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SES always on - no codes other then 12

I am having trouble understanding something.

If the gauge is on the fuel line, before it goes through the regulator, how does it measure the pressure that is getting to the injectors. It seems to me that it is measuring pump pressure.

Or does the filter remove pump pressure from the equation.

Don't I want to measure the pressure after the regulator ?


Or, is the gauge installed on the return line ?

But, if it is on the return line, which just pours back into the tank,

after polishing it, :waytogo:, doesn't the pressure get eliminated since there is nothing to push against when it goes back to the tank ?

While I will still install this stuff I would like to understand how it does what it does.



Also, should I change the name of this tread to something like: Discussion on fuel pressure, regulators and gauges ?
 
The pressure upstream of the regulator is the pressure going into the injectors. If hte regulator wasn't there, and was essentially an open valve, no pressure would really be created in the feed lines.


The return line is essentially a dump back into the tank. No real restriction on flow equals no measurable pressure.
 
dhcomp said:
The pressure upstream of the regulator is the pressure going into the injectors. If hte regulator wasn't there, and was essentially an open valve, no pressure would really be created in the feed lines.
Click to expand...

Exactly my point. The fitting for the gauge, I believe since I have only seen pictures so far, is on the fuel line before it enters the throttle body. It goes through the pressure regulator after the gauge fitting, so how does it actually measure the pressure going to the injectors.
 
Without restriction at the regulator, there would be almost no pressure. It would flow right through the lines back into the tank. Anywhere between the tank and the throttle body inlet connector should be the same pressure. The pump doesn't generate enough flow to create pressure without the regulator acting as a restriction.

The "high" pressure in the fuel line is why GM went to specific fittings for EFI, and not just flare fittings like what was used in carbed applications.

I suppose before/after the fuel filter might show some drop if there was a problem there but that's not something to be concerned with normally.
 
So it is the "back" pressure caused by adjustment of the spring in the regulator that creates the pressure that is being measured ?

It's confusing to me, but I will take your word for it that it works.


Also, since I bought a 3 foot steel braided hose how do you rig it up to be able to see the gauge through the windshield ?

I saw that Royken mounted it to his hood but I want a temporary set up. Do you run it through the top of the firewall and then through the grill in front of the windshield ?
 
Last edited:
THEMCGUIRE said:
So it is the "back" pressure caused by adjustment of the spring in the regulator that creates the pressure that is being measured ?
Click to expand...

Yes

THEMCGUIRE said:
Also, since I bought a 3 foot steel braided hose how do you rig it up to be able to see the gauge through the windshield ?

I saw that Royken mounted it to his hood but I want a temporary set up. Do you run it through the top of the firewall and then through the grill in front of the windshield ?
Click to expand...

Most just run the house out the back of the hood (most have a pretty big gap), and zip tie the gauge to a wiper.
 
Thanks everyone for your help...

I received the adjustable pressure regulator today. But I don't have the permanent gauge adapter, gauge and hose yet.

Will get on it as soon as they arrive.
 
I got all the parts today.

The adapter for the fuel pressure gauge has a Schroeder valve on it.

I do not see anything that will push on this valve to allow fuel to reach the gauge. Am I missing something ?


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Also are pics of bottom of new gauge, and OLD fuel pressure regulator cover. Is this last one stock. The hole for the regulator screw was already drilled out. You can tell it was drilled.

Your thoughts.

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Stock. Can't really tell from the pics, but if the blob of weld at the bottom of the FPR "cup" where the adjustment takes place, is not there, then yes someone has modified it.

Can't help on the Schrader valve, if threads aren't the same on both fittings, going to have to adapt. Although you might just be able to remove the schrader valve and put the right fitting in there?
 
The blob is present. Ok so we think this is stock. Wonder why someone drilled out where the new adjuster screw goes.

I am going to just try to screw the hose onto the Schroeder valve and see what happens. Maybe it is pressing it and I am guessing wrong.

Will advise.


Thanks
 
Attached are picture of the TBI with the injectors and pressure regulator removed. I cannot see how to fit this adapter in there. When I went to the book that came with the auto zone loan a tool test kit they show the adapter being installed between the front of the fuel filter and the fuel line going to the TBI.

Take a look at the pic's and let me know if you agree that there is no way that this adapter can fit between the tbi and the coil.

DSCN0087[2].JPG

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DSCN0083[1].JPG
 
I've heard this is a bear to get in there. The lines should be clamped to the back of the motor so not real flexible at that end.

Are you planning to leave it, or just for testing? As I said earlier, I think it's better to connect where the hard line from the frame meets the flexible line from the motor if testing. But that's assuming you've got enough length to do what you want to do with it. I'd not like that for a "permanent" solution.
 
DO NOT USE that adapter as a permanent installation! It may leak. It is what I use as a temporary gauge!

I recommended the fuel pressure gauge adapter from CFM tech as it is designed for permanent installation!
 
Thanks for the advise.

I could not find any way to get that adapter in that small space. My hands ache from trying.

I gave up and put it back together. I also installed that fat "Y" shaped lifter that is supposed to give 15 HP.

That also needed some minor work to get it in place. The holes were just slightly off and needed a little work to enlarge the screw holes to allow the screws to drop into the holes.

I installed the gauge adapter between the filter and the TB. I will test it tomorrow as it was dark by the time I finished today.

Will it give an accurate reading where I installed it ?
 
I installed the following:

AC DELCO OE SERVICE EP241 Electric Fuel Pump

CFM-Tech Injector Spacer for GM Tbi 4.3/5.0/5.7

CFM-Tech Adjustable Fuel PSI Regulator for GM TBI 2.8/4.3/5.0/5.7/7.4

I used a tbi rebuild kit to replace all the o-rings and gaskets.

I put the gauge from auto zone on. Started the truck. This is a 100 psi gauge. Reads 15 psi, (exactly in between the 14 and 16 psi marks) steady as a rock no variation at all.

When I installed the adjustable regulator I just turned the knob until I felt the slightest of pressure. I believe it is just touching the cap the is installed inside the spring.

I suspect that the cap has compressed the spring a tiny bit.

But 15 psi is too much, correct ?

Doesn't turning the knob increase the pressure ?

So how do I lower the pressure...
 
Don't know how the AFPR's work, but assuming it's the same principle, backing off tension on the spring should drop pressure.
 
I did not put any pressure. Like I said earilier, it is just touching.

Also... Just took it for a 4 mile ride. Same issue with unsteady acceleration.

I mean it goes but acceleration feels slow. I dont have that being pressed back into my seat feeling that I used to have...

there is this deep octave "th th th th th th th th" sound when I press on the gas.

(lol best I can do to convert sound into letters)


I checked the EGR as well. I can move it in and it returns quickly.

Any ideas ?
 
I'll have to let someone else answer about the pressure. 15PSI seems pretty high to me (15% over stock max) but I'd imagine if pressure was the base issue, the problem would be consistent, resulting in something like a bog on acceleration that lasted until you reached a certain RPM, not unsteady.
 
I'd bet the gauge is off! Your using a 0-100 scale for a very low 15 PSI and it's close. If it were a 0-15 scale it would be more accurate.

This is only the 100th time I've seen gauges off at low pressure.

Plus with no tension it should not be that high.

Turn pressure up to 18 and see how it does.
 
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