misfire under load

I'am having the same probablm i will be checking mine out tomarrow i will let u know what i find.

Did you run a cylinder balance test yet? That's where I'd start since you noted the miss is felt at or near idle.

Good luck.

MOTORBREATH53 said:

alright... so I tried to run the cylinder balance test, but the car dies at the end of the regular diagnostic test...
I could read the codes it was showing on my scan tool in the MIL, but then it would idle high as if still testing for approx 2.5-3 minutes. The idle would then just fall off and die.

what am I doing wrong.

Click to expand...

When you start the CBT, IIRC you stab the throttle to WOT real quick. You can tell the puter 'took' the command because it will hold the idle around 1500 RPM (for fudge factor as it shuts cylinders down and an RPM drop occurs). It can take a little time for this to occur. You should hear the cylinders cutting out and back on.

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 http://www.troublecodes.net/Ford/
OR
See http://www.mustangworks.com/articles/electronics/eec-iv_codes.html

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.

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/detailedproductdescription.asp?3829 – It has a 3 digit LCD display so that you don’t have to count flashes
or beeps.. Cost is $33.

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.


One of the tests with the engine running is the EGR function. It opens the EGR with the engine at or near idle. It is supposed to stumble or nearly die. Yours may be dying due to other problems that are happening when this test is run.

I actually cannot remember the time frame you have to initiate a CBT. I just always do it right after the codes are spit.

For no O2's, you're running in FMEM and it will default to a fairly decent tune.

You can try and watch your O2 signals to see how they're doing. They can become very hysteretic before a code is generated.

Good luck.

i just check my car for vac. leak everything was ok.I believe that its in the fuel systom. Mine started just after geting gas last week.

MOTORBREATH53 said:

I have some other 02s in my storage on my smog H pipe. Maybe i'll try those on.

Click to expand...

This would be my next course of action. I didnt say anything before because O2's are pricey and we hate tossing parts at fixes, but when the parts are free, I have not one issue with trying it.