When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
The 3 PSI from the low in tank pumps may be good as it is not really PSI but the flow per hour needed to keep the bowl full.
Holleys can take a little higher PSI than the Eldel as when they get up to the 3 and over PSI the carb will flood as the needle / seat cant take it.
I think I would give the factory pumps a try and see what happens.
If worst comes to worst put a "booster" pump in place of the factory high PSI pump, using the in tank pumps as lift pumps like the factory had them.
Just my .02
Dave ----
When I tested the pressure of my truck's two in-tank pumps they were thirty-five years old. Both pumped at 3 psi.
Homemade inline test gauge.
What the he 🏒🏒 is that!? What is keeping the majority of the fuel and pressure from going straight and bypassing your teed in gauge? Put the gauge inline or at the schrader valve where it belongs.
What the he 🏒🏒 is that!? What is keeping the majority of the fuel and pressure from going straight and bypassing your teed in gauge? Put the gauge inline or at the schrader valve where it belongs.
The problem checking at the valve just before the injectors is do you know if it is 1 of the in tank low PSI lift pumps, dual tanks, or the high PSI frame mounted pump or the FPR?
What if the fuel PSI is low at the valve how would you know if it was a lift pump, plugged filter or bad FPR?
This you would use in line after the lift pumps and before anything else as the lift pumps should show a PSI before the high PSI pump or filter.
I have a John Deere Garden tractor with a EFI water cooled engine and I was having a surge problem when it got hot, only half the yard was cut.
The service book has the test port at the end of the system and no way to know if the in tank fuel pump was failing or the FPR before the injector.
I talked to JD service on how to check and he said take a old fuel filter, it has EFI fittings, and cut them off and make a Tee gauge set up like above and put it where the fuel filter is with a long hose so I can see the gauge when driving the tractor.
Well when it started to surge the fuel PSI would jump all over and then start to drop till the motor shut off. Let the tractor cool and it would start and run to finish the grass.
It was the fuel pump as it got hot it would stop pumping and I would have never known if it was the pump or the FPR from where they wanted you to test at.
So that Tee he made dose the same thing checks the fuel PSI at the beginning not the end.
Dave ----
When I tested the pressure of my truck's two in-tank pumps they were thirty-five years old. Both pumped at 3 psi.
Homemade inline test gauge.
IMHO, you will need to eliminate the ECM control of the fuel system. There are four wires at the fuel pump relay. The on/off is controlled by the ECM. The red is power from the ECM. The tan/ lt green is the ground.
The plan: Disconnect both from the relay leaving the yellow and the pink as is. Ground the terminal on the relay that the tan/lt green wire was plugged onto. Run a wire from ignition on circuit to terminal the red was plugged onto. This will trigger the pumps power when the key is turned to on.
Remove the high pressure frame rail pump and replace with a suitable electric carb pressure pump. Edelbrock and Holly make them. Use existing wiring.
Leave the rest of the fuel system as is.
I believe there is no way your truck's ECM is going to run the existing fuel system or the TFI ignition now that a portion of the EFI components are deleted.
Edit: I forgot to address the FPR and return. The FPR left with the EFI stuff. I think the carb fuel pumps are designed for 5 to 7 psi so no regulator would be necessary. Just dead head the fuel line from the new lo pressure rail pump to the carb. In which case you would plug the return FROM fuel rail at the Dual Function Reservoir. Or keep it with a regulator after the carb if needed.
The original high pressure frame rail pump (capable of up to 100 psi head) would probably work with a regulator throttled back to 7 psi (or what the carb manufacturer specifies)
Another edit: The fuel gauges draw power from separate ignition on circuit.
Your 3 psi test; Was that with the pumps dead-headed? And it did not sound like they wanted to stall out? If so, he should be fine just running those pumps to the carb like you said.
Your 3 psi test; Was that with the pumps dead-headed? And it did not sound like they wanted to stall out? If so, he should be fine just running those pumps to the carb like you said.
Drawing on memory from five years ago.
That test was with the entire system configured as intended. High pressure pump not running, engine not running. Dual Function Reservoir operating as it should.
From the archive.
I wanted to know what the tank pump pressures were and if the two pumps were equal. Gauge read 3 psi.
Another test I did on only one pump was to submerge it in gasoline and observe the flow. Off hand I thought the mediocre flow was sufficient. I should have measured it but did not. Unreliable memory of the flow rate I would guess at least a liter per minute. Maybe three times that.
The overall purpose of the testing was to make an informed decision as to whether I should replace the pumps during my 2020 rebuild. I didn't . I am running the original pumps to this day. Test tool was hose clamped to the Dual Function Reservoir's fuel supply nipple. Plain end simply inserted into the fuel supply line connector.
The problem checking at the valve just before the injectors is do you know if it is 1 of the in tank low PSI lift pumps, dual tanks, or the high PSI frame mounted pump or the FPR?
So that Tee he made dose the same thing checks the fuel PSI at the beginning not the end.
