5.0 Question

get a code reader and pull the codes, after you get the codes pulled stomp the throttle and it will test each injector for you.

5.0's hate platinum plugs, especially Bosch, get some regular copper Motorcraft plugs.

You dont need a code reader for our cars, just a jumper wire or a test light will do fine. The check engine light doesnt have to be on for trouble codes to be present. There are plenty of diagrams on this site that tells you how pull the codes, jrichter might chime in with one of his many "how to's".

I'm a little confused, are you saying it is only running on 3 cylinders, numbers 1, 2, and 5? Cause that's not possible.

I agree that the cylinder misfire situation needs further work. It's probably running on more like 6 cylinders if it even idles worth a poo (That's not to say that those cylinders are all running at 100%).

As noted, the cylinder balance test is the way to figure out which cylinders are not contributing properly (if you can allow the car to run long enough to do this. It sounds like you can).

Alternatively, an inductive timing light on each plug wire can kinda give a clue about the spark for a given cylinder. A noid light can help one see the quality of the signal to the injectors (they receive constant key-on 12 volts and the EEC modulates ground to each one).

Be very sure your firing order is correct.

And while I doubt the plugs are the only issue, when dealing with something like this, I would get some copper plugs (as was suggested). I've seen the difference in idle quality with plats vs coppers on 5.0's and it was noteworthy in said instance. Copper conducts better.

What are you current plug gaps?
You might want to run a slightly closed gap with the fresh plugs (something like 0.045" for now).

Good luck.

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

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.

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.



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



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.

The HO firing order is 1-3-7-2-6-5-4-8.
Non HO firing order is 1-5-4-2-6-3-7-8