Late this spring got the 1999 Corvette out of storage as winter temps were gone, now around 65 degree days
Car had been sitting since late fall so time to get a testrun on it and check everything out

About 5 miles down the road I noticed the electronic Autometer fuel pressure gauge ( $288 cost) reporting fuel rail pressure going as low as 54 PSI
The GM specs for fuel system functions from 55 to 61 PSI so 54 PSI bothered me as in hotter weather that would be lower and cause high lean conditions

Tried the easy swap first, bought and replaced the fuel filter / regulator, did a testrun and still Autometer reported as low as 54 PSI
Then yanked the fuel rail and checked all 16 O-rings for fuel injectors, torqued fuel rail mounting bolts, testrun - same results
Now stuck doing the bitch of buying new pump unit, replacing the left tank fuel pump/ float on jack stands
Which means draining both gas tanks, hassle getting pump unit out and in

OK, fuel system is replaced at lot of money and labor and damn enough do a testrun and the Autometer is still reporting lower PSI values, like WTF
OBD-II live data showed when Autometer gauge reported low PSI the fuel trim, O2 sensors, fuel injector pulse width, etc reported perfect and no signs of lower fuel pressure

Now I suspect the almost new Autometer fuel pressure and gauge, this is a electronic setup, only operates from 0.5 to 4.5 Volts and being Autometer's specs is gauge functions from
zero to 100 PSI that means small amount of mVolts per PSI, fuel pump functions +/- 2 PSI of 58 PSI means the gauge operates in less then about 1 volt, no margin of error for and degrading or drifting.

It dawned on me that the gauge reporting was higher when engine was cold and then values dropped as engine got to operating range where in this Corvette is
185 degrees coolant temp as that is what the Tstat is

Autometer sender is made if thin metal and only 1" by 1" in size.
It mounts to a fitting on fuel rail which of course is at top of engine and where it would be the hottest

Ran some cold morning testruns and then later in 90 deg weather and was clear all along the sender was at fault
Contacted Autometer's support who told me that they only warranty this $288 product for just one year

I then sent a full report with findings to Autometer and got an email from someone in their marketing group
He then sent me a new sending unit free of charge

Installed and tested it to get about the same results !

So now I start doing thermal testing using a J type probe to a Pyrometer, doing testruns and mapping thermal values that was recorded live by laptop software

Found is when sensor is mounted to fuel rail after testrun measured around 130-140 degrees

Then remotely mounted the sensor 16 inches away from engine, close to firewall and did testruns

As long as the sender measured less then 120 degrees, the PSI output it reported was closer to correct

Then dawned on me of another testcase, the Corvette has a custom hood, with scoop and openings for bringing in colder airflow and extracting hot air out

When testing first started the opening were set to reduce airflow about 60% and why testing above, sender was about 130ish deg rather then 185 deg of Tstat

So final testcase, scoop openings set to allow maximum flow, sender still 16" away

Sure enough in several daily testruns over 4 days of testing example below, Cold start gauge reported 59 PSI, after few minutes at idle reported 57 PSI
During several 25 mile runs, in 70 and 90 deg weather gauge now reported correctly staying at 57 PSI most of time, decel a bit and up to 58 PSI
Not once when in colder temp did the gauge report less then 57 PSI so without a doubt the sender degrades output (mVolts) around 120ish degrees and worse by 140 deg.

With the hood scoop fully functional and weather was 70 degrees, as long as car was doing over 20 MPH the sender measured only about 10 degrees higher
and temps only spiked when at idle at around 130 degrees but as soon as car above that 20 MPH the sender temps would drop again.
Only slight increase in temps during WOT.

All this testing was repeated to both of the Autometer fuel pressure senders I had with repeated results

I had sent marketing of Autometer finding and results two weeks ago - ZERO response

So in the end customers spend almost $300 for a electronic fuel pressure gauge,
a simple mechanical one is like $25 so you'd expect for the big bucks
that you could rely what it reports and instead cost a bunch of money replacing the fuel system to find the gauge is prone to degrade as temps increase
and in most cases a stock car with no vented hood, 195 deg Tstat and coolant fans commanded by engine management not to come on till coolant temps
are over 220 degrees would be worse.

Click on any photo to see full size :

To expand on this fuel pump functions mostly at 55-59 PSI
as seen the sender then is only reporting aprox from 2.73 to 2.88 volts

Not much margin of error for any degrading of sender output

VOLTAGE 0-100 PSI
2.73 ........ 55
2.75 ............ 56.25
2.80 ............ 57.25
2.85 ............ 58.25
2.88 ........... 59.37

In the graph below was recording the output of the sender with a digital voltage meter which outputted the voltage values during a testrun to a laptop as a recording
which then is imported into Excel spreadsheet.

As seen the sender was reporting as low as 2.72 volts which equals 55 PSI and as high as 2.87 volts, i.e 59 {SI
This was when sender was cold gauge reported 59 PSI but as sender got hot output was degrading, reporting 55 PSI when in fact
when sender is mounted to a colder location the real reading is 57-58 PSI

Two Years have passed since Autometer's engineering and support group told me it was impossible that their fuel pressure sensors for there digital
gauge cannot be faulty.
Basically telling their customers that after spending around $300 for their product and screw warranty for functioning incorrectly that there is no recourse
in getting their product that works as their marketing claims

This August 2019 I decided to give it one more shot in calling Autometer and again explaining how their fuel pressure sensor degrades over normal or even
less engine bay temp and was again told their products design or quality do not degrade with less then 125 degree engine bay temperature
I spent around 1 hour on hold to even get to talk to anyone there.

Autometer's 0-100 PSI spec'd to function from 0.5 to 4.5 volts alone costs $120-130, that does not include anything else.
I searched internet and found two other brand sensors with the same specs as Autometers

Considering the hood on my Corvette has multi opening to bring in colder air and extract hot air and has a larger flowing radiator with a 185 deg Tstat and
a heat exchanger with 7 quarts of synthetic oil the engine bay is cooler then a normal car yet Autometer sensor still degraded the output to their own gauge

One cost only $18 and the other $22, seems one hell of a profit margin for Autometer

I tested both mounted 16 inches from engine which is cooler then top of engine where last I located Autometers which still degraded and incorrectly reported
out of spec fuel rail pressure
Neither of the two tested failed, even in 90 degree summer weather and even worse case with hood closed and engine at idle for 20 minutes

Then mounted these 2 other brand sensors directly to the fuel rail as shown below and again hard heat tested to where sensors shell reported 140-150 degrees
and at worst dropped 1 PSI where Autometer's reported as low as 54 PSI.

I took apart one of the 2 Autometer sensors, the shell (case) is only 1 mm thick so it cannot heat-sink very well and once heat-soaked the incorrect output values
(voltage levels) maintain and rest of that drive cycle reports PSI incorrectly
Once engine and bay are cooled down ( lower then 100 degrees) then their sensor again reports values correctly so
that shows the flaw is within their sensor ( or who they OEM them from?)

Being all these tests used Autometer's digital gauge and their wiring shows the design failure due to normal and even lower engine bay temps is directly
due to the design or lack of quality control of their $120 plus sensor

You would have thought their people would have wanted to use my testing to solve and better their product but instead they insisted their designs never fail