Fuel pump confusion

Put new OEM dual electrode spark plugs in for the heck of it. Starts up WAY smoother and faster, busy still shuts off right away.

Also tested resistance on the coil packs. 1.0, 0.7 and 0.7 ohms, which, according to the manual is within spec.

Fuel pressure test kit will be here tomorrow. Should yield some helpful info…

 

Hooked up fuel pressure gauge to the driver side fuel rail. Consistently getting 40-42psi immediately after starting. Drops to 26 psi 10 mins later, then 20 psi at 20 mins. Leaky injectors? Could that be the culprit to all of this (start fine then die)? Also noticed a lot of vacuum pressure when opening the gas cap and a gurgling sound inside the tank 10 mins after starting. Can the evap canister plug up and cause it to die?

Attached a pic of my fuel rail setup in case anyone wants to do this. Total cost about $45 all off Amazon for gauge kit and hardware. Had to carefully bend the aluminum backing of the belt cover slightly forward to make it fit (doesn’t interfere with pulley).

 

Have you tried starting it or testing it with the gas cap off? I'm wondering if your gas cap is not venting, thereby interfering with the fuel pressure.

In a much simpler application (lawnmower engine), a clogged gas cap will allow the engine to start but stall after a few seconds. You can deal with the CEL code that you would get later.

 

Try leaving your gas cap off and running it.

 

Great minds think alike...but we have to wait to see if that's true in this instance.

 

LOL
was also thinking of the canister vent valve but not sure where that is on the tacoma. I'm intimately familiar with it on my camry.

 

Thanks all! I tried starting it with the gas cap off, no change in fuel pressure, no CEL and still dies after 1-2 seconds. Also tried unplugging the fuel return line from the evap canister, no changes at all. That line is bone dry and doesn’t leak fuel when starting either (not sure if that’s normal or bad).

Fuel pressure staying at 20 psi 30 mins after sitting

 

Not to jump around too much, but I also noticed this harness unplugged with nothing around it to plug into? No idea what this is for…it’s under the carpet on the floor near where your left foot would rest. As you can probably see I’m completely out of ideas

 

Pretty sure the 4wd controller is there- if it's not the 4wd controller, it'll be some option your truck may not have.

I was going to ask if you had a ODBII reader, or way to look at the ECU fuel trims? But that doesn't make sense is the pressure is low.

I assume you've checked the vacuum lines for leaks, especially the line going to the FPR? Did you replace the FPR already?

I'd really check the wiring to the fuel pump- There is a harness under the drivers seat that.. Maybe it's got a good connection when cold, but as the wires heat up, maybe it doesn't.

 

I just hit “clear codes” on my scanner even though there were none, and it fired up and is running fine right now. WTF is happening!!?

 

The lines are supposed to be dry. On the vent solenoid there should be two lines one large vent hose and a smaller one coming from the gas tank. It's the smaller one that you want to pull.
No worry of fuel coming out - it's just supposed to be vapor. Is that the one you pulled? This should rule out vapor lock on the evap canister side.

 

Gotcha. This is 2wd so that would make sense. I have not replaced the FPR. I thought if the FPR was bad the fuel pressure would be too high?

I’ll check out that harness under the seat

 

Shut it off, now won’t start again. The vacuum lines “look” okay despite being old and brittle. I know there can be leaks you can’t see. I ordered a replacement set of vacuum lines to change out anyway since these are 22 years old

 

Ahhhh I see. Yes This is the one I pulled, I’ll try the smaller one too

 

It might be, but I am going along with the "clutching at staws" ride

 

To answer your question on fuel trims, here’s short and long term when it stayed running. They moved around a little but not much. From what I looked up they appear to be normal

 

Pulled the ECU and ordered a used part number matched replacement off eBay.
Is it just plug and play or do I have to do any fancy tricks to get it jive with my truck?

That’s the last significant part I’m throwing at it. If this doesn’t work I’ll have it towed to a shop as much as that will hurt my pride

Not worth throwing hundreds more at random parts that may not fix it when it could cost about the same (or less) to get it diagnosed…

 

Is this the same kind of fuel line connector in the center of my pic that you connected the kit to? I have another fuel line just above it in the pic and don't know the difference between them. Do you have a link to the kit?

 

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You’re going to want to hook up downstream of the FPR on the fuel rail itself, otherwise you’re going to get an elevated reading since it’s before the FPR. Assuming you want to see the pressure at the injectors, you want to unscrew the banjo bolt on the front of the driver side fuel rail (little more room than other side, see pic). I had to bend the aluminum shroud forward with some pliers to get enough space (red arrow below). Plug your hardware in and hook up your gauge. Here’s links to everything you need:
Control Devices - TV12 Brass Tank Valve, 1/8" NPT

Control Devices - TV12 Brass Tank Valve, 1/8" NPT

https://www.amazon.com/dp/B0081TJO72
Russell 640700 Fuel Pressure Take Off Banjo Belt

$16 RUSSELL/EDEL 640700 Fuel Pressure Take Off Banjo Belt

https://www.amazon.com/dp/B000CPJI8I
BETOOLL 0-140PSI Fuel Injector Injection Pump Pressure Tester Gauge Kit Car Tools (Master)

$31 BETOOLL 0-140PSI Fuel Injector Injection Pump Pressure Tester Gauge Kit Car Tools (Master)

https://www.amazon.com/dp/B00VV29NHM

 

Please don't throw parts at it. You'll just frustrate yourself, waste money, and introduce new variables.

You're still waiting on the Denso fuel pump right? If that doesn't solve it I'm betting on a venting / breathability issue. These pumps are not pulse width modulated so they're full power all the time. The pcm just activates the pump full 12v DC on or off without variation so your fuel pressure dropping out is not related to the pcm in my opinion since you're definitely getting power. Do your fuel trims increase as the pressure decreases?