Hi everyone, wondering if someone can provide insight here on the following situation.

Recently got tuned on flex fuel - mods are:

• MHI 18k, tubular manifold, full exhaust
• Radium fuel rail
• Walbro 450 (not hardwired)
• Venturi drilled with 3/32” bit
• ID 1300
• -6an fuel feed
• Using oem feed as return line
• Stock FPR
• New OEM longblock, 700 miles at tune time

Since tune day/injector install, the car has driven super erratically in one of the following ways:

1. Bogs down with any throttle from a stop or below 3k rpm (full lean)
2. Idles 11-12 afr, sometimes throwing P0172
3. Idles at stoic, but then will randomly go full lean and shut off, slow to start back up
4. Or it drives perfectly fine with no issues

All of these conditions are worse on 93 oct. Took car to tuner who insists it’s fuel pressure related, he set fuel pressure at 42; and the car will show that on startup; however, after driving and coming back to idle, the pressure hangs anywhere between 58-62psi. WOT is perfectly fine always.

Before I go overkill on a whole new set up, I was just wondering if anyone had any thoughts on whether this could be tune related, or a common hardware issue? My main confusion is the fuel pressure rising after some time driving.

 

@Jxmiy Assuming your injectors are clean and balanced, let's focus on getting your fuel pressure under control. It's going to be impossible to tune it if the pressure is all over the place. You should check a few things systematically, one at a time, with a fuel pressure gauge on the rail, to pinpoint where the problem lies.
1. Is your stock FPR sticking? - swap it for a known good one to see if that fixes the pressure.
2. Are the vac hoses to the FPR leaking - check them visually for damage.
3. Is the FPR solenoid stuck? - can cause high pressure at idle.
4. Is your return line (OEM feed) clear? - pull the hoses at each end and blow it out.
5. Is your venturi really drilled out? - pull your pump and measure it with a drill bit
6. What voltage is your Walbro running at idle? - Measure voltage at the pump with a meter. If it is running full voltage it may overrun your stock FRP.

 

@CDrinkH2O Thanks for the quick response. I’ll give these all a look and go from there. I drilled out the Venturi myself and cleaned it, so I don’t think that’s the problem there. Will report back after this weekend hopefully. Much appreciated!

 

You need to add the radium FPR and pulse damper to the fuel rail, drill the siphon to 9/64", and do a proper hi/lo voltage rewire on the fuel pump. You should not be running a stock FPR with the oversized feed/return lines.

 

Yea, fuel pulse damper is the minimum requirement with an aftermarket rail.

Where are you in CT?

 

• Walbro 450 (not hardwired)

So how is this puppy wired exactly?