EFI - Fuel Line Question

[JOP33]

I am running a 302 with a Holley Sniper EFI, I have about 2200 miles on the car now and I have long noticed that if the car sits for more than a day (two days definitely or God forbid three) the Engine tends to hesitate at acceleration, idle rough and then just clears up and runs like a bat out of hell. The system shouldn't be bleeding back...should it? Anyone else ever experienced this and if so what should I check for or investigate? As mentioned it runs awesome about 98%, but if it's been sitting you know it will be rough for what seems like a gallon, gallon and half of fuel.

Thanks

[sethmark]

Battery disconnect? If so, are you killing the memory?

[Bob Cowan]

This fuel system will not maintain pressure over a long'ish period of time. If mine has been sitting a few days, it will run rough and sputter a bit for about 30-60 seconds after start. I turn the key to run, wait a few seconds, turn it off and then back on for a few seconds. Then push start. Problem resolved. If it sits for a few hours, or overnight, I don't need to do that.

[JOP33]

Battery has not been disconnected. The common event is it sitting for at least two days. It has typically been more than a sputter as even when driven on the highway around 70+ mph, I can feel slight hesitations in the throttle every so often. But drove again last night for about twenty minutes after having the issue yesterday morning and ran great. My only thought is that fuel lines drop down from the tank to the very bottom of the chassis, following it for about 40” and then straight up at the firewall to the EFI. I didn’t think that the system would maintain the pressure but also didn’t know if there was a way to minimize or eliminate the bleed back?

Thanks

[sethmark]

Are you giving the computer the opportunity to boot? Can you watch fuel pressure during start up?

[Svtfreak]

Even if the fuel pressure bled off the lines, it shouldn’t be getting air in. Pressure should come back to instantly nearly. I doubt that’s the culprit. Getting air in would be a place fuel would likely come out.

My cobra does something similar. But not nearly as long. I always said it’s just a cold natured b***h even though it’s efi, I just ain’t found the right value to tweak.

That said, that’s longer even than warm up. Your oil is probably just getting up to good operating temp. Can you look at all values in that efi system? Can you look and see what temp it is going into closed loop operating mode? Could that be it? Is there an oil temp sensor maybe that is triggering a change in operating mode? Just brainstorming here, as I don’t know that efi system. Oh, another thought. 302 efi programming has 3 timing tables that if uses depending on altitude, temp and maybe a couple other things (without going look it up). Does yours maybe have that and something is triggering a switch in timing tables (ECT, EOT, something like that?) which may be causing that or clearing it up?

[JOP33]

Thanks I will check into these items. There is an Air Fuel adjustment that Engine Factory advised based off my numbers I submitted, but I have been holding off since the car runs so good the rest of the time...guess I will move forward with it and see if it's a fix.

[HVACMAN]

Has this always been an issue or could it be related to your fuel issue the other day. I know you concluded it was an over fill. Just curious.

[JOP33]

Has this always been an issue or could it be related to your fuel issue the other day. I know you concluded it was an over fill. Just curious.

No this has always been an issue. I have just really gathered enough intel to conclude that it always coincides with the vehicle being "out of commission" for two days or more. No significant changes occur to the vehicles set-up during this time other than the time of it sitting and when it does start running normal again, it idles fine, runs great like nothing ever happened. But it only has ever done when the car has sat, never have I been driving one day and go out the next day and it starts acting up. I actually verified my IAC set-up that Engine Factory had sent to me as well, and my numbers are dead on at 2000rpms, just as they suggest. Could it be (and I am just spit-balling here) that the fuel is bleeding back when sitting for extended periods of time and then the pump is fight gravity within the run to finally "purge" the system again? I haven' tried this, but will the next time the car has sit...I know at first start (for go-carting, etc) they instruct you to cycle the pump several (3) times before attempting to start. Maybe if the car has sat for more than a day, I need to treat it like it has been sitting longer. Couldn't hurt to try I guess.

[Svtfreak]

You cycle the key on initial start up in order to fill all the fuel lines. I actually hot wire the pump to do it and during that time I actually set the fuel pressure (and adjust after running). The system is full of air prior to that. Yours is full of fuel. Even if the pressure bleeds off (not uncommon as regulators don’t seal 100%), the initial 5 second kick should pressure it back up instantly. If you are getting air into your system and that’s what’s causing problems, then likely fuel would come out at that point under pressure. So I think that is unlikely. But, stranger things have happened. We’ve seen vacuum leaks at work that didn’t leak when under pressure. Very uncommon but it does happen. Maybe try tightening all your fuel fittings just a little tiny bit more. But, even if it is air getting in, I really don’t think it should take that long to get it out once running.

[NAZ]

Sounds like air trapped in the system. I've seen canister style fuel filters mounted horizontally trap air in the upper section above the discharge and it takes forever to burp all that air. The larger the can the more trapped air. When mounted before the pump it can cause pump cavitation. When mounted after the pump on a carburetor system the air simply bleeds out the bowl vents. On an EFI, where does trapped air go?

[donshapansky]

Jamie, I would have someone observe the fuel pressure regulator needle behavior 2 different times. Once after a short shutdown period like a few hours and then after a few days to see if the gauge shows any different behavior. I would also check the vacuum sense line for any possible leakage where you are getting a low vacuum signal to the pressure regulator. If the vacuum signal is weak then you would have different pressure thresholds.

[Kamp]

I'm guessing this only happens on a cold start after the fuel evaporates from the manifold and cylinder walls.

