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Old 09-01-2002, 01:21 PM
stevebfl stevebfl is offline
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
A single (or multiple) cylinder misfire should first have the cylinder/s identified. This is done with a cylinder balance test. If you were a well equipted shop you would use your engine analyser to do it for you. It would kill one cylinder at a time by shorting the primary. It would give a reading of rpm drop per event and if a real well equipted machine, it will also give the hydro carbon increase per cylinder by matching up the exhaust gas readings to the cyl shut down one at a time. A misfire will be the cylinder that drops the least when turned off.

The hydrocarbon readout evaluates the balance of fuel flow through the injectors. A cylinder with a clogged or malfuntioning injector will have no hydrocarbon increase when the ignition is stopped. A good cylinder will cause a large amount of hydrocarbon (gas) to exit if the spark is shut off (it goes into the exhaust because it wasn't burned).

If you are out in the woods, one must inovate. The same basic test can be done by pulling spark plug wires one at a time, this can also curl your toenails. It helps to pull the wire at the dist end rather than the plug end, but if you find an open wire (that is one not properly shorted by the sparkplug attached to the other end) then you will be the best ground for 25-30kv.

The D-jet cars can be done by pulling the injector leads and I have done it that way in a pinch, but the harnesses are often so fragile by this time that I would advise caution.

Later cars with idle control require real smart machines that can repetively stop only a precise number of ignition strokes to evaluate rpm differences. This is where your hip comes in. Place your hip against the fender and evaluate the misfire as each cylinder is shut down. The speed won't change but the misfire vibration level can be felt if the difference is one cylinder at a time.
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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