Why Does My Fuel Presure Drop

[TnBlkC230WZ]

I've installed an EZ-EFI system and it has been trying to get it to run correctly. I couldn't get the engine above 2000 RPM. Everything seemed to be installed correctly. Finally got through to someone at FAST who could help trouble shoot and it turns out to be the fuel pressure drops to zero when I rev it up. The fuel pressure is fine at idle. As soon as I give it gas, it drops to zero. It will recover a bit, but not much.

The question is, why is the fuel pressure dropping? I have a Ricks fuel injected tank with a Delco pump. I purchased this tank from a guy on ebay who never installed it. It looked to be unused. I double cheched and it looks like it is installed correctly. The supply is on the right and the return is on the left side of the car.

I also have an Aeromotive 13109 regulator with the return from the fuel rail going into the side and the return to the tank going out the bottom.

[Ollie8974]

Is the regulator connected to manifold vacuum? The regulator needs to be connected to compensate for acceleration.

[CamaroAJ]

check the voltage with a multimeter and watch it when your reving to make sure your not loosing power.

[TnBlkC230WZ]

I do have the regulator connected to engine vacuum. I'll check the voltage tonight. It is wired with 12 guage from the fuse block/relay to the right a piller and 14 guage back to the tank. Mathmetically, it should have .7 volt or less drop from or about 13.6 volts, but I've never actually measured it.

[Doug F]

If it drops to zero free reving it up you have something MAJORLY wrong. Look for something obvious. Make sure it is plumbed correctly, keep track that it has power. To go to 0 free reving the pump is shutting off or the regulator is not resticting fuel at that point.

[Ollie8974]

Check for dirty/plugged filter in the sender.

[DeltaT]

Make sure the tank is vented correctly as well. An unvented/poorly vented tank can start clogging up very quickly as a vacuum builds.

Jim

[Jim Nilsen]

This may sound off base but did you adjust it to the correct pressure with a gauge? Is the regulator open all the way?

I have the same regulator and have no problems and there is no vacuum line to it at all. I also have it in the rear of the car and have the return line there instead of up front off of the rail. I have never had low fuel pressure unles it was in a corner and it lost fuel at the pickup.

The pump may actually be making pressure but not able to produce volume, look for any restrictions. Maybe put the end of it in a bucket from a hose and really see what the volume is? it could be the pump?

I am lucky to have not had this problem and it may be that the configuration is not right. Do you have a diagram of how it is plumbed.

It is really strange and frustrating and I feel your pain.

[TnBlkC230WZ]

Ok, my voltage to the pump was good. I pinched the return line shut where I have a piece of rubber hose. It went to 85 PSI cold, but only went up a couple of lbs when hot. Next, I disconnected the return and ran it to a gas can. When cold, I had a slow stream. I couldn't get 2 gallons in 15 minutes. When it warmed up, the fuel pump got very loud and the return flow slowed to a trickle (less than a gallon per hour).

I replaced the fuel pump with a new Delphi pump and and it is a little better, better, but not much. Still noisy, but a different noise. I still can push the gas beyond 1/2 way. Are these pumps notorious for being bad?

I'm starting to pull out what little hair I have left.

I have a gauge on the regulator so I can see what the pressure is doing. I've double and trickle checked the supply and return line, and it looks ok. Suppy side goes to the throttle body and exits to the regulator and then back to return side of the tank. It is a Ricks tank. I have it vented the same way the carb tank was vented. I've never heard a vacuum when I opened the cap.

[Jim Nilsen]

What size lines are in your system?

Mine is -8 from the tank to the pre-filter then the pump to another filter , then the regulator and -6 to the fuel rail and -6 from the regulator bypass back to the tank.

It still sounds like a pump problem but it shouldn't be. Pumps do lose pressure as the temp goes up normally but the volume usually stays consistent with the pressure.

I had problems with my configuration in the begining and thought I had it right to what the instructions said but it didn't work until I went with the new configuration I have.

There is a thread with all of the info and I just followed what Jody had been doing and it is the same as what the Vettes have for a configuration. You eliminate the return having to come from the engine bay and the heat that is picked up from being there.

You would think that having the regulator on the back side of the throttle body would give it all the pressure and volume it would need. The regultor you have is designed to be put before the throttle body or the fuel rails and go in one side and out the other to the throttle body/ fuel rail and have the bottom port be the return. This also gives you full flow to the throttle body and the return is the left over pressure.

What kind of lines are you running? hardline or hose? My system is all hardline except for the short run from the frame rail to the engine to allow for movement and it is teflon braided line.

Keep at it and you will get it right. I had to redo my whole set of lines to get it right and it was a pain and a big disappointment to have to do that until it worked, then the smile from the effort finally came.

A lot of us have been there and you will get past it in time and the right configuration.

One more thought is , Where is your vacuum being ported from? if you have it in the wrong port you could actually have the regulator working the wrong way and opening up when it should be closing and closing when it should open up and at idle you are able to get the pressure reading you want and when you give it gas it drops causing the problem. This is just a thought and a simple mistake. try disconnecting the vacuum to the regultor and see what happens.

