Air In Fuel Line

Long story but I'm troubleshooting an occasional loss of power, with no codes. It sometimes stumbles at idle. I went to check my fuel pressure and when I disconnected the fuel line, some fuel and a lot of pressurized air came out. (BTW- fuel pressure was 42-ish running, it lost 2-3 psi after 5 minutes, continues to go down). My troubles "seem" to happen at below 1/2 tank (or about 1-1/2 hours towing a #3500 trailer). I thought that it might be a thermal thing but now I'm thinking its fuel related.

Just for a sanity check- air in the fuel line is not normal, right?

And, how does it get in there? I've got a pump on order. I'm supposing that it's sucking air somehow. Or, is it from compression gases through one or more injectors? (FSM says that if fuel pressure drops in 5 minutes it could be the fuel pump or injectors)

Air in the line can explain the stumble at idle too. When the pump slows (with the resistor in place) the fuel flow can't overcome the air in the line.

Thanks!

PS- I have changed the plugs (back to denso) from the ngk's that I put in 15k miles ago.

Only 65k miles on the clock.

 

I wouldn’t think it would be compression gases since our taco engines aren’t direct injection.

 

Air doesn't really make sense, the pump is submerged in fuel, and the injectors are in the manifold with less than atmospheric pressure.

I'd want to see fuel trims when the issue is happening. Also fuel pressure while its driving.

Lastly a fuel volume test, which with Toyotas doesn't have a spec, but it can show a lot.

 

My only thought is one of the lines, in the tank, that run from (feed) or to (return) the pump itself, are split/cracked. (The flex lines). Pumping fuel would create a Venturi effect (vacuum) and suck in air, once fuel in the tank drops below a certain point. Both times towing the trailer, I started with a full tank, there, then back home. So, the same route. At about 1-1/2 hours in, it starts intermittently losing power. Going downhill, if I let off of the throttle, it just dies. No codes.

Just for grins- I replaced the MAF, plugs, all associated relays and fuses.

I've ordered the pump from URD, it should be here Saturday. I'm really curious to drop the tank and see what's going on. I just need to unload some gas first. Anyone have a link to using the fuel pump to empty the tank? According to the schematics, if I pull the fuel pump relay and jumper +12 to one side of the fuel resistor (one side will be slow, the resistor will be in the circuit, the other side will be direct to the pump). I was just wondering if anyone has a track record of doing this first though.

 

This should help:

 

If you had a fuel delivery issue causing a loss of power it should result in very positive fuel trims. Like up around 20-25% and would likely set a code.

I would hold off on the pump for now and keep looking. Try cleaning the throttle body. Buy a code reader that can look at data.

 

Long term, short term or both- fuel trims?

 

Yep, that's what I was looking at, thanks.

 

Yes if you connect 12 VDC to the Black with red stripe wire on the resistor connection it will run the fuel pump high speed. It is handy too as it is located just in front of the battery.

 

So, more research. This is very similar to what happened at 49k miles-

https://www.tacomaworld.com/threads/random-intermittent-dies.461966/

Then I replaced the crank position sensor. Any thoughts? I can't remember if it was auto parts store brand or OEM, though. I will try to pick up an OEM today or tomorrow. And, tomorrow, I should be able to begin dropping the tank. Since I've got the pump on order, I might as well put it in (especially since the air in the line is bugging me). The smoking gun will be, when I try to pump out the tank, do I get a lot of air then too?


I really hate the "Shotgun" approach but I'm trying to nail this down quickly so we can get it a few more camping trips this year. Thanks for your patience.

 

The air in the line is really Odd and makes no sense to be. The pump is submerged in gasoline, it can't suck air and it pushes the gas down the line. Everything down stream of the pump should be under pressure.

 

Measure the fuel pressure.
Standard:
281 to 287 kPa (2.87 to 2.93 kgf/cm2, 40.8 to 41.7 psi)

• If the fuel pressure is greater than the standard value, replace the fuel pump.
• If the fuel pressure is less than the standard value, check the connection between the fuel hose and fuel pump.

Turn off Fuel Pump.
(p) Check that the fuel pressure does not change for 5 minutes.
Standard:

147 kPa (1.5 kgf/cm2, 21 psi)
If the result is not as specified, check the fuel pump and fuel injectors.

 

Yep, all in my first post.

The air came hissing out, along with a mist of fuel, when I disconnected the fuel line to put my gauge on. I measured 42-ish psi running. I put the gauge in, ran it for a few minutes, then shut it down again. It dropped to about 40 when I shut down the engine and lost 2-3 psi over 5 minutes. It continued to drop after that (I have not yet checked it this morning but, I assume, it will be down to zero).

That it mentions fuel pump or injectors is what got me curious about where the air is getting into the line. I have not ever torn apart a fuel pump and can only make assumptions at this point (I have replaced the assemblies though).

 

Both

 

Thats an intrusive and impractical way to diagnose a fuel delivery issue. Again, i cannot stress enough, data is your friend

 

I'm open to suggestions. And, I'm open to suggestions on a code reader.

Fuel pressure, after about 8 hours, was down to zero.

Later today, I'll try to take it for a drive to check trims. I think my OBD app does trims. I'll let you know what I find. Thanks.

 

If you have a laptop I’d look into getting a pirated copy of tech stream and a cable.. the cables start at 40 dollars and go up.. there’s plenty of info and how tos on tacoma world and you tube to get it set up(it’s a little complicated the first time)..

 

Here are some values. You thought that they should be positive? Oops.
First pic is with the handheld scanner, other three are with OBD Fusion app.
The first pic is after it gets into closed loop mode.
The second pic is startup, third is idle, fourth is closed loop again.

I check the fuel line again, no air this time. But, I have not driven it anywhere, these tests were just idling in the driveway.

There was a noticeable stumble every time it went into closed loop.

 

What was the ambient temperature? How long had the vehicle sat? Sounds more like vapor lock. Check fuel line and make sure it isn’t near any heat source.

 

holy jezus -20+% LT fuel trims.

Bone stock i was seeing +-7% with things being normally around 2-4%+ With some maf tuning via hptuners im +- 1.5% now.


Anyways, either injectors are sticking open / leaky, or O2 sensors are fucked. Im gonna probably say the latter, as you mentioned a stumble into closed loop (where fuel trims are utilized on a Realtime basis off of o2 sensor)