Randomly losing power @ WOT

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Helmet
Posts: 72
Joined: Sun Jan 14, 2007 11:25 am
Location: Holland, Europe

Randomly losing power @ WOT

Post by Helmet » Sun Dec 18, 2016 11:07 am

Hi,

Lately I've been experiencing severe hesitation when going WOT. Not constantly though, it happens very randomly.

This is my setup: two tanks teed into one line, to a E vaporizer into a 425 mixer. Electric lockoffs. Now I think it has something to do with it being a two tank setup, since when driving normally, one tank seems to run out of fuel, even though I know it still has plenty of fuel left in it. I switch to the other tank regardless, and after I while I switch back and I can drive for miles again on the tank that acted empty. Now I think this is related to the hesetation at WOT, something is messing with the fuel supply.

Has anyone had a similar expercience? I need to know where to look.

Thanks in advance!
'72 Cutlass Supreme, 455 BBO (out of order)
'85 CUCV, HO454

BigBlockMopar
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Re: Randomly losing power @ WOT

Post by BigBlockMopar » Sun Dec 18, 2016 4:54 pm

Same experience here.
Whenever my tanks get below say, well below half full, I can sense hesitation at hard accelerations, or swift cornering.
This is confirmed by the AFR-gauge in my car, which goes very lean in these situations.

Both my tanks are always 'open' when running. But I have installed one-way T-valve to the mainline going to the vaporizer.
The tank with the most pressure in it empties first. Which is usually the 'warmest' tank for as long as the pressure is higher then the other tank.

I believe the tank's pickup tube can be uncovered during hard accelerations which causes the vaporizer to starve for (liquid) fuel or pressure.
When the hesitation occurs, it usually takes a second or 2-3 before power comes back.
I don't quite get the logic yet of why this happens as the pressure 'should' remain the same in the system and it's impossible the fuelline is emptied that quickly.
https://www.bigblockmopar.com
'73 Dodge Dart - 360ci - 11.3:1cr
MegaSquirt + HEI 7-pin timing control - Edelbrock AirGap - Cold Air Intake
IMPCO E / 425 mixer - A518 OD-trans - 3.55 gears - 225/50/17" tires.

C3H8
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Re: Randomly losing power @ WOT

Post by C3H8 » Sun Dec 18, 2016 5:23 pm

BBM has pointed out one of the issues that can happen, although as mentioned it is uncommon for it to happen rapidly because of the liquid in the line. This was a common problem in our school buses and large trucks with tanks mounted outside the frame parallel to the frame. Climbing long grades in cool weather would cause the fuel to run to the back of the tank and expose the pickup to vapour only. Once the liquid was used up from the line, which was quite quick in vehicles this large the engine would lose power and struggle to climb the rest of the hill. This was solved by adding a second pickup at the back of the tank.

In your case I see two possibilities.
1. Check the electric solenoids for contamination preventing them from opening all the way. This allows enough flow for moderate engine operation but restricts the flow as soon as power is needed.
2. The excess flow spring in the valve has become weak and is closing off when a sudden fuel demand is required. Slowing down, releasing the gas pedal or switching tanks allows the pressure to equalize and the valve reopens. Once the pressure equalizes the engine will run using moderate loads again.

The other thing to check is a visual inspection of the fuel filter and supply line as soon as the problem occurs. If it is a restriction problem frost will form quickly at that point. Depending on your current temperatures it will have to be done quickly as the warmer it is the faster the frost will be gone.

storm
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Location: NSW, Australia

Re: Randomly losing power @ WOT

Post by storm » Sun Dec 18, 2016 6:10 pm

If the problem is occurring with the HO454 (listed in your signature) you may be finding you are reaching the HP limit of flow at the tank outlet. If the pressure of the tank is low (cold day) the fuel flow can be less than the engine requires. On a warm day the tank pressure is higher so fuel flow is also higher. The outlet on the tank can only flow a certain amount of fuel (check the thread linked to in my signature for some calculations) and with only 1 tank, or 1 outlet, feeding at any 1 time anything over 300HP (actually I think it is 275HP) is going to be on the edge of fuel flow limits. So follow the suggestions made in the previous posts and also consider replacing the lock offs for units that allow more fuel flow.
Every job is a self-portrait of the person who did it. Autograph your work with excellence.

