New owner - fuel pressures

Ken MacLean · #1 10-14-03, 09:36 PM

I just bought a 68 T337C, my second Skymaster. My first, a normally aspirated 68 337C was a "bargain" priced original which needed everything done to it. I decided not to repeat that mistake and bought one with new engines, avionics, paint, interior, and so on.

Naturally there are always issues to deal with. The first is that the rear engine will not produce full power at 15,000 ft - but it is fine at 9,000 ft. At 15K the front engine MP is 26" but the rear is only 21" with full throttle. We think the fuel system needs to be set up (rear engine was removed shortly after overhaul due to prop blade damage from ground debris). At 15K with 21" the fuel flow is showing almost 0 on the rear but 8 or so on the front, even though the EGTs are set and pretty equal. Hmm.....am I on the right track? The possibility of the waste gate not closing occured to me too. Anybody experienced similar problems?

What a great forum you guys have going here. I am excited to be a part of it.

Mark Hislop · #2 10-15-03, 11:17 AM

Ken:

The first thing I would do is to check for leaks, holes, loose clamps, etc in the induction system and the exhaust system. Make sure all of the exhaust is going into the turbo, and all of the compressed air is going into the engine. All of the times I have had a failure to hold MP, it has been leaks (for me always in the induction side, not the exhaust side).

The fuel flow readings don't make any sense to me, but perhaps they will be a clue to somebody else.

Mark

Paul Sharp · #3 10-15-03, 04:52 PM

I would recommend checking the turbo system first, also. I suppose if the fuel pump wasn't putting out full fuel levels it could keep the MAP low, but you coudl check that by using either the "low" or "high" electric fuel pump settings and see if it makes any difference. If not I agree that your turbo system isn't getting full input/output one way or another. I think from 8 to 0 might not be that significant when you talk only 21" of MAP. Although, do the two fuel flow gages read the same at sea level? If so but they are diff. at altitude then that's probably a clue, too.

Jerry De Santis · #4 10-15-03, 07:24 PM

Before you spend a lot of money, check the waste gate to be sure it is fully closing. Put mouse milk on the waste gate hing so as to free the movement. If the waste gate not fully closing, power will be low thus fuel consumption on that engine will be lower than the other engine. Check for manifold leaks by hooking a blower (leaf blower will do) into the manifold system and use soap and water.

Good luck
Jerry N34EC

Guy Paris · #5 10-15-03, 08:59 PM

So you went and did it!! Good luck. Guy, the old 72 driver.. N1312L Nashua NH.

Ken MacLean · #6 10-15-03, 09:37 PM

Boy, this is good stuff. Leaf blower and soap - I'll try that - seems like a sensible and inexpensive way to eliminate (or identify) a problem. Mouse milk? What is that?

Clarification - when priming for initial start, the rear engine does not register much fuel flow with the boost pump going. Book says 2-4 GPM then fire her off. The front engine follows book, but not the rear, although setting the low pump and hitting ignition switch provides a smooth start even with incorrect fuel flow instrument reading. Something in the system is not right - instrument, pressures, I don't know.

I will ask my mechanic to read this thread before putting a wrench on the machine.

Hello to Guy Paris - I found one!

FRED-E · #7 10-15-03, 11:51 PM

Mouse Milk Oil can be found on page 54 of Chief Aircraft 2003 catalog, volume 21.
It does sound like the waste gate is not closing all the way.
Fred N358

kevin · #8 10-16-03, 10:21 AM

Ken,

What do you get for fuel flow and power indications at low altitude, say 3000'?

Your fuel flow at start from the rear boost pump is quite wrong, and while I agree with the rest of the thread about looking for leaks, checking wastegate, etc., I would also pay attention to this low fuel flow at start up issue. You can have more than one problem, and you may at least have a leak or other problem relating to your boost pump. If the mechanical pump fails, you need that boost pump, so I'd chase that problem before flying much more. Also, since you can easily duplicate it on the ground, you should be able to fix it easily.

See also my thread on starting that I will post next.

Kevin

Ken MacLean · #9 10-16-03, 09:45 PM

I think Kevin's right - there are two problems here. I sent this link to my mechanic who read it and liked the leaf blower idea, although we're going to use a shop vac. In the past they have run the engine and squirted I'm not sure what around, diagnosing a leak when the engine stumbled. All this while the prop was turning. You guys have helped us find a safer alternative. Good work. I hope that takes care of the manifold pressure issue.

I'll bet the fuel flow issue is coincidental but not caused by the MP problem. I'm going to spring for the fuel system setup after the leak test if things don't return to normal. One thing the shop guys suggested was reversing the feed to the fuel flow instrument to see if readings reverse themselves. Seems like a reasonable diagnostic to me.

I'll keep you posted.

Ken

Ken MacLean · #10 10-20-03, 12:46 PM

So far we found that the throttle cable was mis-adjusted so as not to give full throw at the throttle body. Easy fix. Found one induction leak, ordered gasket. Found the fuel flow instrument to be sluggish, now debating replacement or repair. Anybody have one sitting on a shelf?

Anybody installed a JPI engine monitor?

Ken

Mark Hislop · #11 10-20-03, 01:57 PM

Ken:

I replaced my fuel flow gage with a Shadin unit. I have the original, which was working find when it was taken out 4 years ago. It was from a 1973 P337. If this would work for you, I would be happy to sell it to you.

Mark

Ken MacLean · #12 10-20-03, 04:34 PM

How much? Is this the proper forum or do you want to email? I'm new at this.

Thanks.

Ken

kevin · #13 10-20-03, 04:46 PM

Y'all might consider checking to see if what Mark has is really what Ken needs. As I recall, the fuel pressure (flow) indicators on a '68 T337 are in GPH, and on a '73 they are in lbs per hour. I am not sure the two gauges are interchangeable, legally at least... Also, there may well be a difference in the gauge for pressurized and non-pressurized aircraft. Might ask your A&P about that...

Just a thought. Maybe I am wrong about the 68 gauges...

Kevin

Ken MacLean · #14 10-20-03, 05:57 PM

You're right - 68 T337C is gallons per hour. I'll bet I'd need field approval, POH supplement, and so on to convert. Is that right? Anybody know a good instrument rebuild shop?

Ken

Mark Hislop · #15 10-21-03, 09:41 AM

The original fuel flow gage from my 73 P337 is calibrated in pounds per hour. Sounds like it wouldn't work for your application. Sorry.

Mark