Fuel Cavitation (Air in fuel)

Fuel Cavitation (Air in fuel)

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Racing Roj

Original Poster:

488 posts

162 months

Monday 14th July 2014
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On a 70 mile journey on Saturday I encountered fuel cavitation twice, something I had not had before. It seemed to be the high temperatures of the day that caused the fuel to overheat. I had to wait about 15 minutes before I could start the car and drive on. As far as I know the fuel system is standard factory supply and install. Having spoken to someone who has much experience with Ultimas he has suggested firstly insulating the swirl pot with DEI and then try it again. As the ambient temperatures are going to high over the next few weeks I will be able to do that. If this doesn't cure it he suggested lagging the braided hose fuel pipes. He also seemed to think that the device (not sure what it's called) with the fuel pressure gauge on could also be a problem due to its high mounting point in the engine bay. Has any one else had this problem and if so how did you cure it? Thanks.

Storer

5,024 posts

214 months

Monday 14th July 2014
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Hi Roj
Had a similar embarrassing moment at the Great British Welcome car show at Le Mans when my fuel boiled.

I moved my fuel regulator from the top of the engine bay and did away with the fuel circulating over the engine. It now enters the rail under 59psi and has to go through the engine.
My whole fuel system is now in the l/h side above the tank which has a submersible low pressure pump.

Paul

MarkWebb

983 posts

216 months

Monday 14th July 2014
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There are a number of threads discussing this in detail and I have also suffered and cured the problem. Personally I don't think that lagging anything will make enough difference to put it to bed completely. There are easier, cheaper and tidier ways.
Happy to discuss by PM and/or phone.

macgtech

997 posts

158 months

Tuesday 15th July 2014
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Hi Roj,

Was it at wide open throttle?

First and easiest thing is to clean the filters - you would be amazed at what can end up in there!

Jonny

anonymous-user

53 months

Tuesday 15th July 2014
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"Lagging" the fuel system, unless in very specific places in the engine bay close to direct sources of heat (like exhaust manifolds etc) is not a goo didea, because most of the heat in the system is coming from the fuel pump! (A big fuel pump, pulling 10A @ 12V is 120Watts of heat, pretty much all of which is "sunk" into the bulk fuel mass. With a pump that is moving a lot of fuel (necessary if you have a powerful engine that can consume a lot of fuel at peak power) it will be "cycling" the entire contents of the tanks through the system very regularly indeed.

Best fix is to go to a speed controlled pump, second best is to ensure your swirl pot and lift pump generate a small positive pressure head on the main pump inlet!

macgtech

997 posts

158 months

Tuesday 15th July 2014
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It isn't all converted to heat though is it?

After a run measure the temperature of the pump (or even feel if it is getting warm) which will give you an idea as to whether or not that is a primary cause.

If so, the most efficient source of heat transmission is conduction, so you could heat sink the pump to whatever it is mounted against. Moving the pump into cooling airflow is also an option but more difficult to do.

Heat reflection/shielding is incredibly effective, especially where the pumps are close to high temperature parts.

Racing Roj

Original Poster:

488 posts

162 months

Wednesday 16th July 2014
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Thanks Guys for your input. I have been away for a few days so have only just read the posts. I would answer the points raised as follows: -
1. My knowledge of the fuel system is at the moment minimal but I gave been advised that it is a standard factory system.
2. When the problem surfaced it was on the public roads and definitely not at full throttle in fact very little throttle.
3. There was problem happened at least 30 miles between each event.
4. The ambient temperature was about 23c.
As you can see there has been some conflicting advice so I am a little confused.
I think I will try and insulate at least the swirl pot and check that the pipe work and fittings aren't causing a pressure loss and adding to the problem.

spatz

1,783 posts

185 months

Thursday 17th July 2014
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i think it is time for the factory to comment and advice why you are seeing the problems with the factory system, that has been repeatedely been reported by Richard to be perfectly working.
it is obvious that there are problems with it and i can only recommend to change the current factory setup as e.g. both of my altered
systems work very well and see heat up of fuel only in very hot wheather <35deg and slow traffic. in general the regulated pump with insulated tanks might be the only solution to fix this issue for good.

macgtech

997 posts

158 months

Friday 18th July 2014
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Do the pumps/swirl pot seem hot?

