Parked next to my 85 TA is my 78 C3 Corvette. I installed a TBI system on it a few years back and have run into an issue, hoping the group here can help me out. Car stumbles under load and not going into closed loop. I have a Moates AutoProm, and it seemed like the oxygen sensors were never getting a "rich" signal. Tried three, exact same result on the log. So.... My first step was to check the fuel pressure. Had to order the special adapter, finally showed up last week and redid my fuel lines to accommodate the adapter. Fuel pump I installed at the time of the conversion is the EP241 that is often used for TPI as that is the system I eventually plan to install.

With my pressure gauge, I get 10 PSI all day long. Holds steady when I rev it up, cold idle and hot idle. The tube is too short for me to check while driving, so cannot perform an exact check with it under load.

I decided to modify the fuel pressure regulator to make it adjustable. Just set a drill down into the cup until enough of the brazing was worn away. I cannot get down to cut a slot in the head, so guessing I messed up the procedure somewhere! I can adjust it with the regulator completely disassembled, so I tried a couple of increased settings. One is up REALLY high, was difficult to get the spring and gasket to reset. When I fired it up, 10 PSI.

Today, I blocked off the return line back at the tank. When I turned the key for the ECM to prime the pump, it pegged the gauge at 60 PSI. That leads me to believe fuel pump and filter are fine.

Any suggestions on why the regulator isn't pushing it above 10? I'd like to get it to the 13-15 range so I can verify fuel is not the issue in my stumbling.

Any help, much appreciated!

 

Pic of the install

TBI install on a 78 Corvette. Was a really fun project with a nice improvement in drivability.


With the tab about halfway in the opening, still just 10psi. Originally was very close to the bottom.

My mangled adjustable fuel pressure regulator. Turns ok but has to be totally disassembled.

 

Plugged fuel filter? Supplies pressure, but can't flow much volume?

For the record, misfire causes a false "lean" O2 sensor output.

 

I'm considering the filter, but it is only a few years old and a new fuel tank and lines. Only a few thousand miles put on it since the conversion. Ignition issues are my next area of investigation. Just trying to eliminate any fuel-related items first.
Ideally, I could bypass the filter to test the pressure. However, I'm using the hard nylon fuel lines and bridging them is not a possibility. They worked great on the install, but definitely have some negatives.

 

Here is latest (quick version: no change). I pulled the fuel filter and blew compressed air through it, followed by a good dose of carb cleaner, chased with compressed air. Hooked back up and gauge still reads 10 PSI.

Fuel coming out of filter was clear; no crud, chunks, etc.

AC Delco GF580 is my part number on the filter.

How much does the regulator need to be cranked down to boost the pressure?

As always, any help much appreciated!

 

I've got no more ideas.

 

Solved it! I was not tightening the spring enough. Woke up this morning, thinking about the bolt design and deciding I needed to pop it out of the housing one way or another so I could slot it with my Dremel. Using a bit, I was able to grind away a bit more of the weld, then popped it out with a hammer and punch. After slotting the bolt, reassembled and tightened the spring until the tab was all the way to the top of the housing.

Back on the car and running, bumped my pressure to 13 PSI. Right where I was shooting for, will be giving it a test run later to see if it helps with my stumbling under acceleration.

Also, will create a new thread with pics for the adjustable fuel regulator mod. All the original threads referenced pictures that were no longer there.