TCM Fuel System

Tips on inspection and setup of TCM continuous flow fuel injection systems.


The first step is setting the idle rpm fuel pressure, also called unmetered fuel pump pressure, and is spelled out in step 18 on page six of SID97-3D. The adjustment is made at the low pressure relief valve. Turn the adjustment clockwise to increase idle rpm fuel pressure and counterclockwise to decrease pressure. Tighten the lock nut, re-start the engine, operate it at 1,500 to 1,800 rpm for 15 seconds, then retard the throttle back to idle rpm. Repeat this step until pressure is within the specified limits. Fitzgerald offers a tip. “You’ll want to set your low end low. What that does, it leans out the engine. So in step 19, when you do your fuel air mixture rise, that will force you to adjust that in such a way that will slightly enrich the engine again, and gives you better part throttle enrichment.”

Next, with the engine operating at the specified idle rpm and unmetered fuel pressure, slowly move the mixture control from the full rich position toward the idle cut-off to check the fuel/air mixture. A rise of 25 to 50 rpm should be obtained. A rise greater than 50 indicates the mixture is too rich. A rise less than 25 indicates the mixture is too lean. Adjust to within limits in accordance with SID97-3D.

Last, adjust the full power metered fuel pressure by turning the adjustable orifice screw clockwise to increase fuel pressure, and counterclockwise to decrease fuel pressure.

After all adjustments are made, go back through and re-check all readings. “The mechanic needs to go back and re-check all readings because one adjustment will affect the other,” stresses Fitzgerald. “For example, full power will affect low end, and low end will affect the full. So they need to go back and re-check them again.”

Contaminants
Fitzgerald shares a test indication that would be a telltale sign for contaminants in the fuel system. “Take a look at table 3 in the service bulletin. The IO-550-N, at full power, 2,700 rpm, the metered pressure should be in the range of 19-21.3 psi. If you adjust it all the way up to the high end of 21.3, the unmetered pump pressure at that same rpm is in the 28-32 range. In other words, you should be close to 32. The metered and unmetered should track together. If they don’t, it’s because there’s something clogging the system somewhere. So, if you adjust it up to 21.3, and find out that the unmetered pressure is all the way up to 40, then you’ve got a problem. You need to stop with the procedure and flush the fuel system out to try to purge it of contaminants until you can correct the problem.”

Once all parameters are within limits, you can shut down the engine, disconnect the test equipment, re-connect the engine lines and leak check them.

Having trouble with the fuel system setup on your TCM engine? Fitzgerald stresses that you don’t have to struggle. “If mechanics are having trouble with some of this, and they can’t seem to get the system right, give us a call on our toll-free number at (888) 826-5465. We have our mechanics and IAs in there to answer questions. After all, we are standing by to assist you because you are the first line of service to the pilots, therefore YOU are our customer.”

Teledyne Continental Motors has a DVD titled “Continuous Flow Fuel Injection Set-up” that goes through the fuel system setup. AMT is hosting that video on its website this month. If you would like to see the video and learn more about TCM fuel system setup, go to www.AMTonline.com/videonetwork.

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