ANALYSIS WITHOUT EQUIPMENT by Mac VandenBrink
|LOW SPEED PROBLEMS ARE USUALLY TIME RELATED: 1. Leakage,|
like a poorly seating valve has a greater chance to be
diagnosed at low speed, typically cranking RPM. The reason
is simple, because it has more time to leak down. Example: A
burned valve may feel like a misfire at idle, but
performance wise there is very little negative effect at
high RPM, because the leakage is so minute at that speed. 2.
A vacuum leak drives the fuel trim positive at idle, but
equals out at high speed when the leak has very little
effect. That is how you know the difference between lean
injector and vacuum leak. 3. A leaky injector has more time
to drip at idle, while at high speed there is less time and
may be only a few drops. 4. Carbon build-up may keep the EGR
valve open causing a rough idle. At high speed the EGR valve
should be open anyway to control NOX. Therefore carbon
build-up at EGR has no negative effect at high RPM or load.
HIGH SPEED COMPLAINTS ARE USUALLY VOLUME RELATED: 1. Here
FAILURE AT ANY SPEED: A dead hole at any speed can mean
Final advice! Don’t memorize — analyze!
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