Dave ----
That would depend on the pressure shown at the rail. You aren’t going to get 20 something psi from the in-tank pump but you will from a weak high pressure pump. What do you mean by “dual tanks?” Only the selected in-tank pump operates. The other pump is off. If it runs better on one tank than the other chances are the pump in the tank isn’t keeping the DFR full.
I don’t see how the homemade tester does that.
Originally Posted by Franklin2
Your 3 psi test; Was that with the pumps dead-headed? And it did not sound like they wanted to stall out? If so, he should be fine just running those pumps to the carb like you said.
That would depend on the pressure shown at the rail. You aren’t going to get 20 something psi from the in-tank pump but you will from a weak high pressure pump. What do you mean by “dual tanks?” Only the selected in-tank pump operates. The other pump is off. If it runs better on one tank than the other chances are the pump in the tank isn’t keeping the DFR full.
I don’t see how the homemade tester does that.
I would do this ^^^
Ok you test at the rail at the test port and you have low PSI how do you know if it is a non-working in tank low PSI pump not supplying to the high PSI pump or the high PSI pump going bad or the FPR that is bad?
It can be any 1 or them or even all of them but without testing each item you would never know.
What Digger made test the low PSI pump(s) and nothing else and it is at the beginning of the fuel system not the end.
I said "tanks" because you need to test each tank on a dual tank truck that I think Digger has.
But who am I to tell you how to test the fuel system on your EFI truck, test at the end and tell me what part is bad
Oh I also said that the 3 PSI may be good to use with a carb. The only limiting factor is at 3 PSI what is the flow rate?
If the carb need say 10 gallons and hour under full load and the 3 PSI pump only flows say 7 gallons an hour there may be a problem as the 10 GPH is under FULL LOAD and how often & long are you under FULL LOAD?
Dave ----
From the above it looks like we still do not know the characteristics of the factory tank lift pumps. I do know their job was to solely keep the reservoir/filter assembly mounted on the frame full. So when that was full the fuel most likely free-flowed back to the tank. So we do not know if the factory in tank pumps have a internal fuel pressure regulator, and if they did what that value would be.
From the above it looks like we still do not know the characteristics of the factory tank lift pumps. I do know their job was to solely keep the reservoir/filter assembly mounted on the frame full. So when that was full the fuel most likely free-flowed back to the tank. So we do not know if the factory in tank pumps have a internal fuel pressure regulator, and if they did what that value would be.
You know the only way to find out is dont you
Someone has to be "the first" so give it a try the worst is it will not work.
Maybe it will with a return regulator?
Will not know till tried.
Dave ----
you check pressure at the test port on the fuel rail. Note second paragraph in right column
Based on the test for the DFR: the in-tank pump must put out 3-5psi. See note 2….
step B1 of the high pressure pump test also shows low pressure pump output
low pressure flow/ volume test
Sure we do. The regulator is on the fuel rail. There are a few threads on the ‘87-96 forum where it has been mentioned to momentarily deadhead the pump to check for max pressure see if the pump is getting weak.
EDIT: deadhead test is mentioned for ‘90 and newer fuel systems with high pressure pump in the tank.
Alright so after finally getting some free time and the ability to work on this little idea I have due to y'all informing me that the pump in-tank should be fine, I somehow have a question I didn't know I would have to ask. How exactly am I getting fuel from the return line? I have bypassed the high pressure pump and am now somehow getting fuel from the white fuel line, which I believed was the return line but maybe not. Could it just be because the truck isn't actually on and so the fuel selector is just letting fuel go through the return or is the whole thing shot?
Where are you getting fuel from the return line and going to where? I don’t know because I don’t have any white fuel lines. They are all black nylon on my ‘87 & ‘89 trucks. I’m not sure what you’re looking at- the regulator restricts fuel flow. The reservoir on the frame rail only supplies a path for fuel to and from the engine.
Where are you getting fuel from the return line and going to where? I don’t know because I don’t have any white fuel lines. They are all black nylon on my ‘87 & ‘89 trucks. I’m not sure what you’re looking at- the regulator restricts fuel flow. The reservoir on the frame rail only supplies a path for fuel to and from the engine.
I got my fuel line from after where the two pumps collect on the frame rail, like right under the driver seat-ish. I snipped the lines on each side of the high pressure pump, used a connector piece that looks like a barb piece (not sure what the actual name for it is) and connected the two with some fuel line.
The light gray line is the return to the reservoir and tank.
I may have missed something, if you have a carb installed, why do you have the return line in the loop ? I posted photo's just so people can understand the EFI trucks.
If the carb is getting fuel from a low pressure pump, the float in the carb should shut off the incoming supply as needed. So, I assume there is no need for a return hose...?
The light gray line is the return to the reservoir and tank.
I may have missed something, if you have a carb installed, why do you have the return line in the loop ? I posted photo's just so people can understand the EFI trucks.
If the carb is getting fuel from a low pressure pump, the float in the carb should shut off the incoming supply as needed. So, I assume there is no need for a return hose...?
I'm converting it from EFI to carb. I figured that while I'm working to get everything in order, it shouldn't have fuel moving through there so I haven't removed it yet. When I had the high pressure connected, it flowed correctly, but now it isn't.
