Zd30 fuel issues help

[joshy]

G'day guys,

I've got on going fuel issues with my zd30 and I'm
Having trouble getting to the bottom of it. Will run fine for say 2 hours then starts running like a dog and will stall. Won't start again until I prime it. I have 2 lift pumps in the system and a surge tank, and they won't prime it when it dies. I think the primer is where it's sucking the air from, it was change by Nissan under warranty a few time because of hard starting.
So any chance when someone takes there nav for a drive today, say an hour or so, while its still running could you pump the primer and see if its hard or soft?

Thanks, josh

 

[tweak'e]

what lift pumps and surge tank do you have ?

if the lift pumps are not priming then you have a blockage in them or in the tank, or one pump is failing.
with a lift pump system it should not be able to suck air in. if there is a leak in the primer it should leak fuel.

 

[joshy]

Both lift pumps are working, flow out of the hose into the injector pump is huge. After the hour or two of running the motor will start fluctuating in revs and eventually stall out, no matter how long I run the lift pumps before cranking it won't start till I hand prime. Yesterday when the revs started fluctuating I jumped out n pumped the primer, soft as and came good for a little while.
I put the first lift pump in to try and find a fuel leak, couldn't find one, so then I fitted the surge tank thinkng it was sucking the air on big angles(which it was but now it doesn't happen so surge is workin correctly) but its still doing it.
I also thought my e stop on the injector pump power wire migt have been causing problems. Measured the resistance on it the other day and it was fine, doesn't bring up an engine fault either when it stalls out. Plus when I do e stop it, it will fire up first crank.

The primer use to suck air/drain back when it was still road going, use to have a hell of a time starting it in the morning if the car was facing downhill. I'm thinking its this problem again and might get another brand filter/primer and try that

 

[nakedape]

Try a cav filter/ primer - may be a waste of time but. Sounds like something is working loose when hot - maybe try swapping hoses & clamps etc.

 

[joshy]

That's what I was thinking, when the fuel starts to get hot it's opening something up enough to suck air in

 

[tweak'e]

really need to know details of the setup.

if you have a lift pump then the system should be under pressure and not able to suck air in. so it sounds like something is screwy with your setup to start with.

 

[joshy]

What details?

System flow is
Fuel cell - lift pump - surge tank - lift pump - filter/primer - injector pump - return fuel line - surge tank - fuel cell

Top of surge tank overflow runs into fuel cell, return hot fuel from pump is going into surge tank.

Fuel cell and surge tank are at rear of car, filter is pretty much in stock location.

Doesn't matter how long the lift pumps run there's no fuel leaks. Injector pump is under a year old, filter is a week old.

 

[tweak'e]

what lift pumps?

first problem i see straight off is fuel overheating due to no cooler on the return between IP and surge tank. you might be cooking the pump ecu.

 

[tweak'e]

last minute thought....
either first pump is sucking in air via loose connection including the one on the tank.
or that pump is failing or blocked and not suppling enough fuel and its sucking air via the return line.

 

[joshy]

Should I run the return into the fuel cell instead? Both facet electric pumps, won't be able tiger the specs till thurs.

 

[joshy]

Seems to always have really high flow whenever I check tho

 

[tweak'e]

afaik facet don't make any fuel pumps that flow enough.
ditch the surge tank and put both pumps in parallel and you might get enough flow.

with those pump you won't be getting any fuel pressure other than at idle. so it could suck air in anywhere. fit clear fuel lines and look for bubbles.

if you want to keep the surge tank what you could do is ditch the pump by the IP.
fit a fuel cooler between IP outlet and surge tank. surge tank after filter.
if you want fuel pressure fit a dead head regulator on the return to main tank.

 

[joshy]

If it was the pumps not having enough flow wouldn't it happen constantly, not after over an hour of driving? Ill have to check the specs on em but the flow looks like a few L/min.
Need the surge tank due to the angles...
Is a cooler necessary?, none from factory? My fuel cell is only 20l less.

 

[tweak'e]

all rotary fuel pumps use the fuel to cool the pumps. zd30 pump is especially so as it also houses an ecu. normally they use the fuel lines and tank volume as a heat sink.
if you drive with a lowish fuel tank for a fair while the tank is fairly warm.

i think its one of the bmw's that uses the same type of IP but they run a lift pump in the tank and a non return system. they have a fuel cooler with its own bonnet scoop to handle the heat.

with a surge tank your returning hot fuel from the pump to the surge tank so you will need some form of fuel cooling. your lift pump won't pump enough to the surge tank and back tp main tank to provide enough cooling.

what may be happening is your surge tank to IP lift pump isn't flowing enough so its under vacuum and its sucking air in somewhere along the line. more than likely the surge tank or filter is slowly filling with air which is why you have to prime it to get it going.

the IP flows around 200-300 lph so a 120 lph facet pump just won't cut it.
facet is ok for filling a surge tank but you need a much higher flow rate for the surge tank to IP pump. carter 72gph is a common one.

 

[joshy]

Thanks, makes sense.
I will try running the return into the fuel cell and just having the lift pump run into the surge tank

 

[joshy]

So I've now run both lift pumps into the surge tank and the surge tank goes straight into the primer pump.
Ran it for half an hour without drama will take it for a drive tomorrow but primer pump still felt softish while running, a lot softer then my mates 3.0 which goes hard after a pump or two

 

[tweak'e]

softish while running ?
it will be when running. should only go hard after engine has been stopped.

have you fitted any clear fuel line and looked for air bubbles?

how have you go the returns connected to the surge tank?

 

[joshy]

The other 3.0 went hard while running?
Haven't fitted the clear hose yet, wasn't able to find any the right diameter yest arvo. Return is in through the side of the surge tank still, was hoping running both lift pumps into the surge(two separate lines) would create enough movement between fuel cell and surge to get the hot fuel out.

 

[tweak'e]

ok now that i'm not half asleep....

so fuel system is now..... main tank- lift pump- surge tank- IP- surge tank- main tank.

with this arrangement you will not get any fuel pressure as the lift pumps pumps it through the surge tank and back to tank as there is no restriction to create pressure. so primer will be soft when running.
i guess your mate doesn't have the surge tank so the lift pump pumps direct to IP. that makes pressure (when the pump is flowing more than the IP) so primer will go hard when running.

 

[joshy]

Yeah that's correct on the flow, both lift pumps have seperate lines running from cell to surge.
Drove for about an hour and a half today and no problems so might be fixed.... Fingers crossed.
Thanks for your help.