[TnBlkC230WZ]

My fuel pump is in the tank (Ricks tank) and it has 3/8 hard line comming out with -6 fittings. My supply line is -6 PFTE stainless hose from the tank to the throttle body. The return is mostly hard line. I made sure of my turns are at least a 6 inch radius.

The EZ-EFI requires the regulator to be on the return side of the throttle body. I'll look up Jody's thread.

I have read on-line where it can take two or three of these pumps to find a good one.

Makes me wish I stayed with my original plan of putting in a surge tank. I did get a good deal on a Ricks tank on ebay, but it is starting to get frustrating.

[Jim Nilsen]

Keep talking to Fast about this and make sure you follow their suggestions on how to plumb it. They may know already that it won't work being deadheaded from the rear with one line and then they may not. They may not have done testing to know for sure and you could be the first to try? It has been the concensus that staedy fuel pressure is all it takes to make EFI work correctly no matter how it gets there and the argument to have to have a return line from the front to the rear is still going on for some. I know one line to the front works good for a lot of us here and Corvettes and Cadillacs seem to be fine from the factory that way.

I will be keeping positive thoughts for you !!!

[TnBlkC230WZ]

Still looking for advice. I'm on my third pump and I can't maintain pressure off of idle. I'm currently running a 255 ltr Walbro high pressure pump. If I rev it a little, the pressure drops from 45 to 30 and recovers. If a rev it hard it drops to 10 PSI and stays there. I can get to about 5000 RPM in first and 4500 RPM in other gears. Engine made 320 RWHP at 6200 RPM with a carb.

I had he Walbro pump installed by a reputable speed shop. They said the Delphi pump they took out was good as well.

I'm starting to wonder if the tank can supply the volume of fuel I need. I'm really thinking hard about going back to a stock tank and installing a surge tank.

Could this be a regulator issue?

[MrForce]

Still looking for advice. I'm on my third pump and I can't maintain pressure off of idle. I'm currently running a 255 ltr Walbro high pressure pump. If I rev it a little, the pressure drops from 45 to 30 and recovers. If a rev it hard it drops to 10 PSI and stays there. I can get to about 5000 RPM in first and 4500 RPM in other gears. Engine made 320 RWHP at 6200 RPM with a carb.

I had he Walbro pump installed by a reputable speed shop. They said the Delphi pump they took out was good as well.

I'm starting to wonder if the tank can supply the volume of fuel I need. I'm really thinking hard about going back to a stock tank and installing a surge tank.

Could this be a regulator issue?

Regulators "work" the hardest at idle when they have to bypass the most amount of fuel. Typically a small regulator will spike at idle and be fine as the engine uses more of the total fuel. A bad reg will not respond well, if at all and will leak out fuel out of the vacuum port due to a torn diaphragm. If you want to check it for obstructions that may be holding it off the seat, loosen and remove the set screw to relieve spring pressure, remove the four bolts holding it together, lift the diaphragm off the base, and look for trash between the check ball and return orifice. Clean and re-assemble.

IMHO, Your problem, based on your posts and work, seems to be a fuel restriction leading to the system. I would check pre and post filters, damage to the hardline, and kinks or flattened fuel line.

Rob

[CarlC]

Agreed.

Remove the fuel cap and try again.

Disconnect the return line at the tank and put it in a fuel can. Turn the key on and observe the amount of fuel returned. With that pump it should return 3/4 - 1 gallon of fuel in one minute.

If it returns sufficient fuel then the problem lies on the other side of the regulator. Check for restrictions and replace the regulator.

[TnBlkC230WZ]

Ok, it's back to the basics and troubleshooting. The original fuel pump only had a trickle on the return when warm. I didn't check it with either of the two new pumps. It could be a defective supply line. I guess I'll hot wire the pump and check the flow through one section at a time. Both the TrickFlow filter and Aeromotive regulator are new. However, new doesn't mean they work. I may jack the pressure up to 60 PSI at idle and see what happens. Or perhaps set the pressure with the engine at 5000 RPM.

[TnBlkC230WZ]

Thanks for getting me to refocus on the basics. Turns out it was The filter. It doesn't say The direction matters, but it does.

[H2Ogbodies]

What kind of filters are you running? I use Aeromotive and they show what direction to flow to install. I don't run rubber line from front to rear for two reasons-most braided fuel line is only designed to last 3 or 4 years before getting brittle internally and the rubber line sweats internally (ie water) when sitting so that is why I run aluminum hardline front to rear for carbed applications with fittings. EFI I bend stainless lines. For longevity reasons, OEM companies don't run braided fuel lin that I'm aware of-it's all hardline. For EFI applications, hardline is the best choice for maintaining pump pressure-no pulsations vs. using rubber-even if it is braided.

[TnBlkC230WZ]

It is a Trick Flow filter and there are no markings indicating direction. I probably should have gotten the Aeromotive filter. I may switch out to hard line in the future. I'm currenntly running Fragola PFTE stainless line. It is a daily driver, so it doesn't set much.

[emtcee1973]

You may want to check the pickup sock it maybe dirty.I was going through something similar and i dreaded dropping the tank but when i did i found the sock to be restricted...i blew air through it and it barely went through..just a thought