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oblivion2k
Joined: 12 Mar 2006
Posts: 7
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 Posted: Sun Mar 12, 2006 5:20 pm Post subject: Engine isn't running good |
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I have a 1977 Porsche 924 Martini Rossi Edition.
My engine's being really "gurglely" and it just isn't running good. It seems like it's getting too much gas to the engine and the engine is choking. My dad's thinking it might be the oxygen sensor, but we don't even know if it HAS one, so question is: does the 77 porsche 924 have an oxygen sensor, and could this be the problem, or could it be something else?
Thanks alot guys. Your pretty much my only hope. |
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Ozzie
Joined: 12 Mar 2005
Posts: 4448
Location: Townsville, Qld. Australia
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| Posted: Sun Mar 12, 2006 6:09 pm Post subject: |
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Turbo or NA?
Euro or USA spec?
What is your location?
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance |
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chris24
Joined: 17 Jan 2005
Posts: 334
Location: boston/nottingham UK
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| Posted: Sun Mar 12, 2006 6:33 pm Post subject: |
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double posted 
_________________
1983 - 924 (185K miles) - not mint
1985 - 924 (148K miles) - mint
1990 - 944S2 cab (52K miles)
Last edited by chris24 on Sun Mar 12, 2006 6:34 pm; edited 1 time in total |
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chris24
Joined: 17 Jan 2005
Posts: 334
Location: boston/nottingham UK
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| Posted: Sun Mar 12, 2006 6:33 pm Post subject: |
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Weren't they early US cars? So from what I have heard it should have one. Disconnect and see if the car works better, it may be that it runs a heck of a lot better.
Read this if you half half an hour! 
(can't guarantee its total accuracy mind you!)
| Quote: | From:
http://www.birrabrothers.com/tiger/e36/docs/all_o2sensor.htm
Testing O2 sensors that are installed
The engine must first be fully warm. If you have a defective
thermostat, this test may not be possible due to a minimum
temperature required for closed loop operation. Attach the
positive lead of a high impedence DC voltmeter to the Oxygen
sensor output wire. This wire should remain attached to the
computer. You will have to back probe the connection or use
a jumper wire to get access. The negative lead should be
attached to a good clean ground on the engine block or
accessory bracket. Cheap voltmeters will not give accurate
results because they load down the circuit and absorb the
voltage that they are attempting to measure. A acceptable
value is 1,000,000 ohms/volt or more on the DC voltage.
Most (if not all) digital voltmeters meet this need. Few
(if any) non-powered analog (needle style) voltmeters do.
Check the specs for your meter to find out. Set your meter
to look for 1 volt DC. Many late model cars use a heated
O2 sensor. These have either two or three wires instead of
one. Heated sensors will have 12 volts on one lead, ground
on the other, and the sensor signal on the third. If you have
two or three wires, use a 15 or higher volt scale on the meter
until you know which is the sensor output wire.
When you turn the key on, do not start the engine. You should
see a change in voltage on the meter in most late model cars. If
not, check your connections. Next, check your leads to make sure
you won't wrap up any wires in the belts, etc. then start the
engine. You should run the engine above 2000 rpm for two
minutes to warm the O2 sensor and try to get into closed loop.
Closed loop operation is indicated by the sensor showing several
cross counts per second. It may help to rev the engine between
idle and about 3000 rpm several times. The computer recognizes
the sensor as hot and active once there are several cross counts.
You are looking for voltage to go above and below 0.45 volts.
If you see less than 0.2 and more than 0.7 volts and the value
changes rapidly, you are through, your sensor is good. If not,
is it steady high (> 0.45) near 0.45 or steady low.
Testing O2 sensors on the workbench.
Use a high impedence DC voltmeter as above. Clamp the sensor in
a vice, or use a plier or vice-grip to hold it. Clamp your
negative voltmeter lead to the case, and the positive to the
output wire. Use a propane torch set to high and the inner blue
flame tip to heat the fluted or perforated area of the sensor.
You should see a DC voltage of at least 0.6 within 20 seconds.
If not, most likely cause is open circuit internally or lead
fouling. If OK so far, remove from flame. You should see a
drop to under 0.1 volt within 4 seconds. If not likely silicone
fouled. If still OK, heat for two full minutes and watch for
drops in voltage. Sometimes, the internal connections will open
up under heat. This is the same a loose wire and is a failure.
If the sensor is OK at this point, and will switch from high to
low quickly as you move the flame, the sensor is good. Bear in
mind that good or bad is relative, with port fuel injection
needing faster information than carbureted systems.
