Strong gas smell

Discussion in 'Fox 5.0 Mustang Tech' started by curtisboytejr, Jun 24, 2011.


  1. curtisboytejr

    curtisboytejr Member

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    Hey guys, i have a 93 GT with gas fumes pretty bad while cranked. The engine runs great and i pulled the codes and nothing at all. My question is can you have a bad 02 sensor and it not show up on a engine code? Or do i have another issue. Thanks Curtis
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  2. Mustang5L5

    Mustang5L5 Car used in adult film "Highway Gangbang-InDaButt" SN Certified Technician Founding Member

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    No codes at all?

    Where is the smell from? If it's a bad o2, you'd smell it from exhaust.

    But if you smell it under the hood, you have a leak, or a broken vac line or something else wrong.
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  3. curtisboytejr

    curtisboytejr Member

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    It's out of the exhaust only. Thats why i was thinking O2 sensor. But the no code is throwing me.
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  4. BlackGT89

    BlackGT89 Member

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    So you have a rich exhaust smell from the pipes, not a raw gasoline smell, is that correct. Do you have an aftermarket cam ? Pull the vacuum line off of your fuel pressure regulator and see if there is gasoline in the line. If you have a pressure gauge, what pressure are you running ?
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  5. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    No code 11 (two flashes when the computer dumps the codes)? The 11 code is computer passed its internal self test.

    If you don't get an 11, you have computer or wiring problems.
    Please check and repost.
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  6. curtisboytejr

    curtisboytejr Member

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    Hey guys getting back with you. Here is the stuff i know as of right now. It smell like rich exhaust smell and i do have a code 11 when i pulled the codes. it has factory cam and i will pull the vac line off in the morning to see if i smell gas, if i smell gas what do i do then? Thanks curtis
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  7. Mustang5L5

    Mustang5L5 Car used in adult film "Highway Gangbang-InDaButt" SN Certified Technician Founding Member

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    So you ran the codes woth the engine running and got 11?? Sorry for asking 10 times, but gotta be sure you ran the codes with engine off, and then again with engine running
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  8. curtisboytejr

    curtisboytejr Member

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    Ok guys i got a code of 41 and i see that it is HO2S sensor signal out of range/always lean.
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  9. BlackGT89

    BlackGT89 Member

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    The reason I suggested pulling the vacuum hose off and checking for gas in the line is sometimes the diaphram in the FP regulator ruptures and sucks in raw gas straight into the engine. But according to your codes it looks like you have another problem.

    Look for a vacuum leak or a problem with an oxygen sensor. I did a search and came up with this link (if I may).

    http://www.stangnet.com/mustang-forums/698989-computer-codes-mustang-1987-a.html
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  10. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    Code 41 or 91 Three digit code 172 or 176 - O2 sensor indicates system lean. Look for a vacuum leak or failing O2 sensor.

    Revised 22-Jun-2009 to include 3 digit code and wiring for 94-95 5.0 Mustangs

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

    Code 172 is the RH side sensor
    Code 176 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 87-93 5.0 Mustangs
    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.


    Testing the O2 sensors 94-95 5.0 Mustangs
    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 red/black wire) and 27 (RH O2 with a gray/lt blue wire). Use pin 32 (gray/red wire) 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

    Make sure you have the proper 3 wire O2 sensors. Only the 4 cylinder cars used a 4 wire sensor, which is not compatible with the V8 wiring harness.

    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.
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  11. curtisboytejr

    curtisboytejr Member

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    thanks for the great info. The guy i purchased from had the smog pump removed and had the two vac lines blocked off. I do know the smog tubes were cut off very close to the back of engine but from the looks of it it was done correctly.
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  12. Mustang5L5

    Mustang5L5 Car used in adult film "Highway Gangbang-InDaButt" SN Certified Technician Founding Member

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    Yanked the smog pump, but left the cats on? You should really put the pump back on.

    Also, appears one pf your o2 sensors may be faulty
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  13. curtisboytejr

    curtisboytejr Member

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    Since i didnt pull the smog pump out and i didnt really want it back in any way do i need to remove the cats? Or are the fine in the car?
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  14. Mustang5L5

    Mustang5L5 Car used in adult film "Highway Gangbang-InDaButt" SN Certified Technician Founding Member

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    You can leave them, but they really need the smog pump to function properly, or over time they will begins to fail, clog up, and not work. You might not pass the sniffer anymore if that's critical to you.

    If you remove them, your exhaust will really smell rich.
    #14
  15. curtisboytejr

    curtisboytejr Member

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    how rich it smells now they could already be bad also.
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  16. 89ripper

    89ripper Founding Member

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    Here is another thing to consider and hopefully not bad advice but it worked for me because my car was running "rich", check to make sure your ignition is working fine (cap, rotor, spark plugs and such.) I had a corroded terminal on the cap and it was causing me to run rich.
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  17. curtisboytejr

    curtisboytejr Member

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    i will check cap and rotor monday evening, Thanks Guys for all the help.
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  18. old_blue

    old_blue Active Member

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    just checking on the progress here and also another thought. If they are stock cats then I know they don't function properly without the smog pump. But, what about after market cats that don't require a smog pump or even have the bypass for it?
    #18

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