►3C Intelligent Induction Cleaner
• eBOB DLC Breakout Box
• eSCAN Mode 6 Decoder
• eSCOPE PRO
• eSCOPE ELITE4
• Resistance Decade Box
• Capacitance Decade Box
• eCOP Induction Pickup
►Ruggedized Notebook PC
PRESSURE TRANSDUCER TRAINING
John Anello - Auto Tech on Wheels
I was called to a shop for a complaint of no power on a hard acceleration on a 2002 Ford Focus with 2.0L with only about 53,000 miles (figure 1). The vehicle idled fine with no misfires or codes stored in memory. The shop had already replaced the fuel filter and performed a back pressure check to rule out a partially clogged catalyst convertor. The vehicle just did not have the horsepower it should for this 4 cylinder. The owner was told by the garage that there was a possibility that the fuel pump was bad and suggested that he seek the dealership to have it changed under warrantee. When the vehicle was checked by the Ford dealer they had a different opinion of what was needed to fix the car. The Ford dealer had recommended a transmission due to the lack of driveline torque and a condition of engine flare-up on acceleration. The torque multiplication at the wheels just did not seem enough. The customer at this point called the garage back to let them know about the outcome and the garage recommended a local transmission shop to get a second opinion. A visit to the transmission shop proved the dealer wrong and now the vehicle was back at the garage for further investigation. This poor car was like a carnival
ride where everybody wanted to take a turn in the driver seat. There were too many formed opinions with no solid answers to remedy the problem.
When I arrived at the shop I had to drive the vehicle to get a feel for the problem others had experienced. I warmed the car up and it seemed to rev up fine with no hesitation problems. The engine idled fine with no misfires or apparent roughness. I placed the vehicle in drive and accelerated normally from a dead stop and it did not seem too bad at all. Then I tried it again but this time on a hard acceleration. The vehicle seemed to accelerate fine without holding back but it took too long to come out of first gear due to the throttling needed to get the vehicle going. By holding the throttle down further it created an engine flared up which was followed by a bang into second gear. It felt like a bad transmission but then again it seemed like the engine did not have the top end torque it was designed to have. At this point I needed to run some tests to determine if the engine was experiencing a fuel, air/exhaust flow or a timing problem.I started my diagnosis by checking for codes in memory and there were none present (figure2). The EVAP monitor did not run yet indicating that someone had erased prior codes and stored freeze frame
information but the vehicle did run all the other monitors proving out any fuel trim or misfire conditions. When dealing with a no power condition it is important to know that most failures I have seen in the field usually fall into the common categories of lack of fuel, restricted air intake, clogged exhaust, miscalculation of volumetric efficiency or an ignition/valve timing issue. It was easy to just watch data parameters on acceleration to determine if the problem was fuel related so I accelerated the engine again from a dead stop to wide open throttle while viewing some selected PIDs (figure3). You can quickly see that the ECM maintained fuel control during the whole time indicating that the power loss was not do to a fuel problem. Had it been a fuel problem I would have seen fuel
trims maxed out with an O2 sensor value constantly below 500mV. Providing that the O2 is working properly, this is a quick test to eliminate the need to get too intrusive by hooking up a fuel analyzer to check fuel pressure and volume.
Now that I eliminated a fuel delivery problem, my next test was to perform a volumetric efficiency test to check air flow through the engine. The engine is nothing more than an air pump and the ECM will use the MAF calculation to determine the proper fuel and ignition timing mapping to keep the engine at peak performance. The correct air flow reading is dependant on the proper calibration of the MAF, amount of restriction in the air inlet and exhaust system or valve train integrity. This test has to be done at wide open throttle while driving to be accurate. You also need to take into consideration the ambient
air temp, altitude and engine size. This can be done by recording your captured scan data into a VE calculator or by simply plugging your engine and ambient conditions into the Escan VE program and let it do all the work for you while you concentrate on your driving skills to maintain a steady wide open throttle acceleration to capture the data you need. Once the proper information was entered into the VE program I accelerated to wide open throttle from a dead stop and captured the air flow data (figure4). The actual volume of air was 30 percent below the calculated specification. There were no fuel trim issues
which indicated that the MAF was correct in its findings. The exhaust back pressure was already checked by the garage and found to be below 3 P.S.I. and the air inlet and air filter were checked for restrictions and proved to be okay. This problem was valve train related.
