- Aug 11, 2005
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Need some Input on 1 gas fouled spark plug?
- Thread starter LX-CONV331
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Spark plug not firing
1.) bad spark plug
2.) bad stark plug wire
3.) Bad distributor cap.
Bad injector - Faulty injector or injector wiring. Go to step 2 in the fuel injector test path.
Fuel injectors inoperative, one or more injectors either on all the time or will not squirt.
Revised 27-Jan-2008 to include expanded testing for proper power to injector wiring
Tools needed: Noid light, Multimeter (volts & ohms), 10 MM socket &
extension, & ratchet.
Note: Do all of the steps and do them in order. The results of the
subsequent tests are based on the prior tests being successfully passed.
1.) Each injector has a red power wire to provide power to the injector. Turn the ignition switch to Run and remove
each injector electrical connector and use the multimeter to check for 12 volts on the red wire. Each injector should
have 12 volts +/- .5 volt. More voltage is always better than less voltage. No 12 volts on a singe injector and the wiring
for that injector is broken inside the engine fuel injector harness.
No 12 volts on all injectors:
A.) Check for a bad connection at the 10 pin connector. Check for 12 volts at red wire on the MAF or TAD/TAB
solenoids mounted on the aft side of the passenger strut tower. Good 12 volts
there and you have a wiring problem with the 10 pin connectors or associated wiring.
See the graphic for the location of the 10 pin connectors:
See the graphic for the 10 pin connector circuit layout.
The injector power pin is the VPWR pin in the black 10 pin connector.
B.) Bad ECC power relay. The relay is on top of the computer, it provides power to the fuel injector system.
It is somewhat difficult to get to, since it requires you to remove the computer from its 2 bolt mounting.. If the relay or
socket is bad, you will not have 12 volts on any of the red wires in the engine compartment or to pins
37/57 on the computer. The pins 37/57 are the main power feed to the computer.
C.) Blown fuse link – The blue fuse link for the computer is up near the starter solenoid. Check for no 12 volts
on the ECC relay socket or computer black/orange wires. No 12 volts and the fuse link is blown open. If the fuse link blows,
there is no power for any of the computer functions.
D.) Bad wiring. Broken or damaged red wire to the chassis side of the 10 pin connectors.
Some basics about the computer:
Remember that the computer does not supply power for any
actuator or relay. It provides the ground necessary to complete the
circuit. That means one side of the circuit will always be hot, and the
other side will go to ground or below 1 volt as the computer
switches on that circuit.
2.) Get a noid light from AutoZone or other auto parts store, or even better
a set of them
This set is from http://www.toolking.com/ProductInfo.aspx?productid=12492 and costs about $12-$14.
3.) Use the noid light to determine that the injector pulses and isn’t stuck in the on position.
It you have a set of them install all of them and compare the pulse intensity. Install the noid lights,
turn the ignition switch to Run and crank the engine. A light that doesn’t pulse and stays on has a
short to ground in the computer side of the circuit. That can be either a wiring fault or a failed computer.
If this is the case, remove the passenger side lick panel and disconnect the computer connector.
There is one 10 MM bolt holding it in place. Pull the connector all the way out of the
computer so that you can see the computer side pins.
Use the list from the graphic below to find the fuel injector pins for the injectors that
didn’t turn the noid light off.
4.) Set the multimeter to low scale Ohms and measure between the
computer ground located below the computer and the suspect fuel injector pins. You should
see greater than 100 K Ohms resistance. If you see less than 100 Ohms, the wiring
between the injector and the computer has a short to ground and needs service.
Check the harness and look for damage, kinks or frayed spots.
5.) A single noid light that never turns on is either a wiring fault, or a
failed computer. Either the injector has no DC power or the computer has
failed and cannot switch the injector circuit to ground. Determine if the
injector has power by using the multimeter to check for 12 volts on the red
wire on the suspect injector connector. No 12 volts and you have a wiring fault.
Check the harness and look for damage, kinks or frayed spots. Check the 10
pin salt & pepper shaker connectors for bent pins, corrosion and damage.
If none of the noid lights flash and you have 12 volts at each injector, check
to see that you have good spark. Before you even think about replacing the
computer, see step 6.
Next Check the fuel injector wiring end to end. Each fuel injector has a red
wire (power) and an non-read wire (computer controlled ground). Set the
multimeter to low ohms and measure each non red fuel injector wire from
the fuel injector connector to the matching pin on the computer connector.
You should see less than 2 Ohms. More than that means a bad connection
or bad wiring.
