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Best Location for Fuel Pressure Sensor


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Hi All.

 

I originally purchased a small mechanical gauge to go in the engine bay. This was recently followed by a Prosport electronic gauge (which subsequently turned out to have a range of 0-100psi rather than 0-106 as per the eBay image), so I've now bitten the bullet and paid a handsome sum for an 0-150psi electronic gauge that is apparently used in Kenworth trucks and comes with a lifetime guarantee. Mine is blue digits with black bezel, not red & chrome as per the eBay pic.

 

http://www.ebay.com/itm/322355265485

 

This was after I realised that fuel pressure at the MU is one of the key elements in a PI and I need to be able to monitor it from the driver's seat if the system starts playing silly buggers, ottherwise I'm driving blind.

 

I'm looking for advice as to the best (also read easiest) installation point for the electronic sensor? All comments gratefully accepted.

 

Gavin

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I would suggest by the feed into the metering unit, you want to know what the pressure is at that point. If you measure it at the PRV then I expect there will be some pressure drop down the line to metering unit so the pressure at the metering unit could be lower (depending on the flow rate) than you see at the PRV.

Put a T piece in where pipe enters the metering unit and then put the sensor into the T piece. I have done this and I am surprised at how constant the pressure is!

You can get a T piece with the correct threads from RS components and I expect elsewhere.

 

Mike

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I would not expect a noticeable pressure drop

from rear to front.

 

As said a T-piece is a good way to go.

And that is best fitted at a connection.

 

As its fuel I would fit at the rear and lock

it before the sender.

 

Only when expecting trouble I would unlock

and let the sender work.

 

Reason is that a defect in the sender will destroy the car.

At 8 bars a lot of fuell will be lost that will start to burn

quickly in the engine compartment.

 

I came to that because many mechanical gauges come with

a warnung that they are not for permanent use.

Also a friend of mine got a defect in pressure switch and lost its oil.

 

-Maybe a bit too much of fear, do not know and if I do not

know better I will stay on the safe side-

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If you fit an electronic sensor you should not have any problem. I have used them on lots of commercial oil field systems up to 10000 psi and never had a sensor fail. But a gauge is different, I have seen those fail and its extremely scary when the front glass is blown out of the gauge.... If you look inside a gauge you will see a curved flattened tube (usually soldered) that will try to straighten when pressure is applied to the tube. This movement of the tube is used to drive the needle around on the gauge, usually either the tube or soldered joint can fail....

 

O/T I did monitor the electrical signal coming out of mine as I wanted to see if you could detect the MU discharging to the injectors, but the pressure was very constant, I guess there is enough compliance in the system to damp out any pressure fluctuations.

 

Mike

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Gavin,

 

I would not mount a mechanical fuel pressure gauge in the cockpit, if it leaked or was damage in an accident it would not be nice.

 

If you must, get a cheap electronic gauge and sender for < £14 such as http://www.ebay.co.uk/itm/2-52mm-BLUE-DIGITAL-LED-0-120-PSI-OIL-PRESSURE-PRESS-GAUGE-WHITE-CAR-MOTOR-AUTO-/152296928246?hash=item23759ab3f6:g:LZcAAOSwn7JYEyhP

 

Fit the gauge inside the glove box so that if you need to see it just open the glove box door, else close the door and have an original car dashboard. If after a few months of driving the pump is behaving itself then you can remove the gauge and not leave any trace.

 

Alan

Edited by barkerwilliams
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Thanks for your comments Mike and Andreas.

 

Having decided to spent the money needed to purchase a high quality instrument in the first place made specifically for the task (manufactured in the US - not a Chinese made knockoff), I'm reasonably confident the sender should be fine. That said, It may be a lot easier to install it back at the PRV as Andreas suggests, and with10ft of cable, it will have plenty of length to get back to the dash.

 

Gavin

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Hi All.

 

Received my Teltek fuel pressure gauge and sender unit from the US yesterday. It's a very nice piece of kit and the instructions make reference on how to install it in a Kenworth truck. Accuracy is claimed to be within 1 psi which wouldn't surprise me by the look of the sensor unit. Reminds me of the expensive instrumentation sensors we installed back in my water engineering days.

 

The plugs are unusual with a silicon 3-ring seal on the sensor plug, and what appears to be a telephone plug for the back of the gauge. A few pictures below for those who may be interested including one of the install instructions. Note, the bracket in which the gauge is mounted was purchased locally, it didn't come with the gauge.

 

I plan to mount the gauge below the dash next to my left knee where I can check it at any time but without spoiling the look of the interior. Mounting position for the sensor is still being debated :unsure:

 

post-14246-0-35763800-1487312113_thumb.jpgpost-14246-0-79944400-1487311782_thumb.jpgpost-14246-0-01418200-1487311802_thumb.jpgpost-14246-0-87222100-1487311821_thumb.jpg

 

Gavin

Edited by KiwiTR6
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I don't have a problem with that Stuart, so long as it does the job :)

 

Gavin

No neither do I its just the proud boast in their ad about "Made in America!"

Stuart.

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If possible, I would reduce the number of screwed connections where the sealing relies on teflon tape so avoid a "chismas tree" of fittings.

Rhere is nothing wrong with ptfe dor this service, but reducing rhe number of sealings reduces risk of leakage.

Also, the extended length reduces as a result of this.

Cheers,

Waldi

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If possible, I would reduce the number of screwed connections where the sealing relies on teflon tape so avoid a "chismas tree" of fittings.

Rhere is nothing wrong with ptfe dor this service, but reducing rhe number of sealings reduces risk of leakage.

Also, the extended length reduces as a result of this.

Cheers,

Waldi

 

Took your advice Waldi, and made up a single fitting from several machined brass items which I brazed together with plumber's silfos (5%). My first attempt was a definite fail as I'd used the wrong brazing rod and it leaked badly. My second attempt with the correct rod fixed the leaks, although the finish with this material is not as tidy as say silver solder, so I painted it as can be seen.

 

With the sensor in place and the gauge hooked up to a temporary power supply I got exactly the result I was hoping for - 106psi (engine not running) and the surplus making a noisey return into the tank.

 

The current draw measured at the battery was 12.4A. Comments on whether or not this is normal for a Bosch pump would be welcome :)

 

post-14246-0-50809700-1487463710_thumb.jpgpost-14246-0-59550900-1487463762_thumb.jpgpost-14246-0-76894900-1487463896_thumb.jpg

 

Gavin

post-14246-0-33091000-1487463740_thumb.jpg

Edited by KiwiTR6
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