What is the solution to lean fuel/boiling swirlpot on LS7

What is the solution to lean fuel/boiling swirlpot on LS7

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bluesatin

Original Poster:

3,114 posts

271 months

Friday 17th August 2012
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Hi,

Just been out for the past couple of hours and got caught in traffic for 20-30 mins. Car started to misfire when the traffic cleared. Switched to other tank and all ok for 10 mins then started to misfire again while in built up area eventually stalling and not starting. Thanks to a passing tow I made to a safe place to park up. After 20 minutes the car started fine. OBD2 error code was lean on bank 1 and 2! I have an LS7 with standard factory install including swirl-pot. Any ideas on how to stop this?

thanks

F.C.

3,896 posts

207 months

Friday 17th August 2012
quotequote all
Not an LS7 but am familiar with this scenario.
Nimbus / Cumulus heat shielding to the petrol tanks, mine was picking up radiant heat from the exhaust headers (despite coating) and causing vapour lock in "extreme" traffic conditions. not a hint since heat shielding fitted.

Storer

5,024 posts

214 months

Friday 17th August 2012
quotequote all
I have a temperature sensor on my fuel pressure regulator and the highest I have seen is 34 deg.

Heat shielding on tanks and pipes, plus alloy panel shield with gap between tank and shield. Zircotec coated exhaust which is not Factory standard so higher mounted. Fuel flows from in tank LP pump into swirl pot then straight into HP pump, 10micron filter, into fuel rail, out of fuel rail into regulator back to swirl pot then back to tank. Over supply to the swirl pot returns through a restrictor to raise pressure slightly.

Temperature management under the rear clip is all important to avoid problems. Air intake only sucking air from outside the clip. Heat shielding on airbox. Exhaust shielding (zircotec and wrap). Max airflow through rear - no alloy panels under the engine.

Having said all this I would check your fine filter. The 10 micron filter blocks quite easily and is a cheap fix and needs changing annually.

Hope this helps.

Paul

MarkWebb

983 posts

216 months

Friday 17th August 2012
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I am not proud to admit it but I have plenty of experience of this and I seem to have cracked it. I would recommend checking filters first though. I would be happy to discuss but I think a phone would be better. PM me.

bluesatin

Original Poster:

3,114 posts

271 months

Monday 20th August 2012
quotequote all
Thanks Mark and Paul. Will check through some of the advice first and set up a temp gauge in a few places.

Guy

MarkWebb

983 posts

216 months

Monday 20th August 2012
quotequote all
Sounds like you have done a brilliant heat shielding job Paul. Whilst 34 deg C is not hot at all it is still possible for fuel to vaporise at this temp if it pressure is reduced enough. ie in the suction to the hp pump if there is any sort of restriction in the supply to it ie blocked filter or too small pipe.
Your problem occurred in traffic which is when under clip temps go up but is also when the engine is using hardly any fuel.
I have also had problems in traffic but they do not appear that quickly. I imagine that under clip temps rise rapidly to an elevated level which would warm the fuel fairly quickly. The fact that the engine is using very little fuel whilst the pumps are circulating it at a rate that is fast enough to supply the engine at full throttle causes the fuel to be heated an awful lot by the action of the pumps particularly the HP one. In my case this is definitely a contributing factor. I know this because the occurrence of the problem is directly proportional in time to how much fuel I have in the tank that I am using at the time. The problem also goes away almost instantly if I switch to an unused tank of fuel.
I was lucky enough to be able to experiment with this during an extend (2500) mile trip around Europe. I can't really recommend going to find a traffic jam to sit in for an extended time but if it happens it is worth bearing in mind my findings and experimenting yourself.
Everybody's fuel system will be slightly different and so the problem may not occur at all but may occur after differing lengths of time.
My problem occurs quicker than most because because I have a swirl pot mounted high on the front bulkhead.
I have cured the problem by pressurising the swirl pot to about 5 psi using a carb pressure reg on the return to tank line.

Storer

5,024 posts

214 months

Monday 20th August 2012
quotequote all
My swirl pot is mounted on the side pod so has airflow over it when moving. With the small restrictor in the return, it too creates a small pressurisation of the pot.

I sat in stationary/stop start traffic on the way back from Snetterton yesterday with no problems even though my tanks were almost dry


Paul

MarkWebb

983 posts

216 months

Monday 20th August 2012
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yes a restrictor is better than a regulator coz it passes air/vapour v quickly.

