Fuel pressure issue, very perplexed, need help

I'm operating and IO-360 M1B in my RV-7A

Ok so heres the deal:

PROBLEM: Fuel pressure after flight drops below 15psi when taxing for a minute or two...EFIS warns me in red flashes..and if left without a boost recovery engine will cut off (sometimes, other times just spit and sputter and hover around 12-15psi) .. boost bring pressure back up to 27-28psi..when boost is then cut back off pressure drops into the red again. pressure can not be recovered under higher engine power only under boost. Keep in mind...all is well while flying without boost..this only happens when I land and am taxing back to the hanger.

Now on initial start up and run up there are no fuel prssure issues. Standard start procedure is...3sec of elec boost, then off...Engine start under mechanical pump...warm up and taxi...run up checks good...elec boost on for take off...1200agl boost off...mechanical pump pressures fine for all of flight (stays between..say...23-26psi.

One mechanic has said its vapor locking after landing because of the reduced airflow in the cowling and that in flight airflow is sufficiently cooling the fuel lines to prevent vapor lock...hmmm

Another has said vapor lock does not happen when the engine is running, but only after shut down and sitting and that the fuel pump in going bad and needed to be replaced.

Ok, so I replaced the pump with a brand new high pressure pump. Operation was flawless..Inial ground test showed 29 psi.. no boost with the new pump..test flight flawless...operating pressure..no boost bwt 23-26 in flight...even landed it this time with no boost pump on..everything perfect..right up until i was on the ground and taxing a minute or so and the the problem returned.

Soooooo. I know that the pump was not going bad..$650 bucks spent for nothing (parts and labor of course)...So what gives?...Has anyone had the same experience? is this normal for fuel injection engines?..Ive been told that the pressure after flight without any boost should remain at the same levels that I see in flight..Can I continue to fly and feel confindent that all is well?

Please help me if you can...what can I do?..suggestions?.. Please somebody...

Tango

A search on this forum of fuel pressure and hot taxi fuel vapor would have saved you a lot of money and time.
Take a search around and let of know if you have any unanswered questions.

Keep mechanic #1

Fire mechanic #2

Be sure your last check before any departure is "electric pump on".

You may be able to improve the situation by insulating a fuel line or adding a heat shield to an exhaust pipe.

I am not an A/C mechanic so FWIW

I have the exact same engine and have never experience this issue. My fuel pressure remains as normal when I land and engine operates also normal. The vapor lock issue may come to play if you shut a hot engine and let it sit for a few minutes or more.

What I suspect is the cooling issue on your fuel pump. It may help if you install a blast tub to your fuel pump or insulate it by adding a heat shield as it has been suggested.

As a note, I do not have the blasting tube nor the shield. But I do have two blasting tubes to my Mags which might help cool that area a bit too.

Good luck

Kahuna said:

fuel pressure and hot taxi fuel vapor

Click to expand...

Tango, I'm with Kahuna. We just had a big discussion on this subject a few weeks or months ago, but I can't seem to find the posts. Most of us with FI engines have had the exact same problems you are describing. Wish you would have searched here first, could have saved you time/money.

Thanks guys!!

I hear voices of great wisdom.

I feel like such an idiot! My gut told me it had to be what all of you say.. all of the evidence pointed to it, but I am no mechanic and just did'nt want to take any chances..

With that being said I have good used fuel pump with 200hrs on it for sale! Any takers?

Tango

Next time if you want to troubleshoot further.... you can also get a calibrated manometer (gauge) and check your pump output pressure prior to your FI distribution spider...Vapor lock sucks!

on the ignition side of things....you may want to consider a Slick Start http://www.aircraftspruce.com/catalog/eppages/slickstart.php I have used this in several aircraft and buying one for my current sled! it works great in hot starts! Never ever a problems with hot starts!

Maybe Im being anal, but from my recollection, there is a difference between what was discussed on this forum recently and this case. Previous discussion was simply a rough idle after flight, with no loss of fuel pressure. This can be attributed to vaporization of fuel within the stainless steel injection lines coming off the fuel spider on an injected engine. People referred to it as vapor lock, but it really isnt, as there is almost no pressure in these lines. Other than experiencing rough idle, there is no real hazard from this condition, and it goes away by opening your throttle slightly and increasing your fuel flow.

