees BTC, but I'm still looking for a manual. That's from my tired memory.

Caradiodoc