ANY O2 sensor that will generate 0.9 volts or more when heated,
show 0.1 volts or less within one second of flame removal, AND
pass the two minute heat test is good regardless of age. When
replacing a sensor, don't miss the opportunity to use the test
above on the replacement. This will calibrate your evaluation
skills and save you money in the future. There is almost always
*no* benefit in replacing an oxygen sensor that will pass the
test in the first line of this paragraph.
--
An Oxygen sensor is a chemical generator. It is constantly making
a comparison between the Oxygen inside the exhaust manifold and air
outside the engine. If this comparison shows little or no
Oxygen in the exhaust manifold, a voltage is generated. The
output of the sensor is usually between 0 and 1.1 volts. All
spark combustion engines need the proper air fuel ratio to
operate correctly. For gasoline this is 14.7 parts of air to one
part of fuel. When the engine has more fuel than needed, all
available Oxygen is consumed in the cylinder and gasses leaving
through the exhaust contain almost no Oxygen. This sends out a
voltage greater than 0.45 volts. If the engine is running lean,
all fuel is burned, and the extra Oxygen leaves the cylinder and
flows into the exhaust. In this case, the sensor voltage goes
lower than 0.45 volts. Usually the output range seen seen is
0.2 to 0.7 volts.
The sensor does not begin to generate it's full output until it
reaches about 600 degrees F. Prior to this time the sensor is
not conductive. It is as if the circuit between the sensor and
computer is not complete. The mid point is about 0.45 volts.
This is neither rich nor lean. A fully warm O2 sensor *will not
spend any time at 0.45 volts*. In many cars, the computer sends
out a bias voltage of 0.45 through the O2 sensor wire. If the
sensor is not warm, or if the circuit is not complete, the computer
picks up a steady 0.45 volts. Since the computer knows this is
an "illegal" value, it judges the sensor to not be ready. It
remains in open loop operation, and uses all sensors except the
O2 to determine fuel delivery. Any time an engine is operated
in open loop, it runs somewhat rich and makes more exhaust
emissions. This translates into lost power, poor fuel economy
and air pollution.
The O2 sensor is constantly in a state of transition between high
and low voltage. Manfucturers call this crossing of the 0.45
volt mark O2 cross counts. The higher the number of O2 cross
counts, the better the sensor and other parts of the computer
control system are working. It is important to remember that the
O2 sensor is comparing the amount of Oxygen inside and outside
the engine. If the outside of the sensor should become blocked,
or coated with oil, sound insulation, undercoating or antifreeze,
(among other things), this comparison is not possible. |
AND do what ozzie said because it helps no end!
_________________
1983 - 924 (185K miles) - not mint
1985 - 924 (148K miles) - mint
1990 - 944S2 cab (52K miles) |
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oblivion2k
Joined: 12 Mar 2006
Posts: 7
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| Posted: Sun Mar 12, 2006 6:36 pm Post subject: |
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| Ozzie wrote: | Turbo or NA?
Euro or USA spec?
What is your location? |
NA
USA
Washington area. |
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Paul
Joined: 02 Nov 2002
Posts: 9491
Location: Southeast Wisconsin
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| Posted: Sun Mar 12, 2006 9:52 pm Post subject: |
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Welcome to the board!
No O2 sensor.
Check for air leaks in the intake system, especially all the hoses.
Time for a CIS system pressure check.
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy. |
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D Hook
Joined: 02 Nov 2002
Posts: 3158
Location: Omaha, NE
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| Posted: Sun Mar 12, 2006 10:04 pm Post subject: |
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Lot's of people in the Washington area. If you can be a bit more specific on your location, someone may be willing to come over and take a quick look at it for you. Might be something as simple as a vaccuum leak. Have any of the vaccuum hoses been replaced? Including the large bellows that goes from the fuel distributor to the throttle plate. Like Paul said, check pressures, too. Do you have a Haynes?
_________________
'80 924 n/a SOLD |
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oblivion2k
Joined: 12 Mar 2006
Posts: 7
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| Posted: Tue Mar 14, 2006 2:41 pm Post subject: |
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thanks for the info Paul, I have something to work with now.
And D hook, I'm in Camas Washington, which is about 30 minutes from Portland Oregon. If anybody would like to come down and look, I'd be willing to get a price estimate, but it's up to my dad and he's pretty tight with money. I really don't have any information on the vacuum hoses, but I can certainly check. I might be able to take a look at it again this weekend, but during the week all I do is homework until late at night, so that's not an option.
Thanks for all the help so far everyone.
Oh yeah, I wish I had a Haynes  any idea where I can get one for relatively cheap, particularly online? (unless you KNOW that a shop near Camas has Haynes manuals.) |
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