I recently got a tester for my fuel pressure in my k5. Maybe a dumb question but what side of the tbi does the adapter go on ??? If you are looking at the front of the engine I have it hooked the the right side. I only have 8psi.
CK5
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Tbi Question
- Thread starter dheavychevy38
- Start date
Right side is correct. I think it only fits on one side, the supply and return fittings are different sizes.
8 is pretty low. How old is your fuel filter?
I dont' remember exactly, but something like 11-14 is acceptable from GM. 12-13 seems to be ideal.
Sounds like you are probably looking at a new pump.
8 is pretty low. How old is your fuel filter?
I dont' remember exactly, but something like 11-14 is acceptable from GM. 12-13 seems to be ideal.
Sounds like you are probably looking at a new pump.
FWIW I prefer running the tester at the fuel filter. A lot easier to access IMO, and less likely to screw the threads/fittings up. You can also run it before/after the filter to see what kind of drop you are getting across it.
The filter is pretty old gonna pull it tonight and install the other tester I have in it's place. I am trying to get her back on the road.
Yeah. Mine is at the filter. That's the way to go.
8 psi is definitely not ideal, but the pump isn't the only possible cuplrit. If the clearances in the pump start to open up (wear), it will struggle to build pressure. Obviously if the filter is clogged, you will get a large pressure drop. Also, if your fuel pressure regulator is worn out it may not be allowing it to build more fuel pressure. These werent exactly high precision devices from the factory - it's just a disphragm being held closed by a spring. If fuel pressure overrides the spring pressure, the diaphragm opens and fuel returns to the tank. But after 20+ yrs in operation, those springs weaken which will reduce your fuel pressure by bypassing more fuel back to the tank.
I've seen people put washers behind the spring to get higher fuel pressures which works, but it's a crapshoot. I installed an adjustable regulator and a mini-gauge on the TBI unit. I run 12.5 -13 psi and it really woke the truck up. BTW, it was pushing 9 psi with a new fuel pump and filter before installing the adjustable regulator.
Also, if you get it sorted, try to monitor fuel pressure while driving. If it drops severely under throttle, it's indicative of either the filter, the pump, or the notorious cracked rubber hose on the output of the pump in the tank. To do this, I had my adapter at the filter and the pressure guage run up to the passenger floorboard. Good luck. Hope you get her healthy again.
8 psi is definitely not ideal, but the pump isn't the only possible cuplrit. If the clearances in the pump start to open up (wear), it will struggle to build pressure. Obviously if the filter is clogged, you will get a large pressure drop. Also, if your fuel pressure regulator is worn out it may not be allowing it to build more fuel pressure. These werent exactly high precision devices from the factory - it's just a disphragm being held closed by a spring. If fuel pressure overrides the spring pressure, the diaphragm opens and fuel returns to the tank. But after 20+ yrs in operation, those springs weaken which will reduce your fuel pressure by bypassing more fuel back to the tank.
I've seen people put washers behind the spring to get higher fuel pressures which works, but it's a crapshoot. I installed an adjustable regulator and a mini-gauge on the TBI unit. I run 12.5 -13 psi and it really woke the truck up. BTW, it was pushing 9 psi with a new fuel pump and filter before installing the adjustable regulator.
Also, if you get it sorted, try to monitor fuel pressure while driving. If it drops severely under throttle, it's indicative of either the filter, the pump, or the notorious cracked rubber hose on the output of the pump in the tank. To do this, I had my adapter at the filter and the pressure guage run up to the passenger floorboard. Good luck. Hope you get her healthy again.
that's the reason I got the adjustable to start with...
79rustyk10
3/4 ton status
I thought 12 was a requirement to run correctly?
I can tell you for a fact mine will run with 9psi. I just didn't realize how much it was leaning out until I hooked a gauge to it and then got an adjustable regulator.
I removed the filter and installed the adapter cranked her up and now I have a solid 10 psi. Not sure if I should try a adj regulator or if I should swap the pump.