Fuel flow requirements calculations viewtopic.php?f=5&t=1638

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Steptoe
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Re: Randomly losing power @ WOT

Post by Steptoe » Sun Dec 18, 2016 11:20 pm

I chased something like this around for a long time ... with a sudden lean out in AFR randomly, useually going up a hill constant speed or acceleration at cruising speed. often mild acceleration just getting up to full highway speed.
turned out t be a most minute burr on the main piston inside the 425.
It was C3H8 who suggested it a along shot.

the tolerances between the piston and the walls are very critical.. a worn piston cylinder will do the same thing.

Also had very similar some yrs before.. again chased around for ages... turned out the hose between converter and 425 had de laminated creating a 'flap' inside intermittently restricting flow... the LPG rated hose was not very old either which is why missed it checking stuff.
And before that the little activation pin in the vaccuum shut off was worn... replaced the pin fixed.. a yr or so later same thing.. this time it was the hole the pin sat in.. part of the body... and not rebuild able with out re machining and sleeving. replaced with a new body.
This was all over a period of some 20/ 25 yrs ... same car same set up.
My Spelling is Not Incorrect...It's 'Creative'

kuchen
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Re: Randomly losing power @ WOT

Post by kuchen » Mon Dec 19, 2016 2:40 pm

Those electric lockoffs at least in Europe have to allow a backward flow into the tank when not energized. It is therefore not recommended to feed one line with multiple tanks without using oneway-valves. Even with a throw switch and only one lockoff energized at a time, there is still the danger of overfilling the colder or lower tank with the hotter or higher tank.

I guess I have stated that already in an earlier post, but ECE R67-01 and R-115 have superseded local legislation regarding LPG setups throughout the EU by now. Those documents are public and can easily be downloaded in several languages.
http://eur-lex.europa.eu/legal-content/ ... 001.01.ENG

quoting the R67:

17.5. Further requirements to the fuel container
17.5.1. If more than one LPG container is connected to a single delivery tube each container shall be fitted with
a non-return valve installed downstream of the remotely controlled service valve and a tube pressure relief
valve shall be installed in the delivery tube, downstream of the non-return valve. An adequate filter system
has to be placed upstream of the non-return valve(s) to prevent fouling of the non-return valve(s).
17.5.2. A non-return valve and tube pressure relief valve shall not be required if the backflow pressure of the
remotely controlled service valve in the closed position exceeds 500 kPa.
In that case the control of the remotely controlled service valves shall be constructed such that it is
impossible for more than one remotely controlled valve to be open at any time. The overlap time to allow
switching is limited to two minutes.


I have not managed to attain any information about the exact backflow pressure of the lockoffs from any manufacturer I have asked. Thats why I am afraid that the only legal way to go here is 17.5.1 with the only supplier for such a setup with valves, filter and PRV being Prins, NL.

There is one advantage, though. I guess with this pricey Prins coupler block and all lockoffs open, there should always be liquid fuel in the line.

Helmet
Posts: 72
Joined: Sun Jan 14, 2007 11:25 am
Location: Holland, Europe

Re: Randomly losing power @ WOT

Post by Helmet » Fri Dec 23, 2016 4:46 pm

Some good 'food for thought' posts here, thank you!
BigBlockMopar wrote:Same experience here.
Whenever my tanks get below say, well below half full, I can sense hesitation at hard accelerations, or swift cornering.
This is confirmed by the AFR-gauge in my car, which goes very lean in these situations.

Both my tanks are always 'open' when running. But I have installed one-way T-valve to the mainline going to the vaporizer.
The tank with the most pressure in it empties first. Which is usually the 'warmest' tank for as long as the pressure is higher then the other tank.

