Ever wish you could actually see if there was a restriction in a radiator or condenser? You can, if you use a thermal imaging camera.
The one we’ve been playing with lately is from General Tool and Instruments. Of the thermal imaging equipment on the market, this tool falls right in the middle of price range and features and will do nearly anything you ask of it in the service bay. Take a look at the A/C condenser image I took as Figure 1.
This is the magnified view of the primary coil’s current pattern, used to measure exactly how long it took to turn the current off. Too long results in a weak spark and is usually caused by a failed driver in the control module in charge.
In this image, you can actually see the flow paths through the coils as a bright yellow. Compare that color to the scale you see at the right of the image to get an idea of how hot it actually is. This is with the compressor on; so heated refrigerant from the evaporator is now entering the condenser to pass that heat load on to the outside air. Flow restrictions would be seen as darker areas in the flow path. (Note: The dark area running horizontally across the image is part of the power steering cooler on this car and not an indication of a problem in the condenser.)
There is a learning curve to using thermal imaging as a diagnostic tool, but just imagine the possibilities! How much easier would it be to identify a misfiring cylinder, a dragging brake or failed hub bearing, just to name a few?
Contributing editor Tony Martin recently wrote an excellent feature on thermal imaging for the May 2013 issue. Check out MotorAge.com to read it if you haven’t already.
Weak Spark?
When we’re diagnosing the cause of a weak spark, we often look at a few general, but common, issues like worn secondary wires or bad spark plugs. But have you ever found a weak spark caused by a bad switch?
And by switch, I mean driver, the electronic switch typically found in an ignition control module or engine control module, depending on which type of control governs the current flow through the primary windings of the ignition coil. A weak or faulty driver that does not turn of the circuit cleanly and quickly causes the magnetic field to collapse inefficiently, producing a weaker spark than normal.
You can see this in the current ramp of the ignition primary coil. Simply use your scope’s zoom function to blow up the ramp’s turn off and measure the time it took for the ramp to start it’s downward slope to the point it actually completed it. Anything over 100 microseconds indicates a problem with the driver.
Brake Comebacks
By Craig Truglia, TST member
Most likely after purchasing new rotors from your local part store you have seen a label that states, “No machining required,” or the rotor is “finished and balanced.” Do you believe when you read those labels that it’s OK to just install the rotor and continue on with the brake job? Only if you want to do the job again.
The thermal imaging camera captures the heat flowing from the condenser with the compressor engaged and can aid in locating restrictions to refrigerant flow.
Always clean the rotor mounting surface and perform a rotor run out test to make sure the installed rotor passes specifications. If the rotor/mounting surface is not correct and run out exceeds the specifications, it will allow the rotor to pass through the new brake pads unevenly. This results in wear on some areas of the rotor as the inner and outer pads lightly come into contact with it. Soon, the abnormal wear begins to result in brake squeal and shortly thereafter your customer might experience the dreaded “pedal pulsation of doom.”
One way to make sure that the rotor runs true to the caliper and pads is to perform the resurfacing using an on-car brake lathe. But no matter how you choose to machine worn rotors, don’t forget to clean the new surface by using hot soapy water. Wiping the surface clean with a paper towel or very clean rag should follow. You might be wondering why we did not suggest using brake clean after machining. Studies have shown that the aerosol propellant (a refrigerant) in brake clean can cause small metal particles to freeze to the rotor surface groves. The frozen metal particles can cause a hot spot to develop that results in rotor surface problems along with unusual brake pad wear. On the other hand, hot water opens up the rotor’s surface and makes it easier to brush those small particles away.
A brake job is not complete without cleaning all the brake hardware and lubricating the pins and contact points. To complete a professional job, make sure to properly bleed the brake system and then take the car out to seat the new pads to the freshly machined and cleaned rotor. The “30/30/30” rule is the easiest way to bed in new pads. Make 30 full stops using moderate pressure from 30 mph, allowing at least 30 seconds between each stop to avoid overheating the friction material. Remember that the vehicle is a three thousand pound missile that has to stop when the driver says so. Cutting corners to save a few bucks is no way to perform a brake job, and it’s never a good idea to compromise quality and safety.
For more on how to perform a professional brake service and reduce your comebacks in the process, watch the Motor Age/TST webinar (sponsored by Wagner Brakes) in the AutoPro Workshop or either YouTube channel.
BMW’s VANOS Tips
By Pierre Respaut, TST vice president
This 1994 BMW 325i came in with a complaint of a loud rattling noise from the engine along with an occasional power loss. While test driving the vehicle, I noticed a slight misfire when the engine was cold but didn’t hear any strange noises. Once the engine was at operating temperature I started to notice a small rattle that was coming from the front upper timing chain area.
A corresponding timing retard on the front bank of cylinders was also noticed while monitoring the scan data. After the engine was running for a while, I stated to hear a loud rattle that developed in the same area. Now it was becoming obvious that there was a problem with the VANOS (BMW’s variable valve timing system) unit. I removed the valve cover to inspect the area where the noise was coming from.
Using an on-car brake lathe is one way to insure that the pads ride true to the rotor surface.
There was a big mess along with gummy deposits from an engine that was obviously neglected. After cleaning away some of the sludge, I noticed gear scoring on the engagement gear where it exits the unit. There was also slight wear on the thrust washers from the intake cam chain sprocket. I continued to clean the gummy deposits and replaced the VANOS unit, thrust washer and related gasket. The engine now ran quiet with no timing intervention.
The bottom line here is, when you have a performance complaint without symptoms, look for a sticky VANOS. The VANOS assembly is sensitive to lubrication problems. Tell your customers to make sure they change their oil regularly and use the correct oil and filter.
If you are going to take this repair job on you will need some special tools. The flywheel will need to be locked at TDC using a rod that inserts through the block under the started motor – that is hidden by the fuel filter. The cams will need to be locked by a jig tool as well as the intake cam gear that has to be turned fully clockwise before the VANOS unit is inserted.
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