Two Fuel pressure gauges, two different readings...

[yullose]

Which one is correct ???

I have an Autometer electric FP gauge in the dash and the transducer on the fuel rail...

I also have a large fuel pressure gage that I bought off the Snap On guy...


The Autometer gauge is reading 40psi line off. The signal from the transducer is also telling the Powerlogger 40psi line off.

When I use my mechanical gage, I get 43psi line off.

A 3psi discrepancy... which to ME is unacceptable.

My gut is telling me the 43psi reading from the Snap On gauge is correct, since that's all I've used for the last couple years...
Using this gauge, the O2's look good and the car runs well... I've actually tuned a couple different cars using this gauge.

Assuming I'm correct... is there any way to test, calibrate or adjust the Autometer transducer for better accuracy ?

Pics of what I'm using:

 

[A2000RICH]

Which one is correct ???

I have an Autometer electric FP gauge in the dash and the transducer on the fuel rail...

I also have a large fuel pressure gage that I bought off the Snap On guy...


The Autometer gauge is reading 40psi line off. The signal from the transducer is also telling the Powerlogger 40psi line off.

When I use my mechanical gage, I get 43psi line off.

A 3psi discrepancy... which to ME is unacceptable.

My gut is telling me the 43psi reading from the Snap On gauge is correct, since that's all I've used for the last couple years...
Using this gauge, the O2's look good and the car runs well... I've actually tuned a couple different cars using this gauge.

Assuming I'm correct... is there any way to test, calibrate or adjust the Autometer transducer for better accuracy ?


its hard to find a really accurate gauge if +/- a lb or so is important without spending big money------digital or analog--------i have the same Snap ON gauge you have and it is nearly 2 lbs off in the 3 bar range--------if you really want to know how accurate your gauges are send one of them to me and i will send it back to you with a calibration chart and you can know for sure what is accurate------i have a Wallace and Tiernan DP-250 calibrator that is accurate to .066%-------its what NASA and the US Meterological Service use to calibrate sensitive gauges--------cost nearly as much as a nice GN but its dead accurate................RC

 

[Razor]

Why is fuel pressure so important? You set it and look at your numbers on your scantools. If the car is lean, you can add a few lbs of fuel pressure. Meaning if your Block learn numbers are high.. add fuel pressure to bring them down across the board.. or if they are alllow.. drop fuel pressure.

Every engine is different.. FP requirements on one is going to be different than on another. Its only an issue when you get nit picky

Understand when a chip is made the 43 line-off is just a get you in the ballpark. Meaning if you have lets say 60 lb injectors.. and the chip was burned for 60 lb injectors.. and your injectors all actually flow 62 lbs.. then you'll technically need less FP. Does this make sense.

As long as the transducer records the FP, goes up 1 per 1 on boost, your fine.

If you want to get the guage certified thats ok.

And yes, I have like 6 Guages..and 4 read different. I trust my largest and most expensive.. from there its all a reference. The worst are the rail mounted ones. My best is 5 inch diameter liquid filled.

 

[Razor]

No you cant make changes to the autometer transducer as it is sealed. You can make changes to the offset how it reads on the power logger. On my FAST I can change the reference and make the transducer read whatever I want.. by changing the scaling.

And yes I trust the snapon over the autometer.

 

[pacecarta]

bottom line was your 1st cell blm was 123 with almost no run time ,not that 123 is bad but blm says if anything fuel needs to go down slightly to match chip. what did you do.. turn it up

drive the car see where the blms lean +/- from 128 and adjust to them


ps just looked at your last pl log ..that motors got some vaccum ,

 

[yullose]

Well... as far as gauges are concerned... I have a sore spot when it comes to gauge accuracy...

A story some may find interesting.

My brother and I both worked for Chip Ganassi Racing. My brother lost his job there strictly due to a bad gauge... by overfilling the nitrogen on the rear shocks of the #42 car. (I got caught-up in the last round of layoffs in Jan) This happened in Kansas last year during qualifying and cost Juan Montoya the pole position. Monday morning I went back into the shop and gathered up all the gauges in the shock room and pulled all the gauges from the haulers. I put them all on a common manifold to check for accuracy. Every damn one of them read something different... the one that filled those rear shocks was 30psi low. A simple nitrogen gauge cost a driver the pole position, embarrassed the Chip Ganassi Race team and cost my brother a $100k/yr job.
So yeah, you could say I'm a bit anal about gauge accuracy.

The bottom line is, I want to see "real" and accurate numbers in ALL my powerlogger data. I know the fuel pressure numbers mean nothing in the grand scheme of things... but to me... if I'm going to bother connecting the transducer to the plogger, I want to see accurate info.

