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Fuel pressure problem (kinda long)

Posted By: T-bar

Fuel pressure problem (kinda long) - 01/14/11 09:04 AM

Hello all, I have problem with the fuel pressure staying consistent in my car. It,s a '70 Cuda 440 it has an electric Aeromotive S series pump from Summit it looks like the one to use up to 750hp. It was in the car when i got it so not sure how old it is either but looks fairly new. I have 1/2" line from the pickup to the regulator also aeromotive. I have also put a aeromotive 100 micron filter between pump and tank. Now the problem is when i start it up it has 8.5 psi at the reg take it for a drive and pull up let it idle and check the it and it drops down to anywhere between 2 and 4 psi (gauge is under the bonnet). The previous owner had a 10 micron filter on and i thought that may have been the culprit while it did help it still isn't right. What should i try next.
Posted By: VanishPt

Re: Fuel pressure problem (kinda long) - 01/14/11 12:08 PM

liquid filled gauge?

Next time you check it , take a rag soaked in ice water and hold it around the gauge for a minute or so. Remove the rag and look at the gauge. does it read higher?
Posted By: T-bar

Re: Fuel pressure problem (kinda long) - 01/14/11 01:26 PM

Yes VanishPt it is a liquid filled gauge and i will try that. What is the problem? Thanks for the reply.
Posted By: VanishPt

Re: Fuel pressure problem (kinda long) - 01/14/11 01:37 PM

liquid filled guages are well known for reading low when they get hot. Soak it a few times with ice cold water and see if it starts to go up
Posted By: Andrewh

Re: Fuel pressure problem (kinda long) - 01/14/11 01:38 PM

liquid filled gauges cause a problem where it is hot.

the liquid inside the gauge generates pressure as it heats up, causing it to read low.

that is why I chose a dry gauge for under hood fuel pressure.
Posted By: DANA60

Re: Fuel pressure problem (kinda long) - 01/14/11 01:39 PM

I removed my liquid one because it always would drop as soon as the engine got warmed up. I put a "normal" guage on there and all looked fine since.

Attached picture 6416891-IMG_3311_1_1_1.JPG
Posted By: RapidRobert

Re: Fuel pressure problem (kinda long) - 01/14/11 02:16 PM

Aye mate. You said the 10 micron filter helped. As in it read even lower than 2-4 w the 100 in there? Unless underhood heat as said makes a liquid gauge totally worthless I'd bypass the filter for a 15 minute test (you're not going to pass an exorbitant amt of debris in 15 min) esp since you said going to the 10 micron helped brought the reading up & clean/check the reg and I'm assuming the tank/sock is clean & no pinholes in the hard line/neoprene connector pieces. Holler when you find it
Posted By: T-bar

Re: Fuel pressure problem (kinda long) - 01/14/11 11:18 PM

Thanks for the info on the gauge i will fool around with that. Rapidrobert i went from the 10 to the 100 micron as it was cavitating the pump to much and while that iniatally sent the pressure up from where it was set then i readjusted the pressure all was good until i checked the gauge after driving it.
Posted By: ProStDodge

Re: Fuel pressure problem (kinda long) - 01/15/11 02:19 AM

Most liquid gauges have a rubber plug which you can use to fill (or empty) the gauge. If the problem is heating of the liquid, you can use the plug to "burb" the gauge and equalize the internal pressure. Its not the temperature of the liquid creating the false reading, it is the expansion of the liquid due to the heat.
Posted By: chache876

Re: Fuel pressure problem (kinda long) - 01/15/11 02:34 AM

Quote:

Most liquid gauges have a rubber plug which you can use to fill (or empty) the gauge. If the problem is heating of the liquid, you can use the plug to "burb" the gauge and equalize the internal pressure. Its not the temperature of the liquid creating the false reading, it is the expansion of the liquid due to the heat.



what if you drained the liquid? would that eliminate the false readings or are they somehow calibrated with the use of the liquid?
Posted By: Mr71Bee

Re: Fuel pressure problem (kinda long) - 01/15/11 02:53 AM

Its the pressure caused by the expanding liquid. Had the same problem.

I would say either burp and remove some liquid... or install a non-liquid filled gage
or move the gage to outside on the bonnet.
Don't bring it into the interior!

