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Compression Tests on Mazda Rotary EnginesPosted 12/16/1998By Jim Newkirk
Mazda rotary engines have been around for a number of years now and yet are some of the most misunderstood power plants in the industry today. One of the most common misconceptions is that a special Mazda test tool is required for compression testing a rotary engine. It is true that if the Mazda electronic or thermal graph compression testers are available they will produce quick, accurate and easy-to-interpret results. Terrific if you work in a Mazda dealership, but not so good for the rest of us. The good news is that a manual compression test is possible on the rotary engine using a standard compression gauge set. The rotary engine used in the RX-7 consists of two rotor chambers each containing a three-sided rotor. Each corner of the rotor has an "apex seal" dividing it into three compression producing regions. As a rotary engine turns, three distinct compression pulses are produced for each revolution of the rotor. These compression pulses can be monitored with a compression gauge placed in the trailing spark plug hole. Remove the Schrader valve from the compression tester. This enables the compression tester to register each pulse as the rotor turns. A compression pulse will cause the needle of the compression gauge to jump up momentarily. The compression pulses must be in a regular pattern and even in intensity. This tests the integrity of each apex seal. A failed apex seal will cause the pulses to become uneven in intensity. If the pulses are in a regular pattern and even in intensity, the engine should be able to produce about 85 psi of compression. To test for available compression, replace the Schrader valve in the compression tester and place it once again in the trailing side spark plug hole. Crank the engine - compression should be about 85 psi. The Mazda compression testers test engine compression and apex seal integrity in essentially the same manner as the manual test. In other words, the Mazda testers monitor compression pulses and total compression and provide the technician with an easy-to-read result. While not as accurate as the electronic testers, the manual test will give the technician a good idea of the internal condition of the rotary engine.
Restriction or Carbon Buildup in the EGR Passages of the Ford Crown VictoriaPosted 12/16/1998By Dan Jurkovski
The vehicle is the 1992-1995 Ford Crown Victoria with a 4.6 engine. The symptom is an intermittent "check engine" lamp (MIL) pinging, or possible DTCs 332 or P1407 and/or P1408. The problem is a restriction or carbon buildup in the EGR passages. BACKGROUND: This condition does not normally cause any driveability concerns. The common complaint is an intermittent problem with the "check engine" lamp coming on, which is caused by the EGR passages in the intake manifold restricting - and not allowing - enough exhaust gas into the intake. The EGR port that flows into the intake from the EGR goes into a "half-moon-type" opening that encircles the main air intake. This half moon has three smaller ports that mix exhaust gas with intake air headed into the engine. This is where carbon buildup occurs. Cleaning the half moon, three intake ports and erasing the DTCs will take care of the MIL and any ping that may have been associated with this problem as long as the rest of the EGR system is operating normally. TEST & FIX: Verify that the powertrain control module (PCM) applies at least two inches of vacuum to the EGR valve during the key on, engine running self-test. Using a hand vacuum pump, apply vacuum to the EGR valve to make sure the valve is operational. When opening the valve, the motor shouldn't stall, but it should run rough as though two-three cylinders are misfiring. If checks of the system show it to be OK, with the exception of the noted RPM drop, you will need to clean the EGR passages in the intake. To do this, remove the intake elbow located between the throttle body and where the EGR mounts to the intake (by just removing the EGR valve off the intake you will NOT be able to get at the ports that are restricted). Once the elbow is removed you will have access to the ports to clean them.
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Copyright (c) 1996-2008. Automotive Service Association. All rights reserved.
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