I'm having fuel pressure issues but after doing some testing I'm not sure if it's the gauge or the pump.

I decided to use a manual gauge to attempt to test the accuracy of my electric gauge but there's ~15 psi difference between the 2. I checked at the fuel bowl and at the regulator where the sending unit is screwed in and they're +/- 1 psi of each other on the manual gauge, so I'm not messed up about that part BUT which gauge do I believe?? The PSI that the electric gauge is reading is very close to what it should be for the output of the sending unit according to the chart that Autometer sent me a while back, but how do I test the sending unit to make sure it's outputting correctly. Being an "old school" kind of guy makes it hard for me to question the accuracy of a manual gauge but I don't have a clue if it's accurately calibrated either. I don't really want to drop $115 on a sending unit when there's nothing wrong with the one I have, but how do I accurately test it? I don't have another manual gauge to test with either and don't have the funds to drop on something that's just going to sit in a drawer. By the set screw on the pump (AD2) I should have what the manual gauge is reading (73 psi), and the electric gauge won't push to over 60. What a quandary.......

 

Try Advance or Auto zone for a rental?

 

No, I haven't, Randy, but I will. Never even thought of that.

 

Thanks to Randy, I went to AZ and got a fuel pressure test kit rental and found out that between two manual gauages my pump pressure was set at 70 plus PSI and my electric gauge was reading about 20 psi too low. I'll order a new sending unit and report back after I get it installed.

 

I guess Autometer has their issues. Yours is screwed directly to the housing? Maybe the isolator kit would help. I have it on my Glowshift sender for over a year with no issues.

 

Calibration without a certified source to check against is always a problem, as I've found in these last years.

Along with sending equipment out for cal on a routine basis we used to have our own calibration equipment as every test (3 to 10 days) the instrumentation had to be checked. For some we could do that electronically, but in other cases we used dead weight.

Our dyno lab used to have some interesting older equipment. They had a dead weight tester for pressure gauges that consisted of a series of apply cylinders and test weights. I think it was from the 1930's.

Another older equipment they had was basically a master cylinder that was applied with a screw wheel to develop pressure, and a calibrated gauge to readout and compare your gauge that you hooked up to the kit.

Today they still make equipment like that.

Edit, just found a picture of one.

 

My sending unit is screwed into my regulated return regulator which is mounted to the alternator. It's 10 years old and no telling how long it's been out of calibration or when it "failed". I have no complaints except with myself for not checking it a long time ago. It's probably the reason I've killed 3 fuel pumps in the last 5 or 6 years.

 

Still love the looks of the older equipment.

Doing a calibration or verifying without a standard is a problem. One thing to test with
if you can find the mercury would be a capillary marked in PSI and "Hg. But that will
only give you the lower end.

I happen to like the idea of the dead weights and cylinder. Not really hard to come up
with sighs and the weights for a given PSI output.



Sean <BR>

6.0L Tech Folder

 

I like the look of the old stuff too. Maybe it's not as accurate(?) but it's repeatable in my mind. I'm always amazed at some of the things the previous generation or two came up with. Who needs computers?

 

The good thing is basic physics haven't changed, or has gravity. Weight x surface area of a piston still equals pressure, as long as the weights and cylinder are accurate.

For our brake pedal transducers like every other test facility used a dead weight tester. I wish I had grabbed one of the hydraulic pressure testers when our dyno facility was closed, but I'm sure one of the techs or engineers got it as they were not used with ISO standards.

Here's a Fluke unit sold today.

 

The new sending unit solved my pressure issues. Installed and hooked it up and the gauge jumped to 65 PSI, which I promptly lowered to 60. All is well with the Granny truck again.

 

So do you think the "test" AutoZone test gauge was 5psi high since it showed 70psi?

 

I do, since I had another manual gauge that showed 65 psi like the autometer did. Regardless, without having a certified calibrated gauge, there's no real way to know so I set the pressure within an acceptable operating range and drive.

What I try to achieve with fuel is a balance between pressure and volume since the higher the pressure on the pump the less volume of fuel you actually get AND too high a pressure just shortens pump life.

 

I think it was 5psi too high too. I was just pointing out to everyone that even those units borrowed front the auto stores still can have descrepencies and should not be used as the 'absolute' reading. They don't calibrate these any more then anyone else.

 

I absolutely agree with you. Who knows what kind of use or abuse those rental tools have been subjected to previously? It did, however get me "in the ballpark" and hopefully prevented further damage down the road.

BTW--I loved your battery cable video. That's my next project.