Rear Engine wants to Die!
 

I have a '68 T337C that has 950TT, 100 time on turbo's. The engines start easy, good compression, and run strong. I use it to commute to work about 8 hrs flying a week, usually at 7,500 ft. During takeoff and climb, no problems. However in cruise, about every second flight or so the rear engine will start to die. Let me tell you, the first time was a bit nerve-wracking, but now it has become just an annoying source of concern. What happens on the rear engine, now that I have had a chance to evaluate it many times, is this: I will notice the EGT start to climb for about 10 seconds, accompanied by the fuel flow drop from 12gph to about 8gph. Then the rear motor starts to die, which I quickly remedy by turning on the fuel boost pump to high. Then I operate the engine with the boost pump on low, and it doesn't happen again. Only happens every other flight or so. I don't want to always use the boost pump, since I don't want it to wear when I might REALLY need it. It happens regardless of if I am on the mains or aux. tanks.

I have a few theories, but I am no mechaninc. All help appreciated.

fuel pump
 

From your description, the engine is going lean. TIT rising while fuel flow drops. Sound like it can be your engine driven fuel pump. Since it is not a constant problem perhaps on certain flight conditions the engine driven fuel pump gets hot and excess bypass occurs. Frankly, under the condition you have, I would have it check out asap and not fly it until problem is solved. Big problems start small.

Good luck

Jerry
:confused:

That would be my opinion as well, get it checked before further flight.

Kevin

Things I would check would be 1 the fuel vent system, 2 The line that goes from the throttle body to the fuel pump, 3 The seals in the fuel strainer, they could be letting air in the system, 4 The pump.
Hope this helps
Kim

My Guess
 

Hi all,

This is an additional comment after this am.'s message. The plane flew 5 hours today. On preflight, I noticed that a drip every 10 seconds from the exterior terminus of the line that comes out of the bottom of the electric fuel pump. My mechaninc on the field said it was the diaphram weeping, and we are replacing it. Anybody out there think this could be the problem? Also, during the four 1.2 hr legs we cross-fed the engines with no problems, but on the last 1/2 hr I went to the aux. tanks, and after 15 mins, sure enough, it happened again. It has happened on the mains also, but no question it is much more prone to have this problem occur on the aux. tanks. Anyhow, read below. Thanks,
Ben
____________________________

thanks for the input. Actually, I am a VERY conservative flyer, and won't go if there is any problem and have it fixed ASAP. BUt this problem has occurred since I have had the plane, and it really is no big deal. Just turn the fuel pump to "low" and it has never happened.

Actually, in reading this and other forums on 337s, it confirms my instinctual diagnosis of what is going on. It very much acts like the rear engine fuel system is vapor locking. I read on the other site that a few years ago California planes were having this exact scenario occur at higher altitudes, the reason likely that CA fuel had a change to its refining parameters. Rear engine is higher, so less pressure to the engine driven pump, etc. The fuel line for the rear engine is routed where it can definitely get hot, and vaporizes before it gets to the pump. Will replace the fuel line with an insulated, fire-resistant line next week.

Any thought on this would be appreciated.

Belive me, I am going to take all of your suggestions and check all of those items also, its not only an annoying problem, but makes the passengers a bit nervous!
Thanks,
Ben

several years ago, mine did the same, always at cruise (75%)
between 8500-12k. insulated all the fuel line and it has never
done it sence.

Ben
You may also want to check and make sure the fuel selector is going in the detents correctly.
Kim

Sounds like vapor locking to me. Very common with the Turbo models. Some careful thought to insulating fuel lines will more than likely solve the issue. Even now... now and then I get a little vapor locking if I climb for longer periods (15K+). I run the boost pump on low until I level out and gain some speed to cool things down. Then switch off the pump and enjoy.

WHAT MATERIAL IS USED TO INSULATE THE LINES?