Can you set the "fuel pump" prime time in a Sniper? If the "prime" time out happens to quickly the fuel pressure can be low. Can you run a "Data Log" with a Sniper? It maybe that with a cold tip in you are a bit lean. I haven't worked with the Sniper ECU but a Dominator shares many of the same tables.

[JOP33]

I was going to attempt this with a few cycles of the Fuel Pump prior to my next start after prolonged sitting and see if this helps any. I do believe what you are saying about setting the "prime" time is accurate, but just don't know (or not know) if it would be more effective to manage it as the exception (providing it helps) instead of setting it to extend all the time. Thank all of you for the feedback as I have several areas to check into now.

[TxMike64]

With 21 pages of your build thread I've decided not to go looking for pictures, but could you show us the fuel lines in the engine bay? Where is the FPR? Is this Throttle Body or Multi-Point EFI?

[JOP33]

Lol! I understand! I have over 3500 pics of the build and sometimes I can’t find what I’m looking for and find myself going out to the shop to take another photo. It’s a carbureted engine with the Holley Sniper bolt on efi. The regulator is built into the efi. The blue lines in the pic are the supply and return, they run down from the firewall straight down the lower chassis tube up at the tank. Pre filter, pump & post filter mounted horizontally right below the tank floor. The Engine builder has suggested a spacer between the throttle body to help with fuel atomization.

E8DC902A-0077-4F38-94CD-8989C9CE34CA.jpeg

[TxMike64]

Thanks for the details. I've tuned a fair share of aftermarket EFI systems, but only tuned two of these Throttle Body style EFI systems. Both had off-idle throttle response, and cruise to WOT stumble issues that I was not able to resolve. One owner runs the system (Holley) dealing with the issue as its much better overall than the carb he had on it. The other owner (Edelbrock) switched to Multi-point EFI and he doesn't have any driveability issues at all. So I'm not sure this isn't a normal issue with a "wet" manifold [I have almost no experience with carbs].

I wonder if pressure leak-down isn't exasperated by the fact that your fuel lines go above the injectors. It may be worth using a check valve such as this: Russell Check Valve

[JOP33]

Thanks for the details. I've tuned a fair share of aftermarket EFI systems, but only tuned two of these Throttle Body style EFI systems. Both had off-idle throttle response, and cruise to WOT stumble issues that I was not able to resolve. One owner runs the system (Holley) dealing with the issue as its much better overall than the carb he had on it. The other owner (Edelbrock) switched to Multi-point EFI and he doesn't have any driveability issues at all. So I'm not sure this isn't a normal issue with a "wet" manifold [I have almost no experience with carbs].

I wonder if pressure leak-down isn't exasperated by the fact that your fuel lines go above the injectors. It may be worth using a check valve such as this: Russell Check Valve

Perfect Mike! I have been asking around about a check valve and everyone seemed to think I didn't need it. I will install one just to see if it eliminates the issue.

Thanks again!

[JOP33]

I wonder if pressure leak-down isn't exasperated by the fact that your fuel lines go above the injectors. It may be worth using a check valve such as this: Russell Check Valve

Mike - Quick follow up on this, if you know, would I want to install the check valve in-line closer to the throttle body or closer to the tank?

Thanks

[NAZ]

Something to consider if using a check valve. While easier to install in the fuel line (closer to the tank is better), if you install it in the tank (submerged) it will act as a foot valve preventing drain back but also act as a breakaway valve in a crash. This is mandated by some racing sanctioning bodies along with rollover valves on the filler, vent, and return lines. These valves have a light spring pressure to ensure the poppet seats and is light enough that the pump has enough draw on the suction side to open the valve. I run one in my race car (different brand but basically the same) to eliminate spilled fuel in the event of a crash even if the fuel line is ripped off the tank there will be no leak. When I power the pump it takes less than a second to reach full fuel pressure as the fuel lines stay full. But like a fuel filter, I never run them horizontal -- always vertical to prevent trapped air.

[TxMike64]

Mike - Quick follow up on this, if you know, would I want to install the check valve in-line closer to the throttle body or closer to the tank?

Thanks

I would think at the lowest point in the system, or like NAZ says, closer to the tank.

[Norm B]

A check valve might help the initial start up issue but the lines should be fully purged of air by the time you are out on the highway. Initial startup and off idle issues are probably two separate problems. A couple of questions: What fuel pump are you running? Did you run the return line all the way to the bottom of the tank?

I would dig into the manual and look for an acceleration enrichment adjustment. Also check the IAC reading at warm idle. These could help your hesitation problem.

[JOP33]

A check valve might help the initial start up issue but the lines should be fully purged of air by the time you are out on the highway. Initial startup and off idle issues are probably two separate problems. A couple of questions: What fuel pump are you running? Did you run the return line all the way to the bottom of the tank?

I would dig into the manual and look for an acceleration enrichment adjustment. Also check the IAC reading at warm idle. These could help your hesitation problem.

I have purchased the check valve, but have yet to install it. The issues are consistent and only at concurrent times...meaning when I have the issue at startup, I will have the hesitation issue on the road. The fuel pump is the Holley pump that came with the Sniper system. Return line does run all the way down in the tank. I haven't looked into the Acceleration Enrichment Adjustment, but have confirmed the IAC reading to what Engine Factory advised and it is spot on. For the last three weeks I have made a point to go out and start the car on a daily basis and let it run for about 5 minutes. Since doing this I have had absolutely no issues with startup or hesitation when I do take it out.

Thanks