2UZ fuel path/flow (1 Viewer)

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woytovich

woytovich

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In my quest to get my 2UZ running stand alone (with aftermarket ECU and harness) I have hooked up a 255lph fuel pump and aftermarket OEM style filter. The pump is pumping. I know this because when I disconnected the output of the filter I got a spray of gasoline (!).

I am wondering what the expected behavior of the pump and fuel system should be... In my case when I turn the ignition power to ON the pump turns on for a few seconds then turns off. When I crank the engine it cranks but does not try to start and no fuel comes out of the return fuel line.

What is supposed to happen?
 
What makes you think the cylinders are getting no fuel? Did you pull a plug and smell none? Check pressure at the rail?
 
The second it's hot it should be returning.
The second it's hot you should see 40psi if using the stock regulator.

Where it's probably messy is the crank and hold of the starter until it times out.
Comparing old uzfe to late model.
I think it's common knowledge that fuel will not pump until the crank is turning.

But there's a lot going on to get to that point.
Pre 2003 guys are going to be more in tune with the sequence of those years.
I'd get the book.
 
No. I meant that the fuel pump will not get power until the crank sensor is reading.
There is no stock, fuel pump is turning, with the key in the start position.
 
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With the Spitronics ECU I am using the pump "primes" when the key is turned to the run position (like my Holley Sniper does in my 60). It runs for a couple of seconds then stops. Then when I crank the starter no fuel comes back out of the return line.

I'm thinking many a bad dampener, regulator or a clog int he fuel lines/rain?
 
sounds like something is interrupting the pump when it should be doing the opposite. Does the manual say anything about
what exactly happens when the signal to the pump is shut off after that couple of seconds to prime?

Something interrupts it correct? It's either the sip, or the stock fuse box/relays.
Which manual is it from here? Downloads - Spitronics Support


if it pumps and you get a return the damper is probably fine, same with regulator. There isn't much to those to break, just leak though the diaphram. Or through the crush gaskets. If it works to prime it should work fine. if you continually get the priming the pump operation to occure then I'd think it almost has to be fine.
MAybe you should put a tee in the AN fittings at the filter with a 1/8" npt port for a gauge and then an NPT cap when you remove it.
MAybe your ecu has an input for a electric pressure sensor?

I guess you have the return line open to see when and if it's pumping so you know for a fact it isn't when the starter is turning.
IF you wanted to see it run you could hotwire the walbro to another battery or your own battery with a switch, unplugging it from the sip.





I don't know if the 2004 and < had the fuel pump resistor control/driver. IF it did I'd try to eliminate it. I don't know how that plays with the sip.

it almost has to be the stock wiring/relay set up.
IS there any feedback loop to the sip that would hamper a standalone pump/ relay / switch set up on the dash?
Tell me which ecu it is, I'm no expert but I can read it at least.
The lexus wiring diagram books have more info in them that the LC versions of the same year. Which is helpful sometimes.
I don't know how much money/time I'd spend on books and fittings and gauges, etc when it might be easier to wire in something for almost nothing.
90% sure the damper and reg are fine. I wouldn't just buy those two items without proof.
I think local auto stores have a pressure tester kit as a loner. Other ideas for a gauge- both banjo bolts on the front crossover pipe, both rails have end caps with enough room for another fitting/ gauge.
A tee on your AN fitting.

what about the theft ECU?
do you know if the injectors are firing?
 
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Engine is not in a truck, running only with the Spitronics.

The stock ECU is not int he picture, only The Spitronics Mercury2 ECU so no fuel pump resistor control/driver. I will reach out to my contact at Spitronics to see if he has a suggestion.

Yes, the return is ope.

With fuel disconnected should I be able to blow air through the fuel rail? (to check for obstruction)

I'll check for power at the pump during "start"... maybe power is getting cut - if so I need to figure out why. I might also try direct wire the pump to keep it running instead of prime/stop.
 
I think you could blow through, maybe not from the filter to rail, but damper to regulator maybe. Talking about less that 5psi gauge.
directly powering the pump and letting it flow for a while wont hurt it, being it's an outside the tank pump anyway.
that should be your obstruction test.
That's the way I'd go.
You do see a fairly impressive amount of flow correct? when it's actually flowing? IF that few seconds gets a volume inline with what walbro predicts I would think there isn't an obstruction.
 
I'm not seeing "flow" per se, I did see built up pressure when I disconnected the filter from the fuel rail input hose.

My contact at Spitronics is also suggesting checking pressure. He says the regulator will only open at about 42psi and THEN fuel would flow back to the return line.
He also confirmed that the ECU will "prime" the pump when the key is in "run" then turn off until cranking.
 
I saw mention of the priming in those pdfs.
based on what he said I'd run the pump hardwired and watch the return. Even without a gauge.
As long as there is liquid in the rails, lines, filter etc. It's going to be at operating pressure in an instant. Any stray air bubbles get pushed out very quickly. I've watched that happen on my 2006 with both walbro and stock.
If there is not an almost instant return of serious amounts of fuel you'd be right to suspect an obstruction.
if you feel like pulling a vacuum on the reference line to the regulator you can mimic top volume flow back to the tank.
 
no it will let fuel pass at a point determined by the spring. it is in fact a non return valve, spring operated.

non return subjected to injector leaks, washers and seals, fitting leaks, etc.
You could systematically eliminate air slugs from lines, filter, damper, rails, regulator, if needed.
If you want to check flow, crack open the crossover pipe at the front of the intake. Also you could crack open the end plugs on both sides of the rail (front end)
IF you see flow there, and it will spray pretty good, then assume it's fine. If you don't have return from the line after the regulator assume pressure spec is weak, bad regulator, obstruction.

the most volume that goes back to the tank while its running is at idle. Reference pulls on the spring, hole opens widest, most fuel is returned.

Id say at this point, you might need a gauge
 
I'll do the down and dirty "flow past the regulator" check first. This has been out of a truck and not running for >10 years so it certainly would be possible for a clog (spiders!) or a stuck regulator (maybe time for a gentle tap with a small hammer!).
Then on to a gauge to check the pump.
 
Don't know anything specifically about that ECU but I had similar symptoms with megasquirt ECUs and it was either that the "run" thresholds for RPM, vacuum, etc weren't reached so it never thought it was actually running yet.

Second issue I once ran into was an immobilizer was set in the ECU that would cut the fuel pump after a few seconds.

This isn't really a 2UZ issue just an issue with your standalone ECU.
 
UPDATE: I got fuel to flow. A few taps on the pressure dampener and it started up. YEA!
The engine still is not starting.
Is it possible that the regulator is stuck open not allowing pressure to build? (I have not pressure tested yet)
 
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