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Discussion Starter #1
1998 Ford Taurus ohv v6 just started to run rough (very rough). Checked code at Auto Zone which said "misfire #6". Found #6 injector to be bad (open circuit where others showed 15 ohms or so). Replaced injectors 4,5, & 6 (because they were easy). No change. Replaced all plugs and wires on 4,5,6 (again because they were easy), replaced coil pack (I had a spare). Again no change. Checked MAF and found 1.5v at idle going up and down smoothly with change in rpm. Timing light shows all cylinders getting spark. I am about to go back to Auto Zone to see if there are any new codes and this time check for multiple codes (I only wrote down one the first time but I guess there could be more). Can't see any vacuum leaks (but not sure exactly where to look either). But basiclly I am stumped. What can cause the car to SUDDENLY run this rough? One more thing, a couple of months ago it started leaking water a bit from the pump area. Picked up a new pump but haven't installed it yet. Not sure if that is related...
 

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Welcome to the FFO!

Do get all codes and post.
Is the check engine light on?
How many miles on vehicle?
What area of the country. (Temperature and humidity may play a part)

When you are at Autozone pick up some spray cleaner. When running you will use this to check for vacuum leaks. With engine running and spraying (lightly) around intake and that bank of cylinders, if the engine RPM changes - usually increases - you have found a leak.
It is possible the entire system is lean and #6 (an end cylinder) gets so lean it misfires. This can be due to an air/vacuum leak or to fuel mixture trim.
You measured resistance of old injector. Have you measured the new one?

Check EGR- at idle EGR should be closed. If you open it either mechanically or by vacuum signal the engine should stall. If it does not stall that is an issue.

If the engine has over 100,000 miles have the oxygen sensors been replaced?

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Discussion Starter #3
Thanks, yes the check light is on (solid). About 150k miles. To my knowledge O2 sensor has not been changed. The car is in Concord, CA (warm, fairly dry area). What kind of spray cleaner (I assume there are different kinds)? The new injectors measure roughly 15 ohms, same as old (except for #6 which was open). I will check the EGR (first I have to find it...).
 

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Any spray cleaner, carb, brake or ??? Cheap would be OK. All of that is flammable. In spraying, if there is a vacuum leak the cleaner will get sucked in and burned. If that happens there will be a rise in engine RPM.

Highly recommend replacing all of the O2 sensors. At 150K they are worn out like spark plugs wear out. The function of an O2 sensor is to give feedback to the PCM on how the fuel mixture is getting burned. As an O2 sensor ages it wears out or wears down. The signal then slows down to the PCM to a point the signal means very little and the PCM is getting bad (slow) data. Until the sensor stops working and trips a code. Way before it trips a code the sensor is sending slow signals and the PCM is not adjusting the fuel trim correctly for the situation that is happening in the engine. The fuel trim goes from too rich to too lean and is never adjusted correctly for the best fuel air ratio.

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Discussion Starter #5
Just got back from Autozone. This time they listed 4 codes:
1) P0171 (Fuel system too lean cylinder bank 1
2) P0340Mamshaft position sensor circuit malfunction
3) P0302 Cylinder #3 misfire detected
4) P0303 Cylinder #2 misfire detected.

They listed a suggested part "PCV valve" without saying why. I picked up some spray cleaner and will see what this does...
 

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I would be very concerned with the lack of or an intermittent cam shaft position signal. Without an accurate signal the PCM is making spark and fuel inject calls without knowing of the timing is accurate. That in of it's self can generate a lean run condition as well. And would explain a "sudden" drivability issue.

You may discover there is no RPM change with the engine running using the spray cleaner around the exterior of the intake manifold and air intake from the throttle body to the cylinder head.

Assuming you find the significant issue do not neglect the maintenance. Getting the engine to run smooth is a relief. Getting the engine to run efficient is the result of doing all of the maintenance.

The PCV is maintenance. (Just like filters, spark plugs and O2 sensors) If the PCV has not been changed in the last 30,000 miles it is time to replace.

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Discussion Starter #7
Thanks, because one of the codes referenced the cam position sensor (and I had another one handy) I went ahead and replaced it. No notable effect. Spraying around also showed no rpm change (that I could tell). Pulling off all vacuum hoses I could find (one at a time) also showed no effect. Likewise I disconnected the MAF and the engine idle sped up a bit (and even sounded smoother?). There must be something I am overlooking...
 

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After replacing the camshaft position sensor, clear the code* and drive until the CEL comes back on. It will because yo have not resolved the other issues. Then have the codes pulled.

Then post back if the P0340 has gone away.

There may be two camshaft position sensors. Bank 1 (P340) and Bank two (P345)

*Clearing codes can be done by disconnecting that battery for 30 minutes. I assume yo do not have a reader.