At first it seemed odd to me that it was at low throttle openings, but I suppose if you aren't using much fuel, then it is simply circulating the HP part of the system so ever increasing in temperature. Get an IR temperature prob, put some insulation tape on the parts to be measured (the IR doesn't work well on shiny surfaces) and check various temperatures of the filters, pumps, pot and rails.

Racing Roj

Original Poster:

488 posts

162 months

Friday 18th July 2014
quotequote all
Thanks Jonny
I will check the different parts of the system but I need to find where they first.
What's an IR?

BogBeast

1,136 posts

262 months

Friday 18th July 2014
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Racing Roj said:
Thanks Jonny
I will check the different parts of the system but I need to find where they first.
What's an IR?
Something like http://www.ebay.co.uk/itm/Non-Contact-IR-Infrared-...

macgtech

997 posts

158 months

Friday 18th July 2014
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Sorry was going to post a link! One of those ^^^^^

Racing Roj

Original Poster:

488 posts

162 months

Friday 18th July 2014
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Thanks guys, I have still got one from my racing days so will check with that.

mt308

438 posts

142 months

Sunday 20th July 2014
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Racing Roj said:
On a 70 mile journey on Saturday I encountered fuel cavitation twice, something I had not had before. It seemed to be the high temperatures of the day that caused the fuel to overheat. I had to wait about 15 minutes before I could start the car and drive on. As far as I know the fuel system is standard factory supply and install. Having spoken to someone who has much experience with Ultimas he has suggested firstly insulating the swirl pot with DEI and then try it again. As the ambient temperatures are going to high over the next few weeks I will be able to do that. If this doesn't cure it he suggested lagging the braided hose fuel pipes. He also seemed to think that the device (not sure what it's called) with the fuel pressure gauge on could also be a problem due to its high mounting point in the engine bay. Has any one else had this problem and if so how did you cure it? Thanks.
Hi - I have a problem that I am trying to diagnose. Like your issue it seems to only happen when the car has been run for a long time. Today I drove 70 miles to visit a friend. Then drove 60 miles of the 70 home before the car died. Engine just stopped - right in the middle of a major junction. Pushed it to one side. Waited 10 minutes, started, drove a mile then died. As its not that safe in a fairly busy part of outer London I then called Green Flag. 3 hours later.....they followed me home for the last 10 miles or so. No issues. After 3 hours the car has obviously cooled right down again. Could be coincidence, but heat could be a factor.

Question is, how did you know you have fuel cavitation (as opposed to other issues, e.g. fuel pump issues, electrical issues, etc.)?

The 2nd time mine did it I did think I heard the fuel pump (or one of them - the noisy one) slow down just before it cut out - but to be honest the "tone" of the pumps buzzing against the chassis changes so frequently (and with air con on there is even more background noise) it is hard to start trying to listen up for changes in noise.

My car is now just over a year old and this is an issue I have only had recently.

My gut instinct is that my issues is electrical but I don't rule out a fuel issue. The Green Flag guy thought definitely electrical and suggested cam or crank sensors (but no error codes show up on the scan - on either his or my device).

Any ideas? If electric I have the number of a local electric chap who is highly recommended. But if it isn't electrics then this could be wasted money. But how to rule out the fuel cavitation issue mentioned here? I am running factory set up with a swirl pot and low and high pressure pumps.

As it is I'm losing confidence in taking her out as it is pretty scary cruising at 80ish in the outside lane then losing all power and having cars hurtle up the inside lane as I try to coast into the hard shoulder - where there is one.