The current situation involves loss of fuel pressure, and to me is a bit more serious, in that it may truly be associated with vapor lock, and is preventing the mechanical fuel pump from operating correctly. While higher fuel flows appear to be "fixing" the problem for now, I would still want to take some action in this case for fear of things getting worse and being a problem in the air.

comments welcome

erich

erich weaver said:

Maybe Im being anal, but from my recollection, there is a difference between what was discussed on this forum recently and this case. Previous discussion was simply a rough idle after flight, with no loss of fuel pressure. This can be attributed to vaporization of fuel within the stainless steel injection lines coming off the fuel spider on an injected engine. People referred to it as vapor lock, but it really isnt, as there is almost no pressure in these lines. Other than experiencing rough idle, there is no real hazard from this condition, and it goes away by opening your throttle slightly and increasing your fuel flow.

The current situation involves loss of fuel pressure, and to me is a bit more serious, in that it may truly be associated with vapor lock, and is preventing the mechanical fuel pump from operating correctly. While higher fuel flows appear to be "fixing" the problem for now, I would still want to take some action in this case for fear of things getting worse and being a problem in the air.

comments welcome

erich

Click to expand...

therefore my reccomendation to confirm fuel pressure with a calibrated gauge. if you confirm good pressure prior to the FI Spider, the rest is just eaisier to trouble shoot! Spider, SS Lines, nozzles....thats it! by isolating the simple fuel distribution system in two parts, you'll get to the possible issue eventually.

Unfortunatelly now days A&P's dont take the time to T/S. Customers just wont pay the time to do it correctly and prefer to act like Airlines mechanics with an open source of parts by removing and replacing parts........very broad statement but unfortunatelly very true!

erich weaver said:

Maybe Im being anal, but from my recollection, there is a difference between what was discussed on this forum recently and this case. Previous discussion was simply a rough idle after flight, with no loss of fuel pressure. This can be attributed to vaporization of fuel within the stainless steel injection lines coming off the fuel spider on an injected engine. People referred to it as vapor lock, but it really isnt, as there is almost no pressure in these lines. Other than experiencing rough idle, there is no real hazard from this condition, and it goes away by opening your throttle slightly and increasing your fuel flow.

The current situation involves loss of fuel pressure, and to me is a bit more serious, in that it may truly be associated with vapor lock, and is preventing the mechanical fuel pump from operating correctly. While higher fuel flows appear to be "fixing" the problem for now, I would still want to take some action in this case for fear of things getting worse and being a problem in the air.

comments welcome

erich

Click to expand...

I totally agree. I have two other friends with the same setup/engine and flying with them have not seen such behavior, nor mine has ever done it and my min fuel pressure is set to 19 PSI. The rough start/running typically happens when you shut down the engine and heat builds up but not right after landing and while taxing. My 2 cents as usually.

taverroi said:

Please help me if you can...what can I do?..suggestions?.. Please somebody...

Tango

Click to expand...

Post pics of your fuel line routing. Some simple fuel line changes will likely fix this problem.

Where in your fuel system is the fuel pressure sensed?

Fuel is vaporizing in the line between the firewall and the pump inlet due to residual, radiating heat after landing. The fuel pump will not move vapor, only liquid. That's why the pressure is low. Shield the fuel line from after landing heat and the problem should go away.

With a cold engine start there is no residual heat and no problem, pressure is normal, all is well. In flight all is well because of air flow cooling through the area.

Its the only explanation that makes any sense.

Sorry Guys been outta touch due to heavy work load.

Ok, I will take pics tommorow of fuel line rounting but havent figured out how to post them here on this forum

Fuel senser is mounted on the left most position of the firewall, right up against it (pilot side).

Fuel vaporization on the inlet line sounds most probable. I have purchased special fuel line insulation and have begun insulating all the fuel lines in there intirety. The inlet side line and line to the senser has was insulated today. In additon I ordered the fuel pump cooling shroud kit from vans and will install it when it arrives. Insulation of the outlet side fuel line will be accomplished tommorow. Ive also had a set of louvers for the bottom cowling made (delivered to me today) and will be installing these as well to assist in removing residual heat and to provide a cooler engine inviroment.

Anything else guys. Im taking all suggestions serious and am implimenting all thing possible for the best results possible and the best safty.

Very much apprieciate all of you.

Tango

Tim

get us some pics and we can help, as all Rv's are not created equal. If you still are having issues, fly it over to ridgeland---we have several people over here that can help out.
Tom

Ok...All fuel lines insulated including the fuel line from the andair fuel valve running across the floor board to the firewall.