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Discussion Starter #9
Thanks, I will do this but it will have to wait until next week. But when I drove it to Autozone to check codes, I noticed (besides running rough) the transmission did not shift as usual. It reved much higher than normal (maybe 3000 rpm) even though I was taking it very easy. I also tried disconnecting the PCV value and the engine almost died so I assume this is working ok. Just thought I would mention these things...
 

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Disconnecting the PCV creates a huge vacuum leak. The engine will have a very hard time operating with that kind of vacuum leak.

The transmission is controlled electronically at higher speeds. If the 3 to 4 shift or any other higher gear shifts are an issue the electronics may be attempting to do something that they don't have the proper data to do.

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Discussion Starter #11
Disconnecting the PCV creates a huge vacuum leak. The engine will have a very hard time operating with that kind of vacuum leak.

The transmission is controlled electronically at higher speeds. If the 3 to 4 shift or any other higher gear shifts are an issue the electronics may be attempting to do something that they don't have the proper data to do.

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Discussion Starter #12
Back from vacation. I picked up a cheap code reader to save me from trips to Autozone. The reader now says just "P0171 Too lean on bank 1". I assume bank 1 means cylinders 1-3. Bad injectors? Maybe an O2 sensor problem? Maybe the CPU just THINKS it's too lean and puts in too much fuel? How can I test the O2 sensor? Maybe swap front and rear to see if code changes? I am grasping at straws as you can tell...
I think the trans issue was with only 1st & 2nd but I could be wrong.
 

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Bank 1 is the front bank or as you stated cylinder 1 thru 3.

O2 sensors impact fuel trim lean or rich. O2 sensors have an effective service life around 100,000 miles. Beyond that they may test good by returning a test signal from the PCM. However in service the signal they are generating is sloooooooow. So the PCM gets a signal from the O2 sensor however the data is not relevant to adjusting fuel trim in real time. The PCM is doing things for past combustion events instead of current combustion events like it was designed. At 150,000, ALL of your O2 sensors are well past their prime.

There is software that can be installed that will show the data on a laptop for all sensors while the engine is running. Not just the O2 sensors. However you are playing the game of delaying maintenance. Why would you put off maintenance on a known issue? The comparison is waiting for the spark plugs to fail before replacing them. The spark plugs will work inefficiently until they ultimately stop working.

If you like reading go for the whole article. If you want to get to the point skip to the bottom paragraph. http://www.autotap.com/techlibrary/replacing_oxygen_sensors_preventive_maintenance.asp

And generic O2 sensors will cost below $20 which is common. If you look hard you could get them for less than $10 each. Likely you have 4 wire heated O2 sensors. Do the repair your self, spend $50 on parts and at least that piece of known maintenance is complete. Work from the known to unknown.

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And post back the result of any work that you do on the vehicle.

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Discussion Starter #15
Action, thanks for the advice. The maintenance is long past due I know and I don't mind, however first I would like to see if I can get the car to run reasonably well. Currently it's about undriveable and it sounds like a bad O2 sensor would not cause this bad a condition. Maybe all of the bank 1 injectors are not working? Can't see how this would happen unless an electrical or fuel rail issue were to blame. Also I will check out your article. By the way Firefox works where IE did not!
 

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IT for this site has communicated with me. They have a bunch of sites to works and so we don't get as much priority. I am using Chrome most of the time with good results.

Running rough -
One cylinder not functioning would cause a rough run. Three cylinders only partially working would be difficult to keep the engine running except at high idle and in neutral. It certainly would not be drivable.

If there are other issues you may discover the engine runs differently not necessarily better with poorly functioning O 2 sensors.

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Just an update. I was suspicious of the EGR valve so last night I tried to test it. Hooking a vacuum line directly to the unit I was expecting the engine to almost die but it didn't. It had some effect but ran a bit better if anything. But the valve did make some noise when the line was connected like it was doing something. Strange. Also there is a similar unit on the front of the engine (was is it?). Connecting a vacuum line to this had no noticeable effect. I will see if I can replace the EGR valve in the coming days. Forever hopeful.
 

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Also there is a similar unit on the front of the engine (was is it?).

Would you post a picture?

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Discussion Starter #19
Here is the best picture I could find of the engine. I circled the part I was curious about. It has a vacuum line and plugs into the front exhaust manifold. What is it?
1998_vulcan.jpg
..
 

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Looks like an EGR valve to me. BTW that is the rear of the engine.
How many bolt holes does your EGR valve have?

Taurus has two V6 engines.
3.0 OHV - Vulcan
3.0 DOHC - Duratec


So you have 3.0l Vulcan?


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