Wondering if I can find a cheapish fuel pressure regulator set at about 15psi rather than have to shell out for a fancy adjustable one. Anybody know of something common enough that I can run down to the local parts store and have some chance of getting it? I'm fairly certain at this point that the fancy brand-new adjustable one I just bought is kaput.
Gracias...
Anything carbed, nothing fuel injected.
In reply to NordicSaab:
False. Most carburetors run on 3-6 psi. I don't know of any (stock) that run more than 9 psi.
I'd look at CFI applications for 15 ish psi, IIRC the early GM TBI stuff did 12 psi.
I'm pretty sure that the TBI units on 2.8 S-10s was 11-12psi.
A lot of TBI units are in the 26psi range but some are down in the range you're looking for. UNFORTUNATELY almost all TBI units have internal pressure regulators that aren't easily swappable.
What is kaput about the regulator you have now? If it's an adjustable, you should be able to rebuild it.
Gm tbi is 12-15 lbs spec to 93. 93-95 went 18-21. Unfortunately, not easily adapted to something else.
O'reilly can search by part attributes. Get the experienced guy.
Also, the 20 dollar ebay vacuum reference fuel pressure regulator is cheap, but if you pull it apart, clean it up, and use decent o rings in it, they work surprisingly well.
Yeah, it's a weird range unfortunately. As pointed out, FI is usually way higher, carb'd is lower.
Knurled wrote: What is kaput about the regulator you have now? If it's an adjustable, you should be able to rebuild it.
It seems to not ... regulate. Set the pressure, maintains it at idle, then as soon as you give it some gas (mind you, this is still in the driveway, so no load) pressure drops. Higher the RPM, the more it drops. Take your foot off the gas, and it comes back up to the preset idle. Don't want to build it - it's brand new (or at least it's supposed to be). Pump, fuel lines, filters, everything else is new too and seem to be working properly.
This is a Cummins diesel, btw, if anyone is wondering. Trying to reengineer / improve the stock fuel system and make it easier to service. But now it's turning into a bit of a science fair project tracking this issue down.
That sure sounds like a fuel pump problem to me. Crimp off your return line (gently) with vise grips and see if the problem remains. If it does it's a supply problem.
If you get a cheap adjustable regulator that doesnt go down to 15 you can take it apart and trim the spring until it does.
The first adjustable regulator i ever owned was one i built from a non-adjustable. It started as a 55psi regulator and i dont recall ever looking for the lowest number it would do but after trimming the spring and reassembling i ran it at 30psi to compensate for larger injectors.
As mentioned, the problem finding a stock regulator at that pressure is that most of them are built into TBIs and don't have convenient hose barbs sticking out of them.
Vigo wrote: That sure sounds like a fuel pump problem to me. Crimp off your return line (gently) with vise grips and see if the problem remains. If it does it's a supply problem.
That was my first thought too, but I've now tried two (brand new) pumps with significantly different flow capacities and get the same behavior. Only difference is that the one with the higher flow recovers faster when I let it drop back to idle. Besides, we're talking about running at just over idle sitting in the driveway - the engine's barely using any fuel, be it at idle or 1200rpm.
That's a good idea on the return line though, I'll double check.
Have you checked/watched voltage at the pump? Im being the dumbass here assuming its electric but not knowing diesels much it maybe mechanical?
I do second virgos ideas of taking a higher pressure regulator, taking it apart and trimming the spring until you get the psi you want. This is grm afterall. Or ebay adjustable unit for $20, because this is grm afterall
It sounds to me like the regulator has a pretty bad internal leak and is bypassing almost all of the fuel going to it. It has juuuuust enough of a restriction to make 15psi when there's no fuel demand from the engine.
chiodos wrote: Have you checked/watched voltage at the pump? Im being the dumbass here assuming its electric but not knowing diesels much it maybe mechanical?
Yeah, been watching voltage and current draw by the pump, they are rock solid whether it's running w/o the engine on, engine idling, or engine running above idle. And given the pressure I'm running, the current draw is right on the nose w/ the spec I have for the pump. So I'm inclined to think the pump is fine.
Knurled wrote: It sounds to me like the regulator has a pretty bad internal leak and is bypassing almost all of the fuel going to it. It has juuuuust enough of a restriction to make 15psi when there's no fuel demand from the engine.
