1HD-FTE Losing Prime When Parked

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Hi Everyone,

I recently installed a 1HD-FTE in my FZJ100 and I noticed that I lose fuel prime within minutes of the motor turning off. Funny enough, it needs the same number of hand pumps no matter how long it sits, 5 minutes or 12 hours, everytime it's around 5-6 pumps until the primer stiffens up.

Here are the new parts that I bought, honestly I'm completely stumped.

New OEM Primer w/ new heater and water trap
New 12mm OEM Hoses (yes I'm that kind of crazy)
New 12mm Main Fuel Line
New main and sub tank fuel pickups
New sub tank solenoids
New return fuel damper

The only thing that isn't new is the return fuel line which I had to make myself... I'm wondering if that has some air leaks.

Does anyone know if air getting into the return fuel line can cause loss of prime? I'm completely confused with all these new parts, I'm totally baffled. Any recommendations to diagnose this would be amazing.
 

mudgudgeon

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I don't think a leak in the return line will cause you to lose prime in the pump.

More likely you have a leak in the supply line somewhere between tank and pump.

Could be simply a leaking o ring on the fuel filter. Or a bad copper gasket on a banjo fitting on the pump.

Are all hose clamps tight?
 
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I don't think a leak in the return line will cause you to lose prime in the pump.

More likely you have a leak in the supply line somewhere between tank and pump.

Could be simply a leaking o ring on the fuel filter. Or a bad copper gasket on a banjo fitting on the pump.

Are all hose clamps tight?

Is it possible to have air leaks but no diesel leaks though? I might pull the banjo on the pump as well.

All clamps are tight and OEM hoses and OEM clamps so everything is to spec and tight...
 

mudgudgeon

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Is it possible to have air leaks but no diesel leaks though?

Yes absolutely.

There's loads of threads about people having fuelling issues. Very commonly no visible fuel leak, but air will be finding is way in somewhere through a split hose, loose hose clamp, poorly seated o-ring, loose fitted fuel filter or filter drain tap, perished diaphragm in the primer pump etc

When the engine is running, the supply line is under vacuum. If there's a small leak, air gets in, fuel may not get out.
If there's enough of a leak to break the vacuum in the supply line before the IP, fuel bleeds back to the tank due to gravity. It is usually reported that fuel bleeds back over night. If you have it happening in minutes, you definitely have air getting in somewhere IMO
 
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Yes absolutely.

There's loads of threads about people having fuelling issues. Very commonly no visible fuel leak, but air will be finding is way in somewhere through a split hose, loose hose clamp, poorly seated o-ring, loose fitted fuel filter or filter drain tap, perished diaphragm in the primer pump etc

When the engine is running, the supply line is under vacuum. If there's a small leak, air gets in, fuel may not get out.
If there's enough of a leak to break the vacuum in the supply line before the IP, fuel bleeds back to the tank due to gravity. It is usually reported that fuel bleeds back over night. If you have it happening in minutes, you definitely have air getting in somewhere IMO

So confirmed the fuel is not returning to the tank via main fuel line. When it loses prime, fuel is going back to the tank via return line. This is super confusing to me…
 

mudgudgeon

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So confirmed the fuel is not returning to the tank via main fuel line. When it loses prime, fuel is going back to the tank via return line. This is super confusing to me…

Interesting :hmm:

Is your fuel tank vent clear and functional?

Wondering if you're getting a vacuum in the tank and it's pulling fuel back?

Try running it with the fuel cap off and see if you get the same result
 
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Interesting :hmm:

Is your fuel tank vent clear and functional?

Wondering if you're getting a vacuum in the tank and it's pulling fuel back?

Try running it with the fuel cap off and see if you get the same result

We actually discovered this by putting the return hose in a bottle and as we primed the system it was continuously spilling diesel in to the bottle through the return hose. So we eliminated any issues with the tank
 

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Vaccum leak.
Imagine sucking a beer through a straw with a hole in the straw.
As stated above check all of your previous work.
Try the clear hose method.
 
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No one has been able to give me a straight answer - what specifically would cause loss of prime through the RETURN line and not the MAIN line. Like this should pinpoint where a vacuum leak would be located but it isn't obvious to me, especially since there's a check valve on the fitting from the pump to the return hose.
 

bottombracket

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Switching solenoids hooked up correctly?
 
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Switching solenoids hooked up correctly?

Yup. We eliminated the tank and anything upstream as the issue - we put the inlet hose into a bottle of diesel that supplies the primer and it behaved the same. Also when the return hose is disconnected, it just continuously pours out diesel from the pump.
 

mudgudgeon

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Is the check valve functioning correctly?
Yup I checked that. The spring seems pretty soft, not sure what it’s supposed to be like.

Update: replaced hand pump primer and no change, checked vacuum on the return line on injectors and it’s solid. Literally the only thing it could be coming from is the fuel pump. Checked the gaskets on the fuel inlet and fuel return, all checked out.

I officially have zero clue. Can the fuel pump on the motor cause this issue?
 

mudgudgeon

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You haven't said that you've used a clear hose to diagnose air in the lines?

New hoses, filter, o-rings, copper washers on banjo bolts etc all deserve to be treated with suspicion until you verify the parts and connections are all good.

