Aeromotive AFPR

[olddsmer]

Hello DSMer's
Didn't know how many of you run a liquid filled gage on your AFPR. On Aeromotives' site under the Tech Documents tab, when you click on "Advanced EFI tuning with an AFPR, The second tip says to never use a liquid filled gage when tuning with an AFPR. It says that temperature affects the liquid in the gage and gives unreliable readings. Has anyone ran into trouble when using the liquid filled gage?

Regards
Greg

 

[sparky1987]

I have a summit brand liquid filled gauge and it seems to read just fine. I know that the reason for the liquid is for vibration absorption.

Not sure if the oil is thick enough to cause and issue

 

[romeen]

The reading on my liquid filled gauge stays constant whether the motor is cold or hot. I actually have a spare non-liquid B&M gauge. One of these days I'll throw it on so that both gauges will be connected so that I can compare readings.

 

[daren_p]

The problem with a liquid filled gauge (a sealed gauge) is that temperature changes can effect the pressure inside the case more so then a non liquid filled gauge. So this can in fact throw off your readings. Though in real world, not sure exactly how much of a difference this can make (though I have seen it cause large inaccuracies in an industrial environment, so I would assume the engine bay could be an issue).

For most accurate readings you want the case vented to atmosphere, this will prevent the inaccuracies associated with internal case pressure. Some gauges will have a small tip you can cut off the rubber plug that allows the gauge case to be vented. If the gauge isn't overfilled & kept in the upright position, it should probably be alright to run a liquid filled gauge vented. The liquid filling helps with vibrations, so a liquid filled gauge would be ideal in an automotive environment.

On the other hand, alot of "automotive" gauges are complete crap to start with, so it may not make a difference either way

 

[99gst_racer]

I've never had any issues with my glycerin-filled gauge and I've been running it for several years. I've never noticed any reading indifferences with it from hot to cold.

 

[daren_p]

I've never had any issues with my glycerin-filled gauge and I've been running it for several years. I've never noticed any reading indifferences with it from hot to cold.

Paul, is your gauge vented or sealed?

 

[99gst_racer]

Paul, is your gauge vented or sealed?

Sealed, but it does have a rubber plug on the side. I've always wondered what that was for and now I know.

 

[romeen]

Mine has the rubber plug as well. It's below the fluid level. I wonder if it will leak fluid if I remove the plug?

 

[turboglenn]

I run the liquid filled gauge that came with my AFPR,it's a sealed unit and although i have noticed fluctuations from hot to cold (in engine bay) the readings only vary by about 5psi at most.. I usually just set my fuel pressure when the car is cold and take note of what it reads when hot and if i have to make hot adjustments i just go +/- by psi and not by the total readount(i.e. i'll add one or 2psi instead of trying to set it to say 43psi if i need more fuel and the gauge is hot)

 

[daren_p]

Mine has the rubber plug as well. It's below the fluid level. I wonder if it will leak fluid if I remove the plug?

You could always try drilling a small hole in the rubber plug. That should prevent pressure build up in the case but the fill should stay inside, if its not filled too much.

The easy way to test if changes in temp are effecting the gauge is to pull the vent plug (after the gauge has gone though a temp change, ie after the cars been running for awhile). If the readings change, you have an issue with internal pressure build up.

 

[olddsmer]

Ok guys thanks. I just wondered because in the tech bulletin on aeromotive's site, the word "not" is in bold lettering when referring to using a liquid filled gage. I guess I'll check and see if my gage has that plug you guys were talking about.

Regards
Greg

 

[turboglenn]

don't worry so much about their tech note, at most you may use a non liquid filled gauge but rmove itaftersetting pressure as the fluid in the liquid filleddampens them from vibration that can dmage them (as has been stated)

But most people just use the liquid filled gauges that come with the AFPR setup and get by just fine. The most i can recomend is what i do and that's try to always do the checking and adjusting with the gauge/engine cold, just set it during the first initial startup/warm-up of the engine that day.

I remember almostgoing nuts though wheni first put it on and i'd set it, drive a while and it would be different, so i'dadjust it only to have it be too much at that point and then when cooled again the gauge was back where it should have been. i actually posted about it at one point and even put an old AEM regulator on the car from a customers car because the fluctuating gauge was fooling me into thinking the AFPR wouldn't stay adjusted

 

[olddsmer]

I got it. The tech note was specifically talking about tuning with a non-liquid gage. Maybe like you said, tune it with a regular gage then switch to a liquid gage.

Regards
Greg