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Slow fuel pressure issue.

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ls1 procharged camaro. I have two walbro 340gss in the tank with racetronix hot wire kit. 3/8 stock fuel line and 5/16 return stock. Aeromotive gen 2 boost referenced regulator connected to fuel rail.

The problem is when i go full throttle I only get my base pressure of 58psi if lucky when I should be getting around 68psi at 10psi of boost. I have changed the vacuum source to the brake booster with no luck.

The only thing i can see being a problem is that i have a racetronix 8orb check valve between the regulator and fuel rail. I still hit my target AFR due to adding fuel in that area. I also am using max tow glowshift gauges and wonder if they have lost there accuracy? Maybe one pump isnt working?

Sorry for the long post

Hello, i have seen a similar issue in my workshop it ended up needing larger feed and return. I ran a larger feed and used the original feed as the return

but of coarse check pump flow at the tank first if possible as well as voltages at each pump and don't discount the earths

Regards Ross

I would suggest if possible to attach a gauge onto the regulator itself as a sanity check as well as if possible making a visit to a dyno to run the car up to high rpm and load whilst being able to view this gauge.

Of course as Ross has mentioned do the physical checks on your pumps first.

The return line shouldn’t need to be enlarged if the system isn’t reaching pressure but the feed line might need to be for the two pumps to deliver enough fluid.

Another point to mention as you’ve said is any restrictions in the line; fittings that are not high flow fittings can change the internal diameter of the system causing pressure/flow drops or more inconsistent pressure/flow.

As for the pressure line to the reg I’ve always taken it from the plenum/intake manifold without anything in between, that’s just a preference of mine.

Interested to see how you get on, good luck.

One thing I would add from the other guys would be to check the current draw on the pumps, if they’re pulling too much current for the supply the resistance in the feed increases causing a voltage drop. Try disconnecting 1 pump and see if it can achieve the pressure statically, if so then you may need to increase the gauge of wire feeding the pumps for example.

Hey guys, just giving a update here.

I have changed out the stock rubber fuel lines in my engine bay for some -6 AN lines, the stock ones were turned in such a way they were clearly a restriction. While doing this i also moved the check valve to be before the regulator (its probably not even needed). I also replaced the fuel filter in case it was clogged. I did a pull and the fuel pressure rises to 58psi pretty fast but will not go any higher, what is odd, is the boost gauge only is reading 3 psi. When on the scanner its reading 140-145kpa (6-7psi) via MAP. This is a electronic boost gauge and I just swapped out the sensor with no luck. I added a aeromotive fuel gauge to the regulator and use compressed air to verify my electronic fuel gauge is working correctly. In turn doing this has help with the speed of the fuel pressure and i did noticed my injector duty cycle lowered by 5-10% on my deka 60lbs injectors which is around the 50% duty cycle now.

I will be pulling the pumps out this week to check voltages and looking for any leaks as well measuring the flow as taught in the webinar "how big does your fuel system need to be". I greatly appreciate the time you guys are taking to help me out!!

This might be be an irrelevant statement - but I will mention it anyhow. You mentioned it is a LS1 in a Camaro in your first post without mention of the specific year etc. Most LS1 chassis's would have a returnless system with a 58psi regulator in or near the tank. So your symptom of the fuel pressure not increasing beyond 58psi would kind of fit that scenario of the original returnless reg still in the system. Are you 100% sure this thing doesnt have another reg in the tank?

Put in a couple hours on this issue today.

So at the pump with it turned off I am getting 14.1 volts (measured at relay) which is the same at the battery. With the pump turned on i get 13.5 volts on each pump (measured at 4 pin plug on top of module). Pulled the module and checked for leaks and test the pumps on a bench with no luck of seeing anything abnormal, the stock regulator was not installed, return line dumps into the center of the bucket. Also discovered that the hotwire kit has a pressure sensor to activate on boost, currently its running both pumps full time. Next time I work on this car ill disconnect one of the pumps and do a small pull to see if one produces pressure faster.

Another thought is that the pumps just are not performing well enough anymore, I don't know the history or age of these walbro 340s. How fast is fuel pressure suppose to rise? ill be around 3 psi of boost (120kpa) before hitting 58psi now. My AFR was 11.8 when cmd was 11.5 but injector duty cycle around 40%.

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