Electric fuel pres. fluctuating

[slone56]

I have a scenario going on here that has me currently stumped. I have a Holley Blue pump and a regulator that have been on the car since before I bought it last April. Never had a problem.

This weekend I installed a canister filter on the suction side of the pump. The salesman on Jegs showroom floor told me, it should be an ok thing to do. At the same time I installed a new liquid filled gauge on my double pumper mainfold. The new gauge showed 2.5 PSI less than the old gauge did (7PSI). I just figure the new one was more accurate.

I test drove the car down to Jegs(20 minute drive) to take back a few items, before I adjusted the pressure up on the reg. After all, I wasn't planning on racing anyone. It drove and ran as it should.

20 minutes later, won't start. No fuel pressure. I have no tools to try and turn it up. Waiting on a buddy to rescue me, another 30 minutes goes by and I happen to recheck the pressure. Now it is up to about 3.5 PSI. Tryed to start the engine, and VROOM, starts right up.

Drive it home, pull into garage, with engine still running, 0 PSI on gauge. I turned it up to 7 with it running. Take it back out for a spin around the block. Come back check pressure, about 6.5. turn it up to 7.

Went back out 30 minutes later, turn on pump. 9 PSI????

About 1.5 hours later, 13.5PSI????

So it seems, if the car is hot the pressure drops. As it cools, it raises.

I knew I has 4.5 before, when it dropped to 0, I added 7. Now when it is cold, take the 7 and add it to my original 4.5 and you get what my pressure went up to after it all cooled down, 13.5 PSI.

The fuel filter is the newest thing in the configuration. Could that be my problem?

Or any other thoughts?

 

[slone56]

Took it out again today. Just to see what would happen. Fuel pres started out at 7-8 PSI. I let the car warm up before driving it, pres. dropped to about 6. Went around the block, engine water and oil up to normal temps. and pres down to 4.5. It is cooling down now, I assume the pres will raise each time I check it, as the enigine bay temp drops.

 

[cutty]

maybe vapor lock??????

 

[slone56]

Thought about it, but never happened before. Not to say it can't happen now. Plus I figured the pump would push through it, unless I am wrong. Plus, why would it not start using the fuel that was in the bowl? Unless that fuel evaporated.

 

[jrm81bu]

As far as the pressure goes, there was another guy on another site that was saying something about the liquid filled gauges reading lower after the get warm.

 

[slone56]

OK! That sounds logical. I did put the gage in at the same time. I still wonder why the rapid fluctuation during the one point, but I will put the old one in to eliminate that gauge. Good point to check out. Thanks.

I still wonder about the first ever no start, until it cooled down. It has NEVER embarassed me before. There was obviously something the engine was lacking. And I am fully assuming it was fuel!!!!!

 

[jrm81bu]

Do you have a sumped gas tank or a fuel cell? And is the pump mounted lower than than the fuel outlet? Those pumps are meant to be pushers and should be gravity fed, however i have seen them work even mounted under the hood but it is not ideal and could be causing problems. And where do you have your msd mounted? Had mine under the hood but it wouldn't start after getting hot, it even shut off on me a few times when stopped. Just some more things to think about.

 

[DrP]

Fuel pressure

Liquid filled gages will give varied reading as temp and atmospheric pressure changes relative to the fluid in a fuel line. Remove it; and, set your pressure with a gage (not liquid filled) you know is accurate. Then remove the gage and plug the fitting.
I ran 2 blue Holleys on my street car and they did not like canister filters on the suction side. It is difficult to get the air out and it creats resistance to flow; especially, when higher than the fuel level. You will most likely have continuing fuel delivery problems. Put the filter on the pressure side.
Screened filters are better on the suction side than canister paper elements.

 

[slone56]

Yep, my MSD is under the hood, behind the coolant jug. I thought about moving it, even before this all happened.

I have the original fuel tank, with no sump. I planned on putting a sump on it this winter. My pump and filter are as close as possible to the tank. My pump is about half way up the fuel tank. It is always "SUCKING", with no positive fuel supply.

Which screen filter do you recommend on the suction side? I really need to make some changes here.

Thanks for the info fellas!

 

[DrP]

The filters I used were available from Behrent's, 877.372.2348.
100 micron screens, hex aluminum body, female threads.. I didn't see them in the new catalog.
Summit has a similar filter, like a SUM-230104, pp25 latest catalog. 40 micron screen. These have AN on each end in -6 and -8.
Aeromotive also has them at a higher price.
The 40 is probably more practical.