MarkWebb

983 posts

216 months

Monday 20th August 2012
quotequote all
pasted from the Fuelab website
The most common failure of high flow fuel systems is cavitation, or “vapor-lock”. The combination of too much heat or too much inlet restriction can create this operating condition, where the liquid fuel literally vaporizes (boils) inside the pump assembly. Symptoms of this operating condition may include one or more of the following:
• Dramatic loss of flow rate
• “Gauge Bouncing”
• Ratchet or grinding sounds from pump
• Inconsistent or loss of fuel pressure
• Temperatures above 120°F (50C)
As bad as the symptoms of this condition are, the results of this condition are often permanent, even if what caused the condition in the first place was fixed. Loss of fuel delivery pressure will also result in a lean-out condition as well that can result in engine damage. Typically, even with very short amounts of time of exposure to cavitation (depending on severity) will cause damage to the fuel pump. This damage results in a direct loss of capacity and efficiency. Often as noted when unchecked, this damage to the pump results in operating conditions that quickens cavitation exposure at each use. Eventually, the fuel system resorts to complete failure to build or maintain pressure. For all fuel systems of any manufacturer, this failure can be avoided as it is not a result of a manufacturing defect, but a result of a fuel system design failure.
Two operating conditions can create the cavitating condition:
• High operating temperatures
• High inlet plumbing restrictions
High operating conditions can exist for several reasons, such as high inefficiencies (such as a worn or damaged pump), overly high fuel pressures, high flow rate pumps for long durations with low fuel amounts, or secondary sources of heat such as fuel rail(s), engine or exhaust. Prodigy Fuel Pumps have the distinction of having speed control, inherent in its design. This allows a reduced speed during low engine demand conditions that can add excessive temperatures to the fuel system.
Some refer to pumps as “pushers” or “pullers”. The truth is that all pumps are both. This reference comes from the amount of resistance to cavitation a particular pump has versus another. Minimizing the amount of restriction feeding the pump’s inlet is a critical element to avoid cavitation. This is the main reason why typical OEM fuel systems have their pumps mounted inside the fuel tank. Use of straining filters is required for the inlet of the fuel pump, to have a fine enough filtering to protect the fuel pump, yet coarse enough not to inhibit flow, or capture enough particles to cause a building up of debris. Finer filtration, to protect the rest of the fuel system (such as fuel injectors and regulators) can be accomplished downstream of the fuel pump with a second filter. Typically, straining filters for fuel pumps elements have micron ratings from 25 to 150 micron rating. Fuelab recommends the use of 75 micron rating for Prodigy Series fuel pumps (75-150 micron required). Typically, modern OEM straining filters are at a lower micron rating and made of plastic weave cloth. While these types of filters are adequate and desirable for OEM applications, however typical aftermarket fuel systems have far too high of flow rate to accommodate this form of straining filter easily. The biggest mistake and almost certain doom for a high flow fuel system, is to use a 10 micron filter upstream of the fuel pump. Plumbing size and the types of hose (or tube) play a vital role in the effects of cavitation as well general performance. The larger the flow rate, the larger the line size must be. Always avoid the use of check valves, or cross-drilled fittings when plumbing upstream of the fuel pump.
The second aspect that can cause cavitation is allowing heat to build-up in the fuel system. Most high flow EFI and carbureted fuel pumps are rated as “not continuous duty”. This is due to the amount of heat build-up that occurs over time as the fuel system is operating. When the fuel system has a high enough temperature, then the fuel will start to vaporize at the pump assembly, even with low pressure drop plumbing at the pump’s inlet. To allow for continuous or “street” use, voltage controllers are employed to reduce the pump speed during low engine demand operation, to prevent heat build-up. Once fuel temperatures are above 120°F (50C), then the fuel is prone to vaporizing. A rule of thumb is: if it’s hot enough not to be comfortable to the touch, then it is too hot. Prodigy fuel pumps have a unique feature to allow reductions of speed without the need for an external pump controller. See our forum topic under Speed Control for more information relating to speed reduction for Prodigy Fuel Pumps.

deadscoob

2,263 posts

259 months

Tuesday 21st August 2012
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When these fuel boiling topics come up I always think of Ken and Lee in the US who have no problems and run the cars harder than 95% of us Europeans in much hotter conditions.

Why is that?

738 driver

1,202 posts

192 months

Tuesday 21st August 2012
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Scoob dont be confused by the website PR's error ... when a fuel 'expert' claims 'boiling at 50 deg' theres a big problem.

Fuel will vapourise at low temps but not boil.

Latent heat of evapouration.... when a puddle disappears from the ground it doesnt boil and turn to steam does it... it merely changes state (becomes invisible vapour suspended in air) at much lower temps... fuel is no different.

When a pump is presented with fuel vapour, it struggles to compress is back to liquid form and hence prime itself.. there starts the problem... fuel in gas form cannot be compressed enough by liquid pumps to create or maintain a supply.

The easiest way to avoid this is heat management around the pumps and header/swirl pot plus very importantly have all pumps at the lowest point possible. Fuel as a liquid will most likely be at the lowest point and vapour above it. Carefully planning the best position and location of pump vs header/swirl feed will give great results.

Euro fuel is a slightly different mix to US and maybe this contributes a little. But a simple system that self bleeds vapour and encourages liquid flow to the pump will work fine.


