Troubleshooting: The Evasive Leak

Jan. 1, 2020
Dear Roy, We have a 2003 Chevy S-10 pickup with a VIN H 2.2L engine and an automatic transmission. It came into our shop with a code PO442, indicating a small EVAP system leak ...
The Evasive Leak

Dear Roy,
We have a 2003 Chevy S-10 pickup with a VIN H 2.2L engine and an automatic transmission. It came into our shop with a code PO442, indicating a small EVAP system leak. Using our smoke machine, I found the vent solenoid to be leaking. I replaced it, and tried to run the monitor. It did not run during the drive-cycle, so the customer took the truck. A week later it came back with the same code. Using my scan tool I turned off the solenoid and rechecked it. It did not leak and no other leaks were found. The truck has less than 23,000 miles on it. Your assistance would be a big help.

Danny Upmeyer, technician
Tierra Del Sol Automotive, Alamogordo, NM

Dear Danny,
Some of these small leaks are difficult to find. GM had some problems with leaks at the O-ring on the top of the tank and at the lower filler neck area. Most late-model smoke detectors use a dye that helps to locate the problem area using the proper light. The only other problem with these systems was the tendency of the wire to the vent solenoid to break. This typically resulted in a code P0440.

TDi Lack of Power

Dear Roy,
We have a 2000 VW Golf with a 1.9L TDi diesel engine and an automatic transmission. We replaced the timing belt and now the engine has no power. The injector pump timing is correct.

Could the valve timing be wrong even if injection timing is in spec? The car starts and idles great. Hope you can help.

O’Neil Clark, mechanic
Toronto Brake, Toronto, Ontario, Canada

Dear O’Neil
Yes, there could still be a valve-timing problem. However, my experience with a lack of power on these engines has been carbon build-up in the intake at the exhaust gas recirculation (EGR) valve and faulty mass airflow sensors.

This restricted airflow combined with faulty mass airflow (MAF) inputs will create the condition that you describe. Disconnect the MAF and see if the condition improves. STUMPED? Let Roy take a crack at your problem.Click here to send your question to Motor Age Troubleshooters. Please supply the vehicle year, make, model, engine, transmission, accessories and VIN, as well as your name, address and phone.

If it does, inspect and clean the intake inlet and EGR valve. Check the EGR cooler operation. Replace the MAF sensor and you should be back in business.

Inoperative Front Axle

Dear Roy,
We have a 1996 Chevy K-1500 pickup with a 5.7L engine, automatic transmission and four-wheel-drive (4WD). The problem is that the 4WD is not engaging.

With the truck on a lift, I can switch into 4WD and hear the transfer case activate. The front driveshaft turns, but the front axles do not engage. I have replaced the actuator and checked the movement of the fork. Any ideas?

Pat Holmes, technician
Alfons Haar Inc., Carlisle, OH

Dear Mr. Holmes,
The actuator assembly is activated thermally. The thermal actuator contains a coil, fluid and a plunger. When the coil is heated, the fluid changes to a gas and extends the plunger, which engages the front axle.

Go to the front axle and check for battery power at the light blue wire with the transfer case engaged. Check the black wire for a good ground. These wires activate the actuator heater.

Some owners were complaining about slow engagement when cold, and General Motors (GM) produced a service kit to convert this system to the use of an electric motor to activate the system. This is explained in technical service bulletin (TSB) 76-43-01A, dated September 1998.

Small Engine Oils Decoded

Dear Roy,
I also work on small engine equipment. I have customers that request synthetic engine oil in four-cycle engines. I don’t like using it in small engines. Do you know how it might affect them?

James Maloney, via e-mail

Dear James,
In applications such as high-rpm, high-load small engines, the manufacturer usually specifies the use of SAE 30W petroleum oil, although the owner’s manual never specifically states petroleum oil. These engines operate under extreme rpm, high load and – because most are air-cooled – high heat.
Standard multiviscosity petroleum oils are full of viscosity improvers (VI).

It is these viscosity improvers that are the weak link. As these agents are subjected to excessive heat, load and high rpm, the oil cannot reach its intended high-temperature viscosity, which results in shearing. As this shearing continues, oil film strength decreases, resulting in increased wear and oil consumption issues.

