A How To Carburetor Diagnostic Guide – Part 4

Continued from Part 3...

b. Spark plugs – New or newer lower mileage vehicles have much better combustion processes (less contaminates), which allow you to go longer durations between plug replacements.  However, if you do not perform regular oil changes this can lead to shorter plug lifespan do to combustion contaminate.  Old dirty oil passes into the combustion more easily where it will be burnt thus causing combustion contaminates.  Any broken, excessive burning, etc. warrants replacement.  Note: The longer your plugs are used the less efficient they are and the less your mileage will be, and the more likely your vehicle will breakdown.  

c. Distributor cap – Again much the same as spark plugs.  The longer your distributor cap is used the less efficient they are and the less your mileage will be, and the more likely your vehicle will breakdown.  Any broken, excessive burning, etc. warrants replacement.  Consult a repair manual.  

d. Spark plug wires are quite often over-looked.  All wires have a specific lifetime and resistance value, which can be measured with an ohmmeter.  The average wire should have a measurement of between 3K ohms to 14K ohms depending.  Note: The longer your spark plug wires are used the less efficient they are and the less your mileage will be, and the more likely your vehicle will breakdown.  Consult a repair manual.  

e. Ignition coils – Although this is the least likely of failures it’s still note worthy.  An experienced technician can place a wire at some distance from the coil whilst another person cranks the engine to see if there is a spark between the coil and wire end.  Ignition coils can last the life of the vehicle.  Consult a repair manual.  

f. All related sensors and switches whether electrical or vacuum operated.  I cannot go into this area in detail, as this area is an entire guide unto itself.

Broken, Damaged or Disconnected Vacuum Lines -
The visual inspection should show any problems here.  Start by tracing the vacuum lines around the engine compartment moving towards and paying particular attention to areas where there are heat, oil and/or stretched lines.  Not sure of what you are seeing consult an expert.  

Computer Sensors –
Cars in the late 1980s on up to 1995 are more complex then pre-1980 cars but still can be diagnosed with some effort and may even require a store bought computerized scanner with codes.  

All the above this section applies to vehicles from the 1900s on up to 1995 but does not include 1996 and newer vehicles.  These vehicles have a more complex computerized sensor system known as the Onboard Diagnostic II (OBDII) system that makes diagnosing left for the professionals.  Today’s vehicles are equipped with a plethora of sensors, computers and software.  But it’s these sensors, computers and software that give us the much needed fuel economy.  They also assist in extending engine life.  However, when something goes wrong you almost cannot diagnose it yourself.  This is where a simple visual inspection can sometimes yield a little rare luck.  Here is something you should be aware: The wrong parking or tail light bulb can in some cases cause an incorrect air/fuel ratio, which means poor mileage.  

Contaminated Fuel -
This is where a station has water or dirt leaking into the fuel tanks, but today this is the least likely factor or cause of any running problems. 

Well, I hope this helps.  I’m sure that I will be improving upon it over time between my busy schedules. 

Good luck, TEKAY-INTL - An eBay Store

All Rights Reserved Copyright 2009 Tekay-intl

Disclaimer: You have been advised to read all and any repair manuals and/or consult a professional repair shop.  By no means am I the last or final word for your repair issues.  Don’t just take my word for it before attempting any diagnostics on your own, consult a professional and/or read your repair manual first. 

SEE: PART 1 | PART 2 | PART 3 | PART 4 | TEKAY-INTL