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Fuel pressure and Fuel temperature sensors


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The car has this quirk that when it gets properly up to temperature, ie not just 88c in the coolant but nicely warm oil, engine bay etc, the accuracy of the fuelling changes quite a bit mainly at idle and lower speeds.

To understand if this is related to the fuelling, I'd like to put some sensors in to measure fuel pressure and temp. My hypothesis is that the exhaust is heating the fuel lines, especially as I haven't come up with a good design yet to put a new heat shield in. I have no means of testing if the regulator is doing its job other than inferring from other variables, although it has been very reliable so far.

I've put a photo in of the engine bay, any elegant ideas for how to install one of each? I was thinking perhaps some sort of aluminium block on the bulkhead to screw them into and divert the fuel. Factory cars seem to have these sensors on the rail, but mine doesn't leave a great deal of space to do that. 

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Where is your inlet air temperature sensor? This is the usual culprit. A bit of heat-soak giving a higher-than-true reading will significantly lean the mix.

Fuel pressure is likely fine. Fuel temperature is an interesting one.  It definitely has an effect (leans off as the fuel warms, though not as sharply as inlet air) but it isn’t allowed for by any MS ECU or any modern up to about 2000 that I’m aware of. I asked about it once on the MS forum and the  consensus was “don’t worry about it, there are bigger problems”!  Vitesse fuel temperatures get into the 40s though.....

Practically, I’d suggest adding a couple of Ts at the feed end of the fuel rail.

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Thanks Nick, I'd seen that and disagreed with their sentiment. There might be bigger problems for others, but I'm largely content with the rest of the system. Cooler fuel seems like a reasonable objective given how much the temperature of things can affect power and efficiency so there needs to be a way of measuring it. Plus, why do factory cars all measure it these days if it's not a meaningful variable?

IAT was my first thought, but the IAT sensor is really far forward and the readings are very stable there, I couldn't see a correlation when examining logs or making adjustments. It's beside the K&N filter behind the front bumper. The aluminium air filter ducting was changed after I took this photo for some black PVC material, as that did get a bit of heat soak and was fragile. It fixed those problems but it didn't stop the change in tune after the car got thoroughly hot.

I used to think of it as the 'bypass' effect, as lots of driving around town didn't get the car hot enough, but if I took it on the local bypass up to 70mph for 5-10 minutes, sure enough afterwards the state of tune would change thereafter whatever the weather.

Looks like you can get some pretty neat AN fittings for a T piece, I didn't even realise these existed: https://www.ebay.co.uk/itm/AN-10-FEMALE-MALE-INLINE-PORT-1-8-NPT-Fuel-Oil-Pressure-Gauge-T-Piece-Adapter/302141229016?hash=item46590547d8:g:4REAAOSwiDFYK7DD

Edited by RichardBaines
making it clearer
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Hello Richard

                       This what I did to help cool the fuel.

I think sent the return through the cooler before returning to tank.

I can not say I have monitored it but seemed ok when touring Spain and Portugal.

I did it really because as Nick says the real problem is when the fuel tank is low and I stuck stuff on mine to help with noise so probably insulated!

The cooler I used is off something foreign (BMW or Merc !) so I reasoned the quality was good and they are cheap (I think I paid £15 ish delivered) 

Roger

Spitfire fans-001.JPG

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I don’t disagree that it makes a difference (hell, I know it does), and yet, on petrol engined cars at least it’s only been included in the engine management strategy in relatively recent times. I think previously it’s been compensated for by trimming based on the O2 sensor feedback.

On diesels however, it’s been an important sensor ever since they gained electronic in the late 80s. Sensor usually buried deep in the pump and a right sod to change.

So assuming you get a sensor installed, and note a change that correlates with your tune changes....... what then?  MS doesn’t currently allow fuel temperature compensation.....

Fit a fuel cooler like Roger?

Should also say that for the Vitesse at least, fuel warming seems to have the mostly positive effect of making it more economical when hooning around Europe in hot weather. Probably telling me it should be leaner anyway..... It does get a bit (more) crabby in traffic in hot weather but that is more likely mostly due to IAC heat soak as in a Vitesse engine bay, there is nowhere to hide!

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Perhaps! I do like that idea Roger. My first thought at seeing that was "aagh, susceptible to stone damage?", but I suppose these things are designed in a way that doesn't make the fuel transport inside it quite as vulnerable as it might appear.

It would be interesting to see how much difference the temperature changes fitting when I get round to fitting an alloy fuel tank, to see if the long flouted claims of it cooling the fuel are real. I'm a bit sceptical because there is no airflow going to it and suspect it may only delay the warming of fuel, not reduce it generally. Plus I could do some research around different methods of cooling - I've come across some like yours Roger, and other designs that seem like a flat tray that perhaps may instead lie under a part of the car.

Half the fun for me with megasquirt is having so much data available. There's so many claims made by vendors about performance parts relating to temperature and other metrics, but most of us have no idea how hot our gearboxes or differentials actually get? When those engine bearings got cooked, what temperature did the oil actually get to? Is this design more efficient at keeping the fuel lines cool, or should I route them here? And so on.

Edited by RichardBaines
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14 hours ago, Nick Jones said:

Copper pipe is cheap?  Pressure is minimal on the return side.....

Hello Nick

                Were are you going to fit the 50m coil? Have enough effect.

Roger

Ps I have it serpentine like up and down the chassis?

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I don’t think you need all that much.

I reckon the most beneficial thing I could do is to reroute my return line which is the old carb feed line and way too close to the engine block.

Truth is it doesn’t actually cause me much trouble and has been pretty thoroughly tested.

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Hello Nick

                I think all the pipe in engine compartment is Gates Barricade so I assume does not pick up as much heat!

I did run some 8mm to the cooler but slipped some insulation on that.

I am not sure I need my fuel cooler but it don't half look good and bling!!!

Plus I think you know me by now like to mess as it keeps the OLD brain going.

On a different note I think I should start down sizing the fleet of classic cars and motorcycles before the bottom drops out of the market?(there is only so much space in museums!) all electric 2030!!!!!!!

Roger

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That's new sales though Roger. It does make me feel a bit more anxious to cross off building a kit car from my bucket list though, IVA doesn't seem to be getting any easier even now.

I'm probably not helping matters with my blingy fuel system. Alloy fuel rail and braided PTFE hoses are all potential sources of heat soak, plus those are surrounded by a spaghetti mess of heater hoses that I hadn't quite figured out what to do with yet.

A temperature sensor on the fuel return should help me test some changes there though.

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