I believe the tank's pickup tube can be uncovered during hard accelerations which causes the vaporizer to starve for (liquid) fuel or pressure.
When the hesitation occurs, it usually takes a second or 2-3 before power comes back.
I don't quite get the logic yet of why this happens as the pressure 'should' remain the same in the system and it's impossible the fuelline is emptied that quickly.
Hi Herman, interesting that you're experiencing the same problem, even though our setups are a bit different. My tanks are mounted lengthwise along the frame rails under the cab/bed. They are mounted at the exact same height, and the 'see' the same ambient temperature. One tank was a previously used though, and is a 85 litre compered to the new when installed 80 litre tank. I use the gas/lpg switch supplied with the typical LPG setup to switch between tanks, so I have one 'open' and one 'closed' tank.

Still, this issue occurs in the same circumstances as you, when the tank gets under half full.
I find the thought that my truck is fast enough to make the fuel slosh into the back of the tank highly entertaining. :mrgreen:
It also sounds feasable, although I can remember a time when I did not have this problem, so I'm not totally convinced this is (all of) the issue.
'72 Cutlass Supreme, 455 BBO (out of order)
'85 CUCV, HO454

Helmet
Posts: 72
Joined: Sun Jan 14, 2007 11:25 am
Location: Holland, Europe

Re: Randomly losing power @ WOT

Post by Helmet » Fri Dec 23, 2016 4:54 pm

C3H8 wrote:BBM has pointed out one of the issues that can happen, although as mentioned it is uncommon for it to happen rapidly because of the liquid in the line. This was a common problem in our school buses and large trucks with tanks mounted outside the frame parallel to the frame. Climbing long grades in cool weather would cause the fuel to run to the back of the tank and expose the pickup to vapour only. Once the liquid was used up from the line, which was quite quick in vehicles this large the engine would lose power and struggle to climb the rest of the hill. This was solved by adding a second pickup at the back of the tank.
How was this done? Did they have to weld in a thread in the tank for the second pickup?
[quote/]
In your case I see two possibilities.
1. Check the electric solenoids for contamination preventing them from opening all the way. This allows enough flow for moderate engine operation but restricts the flow as soon as power is needed.
2. The excess flow spring in the valve has become weak and is closing off when a sudden fuel demand is required. Slowing down, releasing the gas pedal or switching tanks allows the pressure to equalize and the valve reopens. Once the pressure equalizes the engine will run using moderate loads again.[/quote]

I'm sorry, where is this valve located?
The other thing to check is a visual inspection of the fuel filter and supply line as soon as the problem occurs. If it is a restriction problem frost will form quickly at that point. Depending on your current temperatures it will have to be done quickly as the warmer it is the faster the frost will be gone.
This is a good one, its far to cold for my liking right now, although still above freezing. But these temperatures will buy me some time to check things out. Thanks!
'72 Cutlass Supreme, 455 BBO (out of order)
'85 CUCV, HO454

Helmet
Posts: 72
Joined: Sun Jan 14, 2007 11:25 am
Location: Holland, Europe

Re: Randomly losing power @ WOT

Post by Helmet » Fri Dec 23, 2016 5:04 pm

storm wrote:If the problem is occurring with the HO454 (listed in your signature) you may be finding you are reaching the HP limit of flow at the tank outlet. If the pressure of the tank is low (cold day) the fuel flow can be less than the engine requires. On a warm day the tank pressure is higher so fuel flow is also higher. The outlet on the tank can only flow a certain amount of fuel (check the thread linked to in my signature for some calculations) and with only 1 tank, or 1 outlet, feeding at any 1 time anything over 300HP (actually I think it is 275HP) is going to be on the edge of fuel flow limits. So follow the suggestions made in the previous posts and also consider replacing the lock offs for units that allow more fuel flow.
Fuel flow limits are certainly something a have thought about alot. Yes, the 454 in full swing is probably over the edge as far as fuel flow capacity goes. However, the hesitation has always occured at low (city) speeds. The 454 is mounted infront of a diesel TH400, which means its governed at 2800ish RPM shifts. The kickdown is also not functional. Which means that at low speeds, the 454 doesnt see a lot of rpm. Yes, it still has enough torque to get my truck scooting along nicely, but the only time the fuel system is tested is when I wind it out on the highway, which I don't really do a lot. Even then, the power seems to just stay the same as rpm increases, its nothing like the hesitation/bog I'm experiencing.

