Surging going uphill sometimes

Hi,

I have a 2013 Tundra 4.6L that is sometimes surging going uphill, and sometimes I notice it when accelerating strongly.

I have explored this thread, and replaced all VVT Solenoids with OEM units.

That thread was about light to moderate acceleration.

I would say my surging occurs under moderate to heavy acceleration, and uphill. And only sometimes. I can go up the same hill at the same speed sometimes smoothly, and sometimes it surges.

When it surges, it is rhythmic, like every second surges forward, then off, then forward, then off.

I posted to that other thread and haven't gotten any responses as to what to try next.

I've been playing with chatgpt, so I put together a plan from that as to how to troubleshoot this.

If you have any other ideas that are better please let me know. I'd rather hear from mechanics and Tundra owners from experience than have to use AI.

Here is what I got:


what would cause surging when going uphill in a 2013 tundra 4.6l

ChatGPT said:

On a 2013 Toyota Tundra 4.6L, surging when going uphill usually points to a fuel delivery, air intake, ignition, or transmission control issue.
Since uphill driving puts more load on the engine, any weakness in these systems becomes more noticeable.

Common Causes of Uphill Surging

1. Fuel Delivery Problems

• Weak or failing fuel pump – Can’t keep up with demand under load.
• Clogged fuel filter or fuel injectors – Starves the engine of fuel, especially during heavy acceleration.
• Dirty mass airflow sensor (MAF) – Sends incorrect air/fuel mix data to the ECU.

2. Ignition or Engine Control Issues

• Failing spark plugs or coils – Misfires may feel like surging under load.
• Faulty throttle position sensor (TPS) – Causes erratic throttle response.
• Oxygen sensor issues – Incorrect mixture adjustments, especially in closed-loop mode.

3. Transmission-Related

• Torque converter shudder – Feels like rhythmic surging when climbing.
• Transmission hunting for gears – If fluid is low/dirty or shift logic is off, it may rapidly change RPMs.
• Clogged transmission filter – Can cause delayed or inconsistent power transfer.

4. Air Intake or Vacuum Leaks

• Cracked or loose intake hose – Allows unmetered air in, leaning the mixture.
• Vacuum leak – Causes unstable idle and power under load.

5. Exhaust Restrictions

• Clogged catalytic converter – Chokes engine at high load, causes power pulses or surging.

First Diagnostic Steps

1. Scan for trouble codes (even if check engine light is off — some codes are pending).
2. Check fuel pressure under load.
3. Inspect spark plugs and coils for wear or arcing.
4. Clean the MAF sensor (with MAF cleaner only).
5. Inspect for vacuum leaks.
6. Check transmission fluid level & condition.
7. Listen for exhaust restriction (low power + high exhaust heat is a clue).

how do I check fuel pressure under load on a 2013 tundra 4.6l

ChatGPT said:

On your 2013 Toyota Tundra 4.6L, checking fuel pressure under load is a bit trickier than on older vehicles because Toyota doesn’t provide a simple Schrader valve on the fuel rail — it’s a returnless, high-pressure system controlled by the ECU.

Here’s how you can do it safely:

1. Tools You’ll Need

• Fuel pressure gauge kit with a banjo bolt adapter for Toyota/Lexus (since no Schrader valve is present).
• OR an OBD-II scan tool that can read live fuel rail pressure (many Bluetooth scan tools with apps like Torque Pro, Car Scanner, or Techstream can do this).
• Safety glasses & gloves.

2. Method A – Using an OBD-II Scanner (Easiest & Safest)

1. Plug in your scanner and select “Live Data.”
2. Look for “Fuel Rail Pressure” (FRP) or “Injection Pressure”.
3. Start the engine, note pressure at idle (usually around 50–60 psi).
4. Drive uphill or under load while monitoring the reading.
   • A healthy system will maintain pressure within a few psi of spec.
   • If pressure drops significantly during acceleration/load, the pump, filter (in-tank), or regulator may be failing.

3. Method B – Mechanical Gauge Test

(For more advanced DIYers or mechanics — involves opening the fuel system.)

1. Depressurize the fuel system (remove fuel pump fuse and run engine until it stalls).
2. Disconnect the fuel feed line at the rail and install the Toyota banjo adapter & gauge.
3. Reconnect fuse, start engine, and check idle pressure.
4. Have a helper drive uphill or accelerate while you watch the gauge from the passenger seat.
5. Compare to spec (Toyota typically expects ~51 psi under load for this engine).
6. Shut down, relieve pressure, and remove the test setup.