Test flight flawless...right up until landing...fuel pressure issue showed its ugly face again...it fell between 9 to 15 with slight fluctuation. Engine sputtered a bit after taxing for a while but it never shut off...like before...hmmm

I cant figure out for the life of me how to post pics. I took a bunch of the fuel line routing after insulation them and was gonna post them with this reply, but unless someone can give me a point by point direction I wont be able to. I've posted pics on other forum in this format before so I'm kinda confused as to why I can do it here. Help if you can.

My next actions are going to be (your opionions please) 1. fuel pump cooling shroud install. 2 Louver vents installed on the bottom of the cowling. 3. Exaust pipe heat protectors strategiclly located in areas of fuel lines.

Any other thoughts or suggestions? I'm confident to fly as this issue clearly does'n show itself initally or in flight...just after landing and taxing. But I would like to figure it out. Do you think I'll just have to live with it?

Tango

Do you have a Van's gascolator?

A neighbor had a very similar issue with his IO-360 RV-6. He was getting air from the gascolator when he pulled the throttle back, but didn't show up until flying for a bit, usually on final. Once it was removed, no more problems.

I dont think that I do. Iwill ckeck tommorow.

HOT FUEL AFTER LANDING

I HAVE HAD TO INSULATE MY FUEL LINES ABOVE THE ENGINE. IT HELPED A LOT TAXIING AFTER LANDING. DENNIS -6, I-O360

Fuel Pressure issue - But are they the same?

Bavafa said:

I totally agree. I have two other friends with the same setup/engine and flying with them have not seen such behavior, nor mine has ever done it and my min fuel pressure is set to 19 PSI. The rough start/running typically happens when you shut down the engine and heat builds up but not right after landing and while taxing. My 2 cents as usually.

Click to expand...

So how much the same are they? Do you both have Mechanical fule pump cooling ? Do you both have fire sleeves on your fuel lines? What else might be different? Are you cowl exits exactly the same? How about the engine baffling? Are you both flying out of the same field under the same conditions?
From the original discription, I'd say that this is a taxi cooling issue for sure. The fact that the Aux pump brings the fuel pressure back up would seem to indicate a hot engine compartment causing vapor lock issues in the fuel lines within the engine campartment, probably BFORE the mechanical pump. The fact that a new high pressure pump didn't change the situation confirms it.
If you don't already have one, add an air blast tube flowing cool upper plentum air onto the mechanical fuel pump. Better yet, put a showd around the mechanical pump with air. Be sure that ALL you engine compartment fuel lines have fire sleeve and that they have air flow onto them.
FWITW, I've seen these issues before, and this is how I've mitigated them....

A gascolator...

... schould not be installed on a FI-engine (correct me if I'm wrong guys), so do you have one installed? (I haven't seen that you've answered that question yet?)

Post pics: try this link: http://load.imageshack.us/

Click "browse", find the folder with your pics, select the size you want (I use the 17' monitor), click "upload now".

After the upload is done, copy the "forum-code" and paste it in your post.

Then you'll see the pics when you click "prewiew"... then send your post.

No. I do not have a gascolator installed.

What is the "forum Code" you speak of?

Working on the posting picture thingy. Thanks for the help.

Ok, hope this works for everybody interested. Here is the link to the fuel line routing photos on my bird. Any thoughts welcome.


http://imageshack.us/g/191/cimg0215g.jpg/


Other info. I cannot view post 18, 19 and 20 of this thread. Page 2 end with 17 and page 3 starts with 21? No idea whats going on there.

ao.frog

Your the man!.

Will never have issues in the future for picture viewing.

Tango

ao.frog said:

A gascolator ... schould not be installed on a FI-engine (correct me if I'm wrong guys)

Click to expand...

There's really nothing "wrong" with installing a gascolator on a FI engine. Its just not necessary, as it is for carb'ed engines.

I ran a gascolator in my RV4 for almost 400 trouble free, fuel injected hours, just as a way of trapping water and heavy sedimentary stuff. Worked fine.

Forum-code.

Tango:

"Forum-code" is the link I copy and paste to get the pic into my post. It's the forth one from the top under the "link to share your image" - page.
(the one you'll end up at when the uploading is done.)

You can use any of the other links too, but I prefer the "forum code" as it places the pics directly into the post in a good size (I select the 17" monitor size)

However, it's ofcourse up to you how you want to present your photos.

I've a couple of comments but I'm no engine-guru, so I hope others can correct me if I'm wrong.

The "silver-cylinder" with the drain-valve in this pic looks like a gascolator to me?





