Lean Sputter/Hard Start Warm

[dgibby]

Have been running my Sniper EFI for about 400 miles now. For the last 100 or so it has started going lean, 25+ on the meter, and sputters on very light throttle at lower speeds. Only does it on very light throttle, trying to maintain cruise speed. No problem taking off from stops or hard acceleration. Worse with Learn off, worse when engine is cold, worse in open loop. Read about false lean with some cams and tried changing RPM range for closed loop, and it was worse also. Started hard starting when warm at same time, stop for gas and have to crack the throttle to start. No restart problem if it sits around 10 minutes or more. Thought it would "Learn" itself and correct the lean issue & hard start, but it hasn't.

[Danny Cabral]

Check your fuel pressure, it should be 58.5-60 psi.

[dgibby]

80 psi going in. Not sure how to check it after the regulator?

[Danny Cabral]

80 psi going in.

Contact Holley Tech Service (LINK).

Not sure how to check it after the regulator?

With a fuel pressure gauge.

[dgibby]

With a fuel pressure gauge.

Not sure where to attach it, that's after the regulator since it's build into the unit.

[Danny Cabral]

Using THIS and one of THESE gauges at the -6AN return/regulator fitting. But I'd first inspect the fuel pressure regulator (LINK) to ensure it isn't clogged with debris.

[dgibby]

Yep, reread your message. Attach at the return regulator. I'll check it tonight. Thanks.

[Danny Cabral]

Yes, that's correct. For the record, I never told you to check the return line pressure, nor am I suggesting it's the problem. However, it's a good idea to check it anyway.

[dgibby]

If I'm checking the pressure coming out into the return line, it kinda seems like the return line would be at the same psi? I guess I'm making assumptions, which I know, I shouldn't do. So is the fuel coming out the unit, into the return line coming out at 60 psi and heading back to the tank? Also, very confused on the return. Holley tech line told me it has less than 5 psi back to the tank, and regular 5/16" fuel line is fine for the return.

[Danny Cabral]

No, the fuel return line should be near zero psi (no restriction), exiting fuel pressure regulator. The supply line should be 58.5-60 psi, because the fuel pressure regulator creates the restriction.

[dgibby]

Think I got it. 80 psi is too high on the supply side. Should be 58.5-60 psi because the regulator is restricting flow. Check regulator for debris and check pressure coming out of regulator and it should be near zero. If there is pressure on the return side, it's a problem that needs to be addressed?

[Danny Cabral]

If there is pressure on the return side, it's a problem that needs to be addressed?

Yes: https://youtu.be/KyTBZypPVcs?list=PL...BB99AF17&t=197 (Holley EFI YouTube Tech Video)

[351C Sniper]

There should be a way to jump the terminals on the fuel pump relay and run the fuel system without starting the engine. That way you could check fuel pressure, leaks or noise. I know the Sniper fuel system should pressurize each time the key is switched to run. But sometimes it's helpful to run the fuel pump for extended intervals to test or troubleshoot.

[Danny Cabral]

Yes, you can jump fuel pump relay terminals #30 & #87.

I use what I call a "Test Relay" for troubleshooting use. All you need is a typical 4 or 5 terminal automotive relay. Disassemble the relay by carefully prying outward on the four tabbed walls. (Notice one of the tabs is notched for aligning with terminal #30.) Then remove the internal components (coil, contacts, terminals, etc.) but leave the exterior terminals #30 & #87 intact. Simply solder the braided wire from terminal #30 to the remains of terminal #87. (If using a 5 terminal relay, the center terminal #87A is difficult to remove, so just cut it off.) Snap the cover back onto the base, and your "Test Relay" is completed (which I often use for many other purposes as well). Of course, a jumper wire works too, but the "Test Relay" is a professional grade tool.

Ensure the fuel pressure is properly adjusted and the "Actual System Pressure" (Terminator - "Fuel Pres") is accurately entered in Engine Parameters. With TBI, the Actual System Pressure is measured anytime engine is running (no vacuum reference hose), or key-on/engine-off pump running. With MPFI, the Actual System Pressure is measured with the vacuum reference hose temporarily disconnected, or key-on/engine-off pump running. The fuel & oil pressure transducers are completely optional. The engine runs the same with or without them. The fuel & oil pressure transducers are used for Data Monitoring, Data Logging and setup Outputs based on fuel & oil pressure. They're "plug & play" into the main harness, and you'll eventually want to use them. And they don't consume any Custom I/O either. This is not to be confused with the "Actual System Pressure" fuel parameter (in Engine Parameters), which must be entered accurately, because the ECU does use this single value for lb/hr calculations. http://documents.holley.com/techlibr...l_injector.pdf (Selecting A Fuel Injector Size) https://www.vaporworx.com/documentat...re-regulators/ (Vacuum/Boost Referenced Fuel Pressure Regulators) http://documents.holley.com/techlibr...owdatarev2.pdf (Fuel Injector Flow & Off Time Data)