When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
If the filter is on the OUTLET side of the pump, it shouldn't be sucking air. If there is a leak, it would be FUEL coming out
I should've been more clear, the worm hose clamp in the picture, that Tugley recommended to put double fuel injection clamps on, is on the outlet side of the filter, which leads to the inlet side of the pump.
I installed a filter in the same place. When I was troubleshooting my fuel pressure drop under load, I removed it completely from the system and had straight hose running from the tank to the pump. It did not change the symptoms/problem at all, so I put it back in there.
Do you still have a filter on the the inlet to the pump? I have just scanned the thread but if you don't have a pre pump screen of some sort, the screen on the inlet to the pump maybe clogged....
Do you still have a filter on the the inlet to the pump? I have just scanned the thread but if you don't have a pre pump screen of some sort, the screen on the inlet to the pump maybe clogged....
That filter is pre-pump. If you look carefully at the body of the filter, you will see the arrow that shows the direction of fuel flow.
Riffraff makes great stuff. Not only is my truck loaded with Riffraff toys, I have many boxes of yellow tape on the shelf for an active project right now. Saying that... I never read the specs on his inline filter - it came out after I bought my Racor PS120. Our OEM pump delivers up to 34 GPH at the correct pressure, and that just happens to be the fuel demand of a stage II stick at WOT. We push that pump to the limit, so everything in the system has to be right. I'd get rid of that worm-drive hose clamp - today.
That filter is pre-pump. If you look carefully at the body of the filter, you will see the arrow that shows the direction of fuel flow.
I see that now and per the OP's earlier clarification. I'm accustomed to seeing only post-pump filters, ever since *someone* warned me about my proposed pre-pump filtration system
Guys, I really appreciate everybody's advice. I haven't had a chance to remove the worm gear clamps.
However,
I did discover the fuel pressure spring was not installed correctly. I paid very close attention this time mounting it flush in the FRx machined housing. Now my fuel pressure is at around 62 most of the time.
Unfortunaley, at WOT the fuel pressure still nose dives down to 25 or so.
How do I get rid of the quick connect fuel line between the fuel pump and the motor?
Racor PS120 Specifications linked and pictured below. The strainer can be located on EITHER side of the pump EXCEPT IT IS LIMITED TO A MAXIMUM INLET PRESSURE OF ONLY 15 psig. It is BEST used on the suction side of a pump.
Sorry, I meant 5/16 I believe is what is on it now. Got in a hurry, have alot on my mind right now. Been threw a lot of test myself and not all are good. Sorry.
Chet
I have stage IIs, an FRX, and a stock fuel pump - and my hottest tune will lathe tires in TCLU without fuel pressure dropping below 50 PSI. I set my fuel pressure at 60 PSI for one reason:
If the fuel pressure drops below 45 PSI, it's not because of the regulator - so that needs to be shoved completely off the table to focus on what's left. When a pressure regulator is doing it's job, excess fuel is returning to the tank - and the plow from the pump is constant. Raise the pressure, and the pump sends fewer GPH of flow as the pressure rises.
Let me reiterate that and let it sink in. The rule of the universe for a pump is as the backpressure builds, the flow SLOWS. When looking for more flow, a reduction in backpressure on the pump gets this done. When your backpressure drops to 20 PSI, this the engine demanding more flow and the fuelsystem (not just the pump) not being able to deliver the flow at a higher backpressure.
Therefore... I set the backpressure at 60 PSI, because that keeps the flow in the fuel lines closer to a constant velocity with WOT. There... I dropped another clue in everybody's lap - the velocity of the fuel in the lines. Anybody who has ever tried to increase flow by raising the pressure will see things go completely the wrong way. A sudden surge of demand (flooring it from idle) will have the fuel pressure plummet to a lower point than before the change for a sec, then recover to a stabilized pressure during the WOT run. This is a shock to the velocity of the fuel in the lines. You are asking for more flow to the engine, but hey... you slowed all the flow down as a starting point when you ramped up the backpressure.
Backpressure - that's what you're changing with that spring in the FRx or the fuel bowl. Backpressure. It's up to the fuel delivery system to make more flow at a higher backpressure. So... I already know my OEM Bosch pump gets it done with those injectors - but i also know what absolutely kills my flow with this pump: A bad job at the Hutch mod. I ultimately dropped my tank 5 times and changed the design of the prefiltration system twice before I got the fuel pressure gauge to telegraph some good news.
Problem 1: Vacuum leaks (plural). The whole system needs a vacuum test from the hose at the pump inlet to the pickup tube. If the vacuum test fails, so does the fuel flow. The factory quick-disconnects are O-ring sealed - bad juju on a vacuum. Those QDs are the root cause of many evils on our fuel system, then getting a good seal on replacement hose is the next hurdle that I failed miserably. Fuel injector clamps, and double-clamp each end of the hose to ward off the loss of suck.
Problem 2: Too much filtration before the pump. The filter on the pressure side gets it done - it has been working just fine for many miles and years. This is one of designs on the truck that works well, so no need to engineer above and beyond with the "more is better" mantra. Many people (including myself) add a fancy filter/water separator before the pump. Without the right design and maintenance regimen, this is a flow killer. I swapped to a pre-pump strainer.
Tugly - I have an update that I want to run by you. I have been crazy busy with work at the end of year, and now got around to messing with the low fuel pressure again.
Here is what my mechanic has found. He has double clamped everything from the tank to the pump with fuel injection clamps, and still no change. The whole system was vacuum tested, with no leaks. This was quite a big job, as the tank had to come back down. We removed the RiffRaff fuel filter, and ran it without, and no change. We also ran the pump with a hose into a bucket, and in a minute, it only flowed a gallon.
This is where my mechanic thinks I have a problem. He does not think the stock pump is flowing enough volume.
Do you know what the stock pump flow rate is supposed to be?
My next thought is to mess with the spring in the FRx, and get the fuel pressure dialed into 60 PSI, right now at idle it's around 68-70 PSI. If that does not work, would it be a good idea to replace the OEM fuel pump with a Bosch 044 and see if that does the trick?
I am starting to loose hope here, and just frustrated.
12-03-2016, 06:05 PM
