Installed adjustable tbi fuel pressure regulator.... not working

[chevymotocross]

Hey guys, I have an 87 r10 with the 305 TBI. It has dual exhaust, tbi spacer, injector spacer, and k&n filter. Truck has been running fine and getting 15 mpg.

I learned that with my simple modifications, it's good to add the adjustable fuel regulator to bump up the pressure a bit. The tbi is rated at 9-13 psi from the factory, but with some modifications, they run better at around 14.

Before adding the adjustable regulator, I added a gauge at the TBI inlet to see what my current pressure is. It was only reading 7.5! Below factory specs. Keep in mind, my tank, pump, and fuel filter are only 1 year old and the truck has been running fine.

I install the CFM-Tech AFPR. I crank the adjuster all the way up. Pressure still only reads 7.5! What do you guys think? I would have thought that by raising that regulator, there would have been pressure changes. This must mean either the filter is clogged, or the 1 year old pump is weak? Am I missing something hear because I would think at only 7.5 psi, the truck would be running horrible with bad fuel mileage.

[VileZambonie]

#1 verify with a different gauge. Pushing fuel pressure up is pointless. The way the regulator works is it circulates fuel back to the tank at the set spring pressure. When manifold vacuum drops it resonds by boosting fuel pressure to eliminate tip in hesitation and to meet driver demand. Verify it is responding to vacuum and that the tbi isn't plugged up in the vacuum circuit. If you Tee in at the fuel filter (before or bypassed altogether) key on engine running check the pressure with a known good gauge. If it's within spec check the filter and then the regulator/tbi unit. If it's not within spec drop the tank and check for leaks. If it's ok replace the pump.

[chevymotocross]

Didn't do those exact things but here is what I did. I replaced the fuel filter with no luck. I forgot to add that my truck has 2 tanks. I don't use the passenger tank since it leaks. Well, for test purposes, I put a bit of fuel in the tank, and tried that passenger side to see if that pump puts out any more pressure. Nope, still only 7.5-8 psi.

[VileZambonie]

Where are you measuring the fuel pressure?

[chevymotocross]

At the fuel inlet directly at the tbi. I am going to check for a bad regulator diaphram (the adjustable one just came with a new housing and adjuster screw, the old diaphram had to be reused). I will check this by pinching off the return line. If pressure rises, I know it is bad.

[VileZambonie]

Did you install the diaphragm upside down when you reassembled it?

[chevymotocross]

Did you install the diaphragm upside down when you reassembled it?

Nope, diaphragm was left in place, only piece that was replaced was the metal cup with the new adjusting knob.

[chevymotocross]

Bought a gauge adapter for the filter location.   Napa actually sells one exactly for this purpose, it goes right in place of the fuel filter, pretty nice piece.   Well, still, I'm only getting 7.  5 psi.   The other tank is putting out 9.   I think it is just a coincidence that the other tank is also putting out low numbers.   I believe that pump is original as well as the tank (that tank rusted and leaks).   But geeze, my other tank and pump are only 2 years old and I used a brand name Carter pump.

I guess I pretty much condemned the pump bad.   Any brands to recommend? Anything else I can check for before replacing the pump? I guess 7.  5 is enough pressure to make the truck seem like it is running fine, although I will say that when entering highways, the truck will "hiccup" for a second and then continue running fine. I read that this is a sign of a weak pump. Should I also replace the sending unit as well?

[VileZambonie]

Only if it's rotted or the gauge is malfunctioning. I just ordered new pumps and senders for mine. I got the pumps from AutoZone and the senders from rock auto. Make sure you replace the hose from the pump to the sender and the sock filter. If you have a pulsator on there eliminate it.