The problem that can occur in petroleum-based motor oils with VI is that under heat, load and shear forces, the molecules of the VI tend to change shape from a round molecular structure to a straightened, or aligned, molecular structure.

When this occurs, the VI is subject to degradation due to shear forces created inside the engine, which can cause a temporary loss of the specified viscosity. Under shear loads, the molecules in the VI align themselves in the direction of the shear stresses so there is less resistance to flow. As the oil cools and the shear forces are no longer present, the VI returns to its original molecular configuration and the original viscosity is returned to the oil.

Where serious problems can occur are under extreme heat and shear loads where the molecular structure of the VI is permanently destroyed and the molecules will not return to their original configuration when the oil cools and shear stresses are no longer present. This is the reason straight-weight petroleum oils are recommended for these types of applications. 

Synthetic oils are much more resistant to this type of failure. They also typically have a higher flash point and the ability to provide better sealing between piston rings and cylinder walls, and they have superior oxidation stability (resistance against reacting with oxygen at high temperatures.)

Synthetics can greatly extend drain intervals, provide better fuel economy, reduce engine wear and enable engines to operate with greater reliability. The downside is the cost of synthetics vs. straight petroleum oils.

The bottom line is that the manufacturer’s specifications are based on petroleum oils, yet the owner’s manual is not going to explain that. Based on the type of use, operating conditions and cost factor, you might consider using premium quality synthetic oil in these types of applications.

Charging Explained

Dear Roy,
In the “Troubleshooting” column of March 2007, your response to Mike Banovich about the “Faulty Alternator” may need some clarification to perhaps set the record straight and prevent further confusion.

1. In older Ford charging systems (pre-1999 or 2000), the activation voltage is provided by the ignition switch to terminal “I” of the voltage regulator through the alternator warning light. This voltage is pulled low by the regulator, activating the regulator circuit and causing the alternator to charge. Once the charging voltage is achieved, this applied voltage bounces back to the battery voltage level. Because voltage is now equal on both sides of the alternator warning light, the light turns off.

2. Since 2000, Ford has classified, activated and monitored warning lamp operation in a different way. The letter you were responding to described what is considered a “class-2 type” charging system, where the actuation voltage is applied by the powertrain control module (PCM), not the ignition switch.

As before, when that voltage is applied to terminal “I” of the regulator, it’s pulled low (but never to zero), and this activates the regulator. Once the system starts charging, this voltage bounces back to the applied level – actually slightly higher because the system is charging and we now have more than 14 volts at the battery rather than 12.6.

This “Dip and Bounce “ of the voltage at terminal “I” is seen by PCM as an “OK” condition. An appropriate bit of data is then applied to the Standard Corporate Protocol (SCP) data bus, and the instrument cluster will decode this data and turn the alternator warning light off.

The problem we have encountered in aftermarket alternators is indeed the use of a voltage regulator intended for the older system that sinks PCM applied voltage lower than what PCM considers normal. And this will raise a flag; appropriate data will not be put on the SCP bus, and obviously, the alternator warning light will stay on, even if the system is charging.

Thus, it is extremely important for you and your readers not to consider all aftermarket alternators the same. Where some rebuilders, because of lack of knowledge or economic pressure, may substitute older regulators for the newer applications, there are many who strictly use original equipment (OE) voltage regulators, and their alternators perform exactly equal to an original equipment manufacturer (OEM) rebuilt [units].

The Automotive Parts Remanufacturers Association (APRA) has been educating participating rebuilders to familiarize them with nuances of more recent charging systems. This is accomplished by APRA’s Electrical Clinics in various locations across the country each year.

It is also important to realize that the rebuilding industry encounters the same obstacles as the rest of the automotive service industry regarding availability of OE information. While each OEM is obligated by law to provide emissions-related data to the service industry, they are under no mandate to release engineering information regarding the design of the voltage regulator and such. So aftermarket electronics manufacturers use tedious reverse-engineering to decode the newer designs. Unfortunately, this effort at times falls behind the curve.

Mohammad Samii, president
Sammy’s Auto Electric Service Inc., Champaign, IL
Coordinator of Electrical Training, APRA

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