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Testing RPM/TACH


lilfordrunner

Active Member
Joined
Nov 12, 2011
Messages
36
Vehicle Year
1987
Transmission
Manual
When checking the RPM/TACH with a multimeter and inductive clamp I get many different readings.

Let me start off by saying, the truck is idling high (still haven't figured out why) around 1900-2000

When you are on the right bank of spark plugs and you put the inductive clamp on right side up you get double what the tach says. if you flip the clamp upside down, you get a pretty accurate read (upside down being the opposite of the the directions say to do)

on the left bank of spark plugs with the clamp right said up you get nearly triple the reading, and upside down you get nearly have the reading from the Tach.

Any ideas?

(93 4.0 dropped into an 87 ranger)
 
Inductive clamp tachs are hard to use on waste spark systems because both sides of the coil fire every time. Since the inductive clamp style determines engine speed by watching spark pulse along the wires and assuming one spark per two revolutions of the engine, waste sparks read about double.

Why it's doing crazy stuff on the driver's side, idunaugh.
 

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