thainglo

iTrader: (1)

I recently completed modifying my fuel pressure regulator thanks to writeups on this site (TBI-AFPR). However, anywhere I searched for pictures, I came up blank. Most of the posts appear to be 10-15 years old, so likely any photos at the time have since been deleted. Thought I could lend a hand by posting up the photos I took during my process.

My TBI setup is a custom one I did on a 78 Corvette. I used all GM parts from a 94-95 truck, including ECM, manifold, throttle body, etc. Was a blast of a project and made the car run so much better than the original quadrajet. If interested, my long, detailed writeup is here (C3 TBI). Over the past few months, I've been fighting a stumbling under load issue. Using my Autoprom and checking out the logs, it really looked like the car was running lean. The pump is used for my install is the EP241 often used for TPI setups and should put out up to 60 psi. After finally getting an adapter installed to read the fuel pressure, I wasn't surprised to find it stuck at 10 PSI. GM quotes 9 - 13 psi as "acceptable." I decided to try and bump up the pressure to the top end of the range and see if that solves the stumbling. If not, I was going to next dig into ignition components.

Disassembly is easy - 8 Torx T20 bolts hold the top of the TBI housing to the main body. Once that is removed, four Torx T15 bolts hold the pressure regulator assembly to the top housing. There is a spring that is under pressure, so keep a hand on the regulator housing as you remove the last bolt.


The setup on my 78 C3 Vette. The 8 screws to remove the top housing are right in the center. Unclip the two injector clips and remove the rubber isolators. The three bolts on the rear of the TBI housing are longer than the five front bolts.

The four T15 bolts to remove the regulator housing. I have also started to drill out the weld that GM put on at the factory.

After removing the housing, it is time to get to work on the weld. I forgot to take a before picture, but there was a little blob of weld in the cup that is shown in the picture above. I first center-punched the weld, then used a split-point drill bit sized as close the the size of the cup to begin drilling. This is where I had no idea what to expect as I could find no pictures of a completed AFPR. Didn't know how far down it was safe to go, but at the point of the picture above, I could turn the bolt from the inside with a set of pliers. There was still enough weld that the bolt wasn't coming loose of the housing. The next tool I grabbed was my Dremel with a grinding bit, and I slowly began to grind away at the remaining parts of the weld.


Picture of the little grinding bit I used to remove the last of the weld. I then used a nail punch to gently hammer out the bolt.

The bolt removed from the platform that the spring perches on.

Used a Dremel with cutoff wheel to make a slot for my screwdriver. In my opinion, a hacksaw would probably make a better cut in this application.

All reassembled and the platform cranked up to the top.

I opted to crank the spring up as high as I could and see what the results would be. I'd earlier tested it at halfway raised and there had been zero difference in the psi rating. Fortunately, with the perch raised as high as it would go, my gauge read 13 psi. Took the car for a test drive around the neighborhood and it runs better than ever. The stumbling is totally gone, so I'm pleased with the final result.

Hope these pictures help if anyone still is tweaking with their TBI system and wants to modify their regulator. If this looks too complicated, the aftermarket still supports TBI with options, but the cheapest seemed to start at $80. Seemed excessive to me, and this was free.

morgsie

iTrader: (1)

I have always broke loose the round part on the bottom of the regulator. while frowned upon by some, i have never had any issues and have done so to a dozen+ units over the last decade. For a stock/OEM spring ALWAYS crank the regulator up as you have. Also always use the TPI pump when doing a TBI "tune up". Another tip, don't bother with new injectors get your oem ones professionally cleaned.