The engine sputtering has never happend on climb, I think because the fuel flow is at a high level for the climb (14.5 gph each). (BTW,it has never actually come close to dying, as I instantly turn on the boost pump). It only happens at cruise, and the more I evaluate it when it occurs, the more I am convinced fuel is vaporizing in the fuel line before it reaches the rear engine. The fuel lines are fairly new, so is there a way to insulate the lines without replacing them with the fire-proof lines, which cost a bundle?

http://www.aircraftspruce.com/catalo...ermoshield.php

Worked well for me.

Ben,

Have you found a solution to the problem yet? I've been experiencing the same thing - description and attempted solutions follow:

I've been experiencing a front engine anomaly since buying the aircraft two years ago. N462DA is a 1968 C337C which started out life as a turbo-charged model, and which was subsequently converted to normally aspirated engines, about 10 years ago. So its fuel system is that of a turbo-charged model, although its engines are normally aspirated Continental IO360s, both factory re-mans. The front engine has about 1.5 years and 140 hours since factory re-man; the rear one has about 1150 hours since factory reman.

I usually climb at 25in/2500RPM to 6,000-8,000 feet, then set 65% power @ 50 degrees rich of peak. After 30 - 45 mins the fuel flow to the front engine starts oscillating, dropping slightly below 9.6 GPH and then right back up again, too slightly to notice. After a few minutes (maybe 5 mins) of gradually increasing amplitude, the anomaly becomes noticeable as a slight power drop, then recovery of power. This gets more and more noticeable, as the fuel flow drops to around 6 GPH. Application of the low boost pump for 30 -60 secs cures the problem, and the engine runs fine for another 30-45 mins, after which the anomaly recurs. During the anomaly EGTs rise and CHTs descend. An EDM 760 with fuel flow option is installed, and I've graphed the anomaly.

We checked the fuel tank vent system, and it's fine, as are all the tank cap vents. We removed the vapor return line from the engine driven fuel pump and blew through it, and heard bubbling in both the left main and left aux tanks, so it appears the vapor return line off the front engine driven fuel pump is un-blocked. I've switched fuel tanks from left main to left aux to X-feed during the anomaly, and none of this helped, so it appears it's not a problem with the fuel system upstream from the fuel selector valve. The anomaly has occurred while feeding both from the left main and from the left aux tanks. Opening the cowl flaps doesn't help. I insulated the fuel supply line from approx. 2 feet behind the firewall all the way up to the engine-driven fuel pump.

The front engine driven fuel pump was removed and sent to Continental, who bench checked it. The 600 RPM setting was fine, but the 1600 and 2600 RPM settings were approx. 10 - 20% low. Continental set these flow settings to midrange, and the fuel pump was re-installed on the aircraft front engine.

A few flights back I tried climbing at full power, then setting 65% power and leaning to 50 degrees rich of peak, and the anomaly occurred almost immediately, and also occurred on the rear engine for the first time since I've been flying the aircraft. Application of low boost pump to both engines cured the problem, albeit temporarily - it re-occurred in the front engine within 30 mins. The next flight I climbed at 25/2500, set 65% power and leaned to 50 degrees ROP, and the anomaly occurred in its usual pattern: in the front engine (after a 30 min. delay), and did not occur at all in the rear engine. Is it possible the problem is vapor lock somewhere, and climbing at full power heated up both engines more than the usual 25/2500 climb power did, and this exacerbated the problem in the froth engine, and caused it to occur in the rear engine also? Continental's position has always been that the problem couldn't be the fuel pump because this isn't the way that this fuel pump would fail - it has no altitude compensation - it just turns its little vanes, has the fuel/vapor separator on top, a jet (that wouldn't go bad with such regularity), and a fuel return line down its side to its lower housing.

The problem persists. I've installed GAMIjectors and now run approx. 20 degrees LOP (that's as lean as I can get without running rough), and the problem still occurs regularly. Let me know how your efforts are going.

Thanks!

Paul462

rear engine dies
 

Hi,

I just yesterday got the plane out of annual, and installed new insulated fuel line on rear engine. Only one flight, but the rear engine did NOT ellicit the problem, so I am optomistic and will report at a later date if it solved the problem. BTW, during this past winter I noticed that the problem occurs much less frequently, but now that things have warmed up it is as frequent as last summer. Also, at higher altitudes (above 15,000 ft) the problem ocurred often. This again concurrs with my theory that the hot engine causes the fuel to vaporize in the higher (less gravity flow), slightly warmer (less air flow), and longer fuel line.

