Misfire/Lacking Power...What can it be?

I had a problem like that . 1st you need to make sure all your cyl are firing. My problem was I had a bad wiring harness that rubbed 2 wires together on my injector. Then it shorted out my computer and would not fire that cyl. Also check your timing. I had to bump mine up to 18deg to really wake it up.

Also make sure your getting enough fuel. Fuel filter/pump ectect

It smells of an electrical problem to me. TFI, or other ignition components operating intermittently or weakly.

My second suspicion would be a vacuum leak. If it is vac, you should be able to detect a rich condition.

+1 for the vacuum leak... but what's the magic trick to see where's the damn leak ? I'm pretty sure I have one on mine i'm running rich as hell I have a crapola of backfires when I down shift and it plunges into the high RPMs.

Well my opinon on when your coming to a stop and it wants to shut off. Try bumping your idle up a little ... mine use to do that also. +1 for vac leak... check your hoses and listen close for hissing

TheDamned said:

+1 for the vacuum leak... but what's the magic trick to see where's the damn leak ? I'm pretty sure I have one on mine i'm running rich as hell I have a crapola of backfires when I down shift and it plunges into the high RPMs.

Click to expand...

A couple cans of engine start (ether) sprayed sparingly around the engine bay. Listen carefully for an idle up.


To the original poster: If you have not pulled codes yet... it's a GREAT place to start!

Tula, when you follow Dagg's excellent advice about pulling codes, run a cylinder balance test. It will help you narrow down if the misfire is random of dedicated to one or more non-contributory cylinders. This greatly helps with diagnostics.

Good luck.

i had a bad fuel pump and would miss fire at high rpms and a bad egr valve and after all that bad coil too

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 http://www.troublecodes.net/Ford/
OR
See http://www.dalidesign.com/hbook/eectest.html for more descriptive help
OR
See http://www.mustangworks.com/articles/electronics/eec-iv_codes.html

For those who are intimidated by all the wires & connections,
see http://www.actron.com/product_detail.php?pid=16153 for what a
typical hand scanner looks like. Normal retail price is about $30 or so
at Walmart.

Or for a nicer scanner see http://www.midwayautosupply.com/pc-7208-90-equus-digital-ford-code-reader-3145.aspx –
It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $30.

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.

Would not having the EGR vac. solonoid cause a miss? The car was originally a 4cyl and I know the solonoid is different for the 5.0 so I haven't purchased one yet (hopefully this weekend). I have done: Coil, Spark Plugs, Wires, Cap, Rotor, TPS, Timing, MAF/Injectors, Cleaned fuel lines, fuel filter, fuel pressure, now looking into fuel pump and strainer. Any other suggestions??? It doesn't always miss, sometimes it will run fine then I give it a little gas and it starts missing.