running lean need help.

How do you know the engine is running lean? Have you dumped the codes? Have you checked for vacuum leaks?

Dump the codes and see what the computer says is wrong…Codes may be present in the computer even if the Check Engine light isn’t on.

Here's the link to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great.



See http://www.troublecodes.net/Ford/
OR
See http://www.mustangworks.com/articles/electronics/eec-iv_codes.html

IF your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.

Codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.

Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.

For those who are intimidated by all the wires & connections, see http://www.actron.com/product_detail.php?pid=16153 for what a typical hand scanner looks like. Normal retail price is about $30 or so at AutoZone or Wal-Mart.

Or for a nicer scanner see http://www.midwayautosupply.com/detailedproductdescription.asp?3829 – It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $35.

cj99 said:

i have done all this before.. that is why i know it is lean.. computer say's left bank lean... plugs are a little white. etc i had a broke ground wire on the left 02.. when i plugged it back up the car mis fireded under a load, when i rebroke the wire its stopped mis firing , but is still a little lean... so being that this is NOT the car i drive to work.. i just want it to run rich as fuel milage is not a problem with it. and it should run better while i trace down other issue's. I know when the computer see's full throttle it goes full rich and this is when the car seems to run at its best, but below that it fill's weaker than it should be. ( one more reason i think its the lean issue on this)
so if there is a wire i can jump or disconnect on the water temp sensor or on the 02 system, to make it think it needs to run full rich than this is the info i need right now
thanks
chad

Click to expand...

You are well intentioned, but way off base.

EFI engines are set to run on the lean side to reduce emissions and fuel consumption. Reading the plugs isn't a reliable method of checking the air/fuel mixture unless you shut the engine off when at full throttle, take the engine out of gear and coast to a stop. Then the plugs will reflect what the fuel mixture is and not the lean mixture that is the result of the computer reducing fuel flow to an engine that isn't creating power.

If you got a code 41/91, that is an O2 sensor problem or a vacuum leak. You should see 14.5"-18"of vacuum at 650 RPM, and 18"-21" at 1000 RPM.

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

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.

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.

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.

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


Here's a book that will get you started with how the Ford electronic engine control or "computer" works.

Ford Fuel Injection & Electronic Engine Control 1988-1993 by Charles Probst :ISBN 0-8376-0301-3.

It's about $20 from Borders.com see http://www.amazon.com/ . Select boo...very good, and I found it to be very helpful.

best way to trick computer is swap the EFI with a carb and jet it rich.

have you tryed pulling the vaccum line off of the fpr? That should give you all the fuel pressure you need and it will give you a rich condition like you asked for.

Or get an adjustable Fuel Pressure Regulator and give it a little more pressure

So if you're breaking the wire and it's improving, that, to me, would tell me that the O2 sensor is probably bad. Does it have issues when its cold, because the ECU isnt going to read the O2's until they heat up.
Otherwise I'd say vacuum leak, if it's only on the left bank maybe you have a bad lower mani gasket?

cj99 said:

new motor.. and no gasket leaks or vac leaks that i can find.
and it runs fine cold. matter a fact that maybe it run best cold

Click to expand...

Now a leaking EGR diaphragm would cause a vacuum leak and be pretty tricky to find if it's ruptured...but it would be lean all the time, unless the computer's cold-start enrichment added enough fuel to compensate....

Well cold is before the computer reads the O2's and before it tries to run closed loop...so likely your problem is somewhere in the closed loop systems. Seriously try swapping that bad O2 sensor, even if it's with another used one somebody has laying around. Hell I must have 3 or 4 in a box in my garage along with "useable" plugwires, plugs, etc...somebody else in your area has got to save that stuff.

cj99 said:

as fas as the EGR goes .. it is on there but no vac line going to it, i removed that so maybe it could be leakig or stuck ope a little. i will have to check that or block it off and removed it all togeather

Click to expand...

Try that and see what happens. But seriously, you obviously have issues with your O2 sensor if you connect it and the car runs like ****. The O2 should be READING that bank as lean, causing the computer to dump fuel.... If youre running better on a DEFAULT value with it unplugged, which is probably some median number, I'm inclined to believe that the O2 on that bank is telling the computer youre extremely rich for some reason, causing it to pull fuel....but I still dont see how it would read LEAN instead of RICH if that were the case.

You know now that I think about it, your symptoms sound more and more like mine that Im having with my car.....I'm gonna have to watch this thread close, maybe we can put our heads together and find some common link. I have a nasty intermittent miss at cruise and slight accel but at wide-open it disappears.

Hey I just wanted to say, I'm in a state of shock. After I heard your symptoms, and how your broken O2 wire fixed the problem....I tried disconnecting both of my O2's, and I'll be damned if doing that didn't fix this random, severe misfire I've had for MANY months. So whatever is going on with both of our cars, I suspect it's the same problem.

Just figured I'd let you know that, it's pretty strange. There must be something going on with the O2's, causing the computer to reak havoc with the short-term trim tables or something.... If I only had a damn way of data-streaming the thing without buying a laptop and tweecer...