Odd Firing Problem

Cylinder balance test: use this to find dead or weak cylinders:

Revised 19-Dec-2015 to update RPM ranges and include a more complete description of the engine running tests that are done prior to the cylinder balance test. Added YouTube video to show the process.

The computer has a cylinder balance test that helps locate cylinders with low power output. You’ll need to dump the codes out of the computer and make sure that you have the A/C off, clutch depressed to the floor and the transmission in neutral. Fail to do this and you can’t do the engine running dump codes test that allows you to do the cylinder balance test.

Here's the way 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, have the clutch depressed to the floor, 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.


Here's how 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.





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. This is crucial: the same wire that provides the ground to dump the codes provides signal ground for the TPS, EGR, ACT and Map/Baro sensors. If it fails, you will have poor performance, economy and drivability problems

Some 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.

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, clutch depressed to the floor 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.

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

Your 86-88 5.0 won't have a working Check Engine Light, so you'll need a test light.
See AutoZone Part Number: 25886 , $10




Alternate methods:
For those who are intimidated by all the wires & connections, see Actron® 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 www.midwayautosupply.com/Equus-Digital-Ford-Code-Reader/dp/B000EW0KHW Equus - Digital Ford Code Reader (3145It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $22-$36.


Cylinder balance test

If you have idle or IAC/IAB problems and the engine will not idle on its own without mechanically adjusting the base idle speed above 625-750 RPM, this test will fail with random cylinders pointed out every time it runs. The IAC/IAB must be capable of controlling the engine speed to run in the 1300-1500 RPM range. Playing with the base idle speed by adjusting it upwards will not work, the computer has to be able to control the engine speed using the IAC/IAB.

Warm the car's engine up to normal operating temperature. With the test jumper in test position, start the engine and let it stabilize. It should flash a 10 and then a 4 and maybe an 11. If no 11, then there are other codes that will be dumped.
One of the first tests it does is to open the EGR all the way, this will cause the engine to stumble and almost die. If the engine dies here then you have EGR problems.
To start the cylinder balance test, briefly floor the accelerator past 2500 RPM and let off the accelerator. The engine will stabilize at about 1300-1450 RPM and the cut off the fuel injectors one at a time. The engine speed will drop briefly and the computer will turn the fuel injector for the cylinder under test back on. Then it starts the process for the next cylinder. 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

See View: https://www.youtube.com/watch?v=HDXrkKS4jTE
for a visual tour through the process. There is no voice narration so you have to listen carefully for the engine sounds.

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/loan. 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 with a plastic screwdriver handle between the throttle butterfly and the throttle housing. 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.

I generally use a big screwdriver handle stuck in the TB between the butterfly and the TB to prop the throttle open. The plastic is soft enough that it won't damage anything and won't get sucked down the intake either.

A battery charger (not the trickle type) is a good thing to have if you haven't driven the car lately or if you have any doubts about the battery's health. Connect it up while you are cranking the engine and it will help keep the starter cranking at a consistent speed from the first cylinder tested to the last cylinder.

dcurtis said:

Well checked way to many things so far, finally just swapped the brand new msd coil for a factory one and problem cleared up for now, didn't drive far but we'll see tomorrow when I try to drive to work

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Another My Spark Died incident. I swear they must have monkeys doing their QC.

Clean and tighten the pins on the salt and pepper shakers. I used to have problems from mine but I cleaned, de-pinned, and lightly squeezed the female wires ends. Just enough to tighten up the connection a little. Add dielectric grease and no worries. I've seen a bunch of guys straight wire the salt and pepper shakers....I didn't go that route.

Carbed is good. Had an edelbrock on my car for a few years...with the efi distributor and drove it every day.

I did it because of an o2 sensor wire. Spent about a grand swapping over with fuel pressure regulators (2), intake, gaskets, carb, air fuel ratio guage, air cleaner, fuel line, accelerator cable bracket, carb spacer, and heater hoses. Been there....done that. Don't do it because some little wire is giving you a problem.

Its not too hard to fix. Can even get a whole brand new harness cheaper than if you convert to carb. Even racecars are going injected. Think about it.

That is an electrolytic capacitor or what is commonly called, a cap. They have a definite life cycle and after 22 or more years, they start to fail. The failure mode is they dry out because the liquid electrolyte leaks out. Then they burn up or blow the top out of the can that they are packaged in. A clue to failure is the top of the can starts to bulge. When you see one bulging it has either failed or is in the process of Many of the automotive computer repair places will replace all of them as a first step in any repair efforts. The capacitors have a voltage rating, a capacitance rating, a tolerance for the capacitance rating, an failing

operating temp rating and a life cycle rating.

The higher the voltage rating, the larger physical size of the capacitor when compared to one with the same capacitance and a lower voltage rating. Most of the ones used in automotive electronics have a 20-35 volt rating since they are used in low voltage circuits. Using one with a higher voltage rating doesn't hurt anything, but it usually doesn't have any benefits either. There may be a size limitation because of the way the circuit board is laid out. That means there are sometimes limits on replacing the 20 volt cap with a 35 volt cap because it won't physically fit in the space allocated on the circuit board.

The higher temp rating and longer lifecycle ratings increase the cost of a capacitor. In automotive circuits, those are important factors, and the highest rating stands the best chance of lasting the longest and working the best. The typical capacitor used in most automotive electronics is less than $1.50 each.

WWW.digikey.com or www.newark.com are good sources for capacitors, resistors and just about any other quality electronic part. Avoid Radio Shack unless it is a temporary repair or emergency situation. Almost all of their parts are less than top quality stuff and a lot of it is just plain junk.

That

dcurtis said:

It wasn't swollen or anything, looks more like one side just corroded, green and just rotted out like a bad battery cable looks

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That's because the electrolyte leaked out...
It is probably time to have all the caps replaced.

dcurtis said:

Entire engine is new and was potent as hell, then a random mis I cannot track?

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TFI, PIP, MSD box and then the computer are the three primary suspects. The PIP is the only thing that you haven't replaced; PIP problems increase as the engine warms up.

The computer needs to be fixed or replaced, regardless of what else may be wrong. I suggest that you check out eBay and find one to the services that fixes you old computer and then returns it to you. These are mostly fixed price deals.

See https://www.google.com/?gws_rd=ssl#q=ecu+repair+service
http://www.ebay.com/bhp/ecu-repair
OR
https://www.google.com/?gws_rd=ssl#q=ecu+repair+service
for some possible sources,