MarkWebb

983 posts

216 months

Tuesday 21st August 2012
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If you have a problem under heavy throttle then you most lightly have a restriction in your fuel LP system. If you have a problem after sitting for a long time in traffic then it is probably a heat in the fuel problem. I have suffered from the later on many occasions because my fuel system is layed out in such a way so as to cause it to absorb a lot of heat when it gets hot under the hood.
I have completely cured the problem by pressurising my swirl pot to about 5psi. I have done nothing else. remember that the return line from the swirl pot enters the tank at a reasonable height if you do not have a non return valve in it it is quite possible for the hp pump to obtain fuel/vapour through this pipe if it is an easier route and your system is plumbed that way.
With a full tank of fuel. Your fuel pump will circulate the tank contents approx 4 times an hour. With 2 galls in it. It will be circulated approx 20 times an hour.
Check filters first. Then create some pressure in the swirl pot.
Depending on your pump type it may be damaged if it was sucking vapour for a while.

mt308

438 posts

142 months

Monday 28th May 2018
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Bluesatin, looks like you no longer have the GTR. Did you solve you fuel issue, and if so how?

I've been trying for 4 years to fix mine ans have posted on here several times. My issue is identical to the one you describe and I have the same engine and fuel setup to the one you had I think. I have replaced every part of the system to no avail.

Just let me down again today. Only when the car is warm/hot, always works fine when cooled down again.

Thanks
Mark

Storer

5,024 posts

214 months

Monday 28th May 2018
quotequote all
I am fairly sure the problem of fuel vaporisation is due to the high pressure fuel pump(s) circulating too much fuel through the pump, filter and regulator. It is not a problem when driving at speed but only when travelling very slowly or in stop-start traffic.
Most of us are guilty of thinking 'I might want more power in the future so I'll fit a bigger pump than I need' and we create an issue. My A1000 Aeromotive pump is way bigger than necessary and pulls 13amps and delivers sufficient for a 1300hp engine rather than my puny 575hp.
Rather than change to a different pump I opted for a Fuel-on-Demand controller that you can adjust using a laptop.
My A1000 now pulls about 6.7amps and delivers a nice steady 60psi for the returnless fuel rail.

My car had no issues in France last year in 37 deg temperatures, even in traffic.

Not sure if you can still get FOD as I couldn't find it but mine had to come from the US.


Paul

mt308

438 posts

142 months

Monday 28th May 2018
quotequote all
Thanks Paul. I have a FOD. Will check its still working as I know the HP pump has grounded in the past (body of pump touching metal which negates FOD). 95% sure it is OK. If it is still working I have no clue why my car doesn't work and others do! Have replaced every part.

Am thinking of more radical action otherwise. Fed up with conking out!

Mark

bluesatin

Original Poster:

3,114 posts

271 months

Monday 28th May 2018
quotequote all
It is worth speaking to Charles Dunn as I think he has now resolved this. Issue is the fuel gets way too hot in the swirl pot. Try insulating everything close to the exhaust as first pass,

mt308

438 posts

142 months

Monday 28th May 2018
quotequote all
bluesatin said:
It is worth speaking to Charles Dunn as I think he has now resolved this. Issue is the fuel gets way too hot in the swirl pot. Try insulating everything close to the exhaust as first pass,
Thanks, car has been back and forth to Charles many times. Problem is it only conks out when its not with him! I'll be talking to him tomorrow again hopefully as if anyone can fix it, he can. Its becoming a real pain - 4 years of intermittently sitting on the hard shoulder. I'm worried one day I'll break down in a dangerous spot.

Mark

georg

43 posts

195 months

Monday 28th May 2018
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Hi All
I celebrated all this several years ago. I solved the problem eventually
1-led more outside air with a strong flow through the engine compartment in the lower and upper parts
2-installed refrigeration with a fan
3 - I have installed two fans in the engine compartment with the air supply from the outside / similarly to the Porsche /. I turn on manually during every stop in the traffic jam.
Four more small modifications to the engine cover

from now on I have been driving to Italy for 4 years in July and August. I often stand in traffic jams even after several kilometers. There was never cavitation of fuel.
This problem of cavitation ended for me finally.
Regards
georg

Storer

5,024 posts

214 months

Monday 28th May 2018
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Sad git that I am I did video the laptop screen and dash after I was happy with the setup.

A boring video to watch but you might find the comparison with your settings useful

https://www.youtube.com/watch?v=iml-9FWg2vA


Paul

mt308

438 posts

142 months

Tuesday 29th May 2018
quotequote all
Paul

Not boring for me! Interesting that your pump is drawing 7 amps at idle. My Bosch 044 draws just under 2 amps at idle and only when seriously poked gets up to about 5.

I am not sure what all the other setting mean. My pressure is also set at 58psi and when testing it it reads like yours.

I noticed I had a prime setting on mine that was set to 0. I changed it to 1 and it now seems to prime when turning the ignition key so starts easier. I very much doubt this setting will make any difference to my underlying problem though.

Mark