Intermittent Cylinder Misfire Subaru Valve Guide Problem

Whenever you remove a Subaru cylinder head you should always look at the valve guides to see if there is any evidence of them moving, particularly the exhaust valve guides. I have seen these guides moves causing misfires or even worse completely drop causing valve to piston interference. The problem seems more prevalent in the 2.5L engines but I have… Read More

Subaru 2.0 DOHC Turbo Cylinder Misfire Broken Valve Spring

I had a 2002 Subaru Impreza WRX in the shop the other day that had me going for a bit. It’s been a long time that I have ran into a cylinder misfire problem that I couldn’t just go directly to the source of the problem by some quick preliminary tests. Here are the four quick tests I will use… Read More

General Powertrain Diagnosis

Despite the sophistication of today’s powertrain control systems, even the most advanced software program cannot disguise a worn camshaft lobe, a burned valve or a loose timing chain. Unfortunately, even though these types of mechanical failures create recognizable symptoms of poor performance, many technicians get caught up analyzing pulse trains without ever considering valvetrains! The fact is, illuminated MILs (Malfunction… Read More

Computerized Powertrain Controls Diagnosis (Including OBD II)

Electronic engine control systems have been standard equipment on most cars and light trucks since the early 1980s. While these systems improve both driveability and fuel economy, their primary purpose is emission control. From a service standpoint, many of the early systems were difficult to diagnose due to their limited self-diagnostic capability. However, serviceability improved in 1988 with the implementation… Read More

Mode 06 Diagnosis

One of the keys to understanding Mode $06, or getting the most out of your scan tool, is to understand what the different modes are and how they are used. How many modes are there? There are 9 modes of scan tool operation. Many technicians have been using 4 or 5 modes for 20 years. Each of the 9 modes… Read More

Ford F-150 Misfire Mode $06 Diagnosis

This article will explain one of the most practical applications of Mode $06. The vehicle has a misfire but the MIL is not ON. It is a used car trade in with 120,332 miles and the repair history is unknown. The first obvious step is to scan it for codes. using a Generic scan tool to check the PCM and… Read More

Fuel And Air Induction Systems Diagnosis

Electronic Fuel Injection (EFI) was introduced to the automotive world in the late fifties, when Chrysler offered the ‘Electroinjector’ system as an option on its Hemi V8. Shortly after its debut, reliability problems forced Chrysler to recall the few sys­ tems that were sold. Ironically, re­ called vehicles were retrofitted with dual four-barrel carburetors. Three decades later the tide would… Read More

Diagnosing Computer Controlled HVAC Systems

Computer Controlled HVAC Pre OBD II Vehicles built prior to the advent of OBD II typically used electronic control modules only to operate their automatic temperature control systems. On these models, the control module was typically contained in the HVAC control head in the same unit housing the driver’s system control switches. Warning indicators may or may not be included on… Read More

A/C System Performance Testing Part 2

A/C Performance Testing A performance test can determine whether the A/C system is functioning properly and if it is not can indicate what is wrong so the system can be repaired.Different vehicle manufacturers specify different methods to conduct system performance checks, but as a guideline, the following procedure may be used.Connect a manifold gauge set as previously described. Hang the… Read More

A/C System Performance Testing Part 1

Automotive Refrigerants The refrigerant used in automotive air conditioning systems from their inception until the early 1990s was a chemical compound called dichlorodiflouoromethane, more commonly known as Freon or R12. R12 is a member of the chemical family known as chlorofluorocarbons(CFCs). Although R12 works extremely well as a heat transfer medium in an automotive air conditioning system, CFCs have been… Read More