I have never had a problem with the front engine, and it doesn't make sense given my theory on the matter. I may be all wet here, I'm not an A&P, but have you tested the elec. fuel pump and especially filter to make sure there is no impediment to flow? Air is about 600 times less dense than avgas, so just because you can blow thru it, obviously the fuel is still impeded. Also, my mechanic told me a story of a fuel flow problem that could not be found, vents seemed fine. But after repair / replacement of the vents, just stabbing at a possible fix, the problem was indeed repaired. I am fairly confident that my theory on the fuel system is correct, especially in light of some of the responses I have received on this thread from people way more knowledgeable than myself. Thus I would recommend going thru your system completely.

These 'Gremlins' are tough to find. Best of luck and safe flying.
Ben

if it not vapor locking, then most likely the system is sucking air at the low settings.
start looking for fuel stains as when it is not sucking the higher setting will make it leak fuel. fuel controller, fuel strainers use "o" rings to seal the shafts i have more problems with old hard "o"ring than anything else. they get hard and crusty with 30/40 years

**This again concurrs with my theory that the hot engine causes the fuel to vaporize in the higher (less gravity flow), slightly warmer (less air flow), and longer fuel line. **


The problem can happen on engines that do not have fuel problems in the system. (those should be eliminated as per the other suggestions in this thread.) The REAL problem is the engine-driven fuel pump. It gets heat-soaked and will vapor lock. The problem is indequate cooling to the fuel pump. There should be a cooling shroud and blast line to it. The cooling shroud is frequently inadequate. Also, as a matter of routine, I turn on the low boost at abotu 5000 feet and go to high aux boost at 10,000 feet in my airplane. This stops the problem, but is only a bandaid as fixing the cooling shroud is the real answer.

I have yet to see this addressed and not have it fix the problem.

Hi guys, and thanks for all the great info.
Well, just made another rount trip to work (1 hr each way), and sure enough the rear engine showed the same loss of power. It is 100 degrees on ground, so its pretty hot, but thought the insulated fuel line would help.

I also rutinely run the aux pump when on aux tank, and any time after it has an incident of power loss. My concern has always been that the elec. fuel pump was probably not designed to run for hours continuosly all the time. With my luck, just when I need it it will fail from all the extra use.

Anyone else feel the same, or should I relax and use the elec fuel pump w/o worries.

Ben

I feel the same as you about continous use of the electric pump. If it were my airplane, I would continue to work to find the problem, not just keep using the electric pump.

One opinion, FWIW.

Kevin

According to the manufacturer of the boost pumps, the electric boost pumps are made for continuous operation. I do not worry about using them to suppress vapor. That's one BIG reason they are there. I've been using one like that for a loooong time. Not yet had one fail, but I've stopped a lot of vapor problems by using it. Allowing vapor lock to continue has the same effcet as leaning the mixture inappropriately. That can destroy cylinders.

We know what the problem is. Insulating fuel lines won't hurt, but is not the answer. It's the engine -driven fuel pump being too hot. It is insufficiently baffled. We're working on an STC'd solution. Cool the pump and there will be no problem (easier said than done). Use the boost pump and the problem will be lessened.

Lots of folks fly T337s in hot weather at 7500' without this problem. I do not believe we know what the problem is, nor that an STC is necessarily needed to fix it.

Running with the boost pump on all the time is not normal for this aircraft. It may be normal in the aircraft you normally fly.

Kevin

Cuh-CHING! Cuh-CHING!
 

No thanks. I think I'll retain my $450+ a-whack AUXILLIARY fuel pumps for their intended purposes... and only 'as needed' per the POH. I guess WA has never experienced a failed carbon vane in one of those puppies bust off and little particles go whacking around in the engine. Yah... my wheel bearings were designed for continuous operation too! What a hoot.

