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Interesting Fuel Pressure Gauge Article

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Hey, Ok so I was reading this article from the Aeromotive website, and they explain how liquid filled pressure gauges are not accurate because with temperature changes the internal pressure of the gauge increases and the extra pressure on the Bourdon tube makes the needle show a lower reading… For those that do not want to read the article they are saying that for ever 1psi increase of pressure inside the gauge pushes on the tube and will make the needle show 1psi less.

Is this one of the cases where a manufacturer is making a solution to a problem that was non existant and providing a product to buy that we do not even need? Reason im thinking that is because yeh the pressure inside the gauge would increase but it would increase consistently all around the tube, So I fail to see how it would push the tube in any direction… Or am I missing something.

Here is the link to the article.

http://aeromotiveinc.com/wp-content/uploads/2014/12/TB_903_Liquid_Filled_Pressure_Gauges_01.pdf

"Is this one of the cases where a manufacturer is making a solution to a problem that was non existant and providing a product to buy that we do not even need?"

I would love to hear the opinion of professionals, but it definitly sound like it for me.

This kind of gauge are usually used only to set the "base" fuel pressure on the regulator (like 3bar/43.5psi) while the engine is not running and nothing more.

If someone would want to monitor precisely the fuel pressure, he'd rather use an electronic pressure transducer connected to a gauge on the dashboard (if not directly on the ECU to be able to datalog it) than a gauge in the engine bay.

By the way, I never seen any filled pressure gauges completely sealed. Sure they have a little rubber cap, but it no where near able to withstand any internal pressure.

Hi-Through the course of my work we use a lot of pressure gauges - Liquid filled and dry . And although I have not read the aeromotive article can confirm if the gauge case is not vented and the gauge gets hot it will read low . At the pressures we work with [ around 50psi] depending on how hot the gauge gets it can make a difference of around 4psi . While these figures are from memory and not dead nuts accurate they illustrate a point . And yip the little rubber cap can hold a bit of pressure . Vent the gauge case though and all is good .

That's quite interesting and definitely not something that had ever crossed my mind. I think by far the larger problem is that most of the gauges we see supplied with aftermarket regulators are not designed as a high accuracy product so I'm not sure I would trust them anyway. Generally when setting the fuel pressure I rely on my own fuel pressure gauge (which by the way is not liquid filled).

For the best results I would recommend using a quality fuel pressure sensor wired into your ECU. I use the Honewell 0-150 psi sensors and have found them to be a reliable and accurate sensor.

The most common from Honeywell is the MLH150PSB06A (1/8npt, 0.5 to 4.5V output)

Yon can get all the specs here:

http://sensing.honeywell.com/product-page?pr_id=31616

The one I use is the one @Ludo86 mentioned.

Sweet! cheers guys, just saved me and my customers some money... Was previously buying them through one of the major ECU supplies at $250.00 each.... $137.00 from this place and free delivery!

Interesting!

How do you guys typically hook them up if wanting to test on multiple cars?

Electrically, I imagine could tap TPS VREF or MAP or some other 5V source, ground to ground, and the output to a multimeter or gauge...?

Physically, is it possible to add an extra fitting in to the fuel rail banjo feed if room? If so, where do you source fitting(s) from?

Thanks in advance..

Hey Suberimakuri, Yep you can use a 5volt source from the TPS/MAP etc or if you want to use it as a tempory setup and do not want to cut any wires, go grab yourself a ciggy socket phone charger... They have inbuilt circuits for reducing 12 to 5v and cheaper then buying the components and making it yourself, Cut the end off and extend the cable and then you have a transportable 5V power and earth. You could read the output with a multimeter altho depending what you have the refresh rate may be too slow.

A More elegant solution would be Innovative solutions SSI-4

http://www.innovatemotorsports.com/products/ssi_4.php

A pair of aligator clip wires on the 12V+ and -ve that you could connect to the battery in 2 seconds, it has its own 5V output and earth and inputs for 4 0-5V sensors that you can configure and then display/log directly to your laptop.

With regards to the physical fitment, will vary from motor to motor... pretty sure the Honeywell sensor is 1/8NPT so you could drill and tap into the fuel rail, If the rail has threaded fittings on the end you could fit a T-peice or inline piece that already has a 1/8NPT or you can get inline fittings with barbs on both ends that can be fitted to the fuel hose. This is how I usually do it when working on cars without a gauge already and I need to check fuel pressure, I have a inline fitting with a gauge fitted, short length of hose on one end and I just need to remove the hose from the end of the rail and slip this inline.

Thanks Reaper.

Cigarette socket is a good idea, that makes the wiring easier.

Mostly just two cars I'm thinking of. I might just make up two feed hoses and swap them when wanting to measure pressure. Cheers!

If anyone is interested in the pressure transducer quoted above, the cheapest price I could find on it is here :

https://www.powell.com/item/Honeywell-Sensing-and-Control-MLH150PSB06A/261737?gclid=CjwKEAiA9qCnBRCb7ZDhvaHSyicSJABGFFHtuvcyjRO5Ltfi6swS_up2eECz2TTlFbfGs34rtghI0xoCeubw_wcB

Just want to share my experience with oil filled gauges, as this post started out with. First time I came across this issue was on a speedway car that had a fuel reg. set up with out the normal vacuum/boost ref. line set up.and as we were tuning I noticed the fuel pressure dropping the longer the car ran. So I adjusted the fuel pressure back up and then noticed that when we added more fresh fuel the pressure would go too high. Let the car cool down for a while and it would go even higher. Put on another reg. and it still did the same thing. Tried another brand reg. still the same. Asked other people if they had come across it and nobody could think of why. Most of the time if you had a vacuum line on you would not notice it but has it didn't have the line you could see it changing. Answer was found after lots of frustration-take the rubber bung out of a oil filled gauge and you will get the right reading. I have since seen it on every car I have tuned since. Set the fuel pressure with the line off to the normal 3 bar, recheck it after a drive and the pressure will read lower [with the line off]than when you set it, take the bung out and it reads right again. Try it and you will go WTF. Always set your pressure after you have removed the bung for a second , I have seen over 1 bar pressure variation. Let me know how you go.

Just want to share my experience with oil filled gauges, as this post started out with. First time I came across this issue was on a speedway car that had a fuel reg. set up with out the normal vacuum/boost ref. line set up.and as we were tuning I noticed the fuel pressure dropping the longer the car ran. So I adjusted the fuel pressure back up and then noticed that when we added more fresh fuel the pressure would go too high. Let the car cool down for a while and it would go even higher. Put on another reg. and it still did the same thing. Tried another brand reg. still the same. Asked other people if they had come across it and nobody could think of why. Most of the time if you had a vacuum line on you would not notice it but has it didn't have the line you could see it changing. Answer was found after lots of frustration-take the rubber bung out of a oil filled gauge and you will get the right reading. I have since seen it on every car I have tuned since. Set the fuel pressure with the line off to the normal 3 bar, recheck it after a drive and the pressure will read lower [with the line off]than when you set it, take the bung out and it reads right again. Try it and you will go WTF. Always set your pressure after you have removed the bung for a second , I have seen over 1 bar pressure variation. Let me know how you go.