wiring experts?

If you're losing spark on individual cylinders, look at your distributor cap and rotor, plus the plugs and wires for those cylinders. It couldn't be the wiring harness because you'd lose spark on every cylinder, being that they're all controlled from the same distributor and ignition coil. Have you pulled codes and run a cylinder balance test yet?

If you have an extra distributor lying around in wait, swap it out. Silly thing may have warped the shaft. Oddly enough same thing happened to my 83 vert. Only the shaft was wobbling profusely by the time I figured it out. Bearing races do go bad.

Worst case scenario: Cyl 2 dropped compression. Have you checked to see if cyl 2 is actually getting fire? You can get a spark tester for $5.

As mentioned, the distributor can wear and cause odd problems with the spark. Sometimes the shutter wheel that covers and uncovers the Hall effect sensor gets bent or wobbles and causes problems.

You sure it's losing spark and not fuel?

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What's this engine's Mods? What's the gap on the plugs? What plugs?

Nothing in the wiring that affects one cylinder when talking about spark.

You have the PIP signal, the Spout wire, the TFI voltage, TFI start voltage, IDM and the Ignition ground all on the TFI connector. Spark will follow the path of least resistance. If the gaps to large it will jump somewhere else. I also wouldnt recommend Platinum Plugs. Autolite 3924 Copper plugs work just fine. Id close the gap on plug number 2 and see what happens.

Find out for yourself if the two cylinders are really having problems....

Cylinder balance test:
Warm the car's engine up to normal operating temperature. Use a
jumper wire or paper clip to put the computer into test mode. Start
the engine and let it go through the normal diagnostic tests, then
quickly press the throttle to the floor. The engine RPM should exceed
2500 RPM's for a brief second. The engine RPM's will increase to about
1450-1600 RPM and hold steady. The engine will shut off power to each
injector, one at a time. When it has sequenced through all 8 injectors,
it will flash 9 for everything OK, or the number of the failing cylinder
such as 2 for cylinder #2. Quickly pressing the throttle again up to
2500 RPM’s will cause the test to re-run with smaller qualifying figures.
Do it a third time, and if the same cylinder shows up, the cylinder is
weak and isn’t putting out power like it should. See the Chilton’s Shop
manual for the complete test procedure

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.
You watch the flashing test lamp or Check Engine Light and count the flashes.

Be sure to turn off the A/C, and put the transmission in neutral when dumping the codes.
Fail to do this and you will generate a code 67 and not be able to dump the Engine Running codes.

Dumping the Engine Running codes: The procedure is the same, you start the engine with
the test jumper in place. Be sure the A/C is off and the transmission is in neutral.
You'll get an 11, then a 4 and the engine will speed up to do the EGR test.
After the engine speed decreases back to idle, it will dump the engine running codes.

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.
You watch the flashing test lamp or Check Engine Light and count the flashes.

See Troublcodes.net Trouble Codes OBD & OBD2 Trouble Codes and Technical info & Tool Store. By BAT Auto Technical





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.



The STI has a gray connector shell and a white/red wire. It comes from the same
bundle of wires as the self test connector.

89 through 95 cars have a working Check Engine light. Watch it instead of using a test lamp.



The STI has a gray connector shell and a white/red wire. It comes from the same
bundle of wires as the self test connector.


WARNING!!! There is a single dark brown connector with a black/orange wire.
It is the 12 volt power to the under the hood light. Do not jumper it to the computer test connector.
If you do, you will damage the computer.

What to expect:
You should get a code 11 (two single flashes in succession). This says that the computer's
internal workings are OK, and that the wiring to put the computer into diagnostic mode is good.
No code 11 and you have some wiring problems.

Do a compression test on all the cylinders.
Take special note of any cylinder that shows up as weak in the cylinder
balance test. Low compression on one of these cylinders rules out the
injectors as being the most likely cause of the problem. Look at cylinders
that fail the cylinder balance test but have good compression. These
cylinders either have a bad injector, bad spark plug or spark plug wire.
Move the wire and then the spark plug to another cylinder and run the
cylinder balance test again. If it follows the moved wire or spark plug,
you have found the problem. If the same cylinder fails the test again,
the injector is bad. If different cylinders fail the cylinder balance test,
you have ignition problems or wiring problems in the 10 pin black &
white electrical connectors located by the EGR.

How to do a compression test:
Only use a compression tester with a screw in adapter for the spark
plug hole. The other type leaks too much to get an accurate reading.
Your local auto parts store may have a compression tester to rent.
If you do mechanic work on your own car on a regular basis, it would
be a good tool to add to your collection.

With the engine warmed up, remove all spark plugs and prop the
throttle wide open, crank the engine until it the gage reading stops
increasing. On a cold engine, it will be hard to tell what's good &
what's not. Some of the recent posts have numbers ranging from
140-170 psi. If the compression is low, squirt some oil in the cylinder
and do it again – if it comes up, the rings are worn. There should be
no more than 10% difference between cylinders. Use a blow down
leak test (puts compressed air inside cylinders) on cylinders that
have more than 10% difference.

See the link to my site for details on how to build your own blow
down type compression tester.