Need some help

scotty said:

Need some help

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I was driving my car home from work about 30 miles of highway. It started to have a miss like it was down a cylinder or something. Got home and checked the plugs they looked pretty good but i put a new set in it anyway still has a miss. Tried a new set of wires same thing still a miss. When your in netural and give it gas it sounds like its on 7 cylinders and when the rpms come back down it backfires a litle bit. Could it be my msd box or coil or TFI module?What should I try next. Im going ******* crazy. Help!!!

89lx
306
ys trim
595 rwhp

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Try the coil. Worked for me.

i've heard bad things about msd boxes and they sound just like this, i am willing to bet on the msd box malfunctioning

have you pulled codes? while doing so, do a balance test to make sure all injectors are firing and doing so within parameters.

then, i would grab my inductive timing light. put it on each wire and hit the trigger. you should find one wire that is not firing as well as the others (indicating that cylinder's ignition, not just wire, is bad).

go from there. 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 99 for everything OK, or the number of the failing cylinder such as 22 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.