Seems the key phrase everyone is missing is "CONTINUOUS-FLOW fuel injection system"... ya think there might be a problem with the F-L-O-W??? Hhhhmmmm.

Oh... and think about this: If Cessna's R&D team really thought there was a 'problem' with the engine driven fuel pump getting warm, erghhh, I mean 'HOT'... HEY... they wouldn't have put it on the damned engine!!! Yep, but there's always snake-oil to sell... think about it.

Of course, maybe them Beech planes weren't quite R&D'd as good as Cessna. Ya think? And besides, the Beech has to pump fuel UP from the wing... Beech forgot all about 'gravity'!!! Maybe that's why them V-tails keep falling off.

SkyKing

FUEL SYSTEM Review...
 

For those of you with 1973 or later 337's, it might be a good time to review Section 7 of your POH -- the one entitled {Airplane & Systems Descriptions} and in particular the section on FUEL SYSTEMS. The LAST THREE paragraphs really lay it out for use of the AUX pumps. Hey by golly, there must be a reason they call it an 'AUXILLIARY' pump... no kidding!!!

And I didn't mean to exclude all of you pre-1973 Skymaster drivers... it's just that the post-1973 POH manuals were standardized format so that we can all be on the same page. With all of the different tanking arrangements and vapor return lines, a review of your specific POH and/or service manual section on the fuel system is a MUST-DO in diagnosing problems.

SkyKing

SkyKing:

**Oh... and think about this: If Cessna's R&D team really thought there was a 'problem' with the engine driven fuel pump getting warm, erghhh, I mean 'HOT'... HEY... they wouldn't have put it on the damned engine!!! Yep, but there's always snake-oil to sell... think about it. **

First, I'm not selling anything.

Second, you might want to do what I've seen done and put a few thermocouples on an engine-driven fuel pump and record the temperatures in flight before makind any big statements. I doubt you (or Cessna) have ever done that. TCM did put a cooling shroud on it, so they must think there's a reaosn to cool it. There is no need to argue about something that has been measured.

"One test is worth a thousand opinons... and a lot harder to get."

Huh?
 

OH REALLY NUMBER ONE!? Exactly when did Cessna or TCM {as the case may be} put a shroud on the Skymaster engine driven fuel pump for testing the temp? Don't think so, as it has NEVER been an issue in the real world. Thermocouples? Why waste time and money on something that is definitely NOT the problem!

OH REALLY NUMBER TWO!? "First, I'm not selling anything." And, "We know what the problem is. Insulating fuel lines won't hurt, but is not the answer. It's the engine -driven fuel pump being too hot. It is insufficiently baffled. We're working on an STC'd solution. Cool the pump and there will be no problem (easier said than done).

Why would you be working on an STC, if you didn't plan on selling/marketing it? The Skymaster doesn't need the specified STC... period... paragraph... as there is NO heating problem with the engine driven fuel pumps on the 337 series. As they say on TeeVee, "Sorry, Charlie!" Find another fish to fry.

OH, but maybe you were referring to a different make & model airplane... like the Beech you own/fly... and of course that'd be like comparing apples to mandarine oranges.

SkyKing

Well, SkyKing, my boy. We got the flight data today at about 4:30pm central time on the temp of the fuel pump.

You're wrong.

One thing I'll say for you is that you may not always be right, but you're never in doubt.

"One test is still worth a thousand opinions."

Good bye, Skymaster forum.

Walter, can you please provide the results of your tests. I occasionally see the fuel flow needles flicker and have long suspected heat somewhere being the problem. That is even with insulated hoses and pretty good baffles, but does go away with AUX pumps on low.

Comment: I think we all know that although Cessna had a great engineering department, they could only test over a realitively narrow range of curcumstances. Our real life experiences are always going to be a bit different.

Further comment on certain suggestions that continuous review and design refinement is not necessary because the original design is fine:

If review did not take place we would still be flying biplanes and computers would never have been invented. Nor would you ever hear about the massive recalls by various car manufactures, nor the positive safety related changes they bring. Nor would the FAA issue AD's or manufactures SB's.

I would suspect we would not have the standard of living we have today if it were not for people continuously challenging the status quo and working hard to make things better.

