Lagging fuel pipes
Discussion
One thing I noticed after a long drive yesterday was that tickover/lumpiness/hunting seemed to be worse when my fuel tank got below about one third. Could warmer/hot fuel be causing some problems and if so, is it possible to lag the fuel pipe(s)to keep the fuel cooler? Or am I just mad?
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One thing I noticed after a long drive yesterday was that tickover/lumpiness/hunting seemed to be worse when my fuel tank got below about one third. Could warmer/hot fuel be causing some problems and if so, is it possible to lag the fuel pipe(s)to keep the fuel cooler?
Doesn't the fuel pump run well above atmospheric pressure (in excess of 3 Bar)? If this is the case, the fuel will have to get pretty hot to form a vapour and the problem is likely to be more exacerbated at high speeds and not tickover. Could it be that there's something wrong with the pump itself?
Lumpiness seems to be pretty common at tickover without going to the expense of remapping etc. Not sure why fuel level would have any impact as the tank isn't exactly deep.... and if you had a problem in the pipes you'd definitely have a problem in the tank!
Have you seen this Fault Finder?
As for the madness... aren't we all?!!
MC
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quote:
One thing I noticed after a long drive yesterday was that tickover/lumpiness/hunting seemed to be worse when my fuel tank got below about one third. Could warmer/hot fuel be causing some problems and if so, is it possible to lag the fuel pipe(s)to keep the fuel cooler?
Doesn't the fuel pump run well above atmospheric pressure (in excess of 3 Bar)? If this is the case, the fuel will have to get pretty hot to form a vapour and the problem is likely to be more exacerbated at high speeds and not tickover. Could it be that there's something wrong with the pump itself?
Lumpiness seems to be pretty common at tickover without going to the expense of remapping etc. Not sure why fuel level would have any impact as the tank isn't exactly deep.... and if you had a problem in the pipes you'd definitely have a problem in the tank!
Have you seen this Fault Finder?
As for the madness... aren't we all?!!
MC
The fuel gets very hot in the fuel rail, and then recirculates back to the tank where it gets a chance to cool off. Problem is when the tank is low the fuel spends less time in the tank and is more vulnerable to heat soak. Combine this with a long journey where the whole tank has time to heat up, and the whole lot can end up quite hot. Then add in heat soak in the engine bay when you stop, and suddenly it's quite easy to get into vaporisation problems. If it gets better when you fill up, that confirms the problem. I used to get this from time to time in the V8S after the bigger engine went in. I lagged the fuel rail, and the problems went away.
Cheers,
Peter Humphries (and a green V8S)
quote:
Doesn't the fuel pump run well above atmospheric pressure (in excess of 3 Bar)? If this is the case, the fuel will have to get pretty hot to form a vapour and the problem is likely to be more exacerbated at high speeds and not tickover. Could it be that there's something wrong with the pump itself?
Lumpiness seems to be pretty common at tickover without going to the expense of remapping etc. Not sure why fuel level would have any impact as the tank isn't exactly deep.... and if you had a problem in the pipes you'd definitely have a problem in the tank!
Have you seen this Fault Finder?
As for the madness... aren't we all?!!
MC
Thanks for the link MC.
I suppose fuel pump trouble is possible, it certainly seems quite loud compared with a week ago, but maybe that was because it got very hot?
It just struck me as odd that lumpiness etc is worse when less fuel is in the tank, on the overrun the car seems less willing to slow down, almost as if there is a partial throttle, this happens for a short time and then the car begins to slow down as normal. As everything under the bonnet seems to get red hot, I wondered if hot fuel might have an adverse effect on things!
I seem to remember someone else posting to say that maybe lagging the fuel pipes might make a difference, does unused fuel at the engine/injection end of the system get returned to the fuel tank? If so, a third of a tank of petrol would get very warm much quicker than a full tank.
It's not a critical fault or anything, I know the HCs are a bit lumpy but it doesn't bother me much. However, if something is feasible to do that could improve matters then I am quite keen to do it!