6.) Use an ohmmeter set on the low resistance scale and measure the resistance of
each injector across the two contacts inside the electrical connector. You should
see between 11-16 ohms. More or less than that is a bad injector. Next measure
between either one of the contacts and the metal on the injector body. You should
see greater than 100,000 ohms. Don’t hold the metal probe tips with your bare
hands when you make this measurement. It will give incorrect results if you do.
Once you have determined that the suspect injectors have good power and
good wiring, the computer is the likely suspect, since a ground is required
to complete a circuit and make it function. The computer provides the
ground: if doesn’t, then the noid light will not flash.
7) If you have gotten this far, then the problem is likely ignition
related. Remember the noid test using all of the noid lights? All of them
were supposed to be equally bright. Since you have already tested all the
electrical side of the fuel injector circuit, the one remaining common item is
the pip sensor inside the distributor. A failing pip sensor, damaged shutter
wheel or bent distributor shaft could all cause the pulse delivered to the
injectors to be faulty. A bad pip sensor will cause all the injectors not to fire
and you will have no spark. Dumping the codes will show a code 14.
8) Spark plugs indicate one or more cylinders not firing: use the
multimeter to measure the resistance of the spark plug wires. The wires
should measure 2000 ohms per foot of length. A 2 foot wire would be 4000
ohms and a 3 foot wire would be 6000 ohms. Some Taylor and Accel wires
have metal cores and will measure much less: that’s OK.
Next examine the spark plug wires very carefully for burn spots, cracks and
damaged insulation. One good thing to try is to start the engine while the
car is a very dark area, open the hood and look for sparks or blue glow.
They indicate the electricity is leaking out of the spark plug wires.
Thanks to Tmoss & Stang&2birds at Mustang FAQ - Engine Information for some of the graphics
Thanks also to Ford Fuel Injection for some of the graphics.
1.) bad spark plug
2.) bad stark plug wire
3.) Bad distributor cap.
Bad injector - Faulty injector or injector wiring. Go to step 2 in the fuel injector test path.
Fuel injectors inoperative, one or more injectors either on all the time or will not squirt.
Revised 27-Jan-2008 to include expanded testing for proper power to injector wiring
Tools needed: Noid light, Multimeter (volts & ohms), 10 MM socket &
extension, & ratchet.
Note: Do all of the steps and do them in order. The results of the
subsequent tests are based on the prior tests being successfully passed.
1.) Each injector has a red power wire to provide power to the injector. Turn the ignition switch to Run and remove
each injector electrical connector and use the multimeter to check for 12 volts on the red wire. Each injector should
have 12 volts +/- .5 volt. More voltage is always better than less voltage. No 12 volts on a singe injector and the wiring
for that injector is broken inside the engine fuel injector harness.
No 12 volts on all injectors:
A.) Check for a bad connection at the 10 pin connector. Check for 12 volts at red wire on the MAF or TAD/TAB
solenoids mounted on the aft side of the passenger strut tower. Good 12 volts
there and you have a wiring problem with the 10 pin connectors or associated wiring.
See the graphic for the location of the 10 pin connectors:
See the graphic for the 10 pin connector circuit layout.
The injector power pin is the VPWR pin in the black 10 pin connector.
B.) Bad ECC power relay. The relay is on top of the computer, it provides power to the fuel injector system.
It is somewhat difficult to get to, since it requires you to remove the computer from its 2 bolt mounting.. If the relay or
socket is bad, you will not have 12 volts on any of the red wires in the engine compartment or to pins
37/57 on the computer. The pins 37/57 are the main power feed to the computer.
C.) Blown fuse link – The blue fuse link for the computer is up near the starter solenoid. Check for no 12 volts
on the ECC relay socket or computer black/orange wires. No 12 volts and the fuse link is blown open. If the fuse link blows,
there is no power for any of the computer functions.
D.) Bad wiring. Broken or damaged red wire to the chassis side of the 10 pin connectors.
Some basics about the computer:
Remember that the computer does not supply power for any
actuator or relay. It provides the ground necessary to complete the
circuit. That means one side of the circuit will always be hot, and the
other side will go to ground or below 1 volt as the computer
switches on that circuit.
2.) Get a noid light from AutoZone or other auto parts store, or even better
a set of them
This set is from http://www.toolking.com/ProductInfo.aspx?productid=12492 and costs about $12-$14.
3.) Use the noid light to determine that the injector pulses and isn’t stuck in the on position.