My two cents worth.

If that were true, that the original design was fine, they would never have gone beyond a 337B.

Engineers are tinkerers, they like to make improvements. What is a good idea today may be a bad idea tomorrow. What was not possible yesterday, may be accepted practice today.

The improved baffle design reduced the temperature of the fuel pump 21 degrees. That was enough to stop the vapor locking on a 100+ degree day. We hope to do even better.

It's all in the science.

Anyone interested in communicating with me on these types of subjects, please feel free to do so by private e-mail as I will no longer be visiting this forum. Thank you and I wish you all well.

Bogus, bogus, bogus....
 

Message removed by webmaster due to its insulting tone. Members of this board deserve politeness and respect in all the messages posted here.

Kevin
Webmaster

Ah-HUM!!
 

Message removed by webmaster due to its insulting tone. Members of this board deserve politeness and respect in all the messages posted here.

Kevin
Webmaster

Insulated lines DID NOT fix the problem
 

Just a quick note, since I started this whole thread. I have had the same problem addressed earlier on every flight this summer. I suspect that WA might be on to something, since we have just about tried everything else to solve the problem.

There is no evidence of fuel leak, and fuel system has been pressure checked for leaks.

If anyone has anything CONTRUCTIVE to say (there is enough kvetching and sarcasm from SK), I and anyone else having the same problems would be EAGER to hear them.
Thanks,
Ben

Ben:

If you wish to contact me directly, I think I can help you with your problem.

i HAVE HAD THE SAME PROBLEMS WITH MY TURBO .....IT IS HEAT! VAPORIZING THE FUEL. THE BLAST TUBE WILL SOLVE THE PROBLEM, BUT SO WILL THE LOW BOOST PUMP. LOOK AT ALL THE PEOPLE HAVING THE SAME ISSUES, WE DON'T ALL HAVE VENT PLUGS OR BAD FUEL PUMPS OR SUCK AIR ....WE ALL HAVE HEAT

A question about flying with the aux pumps. My 1969 O2-A does not have pumps in the aux tanks, just the mains. Do later 337's have pumps in both tanks? Are you just writing off the fuel in the aux tanks?

I don't think any 337 had aux pumps on the auxiliary tanks; see the Fuel Management page in my backup site, www.SkymasterUS.com

However, in later models with the extended-range tanks, the extra capacity was built into the main tanks (not into separate auxiliary tanks), so that the aux pump could access all of the fuel on board.

Ernie

Ernie,
I was figuring the answer was something like that. I did visit your site a while back and took your quiz. I only missed one and went away knowing more about the fuel system. Thanks for your time and research efforts!

Hot Fuel
 

In another thread, I referenced page 2-3/2-4 of the 1974 P337 owner's manual. This is a discussion of the operation of the auxiliary fuel pump switches. I agree with others that there is no reason for sarcasm. We are all just trying to fly airplanes.

I understand some have reservations about running the fuel pumps for extended periods and I can understand that. However, everything in the owner's manual must be approved or at the very least accepted by the FAA. Obviously, heat has something to do with the problem and altitude would only aggravate the heat issue.

I was interested to see that someone had taken the time and effort to do the research to cool the engine driven fuel pump. (I am wondering if the affected aircraft had intercoolers). However, if cooling the pump works, sounds good to me. If someone gets an STC to do that, great, if you don't like it, don't do it.

I just hate to see people taking pot shots at folks that are just trying to resolve a legitimate problem. As a not so great American once said, "can't we all just get along?". I was disappointed to see that one individual stated that he would not be visiting this forum again. I agree he did not need the abuse, but I hate to see him go.

Moreover, Kevin, if we are having a recurring problem sounds like maybe the occasional deleting of comments is not enough and stronger measures are in order. I will back you 100%.

P.S. If the individual blasts me, I guess that will confirm all I just said, (I did not name the individual) but if the person responds that will confirm what I just said.

Mark:

**I understand some have reservations about running the fuel pumps for extended periods and I can understand that. **

The boost pumps are designed to run for extended periods without difficulty. It should not be a problem in any way.

