JT8D-9A N1 readings [Archive]

Toobold

13th Dec 2007, 13:28

We are having problems with our N1 readings on our C-9B aircraft. There is a flucuation in indication sometimes. Others times it works perfect. We have replaced the N1 Tach-Generator and the cocpit display. After doing this it stillcontinues to flucuate. We did a eng. run up and on eng. start N1 read 0 not dashes, so i know its getting a signal. As i ran the eng. up to 1.2 epr it began to flucuate and then at 1.2 returned to normal and continued to read normal for the rest of the turn. Any other ideas what to check for this problem...Thanks

Firebird

13th Dec 2007, 16:32

Check the pins and condition of the cannon plug on the N1 tach, then check the wiring where it comes out below the engine. That is where the wire is spliced due to fan changes etc. Cannon pugs may look OK but when you dismantle them you may see another story.

Good Luck

mainwheel

13th Dec 2007, 16:37

Drain the PS4 watertrap on the FCU.

Have you filled the FCU bellows with silicon oil, thats 2 beers.....:)

Toobold

14th Dec 2007, 17:02

If moister trap is clogged, would it affect EPR also...EPR reading is steady. This fluctuation is in flight and on ground.

mainwheel

15th Dec 2007, 17:33

It normally does.

The trap has a calibrated bleed orifice. Maybe it is the wrong type or dosen't match the FCU. Changing it has fixed fluctuations.

Have you serviced the Bellows with Silicon oil, that should be the first thing to do.

Would like feedback..........:8

Firebird

16th Dec 2007, 16:58

Normally the engine would have all parameter fluctuations if the FCU were faulting. The crew would definatly let you know. Slow to spool is an indication to add silicon to the bellows.

Toobold

17th Dec 2007, 20:51

FF,EGT,EPR, N2 are right on the money. There is not flucuation with any other displays. Could it be the houseing that the N1 Tach rides in? When i removed the Tach Gen (N1), the houseing looked fine and the spline shaft on the old one looked good. No indication of slipping or anything. Thanks for all the inputs everyone.

2FarNorth

25th Dec 2007, 15:10

This is old now, did you find the problem.

Have you checked the pin friction on the plugs?

Try swapping tach/gens side to side even if new one installed.

mainwheel

10th Jan 2008, 14:38

Is the jury still out on this?

Some feedback.............

Toobold

12th Jan 2008, 16:43

Sorry it took me so long to get back to this subject. We did find the problem after several days of troubleshooting and replacement of parts. There are two terminal boards on top of the JT8D-9A. The boards are 913/914. Come to find out the board was several corroded and several of the leads were loose. After cleaning the termianl and tightening the captive nuts on them, we solved two gripes we had. One as stated was the fluctuation of N1 and the other was high fuel temp. on the same eng.. We knew it was a reading problem on temp, because no increase in oil temp. You got to enjoy putting all knowledge to the test on a very complex, but simple gripe...Once again thank you all for the inputs..