Mechanics

POOR GAS MILEAGE

1994 Dodge Spirit

Engine Performance problem
1994 Dodge Spirit 4 cyl Front Wheel Drive Automatic 107000 miles

I have black smoke coming from exhaust pipe and very poor gas mileage (8 miles per galllon). Please help
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Luclin
June 15, 2010.



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

Caradiodoc
Jun 16, 2010.
We thought it could be the oxygen sensor but haven't checked yet. Did the codes and got a 33 which says something about the air conditioner but when we switch the AC to on position before checking code again we then get a code 12. We are only getting 8 miles per gallon which is ridiculous

Tiny
Luclin
Jun 16, 2010.
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

Caradiodoc
Jun 16, 2010.
Ok I will take at look at it today and check these things and let you know. Thanks for your help so far

Tiny
Luclin
Jun 16, 2010.
Ok I changed the MAP sensor and Coolant sensor switch, still only getting 10mpg on fuel. Haven't changed the O2 sensor as yet. Do you think this might work?

Tiny
Luclin
Jul 23, 2010.
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

Caradiodoc
Jul 23, 2010.
Don't worry ur not getting old yet, lol. But thanks for the info.I will take a look at these points and see what happens, will get back to you after. Thanks again

Tiny
Luclin
Jul 24, 2010.
Hi, its been awhile since i've posted. But can you tell me what the voltages should be on the map sensor? I get 5 going in but what should I have coming out?

Tiny
Luclin
Nov 23, 2010.
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

Caradiodoc
Nov 23, 2010.
Yes, lol. One and same person.I just asked another question. What color should the signal wire be?

Tiny
Luclin
Nov 23, 2010.
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