deductive reasoning on isolating ignition problems



deductive reasoning on isolating ignition problems

Postby grumpyvette » February 2nd, 2010, 1:55 pm

heres a great example of an easy test to do, these plugs came from an engine with a slight miss at idle, the owner suspects its either a bad plug or a bad plug ignition wire, hes done a great job by first inspecting the plugs and labeling them as they were removed for inspection
obviously verifying the ignition voltage and ignition wire connections, coil function and voltage and connections and the firing order before doing a test is mandatory
the way the engine functions will tell you a good deal about the potential source of a problem,indicators like plug condition, cylinder temperature, the ignition spark, or the rpm range a problem occurs at help locate the problem.
use your VOLTAGE METER SET ON OHMS to measure ignition wire resistance, from end to end, good ignition wire rarely reads over 400 ohms per foot. ideally it reads under 100 ohms per foot

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a simple test that will take less than a 1/3 of an hour in most cases can be performed,obviously you can use a V.O.M. meter, on the ignition wires, to find an obvious high ohms resistance reading, or install all new plugs and wires, might solve the issues but it won,t tell you the cause, but a simple test gives you more info,
swap that #3 plug to #4 as it seems to be burning cleaner and see if the problem remains with #3 or moves to #4 if it stays its certainly not the plug, if it moves its obviously the plug,if its not the plug after a test run of about 20 minutes the plug should clear up in its new location if its not badly fouled, if it does you then swap the #3 ignition wire with the # 4 ignition wire (ASSUMING THEY WILL REACH) if the problem follows the wire, then obviously the wires defective.
lets assume the problem remains at #3 location after both tests and both the plug and wire check out ok in the #4 location but the previously good wire and plug moved from the previously good #4 both now still allow the plug to foul.
that indicates its probably in the distributor cap, or a badly adjusted valve,because its related to a single cylinder or bad valve seal leaking oil or its related to the fuel/air supply at #3 or its a mechanical issue like a bad injector carb jetting, a worn cam lobe or badly adjusted valve,each factor can be tested, individually, etc. its simply a process of elimination.
example
If one whole side of the engine ran richer it could be cabs jetting in a carb engine, or a bank of injectors getting the wrong pulse duration, in an injected engine, but if its only one or two cylinders, running lean, or richer than the others its slightly more likely to be a bad injector(S) or a bad o2 sensor or a defective carb or a vacuum leak, all of which can be tested for. the key to isolating the cause is thinking thru the potential causes and testing each and eliminating each until its obvious which is the source of the problem,and pulling trouble codes, use of a shop manual and some common sense and a few tools like a timing light, v.o.m. meter, vacuum gauge , IR temp gun , and understanding basic engine tuning and function sure will help

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videos
http://streetmuscleaction.com/engines/hei/
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
grumpyvette

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