On the subject of madness, yes, I am quite mad. I hear noises. And sometimes I see small green creatures with temperature gauges for heads dancing around the bonnet vents when I am in traffic.
quote:
The fuel gets very hot in the fuel rail, and then recirculates back to the tank where it gets a chance to cool off. Problem is when the tank is low the fuel spends less time in the tank and is more vulnerable to heat soak. Combine this with a long journey where the whole tank has time to heat up, and the whole lot can end up quite hot. Then add in heat soak in the engine bay when you stop, and suddenly it's quite easy to get into vaporisation problems. If it gets better when you fill up, that confirms the problem. I used to get this from time to time in the V8S after the bigger engine went in. I lagged the fuel rail, and the problems went away.
Cheers,
Peter Humphries (and a green V8S)
Aha! I thought so. Peter, what did you use to lag the fuel rail and where is the fuel rail? Knowing me I'd lag a brake pipe
Thanks for the correct advice Pete. Any idea what sort of temperatures the fuel rail would get to? Would most of the heat come from the exhaust manifold as wouldn't most of the block be in the region of the cooling water temp (maybe upto 20 - 30 C higher)? Has anyone with an Infra-red thermometer had a look at various parts of the engine?
Having see the recent discussion on insulating the exhaust manifold which method would be more effective in helping out the fuel rail?
Does the fuel pressure control valve reduce the fuel rail pressure at low speeds?
MC
Having see the recent discussion on insulating the exhaust manifold which method would be more effective in helping out the fuel rail?
Does the fuel pressure control valve reduce the fuel rail pressure at low speeds?
MC
The fuel rail is the metal pipe running across the top of the heads, with the injectors hanging off it. You should be able to get some heat reflective coverings from the likes of demon tweeks - they do heat resistant sleeving with velcro closure which would do the job, or wrap similar to exhaust heat wrap to wind around.
If you have air con, the fuel is cooled via a small heat exchanger. Even if this is not switched on, it still helps. If you have PAS as well, getting access to the fuel rail is an absolute swine as the two PAS reservoir pipes, spark plug leads, air con (optional), ignition module and coil are all on the driver's side of the plenum.
AS for exhaust wrap, saw my first manifold casualty caused by this stuff corroding the manifold through. Don't know if the manifold was S/S but it had died in just over a year.
I would also see if the problem comes up on a cold day. If so it could well be the 500 lumpyness and nothing less.
Steve
AS for exhaust wrap, saw my first manifold casualty caused by this stuff corroding the manifold through. Don't know if the manifold was S/S but it had died in just over a year.
I would also see if the problem comes up on a cold day. If so it could well be the 500 lumpyness and nothing less.
Steve
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The fuel rail is the metal pipe running across the top of the heads, with the injectors hanging off it. You should be able to get some heat reflective coverings from the likes of demon tweeks - they do heat resistant sleeving with velcro closure which would do the job, or wrap similar to exhaust heat wrap to wind around.
Thanks for the help, I'll have a look for some sleeving and give it a go, hopefully it should do the business.
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If you have air con, the fuel is cooled via a small heat exchanger. Even if this is not switched on, it still helps. If you have PAS as well, getting access to the fuel rail is an absolute swine as the two PAS reservoir pipes, spark plug leads, air con (optional), ignition module and coil are all on the driver's side of the plenum.
AS for exhaust wrap, saw my first manifold casualty caused by this stuff corroding the manifold through. Don't know if the manifold was S/S but it had died in just over a year.
I would also see if the problem comes up on a cold day. If so it could well be the 500 lumpyness and nothing less.
Steve
Hmmm, I have PAS but no air-con, so suddenly I am less enthusiastic about wrapping the fuel pipes given your descrption Steve. When you say a manifold had failed, I take it you mean exhaust manifold? What would the implications of just wrapping the fuel rail be (assuming I could do it with all the PAS piping blocking access)?
TVR obviously see a problem in that area or they wouldn't have included fuel cooling on air-con equipped cars. Perhaps some sort of cooler on the return pipe might help? A large fridge on a trailer perhaps
The exhaust wrap is the one I was referring to. It does trap moisture and this with the high temps causes corrosion. I don't know if the manifold I saw was SS or if that should be better but it is something to consider. the wrpping hold the corrosion in place until its too late. The replacement manifolds I have for the 520 are going to be painted several times before th exhaust wrap is fitted.