A clear hose BEFORE the filter will tell you if there's an air leak between tank and primer. A clear hose AFTER the filter will tell you if there's a leak in the filter or primer assembly.
No air bubbles anywhere after this test only leaves the final banjo bolts at the pump, or the pump itself.


I think an air leak in the supply side could potentially allow fuel to syphon back via the return line.

I'm not sure the check valve is gonna be a problem. If it's on the return line, it's got to allow fuel to flow back to the tank.

Same with the injector pump. Once residual pressure bleeds off, if the supply line is sealed, any fuel draining back will create a vacuum in the lines stopping fuel bleeding back.
 
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You haven't said that you've used a clear hose to diagnose air in the lines?

New hoses, filter, o-rings, copper washers on banjo bolts etc all deserve to be treated with suspicion until you verify the parts and connections are all good.

A clear hose BEFORE the filter will tell you if there's an air leak between tank and primer. A clear hose AFTER the filter will tell you if there's a leak in the filter or primer assembly.
No air bubbles anywhere after this test only leaves the final banjo bolts at the pump, or the pump itself.


I think an air leak in the supply side could potentially allow fuel to syphon back via the return line.

I'm not sure the check valve is gonna be a problem. If it's on the return line, it's got to allow fuel to flow back to the tank.

Same with the injector pump. Once residual pressure bleeds off, if the supply line is sealed, any fuel draining back will create a vacuum in the lines stopping fuel bleeding back.

Yup I've done the clear hose.

Basically what happens is fuel prime stays SOLID upstream of the prime pump.

Downstream, going to the IP, the fuel depletes and exits through the return line. The primer is good and so is the hose (it's OEM Toyota 12mm hose lol).

So I'm pretty sure it's the IP. Perhaps the HDJ101 that the motor came from had an issue and that's why it got parted out... maybe the previous owner got a giant quote to fix the truck and decided to sell it to a wrecker. Who knows.

Have you heard of prime issues from IP? I've confirmed the copper connections are good by removing them and inspecting, so that leaves gaskets and o-rings....
 

mudgudgeon

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Yup I've done the clear hose.

Basically what happens is fuel prime stays SOLID upstream of the prime pump.

Downstream, going to the IP, the fuel depletes and exits through the return line. The primer is good and so is the hose (it's OEM Toyota 12mm hose lol).

So I'm pretty sure it's the IP. Perhaps the HDJ101 that the motor came from had an issue and that's why it got parted out... maybe the previous owner got a giant quote to fix the truck and decided to sell it to a wrecker. Who knows.

Have you heard of prime issues from IP? I've confirmed the copper connections are good by removing them and inspecting, so that leaves gaskets and o-rings....

Sounds like by process of elimination, you're left with the pump. Unless you've overlooked something simple

I don't know enough about the differences between the fully mechanical HD-T/HD-FT/HZ pump and the electronic HD-FTE pumps.

I do know HD-FTE pumps often have an issue with the spill control valve and associated electronics.

No idea if this may be related, but may give you something to search up
 
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mudgudgeon

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I've confirmed the copper connections are good by removing them and inspecting

You may already know, but another level of checking and testing is to anneal the copper o-rings.
If they are in good condition, copper o-rings can be rejuvenated by heating to cherry red with a torch, and allowing them to air cool.
This softens the copper and you'll more reliably get a complete seal.
Copper washers work harden when they are tightened down. For this reason they are considered single use. Annealing let's you reuse. Or buy new ones for $0.20c each
 
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I would guess it is either a air bubble caught in the line (bleed the system closed to eliminate air like you would bleeding an injector) or possibly it is the diaphram inside the pump. I had a '96 Ford diesel that did the same thing, I replaced the pump and fixed it. It also had a splitter on top of the engine that fed the fuel pump filter housing and then to the injector pump. It was leaking air in at the fitting which is on top the engine so no fuel would leak out but that didn't fix it. Is your return lines from the injectors leaking at any of the the injectors ?
 
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A couple of thoughts Nick - what are your symptoms apart from loss of prime? Hard starting? Rough running? I’m not guaranteeing, but could the “loss of prime” be a red herring? The primer pump never stays hard, my fte takes a few pumps (just tried it cold - took 10 after its been sitting for a week but I know it’s start straight up), I’ll try it straight at the I’ve turned it off next time but it always takes a few - even my brand new VDJ79 takes 3 pumps straight after shutting down. The fuel should always leak back through the return line - the check valve in the pump keeps the low pressure delivery side at a certain pressure (probably around 2-6psi at a guess), and the primer pump must be able to produce more than this so it will always be able to cycle fuel through it and it must escape via the check valve after running or pumping. Try another Toyota diesel and see if it does the same - at a guess it will behave the same.

If loss of prime through the IP is really the issue - a simple replacement of the check valve is all that would be needed. I’ve done it a few times on big truck pumps and it’s a pretty routine job. Admittedly it’s not something I’ve across with Toyotas or rotary pumps.

EDIT - just tried my HZJ75. 10 pumps cold (it always starts instantly), straight after shutting it down 8 pumps till it’s hard
 
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