As long as where on the topic of fuel flow, does anyone have any litre per minute of hour ratings for the tank outlet, various lockoffs, and mixers? It would give me some insight on what is needed for a project down the line.
'72 Cutlass Supreme, 455 BBO (out of order)
'85 CUCV, HO454

Helmet
Posts: 72
Joined: Sun Jan 14, 2007 11:25 am
Location: Holland, Europe

Re: Randomly losing power @ WOT

Post by Helmet » Fri Dec 23, 2016 5:05 pm

Steptoe wrote:I chased something like this around for a long time ... with a sudden lean out in AFR randomly, useually going up a hill constant speed or acceleration at cruising speed. often mild acceleration just getting up to full highway speed.
turned out t be a most minute burr on the main piston inside the 425.
It was C3H8 who suggested it a along shot.

the tolerances between the piston and the walls are very critical.. a worn piston cylinder will do the same thing.

Also had very similar some yrs before.. again chased around for ages... turned out the hose between converter and 425 had de laminated creating a 'flap' inside intermittently restricting flow... the LPG rated hose was not very old either which is why missed it checking stuff.
And before that the little activation pin in the vaccuum shut off was worn... replaced the pin fixed.. a yr or so later same thing.. this time it was the hole the pin sat in.. part of the body... and not rebuild able with out re machining and sleeving. replaced with a new body.
This was all over a period of some 20/ 25 yrs ... same car same set up.
So in other words, lots of things to check! Gotcha :mrgreen:
'72 Cutlass Supreme, 455 BBO (out of order)
'85 CUCV, HO454

Helmet
Posts: 72
Joined: Sun Jan 14, 2007 11:25 am
Location: Holland, Europe

Re: Randomly losing power @ WOT

Post by Helmet » Fri Dec 23, 2016 5:12 pm

kuchen wrote:Those electric lockoffs at least in Europe have to allow a backward flow into the tank when not energized. It is therefore not recommended to feed one line with multiple tanks without using oneway-valves. Even with a throw switch and only one lockoff energized at a time, there is still the danger of overfilling the colder or lower tank with the hotter or higher tank.

I guess I have stated that already in an earlier post, but ECE R67-01 and R-115 have superseded local legislation regarding LPG setups throughout the EU by now. Those documents are public and can easily be downloaded in several languages.
http://eur-lex.europa.eu/legal-content/ ... 001.01.ENG

quoting the R67:

17.5. Further requirements to the fuel container
17.5.1. If more than one LPG container is connected to a single delivery tube each container shall be fitted with
a non-return valve installed downstream of the remotely controlled service valve and a tube pressure relief
valve shall be installed in the delivery tube, downstream of the non-return valve. An adequate filter system
has to be placed upstream of the non-return valve(s) to prevent fouling of the non-return valve(s).
17.5.2. A non-return valve and tube pressure relief valve shall not be required if the backflow pressure of the
remotely controlled service valve in the closed position exceeds 500 kPa.
In that case the control of the remotely controlled service valves shall be constructed such that it is
impossible for more than one remotely controlled valve to be open at any time. The overlap time to allow
switching is limited to two minutes.


I have not managed to attain any information about the exact backflow pressure of the lockoffs from any manufacturer I have asked. Thats why I am afraid that the only legal way to go here is 17.5.1 with the only supplier for such a setup with valves, filter and PRV being Prins, NL.