As for the fuel pipe, that is different. Again I am not quite so convinced that it is this. Lagging doesn't cost much so worth a try but the fuel pipes to and from the tank are routed differently to an S and are much less susceptible. Access as I said is a swine but only you can make a call on that. The Air con doesn't mean that this confirms a problem. It is very common practice because the air con can increase the engine's temp by 5-15 degrees and then you can get into vapourisation problems amongst other things.
Steve
www.tvrbooks.co.uk
As for the fuel pipe, that is different. Again I am not quite so convinced that it is this. Lagging doesn't cost much so worth a try but the fuel pipes to and from the tank are routed differently to an S and are much less susceptible. Access as I said is a swine but only you can make a call on that. The Air con doesn't mean that this confirms a problem. It is very common practice because the air con can increase the engine's temp by 5-15 degrees and then you can get into vapourisation problems amongst other things.
Steve
www.tvrbooks.co.uk
Just a thought, and those that know their engines far better than I do can problem straighten me out, but I was reading some info on RPi's site. I presume that there's a fuel pressure regulator on most TVR engines.
Petrol being a mixture of a large number of chemicals has a boiling range rather than a single boiling point. Standards require that at various temperatures, only a certain proportion of the petrol vapourises off.... For a full spec see here. Hence my quesion about temperature.
Assuming that the fuel rail temp stays below say 120°C, then, so long as the fuel rail pressure is maintained above 2 bar (3 bar absolute) any vapours should be compressed so that they are liquefied. There will be a small amount of uncondensables entrained in the fuel (from air and impurities dissolved in the fuel) but these are fairly minimal. So, if fuel pump isn't working properly or fuel regulator valve is faulty this could lead to more problems. Even at 180°C, when all of the petrol is boiling, the pressure required to reliquefy the vapours would be less than 2.5 Bar absolute (by definition, the vapour pressure of a boiling liquid is equivalent to atmospheric pressure and if you then heat that vapour to X°C the pressure becomes (X+273)/(Bpt+273) times atmospheric pressure). It's an over simplification so was just wondering what else people have changed to attempt to control the problem. Sorry for wondering off into Geeksville Techno Twaddle
MC
Petrol being a mixture of a large number of chemicals has a boiling range rather than a single boiling point. Standards require that at various temperatures, only a certain proportion of the petrol vapourises off.... For a full spec see here. Hence my quesion about temperature.
Assuming that the fuel rail temp stays below say 120°C, then, so long as the fuel rail pressure is maintained above 2 bar (3 bar absolute) any vapours should be compressed so that they are liquefied. There will be a small amount of uncondensables entrained in the fuel (from air and impurities dissolved in the fuel) but these are fairly minimal. So, if fuel pump isn't working properly or fuel regulator valve is faulty this could lead to more problems. Even at 180°C, when all of the petrol is boiling, the pressure required to reliquefy the vapours would be less than 2.5 Bar absolute (by definition, the vapour pressure of a boiling liquid is equivalent to atmospheric pressure and if you then heat that vapour to X°C the pressure becomes (X+273)/(Bpt+273) times atmospheric pressure). It's an over simplification so was just wondering what else people have changed to attempt to control the problem. Sorry for wondering off into Geeksville Techno Twaddle
MC
quote:
The exhaust wrap is the one I was referring to. It does trap moisture and this with the high temps causes corrosion. I don't know if the manifold I saw was SS or if that should be better but it is something to consider. the wrpping hold the corrosion in place until its too late. The replacement manifolds I have for the 520 are going to be painted several times before th exhaust wrap is fitted.
As for the fuel pipe, that is different. Again I am not quite so convinced that it is this. Lagging doesn't cost much so worth a try but the fuel pipes to and from the tank are routed differently to an S and are much less susceptible. Access as I said is a swine but only you can make a call on that. The Air con doesn't mean that this confirms a problem. It is very common practice because the air con can increase the engine's temp by 5-15 degrees and then you can get into vapourisation problems amongst other things.
Steve
www.tvrbooks.co.uk
The manifolds I've seen were corroded through from the inside, though. Don't buy the 'exhaust wrap traps water' line, the bonnet keeps rain off my exhaust and the only water it gets is when I'm driving through spray. And it gets above the boiling point of water after it's been running for thirty seconds or so so no way this is going to hang around. Compare that to the very real heat damage I was getting round the engine bay that went away when I wrapped the manifolds, and I think it's a no-brainer; just do it.