Is this the elec fuel-pump? (I've never seen one like this before)





Also: it looks as the fuel-lines going horizontally are somewhat close to the exhaust-tubes?

I think I've read somewhere that one schould avoid 90* connectors in the fuel and oil-lines as much as possible?

But as I said, I'm no guru, so I'm sure others will chime in with the correct info.

Good luck and please post updates regarding your engine-problem.

taverroi said:

No. I do not have a gascolator installed.

Working on the posting picture thingy. Thanks for the help.

Click to expand...

A couple of items noteworthy,
It does look like you have a gascolator installed (pix 5) unless I am mistaking it in the photo. Also, it is not clear in the same photo but it looks like that device (gascolator) is mounted directed to a AN fitting thru the firewall without itself being mounted on the firewall. If so, this can be dangerous as its weight is only supported by the AN fitting on one end and it could break the fitting by vibration.
Regarding the issue, I would suggest to try the easiest and cheapest way first. Adding a blast tube from the top of the engine baffle to the fuel pump is both very easy and cheap. It is also a good thing to have regardless. Next, I would check the fuel line in the tunnel to see if that is getting hot and creating the vapor. Perhaps you can fly one day with the cover removed which gives it both access to check for heating and/or a bit of cooling by not having the cover and more air circulating. If you have not checked it, it ought not be laying directly on the bottom skin. That fuel line typically is a hard line and not covered.

If it were me I'd do the following:

1) Get rid of the gascolator, install a filter in the cabin after the fuel selector.
2) Remove the firewall mounted aux fuel pump (weldon) and mount it or another style pump inside the cabin (away from the heat).
3) Reroute the cabn fuel line to exit in the center of the firewall (like it should be for a FI engine) so you have a short line to the engine fuel pump.

Basically bring the fuel system back to "original" design spec.
With both the gascolator and fuel pump FWF you have 2 major heat sinks boiling your fuel!

Listen to Walt on this one.

fuel pressure

I agree with Walt.
The gascolator is not needed. The horizontal line off of the gascolator looks too close to the exhaust. If you get vapor in that line, then the fuel pump can't work. I would get rid of the gascolator, move to an andair or Vans electric pump and filter system that is in the cool cabin environment.

Also, I think most lines up to the engine fuel pump are 3/8. It looks like you have a 1/4 inch line off of the gascolator, and that going right accross the exhaust pipe. Could the lower fuel mass in the small line heat up quicker and cause the vapor?

It looks like you really have the lines insulated well. What insulation did you use and where did you get it?

I also have an IO 360 in my RV7a. Just moved it from the garage to the hangar about a week ago. Hope to fly soon.

Ok Gents,

Just so all know.....I purchased this aircraft already built and flying. Up to this point I have had 50hrs of problemless operation.

I am learning as I go and could not possibly hammer through all this without all of you. The support is unpresidented.

This forum is priceless and worth a mountain of Gold. Here is some answers to ya'lls questions and thing that will be done (per suggestions) at my upcoming condition inspection which is this month.

1. Fuel injection lines off of the spider will be insulated.
2. Fuel pump cooling shroud installed with blast tube. (Already in hand from
Van's Aircraft) Another blast tube will be directed at the Mags (just
because)
3. Apparently I do have a gascolator. My bust. Sorry still learning here.
4. Yes, that is the elec fuel pump in the picture.
5. Gascolator will be either supported to the firewall or removed asap!
6. All fuel lines are firesleeved and fire insulated as well.
7. The horizontal fuel line is further away from the exausts than it appears
but was insulated as well in both the areas you have spoken of. Heat
shields will be installed on the exaust pipes in these areas.
8. The fuel line from the selector valve to the fire wall was wrapped in some
type of thick plastic band but still laying on the floor. This fuel line has
been fire insulated as well with the same silver insulation seen in the other
pics.
9. Elec fuel pump and Gascolator/fuel filter will be relocated inside the cabin
and fuel line rerouted throught the center firewall at the condition
insp....But first I have one last suprize effort (idea) to reduce the engine
compartment heat issues on my plane. Will post pics and data when
installation and test flights are complete.

I think I've addressed all questions and action items. Times gonna tell this story...Stand by for the flight test results of my "get the hot air out of the oh so tightly cowled enging compartment" idea!

Very much apprieciate all of you!

Tango

Tango,
I really believe all the action items that you have listed, even if they don't resolve the issue, will result in a safer and better fuel lines for the long run and the life of your plane.

Good luck.