Mr Bee

Posted By: T-bar

Re: Fuel pressure problem (kinda long) - 01/15/11 03:58 AM

Thanks all, i'll try everything before a new gauge. I did look at an electric pressure gauge for the interior but they are a bit dear (autometer) so i'll stick to the one under the bonnet for now. The non liquid ones are pretty cheap so that might be the go.
Posted By: ProStDodge

Re: Fuel pressure problem (kinda long) - 01/15/11 10:02 AM

Quote:


what if you drained the liquid? would that eliminate the false readings or are they somehow calibrated with the use of the liquid?



Yes, you can remove/drain the liquid out and the gauge will work properly.
Posted By: T-bar

Re: Fuel pressure problem (kinda long) "Update" - 01/16/11 01:10 AM

Just tried the ice rag on the gauge and pressure reading shot straight up so now i'll remove gauge and drain some liquid. There isn't any rubber plug in the back of it but three screws so i'll take them out split the gauge and see whats there. Thanks again.
Posted By: Challenger 1

Re: Fuel pressure problem (kinda long) - 01/16/11 01:33 AM

Quote:

Hello all, I have problem with the fuel pressure staying consistent in my car. It,s a '70 Cuda 440 it has an electric Aeromotive S series pump from Summit it looks like the one to use up to 750hp. It was in the car when i got it so not sure how old it is either but looks fairly new. I have 1/2" line from the pickup to the regulator also aeromotive. I have also put a aeromotive 100 micron filter between pump and tank. Now the problem is when i start it up it has 8.5 psi at the reg take it for a drive and pull up let it idle and check the it and it drops down to anywhere between 2 and 4 psi (gauge is under the bonnet). The previous owner had a 10 micron filter on and i thought that may have been the culprit while it did help it still isn't right. What should i try next.



A return would help alot...You sure you have unostructed flow from the tank? I'd get rid of the 100 micron filter also and try it without for while. I bet that helps alot...
Posted By: chache876

Re: Fuel pressure problem (kinda long) - 01/16/11 01:41 AM

Quote:



A return would help alot...You sure you have unostructed flow from the tank? I'd get rid of the 100 micron filter also and try it without for while. I bet that helps alot...



Also, if you already have a sock on the pickup tube, theres no need for a filter between the tank and the pump
Posted By: chache876

Re: Fuel pressure problem (kinda long) - 01/16/11 01:46 AM

Quote:



Yes, you can remove/drain the liquid out and the gauge will work properly.



Whats the point of it? Acts as a damper?
Posted By: T-bar

Re: Fuel pressure problem (kinda long) - 01/16/11 01:54 AM

I have a return line on it from the reg back to the pickup. The pickup is an aftermarket 1/2"type with about a 3/16" return line in it also. There isn't a sock on the pickup, i would like to put the brass type strainer on but can't seem to source one here that's 1/2".
Posted By: Challenger 1

Re: Fuel pressure problem (kinda long) - 01/16/11 02:42 AM

Quote:

I have a return line on it from the reg back to the pickup. The pickup is an aftermarket 1/2"type with about a 3/16" return line in it also. There isn't a sock on the pickup, i would like to put the brass type strainer on but can't seem to source one here that's 1/2".



Then I would say your experiencing cavation, which means not enough free flow into the pump, I'll bet ya.

Gasoline is very hard to suck, A hi performance pump needs to be supplied with lot's of gasoline so it don't cavatate.
Posted By: ProStDodge

Re: Fuel pressure problem (kinda long) - 01/16/11 06:21 AM

Quote:

Quote:



Yes, you can remove/drain the liquid out and the gauge will work properly.



Whats the point of it? Acts as a damper?



Yes, the oil is strictly a damper for the needle to reduce vibrations or damper fluctuations to make the gauge easier to read.
Posted By: T-bar

Re: Fuel pressure problem (kinda long) - 01/16/11 07:30 AM

Dropped the fluid out of the gauge, took the car for a good run when pulled up and checked it was holding steady at 7.5 psi so she's all good.
Posted By: RapidRobert

Re: Fuel pressure problem (kinda long) - 01/16/11 02:39 PM

Quote:

she's all good.

that was too easy . Glad ya got it. I'm amazed that heat screws up a liquid gauge that bad
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