Thanks

Mark

Racing Roj

Original Poster:

488 posts

162 months

Sunday 20th July 2014
quotequote all
Mark
The reason I suspect air in the fuel is as follows: -
1. Only occurred on a very hot day so possible fuel boiling.
2. I heard a noise prior to the the car cutting out which sounded like a fuel pump pumping air.
2. The car did not cut out immediately but took about a mile or so.
4. After the car cooled down for about 15 minutes it started again with no problem.
The factory also advised me to check the fuel filters before I so anything else but haven't had time yet. I did have the filters checked only 3 weeks ago during a service so unless there is some dirt in the fuel thus may not be the problem.
When I gave drawn out the fuel system, checked the filters and tried one or two other suggestions I will post an update.
Roj

mt308

438 posts

142 months

Sunday 20th July 2014
quotequote all
Racing Roj said:
Mark
The reason I suspect air in the fuel is as follows: -
1. Only occurred on a very hot day so possible fuel boiling.
2. I heard a noise prior to the the car cutting out which sounded like a fuel pump pumping air.
2. The car did not cut out immediately but took about a mile or so.
4. After the car cooled down for about 15 minutes it started again with no problem.
The factory also advised me to check the fuel filters before I so anything else but haven't had time yet. I did have the filters checked only 3 weeks ago during a service so unless there is some dirt in the fuel thus may not be the problem.
When I gave drawn out the fuel system, checked the filters and tried one or two other suggestions I will post an update.
Roj
Roj
Thanks - that's helpful and got me thinking. I've had mine on the road for over a year and have had it out in hotter days than today and for longer runs. Only the last 3 weeks I've had this issue and 3 weeks ago was not that hot a day.
3 weeks ago I thought it was also accompanied by some weak electrics - hazards and fans not operating properly but otherwise same engine dying symptoms. Today I didn't really notice the weak electrics.
Mark

macgtech

997 posts

158 months

Monday 21st July 2014
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Interesting - worth checking the wiring to the ignition switch. Previously we had an issue on a hot day with intermittent behavior and it turned out to be an issue in this area.

mt308

438 posts

142 months

Monday 21st July 2014
quotequote all
macgtech said:
Interesting - worth checking the wiring to the ignition switch. Previously we had an issue on a hot day with intermittent behavior and it turned out to be an issue in this area.
Thanks. Was is the connectors onto the switch? Were they heat damaged or just loose?

On your other thoughts (going back to the possibility of hot fuel) my tanks and swirl pot are not wrapped in anything and both get very hot (at least on the outside). It seems to make sense as a precaution to put some gold foil on the tanks and the swirl pot, but the pumps themselves I think probably need to be left open as they generate their own heat. What would be your thoughts on exactly what to lag, and also the best material - gold foil?

Many thanks - and good luck with the racing!

Mark

Steve_D

13,737 posts

257 months

Monday 21st July 2014
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The ignition switch issues have been done before. Basically a little to much current is passing through it. Mine got to a point where I burnt my finger on it.
Simple fix is to fit a relay in the back of the fuse box to take the load.

Steve

macgtech

997 posts

158 months

Monday 21st July 2014
quotequote all
It was heat damage on the wiring, as Steve suggested. A few inches from the switch if memory serves correct.

With regards to heat shielding, I would gold foil anything metallic that could be exposed to heat.

As conduction is the primary source if heat transfer, the first thing to do is to check that there is nothing sill gong on such as fuel pumps/filters etc coming into direct contact with a source of heat such as coolant pipe or engine block. The alloy brackets that the various swirl pots etc are mounted to are thin alloy as they are reasonably high thermal resistance (as high as aluminium could ever be!) due to the thin material section.

To limit radiant heat, the gold foil on metallic surfaces is a must. Fuel lines themselves don't need it - think rails, filters, pumps, tanks (including oil!) etc. The pumps do generate their own heat to some extent, but should be cooled by the fuel.

As an aside, the nimbus style aluminium heat shielding can also be used as a bit of a 'duct' to manage air flow over critical parts.

Cleaning the filters is a must - and if there is a lot of gunk in the 10 micron filter it could suggest pump damage which will obviously hurt performance.

Bear in mind getting heat out of the engine bay is critical too, and in slow moving/stationary traffic etc the only way heat is going to get out (without fans) is upwards - so opening up the clam is a solution - without hacking away bodywork this can be done by removing the grills.