When I said I lagged the fuel rail, I did mean the fuel rail rather than the fuel hoses. The fuel rail is metal (i.e. non-insulating) pipe running round the heads which are the hottest part of the engine, with relatively little ventilation. It is a little fiddly to lag but OK using velcro closing tube pushed on from one end, with openings snipped out to let the injectors through. It may be worth lagging the fuel pipes too depending where they're routed, but that's a harder job with less obvious gains.
Cheers,
Peter Humphries (and a green V8S)
Oooeeerrr missus, this looks like a fine can of worms I've opened
MC - so if pressure valve and pump are ok, then fuel vapourisation shouldn't happen anyway. Maybe it isn't a fuel vapourisation problem, could extremely hot petrol produce different combustion or injection characteristics which might throw off the ECU and result in differing idling speeds then? Possibly a dumb question but I'm just fishing here.
I'm sure I read in the bible that lagging the exhaust manifolds will just transfer the heat to another part of the car, further down the exhaust i.e. under the floorpan/gearbox area which might cause other problems?
Anyone else lagged their manifolds (matron ) who can offer info regarding temperature/running improvements or problems?
>> Edited by keiths on Tuesday 1st October 12:34
MC - so if pressure valve and pump are ok, then fuel vapourisation shouldn't happen anyway. Maybe it isn't a fuel vapourisation problem, could extremely hot petrol produce different combustion or injection characteristics which might throw off the ECU and result in differing idling speeds then? Possibly a dumb question but I'm just fishing here.
I'm sure I read in the bible that lagging the exhaust manifolds will just transfer the heat to another part of the car, further down the exhaust i.e. under the floorpan/gearbox area which might cause other problems?
Anyone else lagged their manifolds (matron
) who can offer info regarding temperature/running improvements or problems? >> Edited by keiths on Tuesday 1st October 12:34
quote:A different car but there was a discussion on EXHAUST WRAP on the Chimaera board... with probably similar comments!
Anyone else lagged their manifolds (matron
MC
The 520 manifolds were lagged from the engine to the exhaust box because I was concerned with the heat as I was doubling the power of the engine. It does help and does what it says on the tin. The exhaust box is under the car and so does get cooled so this was less of a problem.
With a Griff, the cat's get very hot and wrapping as far as the cat is probbally good. Am I going to do it with my Griff? The stuff is sitting on the shelf currently as I don't think it is required as an inspect with the old IR thermometer and visual inspection doesn't reveal a problem.
The corrosion or potential corrosion problem is a bit worrying. The 520 manifold is on its last legs and where the wrapping has worn off there is damage and so I will be spraying the manifold as a precaution when the new ones get wrapped and fitted. Early days to say whether there is a problem with Griff/Chim ones but it has been reported with other cars.
As for vapourisation. The issue is really when the fuel gets injected as I understand it where the atomisation and spray pattern is disturbed and this causes the usse rather than anything like a lock in the pipe work.
As I see it, the problem could be the 500 lumpyness or something else. It doesn't cost too much to lag the fuel rail (access can be a swine though) and see if it improves the situation or not. I wouldn't immediately wrap the exhaust though. If you don't, you just won't get an invite to the Mummy's ball, that's all.
Steve
With a Griff, the cat's get very hot and wrapping as far as the cat is probbally good. Am I going to do it with my Griff? The stuff is sitting on the shelf currently as I don't think it is required as an inspect with the old IR thermometer and visual inspection doesn't reveal a problem.
The corrosion or potential corrosion problem is a bit worrying. The 520 manifold is on its last legs and where the wrapping has worn off there is damage and so I will be spraying the manifold as a precaution when the new ones get wrapped and fitted. Early days to say whether there is a problem with Griff/Chim ones but it has been reported with other cars.
As for vapourisation. The issue is really when the fuel gets injected as I understand it where the atomisation and spray pattern is disturbed and this causes the usse rather than anything like a lock in the pipe work.
As I see it, the problem could be the 500 lumpyness or something else. It doesn't cost too much to lag the fuel rail (access can be a swine though) and see if it improves the situation or not. I wouldn't immediately wrap the exhaust though. If you don't, you just won't get an invite to the Mummy's ball, that's all.
Steve
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