It you have a set of them install all of them and compare the pulse intensity. Install the noid lights,
turn the ignition switch to Run and crank the engine. A light that doesn’t pulse and stays on has a
short to ground in the computer side of the circuit. That can be either a wiring fault or a failed computer.
If this is the case, remove the passenger side lick panel and disconnect the computer connector.
There is one 10 MM bolt holding it in place. Pull the connector all the way out of the
computer so that you can see the computer side pins.
Use the list from the graphic below to find the fuel injector pins for the injectors that
didn’t turn the noid light off.
4.) Set the multimeter to low scale Ohms and measure between the
computer ground located below the computer and the suspect fuel injector pins. You should
see greater than 100 K Ohms resistance. If you see less than 100 Ohms, the wiring
between the injector and the computer has a short to ground and needs service.
Check the harness and look for damage, kinks or frayed spots.
5.) A single noid light that never turns on is either a wiring fault, or a
failed computer. Either the injector has no DC power or the computer has
failed and cannot switch the injector circuit to ground. Determine if the
injector has power by using the multimeter to check for 12 volts on the red
wire on the suspect injector connector. No 12 volts and you have a wiring fault.
Check the harness and look for damage, kinks or frayed spots. Check the 10
pin salt & pepper shaker connectors for bent pins, corrosion and damage.
If none of the noid lights flash and you have 12 volts at each injector, check
to see that you have good spark. Before you even think about replacing the
computer, see step 6.
Next Check the fuel injector wiring end to end. Each fuel injector has a red
wire (power) and an non-read wire (computer controlled ground). Set the
multimeter to low ohms and measure each non red fuel injector wire from
the fuel injector connector to the matching pin on the computer connector.
You should see less than 2 Ohms. More than that means a bad connection
or bad wiring.
6.) Use an ohmmeter set on the low resistance scale and measure the resistance of
each injector across the two contacts inside the electrical connector. You should
see between 11-16 ohms. More or less than that is a bad injector. Next measure
between either one of the contacts and the metal on the injector body. You should
see greater than 100,000 ohms. Don’t hold the metal probe tips with your bare
hands when you make this measurement. It will give incorrect results if you do.
Once you have determined that the suspect injectors have good power and
good wiring, the computer is the likely suspect, since a ground is required
to complete a circuit and make it function. The computer provides the
ground: if doesn’t, then the noid light will not flash.
7) If you have gotten this far, then the problem is likely ignition
related. Remember the noid test using all of the noid lights? All of them
were supposed to be equally bright. Since you have already tested all the
electrical side of the fuel injector circuit, the one remaining common item is
the pip sensor inside the distributor. A failing pip sensor, damaged shutter
wheel or bent distributor shaft could all cause the pulse delivered to the
injectors to be faulty. A bad pip sensor will cause all the injectors not to fire
and you will have no spark. Dumping the codes will show a code 14.
8) Spark plugs indicate one or more cylinders not firing: use the
multimeter to measure the resistance of the spark plug wires. The wires
should measure 2000 ohms per foot of length. A 2 foot wire would be 4000
ohms and a 3 foot wire would be 6000 ohms. Some Taylor and Accel wires
have metal cores and will measure much less: that’s OK.
Next examine the spark plug wires very carefully for burn spots, cracks and
damaged insulation. One good thing to try is to start the engine while the
car is a very dark area, open the hood and look for sparks or blue glow.
They indicate the electricity is leaking out of the spark plug wires.
Thanks to Tmoss & Stang&2birds at Mustang FAQ - Engine Information for some of the graphics
Thanks also to Ford Fuel Injection for some of the graphics.
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- Aug 11, 2005
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Thanks for the detailed info! I should have stated what I have chased down so far:
. Motor has new wires. plugs, cap, & rotor
. Switch number 1 cyl fuel injector (one that burns perfect) to number 2 cyl injector (the one that fouls the plug) and it still does it.
. Did compression check (everything is fine across the broad
. Checked for spark and all is fine there
So before I get crazy I figured I would post on here thinking someone might of had a problem like this before! Now I will use the info you sent & see what I come with. Thanks again Mike
. Motor has new wires. plugs, cap, & rotor
. Switch number 1 cyl fuel injector (one that burns perfect) to number 2 cyl injector (the one that fouls the plug) and it still does it.
. Did compression check (everything is fine across the broad
. Checked for spark and all is fine there
So before I get crazy I figured I would post on here thinking someone might of had a problem like this before! Now I will use the info you sent & see what I come with. Thanks again Mike