I'm thinking the feedback mechanism (spring / diaphragm / whatever they use in this one) is kaput, and so whatever orifice size results when I adjust the pressure ends up being the orifice size regardless of fuel demand. I can set it to 20psi and I get the same behavior. I also have noticed that if I adjust the pressure with the pump running but the engine off, I instantly lose about 1psi when the engine is idling. And then the more gas the engine uses, the more pressure it loses.
Sounds like a flow rate issue more than a pressure issue.
Have you pulled the pump outlet line and checked to see how much flow it has? If it's low, try the same test with the inlet connected to a hose in a portable gas can to see if it improves.
There may be something restricting the flow into or out of the pump. If the fuel is restricted getting to the pump, there is nothing you can do on the outlet side that will fix it.
One possible culprit is the screen on the tank pickup. You can try clearing with compressed air blowing back into the tank.
Pressure and flow in the fuel system are interconnected. Some people think that a pump can make adequate pressure but not have enough volume, and that because of that a fuel pressure gauge is an incomplete picture. The pressure gauge DOES tell you if you have sufficient volume, but only if you're looking at it under the circumstances where the symptom occurs.
Most of the time the pump is flowing more than the engine uses. When you look at a pressure gauge, you're seeing that the pump is able to move the volume the engine requires (or more) at X psi. At idle the volume it has to flow at X psi is low. As your fuel requirements increase, the pressure gauge is showing that the pump can flow that larger volume at X psi. Once the pump falls even a little bit short of the volume requirement, the pressure will start falling on the gauge. At that point there is NO excess going out the regulator to your return line.
So the pressure gauge DOES show you whether you have adequate volume because as soon as you don't, pressure drops. The problem most people have is that they only look at fuel pressure at idle and not under high rpm&load where the fuel requirements are greatest.
jstand wrote: Sounds like a flow rate issue more than a pressure issue. Have you pulled the pump outlet line and checked to see how much flow it has? If it's low, try the same test with the inlet connected to a hose in a portable gas can to see if it improves.
Crap. It's this. Ran the pump outlet to a "calibrated" 5 gal bucket and it spat out like 40% of what I expected. Pulled the input line, ran a separate line from the pump directly into the fuel tank via the filler neck, repeated the test, and output went to about what it's supposed to be. Put the pre-filter back in, got about the same result. Ran the truck in the driveway like this, and saw a very minimal drop in psi between idle and holding at 2000rpm.
So the fuel pickup is hosed, which means dropping the tank. Again. Apparently I screwed up the install of the new and improved pickup 
I think the 80's Ford truck stuff used an external fuel pump around 15psi. Look at like an '85 E250 van or something.
Sounds like we helped. You'll have it fixed quicker now than if you spent time and money with regulator stuff.
Well, spent all day yesterday wrestling with this and things are better, but not fixed. As mentioned, somehow the fuel pickup was not working right when I ran the pump output to a calibrated bucket. I gradually started disassembling, testing, and reassembling to figure out where the problem was and it did seem like the fuel pickup tube was somehow not aligned properly. So as I was putting it back together, I continued to test along the way and things seemed okay - idling in the driveway it would hold pressure fine, and I could hold the throttle down to 1500 or 2000 rpm and it would drop a little, but hold steady. Same psi at both 1500 and 2000 rpm.
So, took it for a test drive and similar symptoms gradually returned - I could pull it down to basically 0 psi, and even if I sat there idling, it wouldn't come back up, at least not with any sort of speed. My last guess was the new filler cap (which was a separate debacle) wasn't letting in any air and a vacuum was developing in the tank, so I took it out this morning w/ the cap off and no real change. Maybe a hair better, but not much. I'm really completely stumped at this point.
Is there a sock on the end of the pickup?
Any chance the sock is collapsing or being pressed against something in the bottom of the tank that is cause it to restrict flow.
Nope, just a plain old stiff plastic tube w/ an angle cut on the end.
I'd use some compressed air (low pressure) to see if the line between the pump and tank is blocked.
If you let it sit for a while without running, will it do back to working correctly (at least for a short time)?
My next step would be to check the lines and see if any are getting pinched or have sharp bends.
They may not be closed off completely, but the draw from the pump may gradually cause them to collapse until the restrict flow enough to cause problems.
If the rubber lines between the tank and pump haven't been replaced, it might be a good idea to change them. They could be collapsing internally under vacuum cause the gradual restriction.
I'd recommend testing with the tank lowered to see if you get any pressure drop, and then test with it raised into place before securing the straps.
That way all the lines are visible and you can see if it's a problem with the actual lines/pickup or if the problem shows up due to routing of the lines.
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