That's actually not too bad. The filter is going to have SOME pressure drop across it to actually be effective. 2 psi doesn't sound horrible, but I'm not sure what specs the filter has. In any event, I wouldn't run long without the filter. No telling what trash is in the tank.
I'd drive it to see if it can maintain pressure under load without a large pressure drop. If it cant, its probably the pump. Revving it in park doesn't test this very well.
Otherwise, id temporarily try the washer behind the spring trick in the regulator. If the truck now runs at a higher pressure, the pump is fine. Get a regulator rebuild kit or an adjustable unit.
I'd drive it to see if it can maintain pressure under load without a large pressure drop. If it cant, its probably the pump. Revving it in park doesn't test this very well.
Otherwise, id temporarily try the washer behind the spring trick in the regulator. If the truck now runs at a higher pressure, the pump is fine. Get a regulator rebuild kit or an adjustable unit.
4xcrazy
3/4 ton status
I dunno, my personal preference, if I see 10psi, I'm changing the pump. It's always seemed to lean out too much under decent load. Start getting below 9psi and it'll start to buck and starve out.
I don't disagree. I'm just saying that sometimes the old pump is capable of more, but the regulator is relieving too soon. New pump won't help that.
In fact I did this very thing. Replaced the pump, filter etc, because I didn't fully diagnose. Problem wasn't solved until I fixed the regulator. New spring raised the pressure from 9 to about 11. I had to put in an adjustable to get 12.5.
In fact I did this very thing. Replaced the pump, filter etc, because I didn't fully diagnose. Problem wasn't solved until I fixed the regulator. New spring raised the pressure from 9 to about 11. I had to put in an adjustable to get 12.5.
If you get creative you can simply shim the stock regulator spring some, but it helps to have gaskets handy.
So at this point I think from what I have read should I get a pump from something else with higher pressure and get a adj regulator ??
I'm getting 12-13 from a stock replacement pump. But I had to get an adjustable regulator. Rebuilt stock regulator was opening around 11 psi so pressure would never go higher than that no matter what pump is back there.
I did notice that I didn't have pressure with the key on engine off only once it was running.
From my experience, a proper pump/fuel tank hose will hold pressure after that initial prime for some time. With a split hose (as an example) pressure bled off immediately. Still got pressure on prime, just not much (about half of spec), and it dropped rapidly as soon as the pump stopped. And that was with a massive tear in the hose.
As mentioned, regulator doesn't care how much pressure is on one side, it will only allow pressure up to what it's set at...thus why some use a TPI pump (43.5PSI system pressure spec) in place of the TBI pump without issue.
The regulator is essentially just a calibrated leak back to the tank. You'd really want to put a new pump in, then measure pressure again to determine if you need to modify the system pressure via the regulator. If there is a pump/pressure issue that is not the regulator, the possibility exists that pressure would be 13, but due to whatever problem exists, it's not hitting it. *Personally* I don't see the need for an adjustable FPR, since once it's set there should never be a need to change it, but it does make setting it initially a lot easier than shimming the stock one. Time vs. money I suppose.
As mentioned, regulator doesn't care how much pressure is on one side, it will only allow pressure up to what it's set at...thus why some use a TPI pump (43.5PSI system pressure spec) in place of the TBI pump without issue.
The regulator is essentially just a calibrated leak back to the tank. You'd really want to put a new pump in, then measure pressure again to determine if you need to modify the system pressure via the regulator. If there is a pump/pressure issue that is not the regulator, the possibility exists that pressure would be 13, but due to whatever problem exists, it's not hitting it. *Personally* I don't see the need for an adjustable FPR, since once it's set there should never be a need to change it, but it does make setting it initially a lot easier than shimming the stock one. Time vs. money I suppose.
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Ok one more question. With the fuel filter removed and the adapter installed directly after the pump shouldn't that see the full pump pressure before it even gets the regulator ?? Or is it only gonna show what the regulator is allowing.
Only what the regulator allows. The regulator controls the pressure of the entire line.