**However, everything in the owner's manual must be approved or at the very least accepted by the FAA. **

That is a commonly held belief, but is misplaced. The FAA only has anything to say about items that are listed in the LIMITATIONS section. Other items are not passed on by the FAA.

**Obviously, heat has something to do with the problem and altitude would only aggravate the heat issue.**

The issue is the vapor pressure of the fuel. It generally runs in the 7 psi range but can vary a bit. This is altered by heat and greatly affected by altitude Ambient pressure). By 18k feet, the ambient pressure is 7.3 PSI. Using the boost pump can raise the vapor pressure altitude. The hotter the fuel, the lower the vapor pressure altitude.

**I was interested to see that someone had taken the time and effort to do the research to cool the engine driven fuel pump. (I am wondering if the affected aircraft had intercoolers).**

"A man without data is just another person with an unsupported opinon." If I have an unsupported opinion, I will not offer it without saying that it is unsupported by any data. As for the intercoolers, they have NO effect on this issue in any way.

I visit seven forums each day, answering questions about the specifics of engine management. I have never been exposed to the vitriolic attacks anywhere like what goes on here. That says something about a group which allows that sort of behavior. Every other forum I visit has rules of behavior which restrict personal attacks. Heated debate is welcomed and in many cases quite healthy, but personal attacks are not. Besides, the DATA is the expert. If you have no data to offer to support your opinion, it is just another unsupported opinion and that is all there is to it. I visited here because one of your members asked me to participate in an effort to correct a lot of the unsupported opinions which were being shoved down your throats by forum bullies. Much of those strong opinions are not supported by the science or the data but are shoved down your throats by your forum bullies anyway. It appears that this forum's moderators are unable/unwilling to enforce even a moderate level of civility. I don't have the time nor the inclination for that childish behavior as there are other places where the science and the data are appreciated and anyone acting as a forum bully is immediately excluded. I addition, the better forums require that people use their real names. It's a simple act that is polite. We all like to know who we are talking to. In my opinion, that is another reason this forum gets out of line and people are rude. It has been my observation that the only reason people are rude, is that they can get away with it.

If this forum were to adhere to a few simple rules of being polite and began using their real names, then I might be inclined to participate. Skymasters are really cool airplanes and there are a number of really neat people who own and fly them. 'Tis a shame that the group has allowed a few forum bullies to ruin it and shove information that is incompatible with the known science down its throat.

Good luck and if that were to change, somebody let me know and I'll consider returning for the SOLE purpose of offering educated and data-backed information on engine management.

your word is your honor
 

you stated that you were not going to return to this forum. well you have for the second time this month, shame on you, your word means nothing which equals that you are nothing and have no honor! on both peter's and this site you have created much discontent, shame on you, man of no honor

rick bell

Based on your personal attack, nothing has changed here.

Have a nice day.

I attempted, without much luck, to diffuse the original spat three years ago between GMAs and the supporters of lean of peak ("LOP") operation (including Walter). Let me try to cool things again.

First, Walter returned to this forum, at least in part, because some members (Mark McConaughy among them) value his inputs and prefer that he stay. Thus, I think Big Al 08's comments above are unwarranted. Maybe he'll re-think the matter and buy my argument that some of the other members want Walter's participation.

Second, the abusive participant was warned, then edited, and finally kicked off the forum several months ago. And this was the second time, since the same happened three years ago. Therefore, Walter's comments that this forum allows bullies to interrupt scientific dialog and that the forum's moderators are unable/unwilling to enforce civility is also unwarranted.

At this year's Skymaster Meeting and Fly-In in Key West I took the "against" LOP side of that debate, so I don't see fully eye-to-eye with Walter. But I still think he's very knowledgeable about engine operation -- especially combustion matters -- and welcome his input. You don't have to agree with him, but we're all entitled to listen to what he has to say. Especially now, Walter, given the forum's moderators continuing efforts to foster civil dialog.

Ernie

P.S. I wrote this after Big Al 08's message, hoping to post before Walter read the forum, but he read it while I was writing.