There is one advantage, though. I guess with this pricey Prins coupler block and all lockoffs open, there should always be liquid fuel in the line.
I'll have to check to be totally sure, but I think a oneway valve was used. However, I don't have a filter, so it is actually possible the valve is fouled.
'72 Cutlass Supreme, 455 BBO (out of order)
'85 CUCV, HO454

storm
Posts: 566
Joined: Wed Jan 10, 2007 10:10 pm
Location: NSW, Australia

Re: Randomly losing power @ WOT

Post by storm » Fri Dec 23, 2016 6:52 pm

Helmet wrote:As long as where on the topic of fuel flow, does anyone have any litre per minute of hour ratings for the tank outlet, various lockoffs, and mixers? It would give me some insight on what is needed for a project down the line.
You would need to find the datasheets for each item from the manufacturer or supplier. Be aware that mixers don't, or at least shouldn't, flow raw liquid so a l/m fuel figure is no use for the mixer. In my experience (and I am no where near as experienced as Franz, C3H8, and Frank) the limiting factor is the lockoffs in the 1st instance and the number of tank outlets in the 2nd instance. A 425 will flow enough air for 300 crank HP (1.5 cfm per HP), the E regulator/vapouriser flows enough fuel for 325 crank HP.
Every job is a self-portrait of the person who did it. Autograph your work with excellence.

Fuel flow requirements calculations viewtopic.php?f=5&t=1638

C3H8
Posts: 1003
Joined: Fri Sep 09, 2005 11:23 pm
Location: Winnipeg, Canada

Re: Randomly losing power @ WOT

Post by C3H8 » Fri Dec 23, 2016 10:10 pm

[quote/]
In your case I see two possibilities.
1. Check the electric solenoids for contamination preventing them from opening all the way. This allows enough flow for moderate engine operation but restricts the flow as soon as power is needed.
2. The excess flow spring in the valve has become weak and is closing off when a sudden fuel demand is required. Slowing down, releasing the gas pedal or switching tanks allows the pressure to equalize and the valve reopens. Once the pressure equalizes the engine will run using moderate loads again.
I'm sorry, where is this valve located?
[/quote]

I am expecting the solenoid valves you have are located right at your tank. These solenoids will only shut off fuel in one direction. They act as both a shut off and a relief valve. When shut off fuel cannot flow out of the tank, however if the pressure increases in the line above tank pressure for any reason fuel is pushed back into the tank and can be vented (if necessary) out the tank relief valve as vapour. There have been several cases where the tank solenoid piston is restricted from opening all the way due to a black iron oxide powder that has migrated to the top of the piston and keeping it from opening all the way. Basically solenoids are electro magnets and the strongest magnetic area is above the solenoid piston to pull it open. The Black Iron Oxide powder is magnetic can be pulled above the piston any time the solenoid energizes. The build up of powder on top of the piston restricts its movement preventing it from opening all the way. It is easy to check, however the tank must be completely empty to do this.

The excess flow is built into the electric shutoff valve and is on the liquid side of the valve inside the tank. It is strictly a ball or flapper held open by a spring. Its main purpose is to close if a line is ruptured in an accident. The sudden escape of fuel will be stronger then the spring and cause the valve to close keeping the fuel in the tank. Typically these valves are set at 1.7 GPM. A very minor amount will continue to escape through a tiny balance hole. In some cases the spring loses it's tension or strength and the excess flow can close restricting the fuel flow. This is usually evident as a possible cause by immediately shutting the engine off, waiting for a few minutes and seeing if power is restored. If your in a really quiet area you may even hear the valve open with a click a few seconds to a minute after you shut the engine off.

Referring the double dip tube. I never did see how they did it but Sleegers figured it out. There is a possibility they may have just relocated the tube to the rear of the tank. Vapour on a downhill coast may not have concerned them as fuel demand is low. My understanding was they just welded a piece of pipe at the base of the original downtube leading to the rear of the tank. I guess it is possible they just relocated the pickup.

Hillbilly
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Joined: Wed Jul 28, 2010 2:12 pm

Re: Randomly losing power @ WOT

Post by Hillbilly » Fri Jan 13, 2017 6:09 am

When I asked Franz about using dual 425s and Dual Es he told me my single electric block off would flow plenty. Idk I should go back and see if I can find that email.

Welding a new bung into a pressure vessel requires a you have a "R" stamp to meet ASME requirements in this country and I am betting other countries have the same/similar requirements. If caught modifying a tank legally the bung must be cut out and rewelded.

I did see a "saddle tank" style LPG tank that would mount parallel to the frame on a 73/87 Chevy. I know the filler was on the bottom but not sure where the pick up was.

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