And to answer pace... yes I bumped the pressure up .5 psi.
I didn't concern myself with the earlier Powerlogger data strictly because I was fooling around with too many things, unplugging the ECM and only idling it in the garage.
Once I take it out on a roadtrip and start tuning... I'll pay more attention to it.
After bumping the FP up, I reset the ECM again. The last Powerlogger file was saved after doing this. (Cell #1 went up to 125)

 

[TurboDave]

Bottom line is... Unless the gauge you're using has been calibrated by a certified facility, the readings are pretty much meaningless unless of course there's a huge disparity.

The 3# difference seen by the two gauges the OP has is meaningless because neither was calibrated and there's no way to know which is correct. They both may very well be wrong.

Like Razor said, the different pressures of different gauges is all relative. Get it set where you like it, and watch for trends. Use it as another tool, not a calibrated standard.

 

[A2000RICH]

Well... as far as gauges are concerned... I have a sore spot when it comes to gauge accuracy...

A story some may find interesting.

My brother and I both worked for Chip Ganassi Racing. My brother lost his job there strictly due to a bad gauge... by overfilling the nitrogen on the rear shocks of the #42 car. (I got caught-up in the last round of layoffs in Jan) This happened in Kansas last year during qualifying and cost Juan Montoya the pole position. Monday morning I went back into the shop and gathered up all the gauges in the shock room and pulled all the gauges from the haulers. I put them all on a common manifold to check for accuracy. Every damn one of them read something different... the one that filled those rear shocks was 30psi low. A simple nitrogen gauge cost a driver the pole position, embarrassed the Chip Ganassi Race team and cost my brother a $100k/yr job.
So yeah, you could say I'm a bit anal about gauge accuracy.

The bottom line is, I want to see "real" and accurate numbers in ALL my powerlogger data. I know the fuel pressure numbers mean nothing in the grand scheme of things... but to me... if I'm going to bother connecting the transducer to the plogger, I want to see accurate info.

And to answer pace... yes I bumped the pressure up .5 psi.
I didn't concern myself with the earlier Powerlogger data strictly because I was fooling around with too many things, unplugging the ECM and only idling it in the garage.
Once I take it out on a roadtrip and start tuning... I'll pay more attention to it.
After bumping the FP up, I reset the ECM again. The last Powerlogger file was saved after doing this. (Cell #1 went up to 125)

i agree with you-------its hard to believe that a top name NASCAR shop doesn't have a calibration department-------they don't need to fire their workers they need to fire the management--------i can work with a gauge thats wrong IF i know how far off it is-------thats why i have calibration equipment for nearly everything in my shop-------between fuel, boost,oil,hydraulic etc gauges i have no two that agree EXACTLY-------in fact the most accurate fuel gauge I have (at the moment) came from autozone probably didn't cost more than 25 bucks-------i was so impressed i want back and bought another one-------it was off by several pounds---------another problem is that nearly all gauges may be close somewhere on the scale but at other pressures they tend to exhibit more error and with constant use you can expect them to change in a very unpredictable way--------every gauge in my shop has a calibration sheet kept with it that shows its actual vs displayed pressure over its entire range--------before i start an engine i check the accuracy of my torque wrenches--------i check the accuracy of my micrometers and bore gauges with blocks and gauge rings--------i check the accuracy of my scales that i do engine balancing with reference weights-------i even occasionally check the accuracy of my DMM's with a meter calibrator-------i check the accuracy of my flow meters and flow benches--------and usually once a year i send my calibration equipment to a NIST certified lab to have them double checked-------one of my businesses is a licensed defense contractor and calibration and tracability is a way of life---------its hard to do quality work with a rubber ruler..............RC

 

[gndoug]

and usually once a year i send my calibration equipment to a NIST certified lab to have them double checked-------one of my businesses is a licensed defense contractor and calibration and tracability is a way of life---------its hard to do quality work with a rubber ruler..............RC

That is just my line of work. I work for a company that does Instrumentation contract work among other automation and electrical engineering work. I've worked at places that have FDA and cGMP regulations that they have to follow for their instrument tracability and calibration schedule/history. Analog gauges/bourdon tube type gauges CONSTANTLY have to be adjusted for their offset. They are usually (unless brand new) right at their action limit inside of calibration tolerances. That snap on gauge is probably wrong, but occasionally electric pressure gauges can wander off from their zero and span... but I'm talking every 20 bourdon tube gauges to 1 electronic gauge-pressure gauge being off.

We calibrate field instruments with secondary standards (dmm/flow carts/hertz generators etc...) that have been calibrated with a PRIMARY standard. To check the precision and accuracy of the gauges you would need to test them with a dead weight tester (being a primary standard-- using pascals law...p=f/a). But good luck finding one of those outside of an instrument shop/metrology shop.

There is even testing the gauges agains another pressure standard such as a druck hand pump that also reads pressure, but you will still find those in the same places you would find a dead weight tester.

Sorry for the novel, I could go on forever... this is what I do all day:biggrin:
If you are really concerned about the accuracy of the gauge/pressure signal you could send them to me, but I have no idea how to calibrate the electronic pressure sensor if it is off... but I could verify which one is reading accuratly. (if either are)