Mechanics

CHRYSLER NEW YORKER SENSOR PROBLEM

1995 Chrysler New Yorker • 120 miles

Motor turns over but will not start. It started with running real rough, like an injector was plugged so we ran injector cleaner through it for several tank fulls. Finely it just would not start, so I brought it into the yard and started checking things. This is what I have checked, Fuel pump turns on and pumps fuel, injectors getting a pulse signal while turning over, Spark from plugs are snappy and blue, Checked power going to Crank Shaft and Cam shaft sensors, in specs. Timing belt is good and lined up. Pulled intake manifold off and jump injectors over to battery and got a good fine spray from all injectors. Checked coil, ohm was within specs between lugs. I have read every post I could find about this, and I do not have the money to through new parts at it, so am very willing to test, test, test. I have a dig. Multi meter and a test light. Not sure if this is relevant, heater would come on full blast high heat and the control lights would go out so you could not turn it off or down, then for no reason the control lights would come back on and work fine. BCM? If so how do I test to make sure. Any help would be very helpful.
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Dan-o1234
January 5, 2013.




Disconnected to MAP sensor and it STARTED, ran very rough, but it ran. Going to replace MAP sensor.
Ok replaced MAP sensor and it starts and runs. Also checked the vacuum line to the fuel pressure regulator and it is dry. I would like to thank you for all of your help. I will drive it for a few days and let you know if it stays running.
Dan-o.

Tiny
Dan-o1234
Jan 16, 2013.
Tried to start it this morning and it would not. It acked the same as it was yesterday before I replaced the MAP. I disconnected the MAP and it started, very rough. I reconnected the MAP after I ran it a little and it started and ran better. Is there somwthing else wrong?

Tiny
Dan-o1234
Jan 17, 2013.
It's hard to know what's going on without having a scanner to look at. The things I would look at first are the MAP sensor voltage and the intake air temperature sensor reading. A bad connection will cause an increase in resistance in that circuit which would equate to a lower temperature. That can command more fuel, and the engine may be flooding.

Excessive fuel pressure will also cause more fuel than expected to enter the engine. A leaking vacuum hose to the fuel pressure regulator will cause the pressure to increase, AND can cause the MAP sensor to see a lower vacuum which equates to acceleration and the need for more fuel.

Caradiodoc
Jan 17, 2013.
Pulled the Air temp sensor out and wiped it off, looked kind of nasty, but not real bad. All of the vacuum hoses that pushed on real easy I took some O-rings and found the right size to fit over the outside of the female hose fitting. Once I slipped them together, I rolled the O-ring to the end to pinch it tight. It started right up and ran great. Again I will drive it a few days and get back to you here to let you know. Thank you, Dan-o.

Tiny
Dan-o1234
Jan 17, 2013.
Three days and it has been running fine. But, now it is getting real bad gas mileage. Do I have to wait for awhile for everything to find its happy spot for it all to mesh and run right? Is there something else going on?

Tiny
Dan-o1234
Jan 21, 2013.
Fuel should straighten out right away. The Engine Computer memorizes short and long-term fuel trim data. It starts out with pre-programmed values from the factory that cover any combination of speed, load, air temperature, coolant temperature, and barometric pressure. That gets fuel metering real close, then the computer looks at the oxygen sensor readings to see how it's doing with that fuel / air mixture. It modifies the amount of fuel being delivered based on those O2 sensor readings, and it remembers how much it had to modify them. That's called the "short-term fuel trims", (STFT).

When the computer sees that it is constantly making the same corrections over a period of time, it moves those values into the long-term fuel trims, (LTFT). From then on those are the values it runs on instead of those pre-programmed values. The goal is to make the long-term numbers be so accurate that the short-term numbers are real close to "0". That means the mixture is correct and no modification is necessary.

The way to tell how the system is working is to view those numbers on the scanner. If you see a positive long-term number, that means the computer is requesting more fuel than what was programmed in at the factory. If you see a positive short-term number, that means the computer wants more fuel than what it has updated its memory to, to meet some current condition. Negative numbers means it is reducing the amount of fuel desired.

Based on the readings from the oxygen sensors, the computer can only add or subtract fuel by about ten percent. When you see numbers that high, something is usually wrong that is beyond the computer's ability to control it. Common causes are low or high fuel pressure and vacuum leaks. Also, misfires related to spark can send unburned oxygen into the exhaust where the sensors will detect it as a lean condition. You will smell unburned fuel at the tail pipe but the computer will be trying to add more fuel. No matter how much fuel it adds, it will continue to see a lean condition. That's one way it can lose control and display very high positive fuel trim numbers.
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Caradiodoc
Jan 22, 2013.
I do smell a strong gas smell at the tail pipe and poor fuel mileage, So should I replace the O2 sensor, it is not sending a code.

Tiny
Dan-o1234
Jan 23, 2013.
Nope, you don't replace the messenger when you don't like the message. The O2 sensors are sending out signal voltages that the computer sees as acceptable so no codes will be set. A scanner will show how the sensors are responding. You can introduce extra air by unplugging a vacuum hose, and you can introduce extra fuel by opening a propane torch near the air filter to see if the oxygen sensor voltages change.

If you see the O2 sensors are reporting lean conditions, the computer is adding fuel to try to correct that, and you're smelling that fuel at the tail pipe. If they're reporting a rich condition, which is what it appears you have, the computer has lost control and is unable to adjust the mixture enough to make it right. In that case the computer knows it's rich but can't fix it. Suspects would be fuel pressure too high, or an injector stuck open due to varnish buildup or a shorted driver circuit in the computer. Fuel pressure would affect both sides of the engine. An injector problem would affect just one side.

Take note of the catalytic converters too. Too much unburned fuel will overheat them and can make them glow orange if it's bad enough. If you see one or both are glowing, stop the engine to prevent melting the catalyst. That is how they become plugged.

Caradiodoc
Jan 23, 2013.

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