Air In Fuel Line

I should have it all back together tomorrow after replacing the fuel pump today.

I don't know why I didn't think of a flow test earlier. I guess that I thought that it would be too involved, I would just wait until I received the pump to try it. The method of running (as stated earlier in this thread) the fuel pump to drain the tank worked like charm. And was really easy. Except!...

My new pump is rated at 255 lph (I assume stock is close to that), that works out to about 1.1 gallon per minute. Mine took more than 20 minutes to fill a 5gal gas can. Whoops. And, the flow would start out really strong then taper off. Then it would surge and ebb. But never to full strength like the start. Like there was a restriction in the line.

This was obviously a problem but I'm not sure why the bad pump would cause the fuel trims to be that far in negative territory. After a test drive, we'll see what they are like now.

(I'm an old man, so forgive me- I have a video of the piddling fuel pump on my iPhone but I don't know how to post it here.)

 

Case closed!
It was, indeed, the fuel pump. Back to working normally.
The wildly negative trim values were-

Because of the damn aftermarket (duralast) MAF!!!

I put the original back in and the LTFT values hover around the -4 range.
I guess that I'll put a new denso in.

Thank you, thank you everyone for all of your help!

 

It is great news that you got it sorted.

Thanks for the updated information.

 

Threads like these make me want to replace my fuel pump as a preventative maintenance item. Glad you got it sorted out OP.

 

You may want to, before you're on a two hour jaunt, towing a trailer and it decides to give you fits.
Mind you, I'm the original owner, it's always been babied and only 65k miles.

A question on my external filter-
I understand that closer to the tank is better for an installation location but what about the engine bay? More convenient, less vulnerable and only about 7' further down the line.

 

Hmm, realistically i dont think filter placement would make any difference but i like the idea of down by the tank as it keeps a the volume of fuel away from the heat of the engine bay.

 

OEM Hilux's have it in the engine bay.

It is strictly preference.

 

I'm fixin to do my fuel pump this weekend. similar issues. Conditions very similar to vapor lock which i've had on the 3.0l toyota race truck and my motorhome. The few times it's happened to me has been super hot ambient temps running 87 octane fuel and the engine running all day (gotta keep the ac on, duh). After letting the truck sit for 30-45 mins fired right up and drove home. 159k on an 05. Techs say no way the fuel pump, they should last 300k. So this thread with a fp fixing the issue is very positive for me that this will fix my issue.

 

And for those still following along-
I haven't checked the forum but my own research indicates that Fram G3870 and Motorcraft FG872 are the same fuel filters as can be purchased from URD.

 

Bad news- I'm back at this.

After 4 months and a new fuel pump, it bucked again. Merging on to the highway, under acceleration, I let up on the gas to adjust my speed for the merging space that I was aiming for. When I pressed the gas pedal again, it bucked. Just once. That was 2 days ago. Today, I was slowing down to make a turn and it just died. I got it home, disconnected the fuel line and it was the same thing- pressurized air/gas mix spewing forth. Put the pressure gauge on it, it goes up and right back down to zero when I shut it off (which is puzzling because a moment before it was pressurized with the air/gas mix, huh? WTF?). I ran a flow test on the pump and it ran like a champ into a gas can, for a steady 5 minutes. I am wondering if the new pump was either part of the original problem and/or masking this problem that I still have, that "seemed" to have gone away for the past 4 months.

My thoughts:
1) It sounds like the low speed fuel pump resistor may be involved. I ohm'd t .9 ohms. It does have a couple of cracks in the ceramic part. A thermal issue? I am going to bypass it for now and get a new one, just for grins if nothing else.

2) It still sounds to me like I have an injector(s) stuck open. As discussed previously in this thread, that doesn't really seem possible, but it would explain why my fuel pressure drops right away. (Anyone replace their own injectors yet? How hard was it?)

3) Shoot myself.

 

Oh yeah, since it was just a quick run into town, I didn't have my app going that would show me the trims and such. I will next time though. I plan on taking it for a spin tomorrow, on my way to get the new fuel pump resistor.

 

Fuel trims were normal and no bucking today.

Any help?
Please?

 

I do wish I had more to offer. I think you have a point with the pressure dropping as it does as you said in a previous post. It should Not do that as per the testing procedure. A leaking injector is a distinct possibility. You can bypass the fuel pump resistor as a test using a wire jumper in the connector.

 

Toyota had no insight into this problem either. I took it the dealer for a diagnostic. No news.

It was approx 1000 miles since I replaced the fuel pump and the problem went away, for awhile. Maybe every month, I burp the fuel line. It doesn't get the air/gas mix problem again immediately.
The Toyota tech did say that, for him, it was holding fuel pressure. What am I doing differently? I am going to test it again today. If it holds pressure, it must be very intermittent.

I am going to bypass (I still haven't replaced it) the fuel pump resistor. And then drive it like a madman.

Meanwhile, I having a leaking rear diff and a leaking water pump. At 14 years old, I could see those as being problems but at only 66k miles, that is a bit much.

 

Okay, so I'm really reaching here...

4 years ago, in this thread

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

A similar situation was occurring, then I replaced the ckp. Notice that it was in 2016, right when they were having problems with those sensors and a recall. Yes, I understand that it was due to the anti-corrosion coating internally but, like I said, I'm reaching. Today I'll go get a new sensor, pull the old and see if they are different versions.

Where I'm really reaching is:
At speed, if the ckp fails momentarily, is it somehow possible for the compressed air/fuel mix from a cylinder to leak past a valve and pressurize the fuel rail? Today, I am also going to call around to see if any mechanics have heard of air in the fuel rail. Google has disappointed me there. Since there is no "pickup tube" in the fuel tank, any pinhole would expel gas rather than suck in air. Once shutdown, it may leak down and draw in air but that would be quickly pushed out when the pump started again.

 

And, just for grins, I took out the fuel pump resistor. I heated it up with a heat gun. I was curious because I saw two small cracks in the ceramic. Resistance slowly increased with the heat applied (standard electronics theory- heat increases resistance). It went up to 2 ohms but that was at 650*. I hope it never gets that hot under my hood. At that point, it never created an "open" circuit, which I needed to eliminate as a possible cause of my problem.

 

@dbbd1 Whatever happens, I appreciate your posts on your way to diagnosis. Valuable details for folks looking for solutions to their own problems.