I next hooked up my scope and tagged the crank and cam sensors to perform a correlation check by viewing the signals in a superimposed format (figure5) to prove my suspicions. By pulling up a good known pattern from my Ace Misfire database (figure6) you can see that the crank and cam correlation was off by about 60 degrees. This test is a quick and easy check to validate mechanical timing issues with trigger points but it alone still can not prove out a jumped timing chain or belt. There have been too many situations where I have found loose trigger wheels that lost their indexing, damaged flywheels or worn crank pulley keyways. The only true way for me to quickly prove out a valve train problem would be with the use of a 300 P.S.I. pressure transducer in a cylinder chamber to get a true indication of piston and valve correlation.
I removed the spark plug and placed a spark tester on the wire using a spark tester. I next screwed the pressure transducer and adapter assembly into the cylinder and started the engine to capture a waveform. I shut down the engine and zoomed into the pressure pattern to view my peak to peak pressure rises indicating one combustion event of 720 degrees. I placed my cursors on my peak to peak compression rises and then hit the Cam Timing button within the EScope program (figure7). The program automatically placed 5 large purple cursors creating 4 divisions of 180 degree of crankshaft rotation and 5 smaller purple cursors creating 6 sub-divisions of 30 degrees on the screen. You could now see that the exhaust valve was opening at about 75 degrees before BDC of the power stroke (take note the lowest fall after the compression rise is where the exhaust valve begins to open). Having seen many waveforms showing exhaust
valve openings between 30-45 degrees before BDC of the power stroke, this engine's valve timing was definitely off by 30 degrees or better. It was now safe to instruct the garage to pull apart the front timing cover which involved supporting the engine with a jack, removing an upper engine support and removing an upper metal timing housing cover just to expose the timing belt.
Once the timing belt cover was removed I marked the gears with white out (figure8). The cam gear was found to be off about two teeth. The belt also had some slop indicating that the timing belt self adjuster was not doing its job to compensate for timing belt stretching. The fix here was to sell the customer a timing belt and new belt tensionor. I also recommended replacing the water pump that ran off the belt as a preventative maintenance measure. Prior to being a mobile technician for the last 15 years I worked in an engine rebuilding shop for 5 years and as a dealer technician for another 10 years and I have seen so many guys in the field skim on many types of jobs just to save a customer money by not replacing a component that may involve an overlap in labor time. An experienced mechanic or technician should understand that educating a customer is the best way to sell needed work on a vehicle. This can only help to prevent a return visit of the vehicle on a hook because you decided to do a good deed by keeping operating costs low on a job to be competitive with shops in the area. I find that whenever you try to save a customer money you always loose in the end.
It’s amazing to me how this Focus timing belt went undetected by the ECM or even a dealer tech that knew and understood the Ford product well. But I can see this happening to any tech because there were no obvious signs that you would normally encounter with others engines such as poor engine vacuum, rough idle, engine misfire, total loss of power, erratic electronic spark operation or even popping through the intake. This was a Hocus Focus that performed a trickery act of deceiving and fooling those into thinking that anything could have been at fault except for the timing belt. Even when I drove the car I thought the engine was alright and I was leaning towards performing a transmission stall speed test because it did seem like a transmission problem. I believe that the key to resolving power issues are to keep it simple by performing pinpoint tests to validate engine performance. Engine performance can have an effect on transmission
performance and using the “feels like” or failure pattern tactic will only lead you down a dead end street with no resolution to the initial problem. I always strive to find new ways to fine tune my diagnostics in order to cut down on time wasted by performing intrusive tests or component removal that leads to unwanted labor tasks. As technology in equipment advances it can only help us to achieve new levels in our diagnostic strategies. I hope this story can only enlighten you to help you choose the right path when you hit that diagnostic fork in the road.
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Established in 2001, ATS manufactures oscilloscopes, OBD II generic scan tools, misfire detectors, pressure transducers, leak detectors, gas analyzers, borescopes,
engine simulators, ignition analyzers, and a number of high tech training products to serve the automotive technician.
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