Ok, I see. If that were the case then it would catch - on the priming fuel - but not continue running, right? I don't get that. And it never stops while running & no codes.
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NeverFinis
SILVER Star
Yes, I believe it would catch, stumble and die in that scenario.
If it isn't a sensor issue, I would go over the harness and its connections to the fuse block/relays.
tmxmotorsports
SILVER Star
It's not blowing the fuel pump fuse?
Nope.
tmxmotorsports
SILVER Star
Ok then there has to be a loose connection. Check all ground points also check the pin going to the ecm at the ecm that triggers the fuel pump then wiggle all the wiring around and recheck. A short to ground would blow the fuel pump fuse. Also check the wiring right at the fuel pump there is also factory wiring that comes out of the cab through the floor that goes over to the fuel pump there is a connection/ connector if you look under the vehicle right at the driver rear door check to see if that is good too. A quality relay will last a very long time .
Tommy
tmxmotorsports
SILVER Star
Also pull the fuel pump fuse out and take a really good look at it fuses now days can be cheap crap check the connection holding the fuse could be loose or corroded.
I think it has to be on the signal or ground sides of the relay, because when it fails the relay doesn't activate.
Certainly can't be the fuse since it's working now and I haven't changed the fuse.
You could read continuity through the relay but it might not be able to carry enough current to run the fuel pump. You could also have a bad relay base. I have come across both of these on many occasions.
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Those fuse boxes are pretty low quality. Remove them and check the underside.
The problem is that the relay isn't closing. When the relay closes, it works fine.
I did have it out. Looks ok, contacts and the crimp connections to the wires seem solid as far as I could see. Poked and pried at em with a probe.
As far as I can tell the signal side is one wire straight to the big ECM connector. I couldn't trace the ground side. I haven't pulled the ECM connector off yet.
I did use a small screwdriver to pry the sides of the relay socket contacts in a bit so they're tighter. Felt tight plugging in and removing relays, but figured it couldn't hurt.
I guess the part that bugs me about the loose connection theory is that it's never happened while driving. Thousands of miles, days at a stretch off road and it's never skipped a beat. It's only happened on starting in a parking lot. Two times about 8 months apart.
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It takes more current to start than to run constant. If it's a bad connection it can't get enough current to start the motor or in this case the fuel pump. But it could be another issue with one of the other wires going to the ECM
thatcabledude
GOLD Star
^this. Could be barely making connection. Poor connection causes it to heat up and expand enough to make connection worse.
I too used the psi. For some reasons my psi fuel pump relay didn't work so I ran a new fuel pump relay setup (the wiring from the new relay runs to the fuel pump wire. Don't use cheap relays they can go bad sooner. Have you check your fuel pressure?
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tmxmotorsports
SILVER Star
Psi harnesses are not all that great
I’m looking into these part numbers. The Denso ones seem to be nowhere found. The Toyota one is god awful expensive haha. I was looking into Walbro pumps. Do you or anyone have experience with these? Do they plug and play as if I was using a Toyota pump? Fairly easy install?
Well, it happened in traffic today - stalled at a light and wouldn't start.
I picked up one of these the other day
And it worked great. Swapped it for the relay, flipped the switch and it started and ran the rest of the way to work. Only had one horn blown at me, lol. Gave him the mud salute. Will definitely be part of my kit going forward.
So I'm pretty confident it isn't the power circuit to the fuel pump or the pump itself. I'll be taking as close a look as I can at the relay triggering circuit.
How old is your fuel pump? maybe it's failing. Alternator, battery condition? If you go back a couple of months on this thread. Neverfinis shared the model numbers of the fuel pumps. I used the 4 runner v8 fuel pump cost like 140 bucks.
Would you like help diagnosing based on a specific situation or vehicle type?
Mechanical or Engine-Related Issues:
- Fuel delivery problems:
- Clogged fuel filter
- Failing fuel pump
- Empty or contaminated fuel tank
- Ignition system issues:
- Bad spark plugs, wires, or ignition coils
- Distributor problems (in older vehicles)
- Air intake problems:
- Dirty or failing mass airflow sensor (MAF)
- Vacuum leaks
- Clogged air filter
- EGR valve stuck open:
- Causes too much exhaust gas to recirculate, disrupting combustion.
Electrical or Sensor Failures:
- Bad alternator or battery:
- Especially if stalling happens when idling or using accessories (AC, lights, etc.)
- Faulty sensors:
- Crankshaft or camshaft position sensors
- Throttle position sensor (TPS)
- Engine coolant temperature sensor
- Malfunctioning ECU (Engine Control Unit):
- Rare, but a failing ECU can send incorrect signals.
Driver or Operational Issues:
- Manual transmission stall:
- Releasing the clutch too quickly or under-revving can stall the engine.
- Automatic transmission problems:
- Torque converter or transmission fluid issues can cause stalls when stopping or accelerating.
- Low idle speed setting:
- Engine may not get enough power to keep running at idle.
When Does It Stall? (This helps narrow it down)
- At Idle/Stop: Often fuel/air/sensor issues.
- While Accelerating: Possible fuel delivery or ignition issues.
- While Driving: May indicate more serious electrical or fuel system problems.
Would you like help diagnosing based on a specific situation or vehicle type?
You said:
failing fuel pumps symptomsChatGPT said:
A failing fuel pump can cause a range of symptoms depending on how and when it's starting to break down. Here are the most common signs:
Common Symptoms of a Failing Fuel Pump
1. Engine Sputtering at High Speeds
- Feels like the engine stumbles or briefly cuts out while driving.
- Caused by inconsistent fuel delivery under load.
2. Difficulty Starting (or No Start)
- Engine cranks but struggles to start or won’t start at all.
- Could be because the pump isn’t generating enough fuel pressure.
3. Loss of Power When Accelerating or Uphill
- The vehicle may hesitate or bog down under acceleration or climbing a hill.
- Not enough fuel getting to the engine.
4. Stalling
- Especially while idling or under stress (e.g., stop-and-go traffic).
- The pump may be overheating or intermittently failing.
5. Surging
- Engine randomly speeds up without throttle input.
- Caused by inconsistent fuel flow or pressure spikes.
6. Whining Noise from the Fuel Tank
- A loud, high-pitched whining sound can indicate a worn-out pump.
- Especially noticeable when the car is idling or after starting.
7. Decreased Fuel Efficiency
- Faulty pump may affect injector timing or cause incomplete combustion.
8. Check Engine Light
- May trigger codes like P0087 (low fuel rail pressure) or P0230–P0232 (fuel pump circuit issues).
Quick Diagnostic Tips
- Fuel Pressure Test: Using a fuel pressure gauge can confirm low pressure.
- Fuel Filter Check: A clogged filter can mimic pump failure.
- Listen at Start-Up: Turn key to ON (not START) — listen for a 2–3 second whirring sound from the tank.
NeverFinis
SILVER Star
I added the 4.7L V8 Toyota 4Runner Fuel Pump to that post: Denso 950-0226
Should be plug and play and is available for $80.
Is that a 255lph by any chance I’m trying to find the specs, no luck. I’m at work so it’s hard as well.
