UPDATE: Down to code 41/91 - Please read - Jrichter where are you?

i put a tire gauge on the valve on the fuel rail. theres a black cap take that off and check fuel pressure there not sure if that helps or not

Smoke out the intake and make sure there are no vac leaks. Don't use the "tried and not so true" carb cleaner spray technique, that might work if you have a serious vac leak, but for a minor one, smoke it out.

You pump smoke into the intake and see if it comes out anywhere it's not supposed to.

Go through the code test path to find your problem...

Code 41 or 91 - O2 indicates system lean. Look for a vacuum leak or failing O2 sensor.

Code 41 is a RH side sensor,
Code 91 is the LH side sensor.

The computer sees a lean mixture signal coming from the O2 sensors and tries to compensate by adding more fuel. Many times the end result is an engine that runs pig rich and stinks of unburned fuel.

The following is a Quote from Charles O. Probst, Ford fuel Injection & Electronic Engine control:
"When the mixture is lean, the exhaust gas has oxygen, about the same amount as the ambient air. So the sensor will generate less than 400 Millivolts. Remember lean = less voltage.

When the mixture is rich, there's less oxygen in the exhaust than in the ambient air , so voltage is generated between the two sides of the tip. The voltage is greater than 600 millivolts. Remember rich = more voltage.

Here's a tip: the newer the sensor, the more the voltage changes, swinging from as low as 0.1 volt to as much as 0.9 volt. As an oxygen sensor ages, the voltage changes get smaller and slower - the voltage change lags behind the change in exhaust gas oxygen.

Because the oxygen sensor generates its own voltage, never apply voltage and never measure resistance of the sensor circuit. To measure voltage signals, use an analog voltmeter with a high input impedance, at least 10 megohms. Remember, a digital voltmeter will average a changing voltage." End Quote

Testing the O2 sensors
Measuring the O2 sensor voltage at the computer will give you a good idea of how well they are working. You'll have to pull the passenger side kick panel off to gain access to the computer connector. Remove the plastic wiring cover to get to the back side of the wiring. Use a safety pin or paper clip to probe the connections from the rear. The computer pins are 29 (LH O2 with a dark green/pink wire) and 43 (RH O2 with a dark blue/pink wire). Use the ground next to the computer to ground the voltmeter. The O2 sensor voltage should switch between .2-.9 volt at idle.

Note that all resistance tests must be done with power off. Measuring resistance with a circuit powered on will give false readings and possibly damage the meter. Do not attempt to measure the resistance of the O2 sensors, it may damage them.

Testing the O2 sensor wiring harness
Most of the common multimeters have a resistance scale. Be sure the O2 sensors are disconnected and measure the resistance from the O2 sensor body harness to the pins on the computer.

The O2 sensor ground (orange wire with a ring terminal on it) is in the wiring harness for the fuel injection wiring. I grounded mine to one of the intake manifold bolts

Replace the O2 sensors in pairs if replacement is indicated. If one is weak or bad, the other one probably isn't far behind.

If you get only code 41 and have changed the sensor, look for vacuum leaks. This is especially true if you are having idle problems. The small plastic tubing is very brittle after many years of the heating it receives. Replace the tubing and check the PVC and the hoses connected to it.
A secondary problem with only a code 41 is for cars with an intact smog pump and cats. If the tube on the back of the heads clogs up the driver’s side, all the air from the smog pump gets dumped into one side. This excess air upsets the O2 sensor calibration and can set a false code 41. The cure is to remove the crossover tube and thoroughly clean the insides so that there is no carbon blocking the free flow of air to both heads.

Just curious, because I had a similar problem with my car... is the ground from the drivers side firewall to the drivers side head connected, or clean? Mine was loose and I had almost the same symptoms. You probably already checked this, but its worth a shot.

fastfiftymike said:

Yup, cleaned and checked that last night. Matter of fact i cleaned EVERY electrical connector and ground I could find. Im gonna go through the O2 checklist tonight but the problems are still there in closed loop when the computer is not using the 02's ...

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By definition, closed loop is when the computer does use O2's.

And open-loop info from the O2's is utilized.

In order to get any useful information on th O2 sensors, you need to read the voltage at the computer with the engine running.

The 4 wire O2 sensors seem a little odd. All the ones I have use 3 wires. The 4th wire is probably the heater circuit ground. That missing heater ground could cause problems with the O2 sensors on cold starts.

fastfiftymike said:

Also I dont know if you saw my other thread about the problem where it stands now

Car runs like ok, bieng rich, on start up. After a minute or so, its runs like garbage. after 10 minutes check engine light comes on, then goes off and the car runs fine, just rich afterwards. If you idle for a while it starts running like crap again, or if you cruise at low speed.

That definitely sounds like the 02 Heater...what do you think?

Mike

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I would replace the 4 wire O2 sensors with the correct 3 wire sensors. I think the 4th wire is the heater ground, but I have no definite proof that it is.

fastfiftymike said:

SON OF A BITCH -

Just did some research.


1990 2.3 4cyl cars use 4 Wire 02's.... V8's use 3 Wire 02's....

>.<

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Damn, I didn't know that either. I figured they were all 3 wire, especially since I sold my friend an X pipe with V8 o2 sensors and they worked fine in his car...(4 cyl car converted to 5.0)

Unless you can run that 4th wire to a ground but might as well just get the right ones....And on a fox there is no o2 sensor ground, it grounds itself out on the metal exhaust pipe, but the o2 sensor heater ground goes to the back of the intake, mine's an orange wire with an eyelet on my 87, not sure if it's the same on others...

Learn something new everyday :SNSign:

I will do that, and thanks for the input.

The importance of an someone to carefully examine things as you did cannot be overestimated. It is often very difficult to fix what you can't see firsthand.