4. What to Look For

• Pressure drop under load → Weak pump, clogged in-tank filter, or failing regulator.
• Fluctuating pressure → Electrical issue to pump, bad fuel pump relay, or wiring.
• Normal pressure but surging → Problem is likely ignition, air, or transmission related instead.

Alright — here’s a step-by-step load-test procedure for diagnosing uphill surging on your 2013 Tundra 4.6L without throwing parts at it.

Step 1 – Pull Codes (Including Pending)

• Use an OBD-II scanner.
• Check for both stored and pending codes.
• Even if no check engine light is on, pending codes (like P030X misfires or fuel trim codes) can give clues.

Step 2 – Fuel Delivery Load Test

Option A – Using OBD-II Live Data

1. Monitor Fuel Rail Pressure (FRP) while driving uphill.
2. Idle should be around ~51 psi (Toyota spec).
3. Under load, pressure should stay within 2–3 psi of spec.
   • If pressure drops → suspect pump, filter, or regulator.

Option B – Without Scanner

• Accelerate uphill in 2nd gear at steady throttle.
• If surging worsens as RPM rises, it’s often a fuel starvation issue.

Step 3 – Ignition System Test

1. With scanner, monitor misfire counts per cylinder while going uphill.
2. Swap coils from a misfiring cylinder to another cylinder and re-test.
   • If misfire moves → bad coil.
3. Check spark plugs for gap, fouling, or oil.

Step 4 – Air & Sensor Check

1. Inspect intake boot for cracks or loose clamps.
2. Clean MAF sensor (only with MAF cleaner).
3. Check long-term fuel trims (LTFT) under load:
   • +10% or more means lean (possible fuel delivery or vacuum leak).
   • -10% or more means rich (possible injector leak or O2 sensor issue).

Step 5 – Transmission/Torque Converter Check

1. Drive uphill at steady throttle around 45–55 mph.
2. If RPM fluctuates without a gear change → torque converter shudder.
3. Check transmission fluid:
   • Level correct?
   • Fluid still red and clean, or brown/burnt smelling?
4. If shudder goes away when you slightly press the accelerator → torque converter lockup problem.

Step 6 – Exhaust Restriction Test

1. At idle, measure vacuum at intake manifold (should be ~18–22 inHg).
2. Increase to 2500 RPM and hold:
   • If vacuum drops steadily over a few seconds → possible clogged catalytic converter.

Step 7 – Narrow It Down

• Fuel pressure drop + lean trims → Fuel delivery problem.
• Misfire counts spike under load → Ignition issue.
• RPM fluctuates without misfire/fuel drop → Transmission/torque converter.
• Loss of power + rising exhaust heat → Exhaust restriction.

 

What have you done maintenance wise to your truck? Start there, which it may need anyway, and see if that fixes your surge issues.

 

1. Engine oil and filter: 5k miles
2. Spark plugs: 30k to 60k, use only OEM or Denso equivalent.
3. AFR/o2 sensors(Upstream Sensors): 60k, use only OEM or Denso equivalent.
4. Engine Air Filter Clean/Replace: 15k
5. Clean MAF and TB: 15k
6. Coolant flush: First 100k, then every 50k there after. Replace Thermostat and radiator cap along with flushing, and only use Toyota pink.
7. Belts and hoses: 50k or at least with every coolant exchange.
8. Power Steering flush: 15k to 30k
9. Brake fluid flush: DOT 3/4 at least every 30k and DOT 5+ at least every 15k.
10. Transmission drain n fill: 30k
11. Differential and Transfer case drain n fill: 30k
12. Fuel injector service and/or fuel filter replacement: 15k, note that many vehicles have in tank filter and is not serviceable.
13. PCV valve clean/replace: 15k

 

Keep in mind, going uphill your fuel is running to the back of the tank. Could you be sort of starving the pump at times because the fuel is not always filled when this surging happens?

 

I bought the truck in February and have done this so far:
Air Filter
Oil and filter 2x
Laser iridium spark plugs
VVT solenoids (all 4 OEM)
6 transmission drain and fills, about 3.5 or 4 quarts each time. Valvoline Extended Protection ATF
2 bottles of Sea Foam in a full tank of gas, after the truck had sat for months waiting for reg and title
Throttle body cleaned, MAF cleaned
Coolant drain and fill with Prestone Max red. Got 6.5 quarts out. Was very clean, looked new.
Cataclean treatment - followed directions, full can in fuel tank when 4 gallons left in tank, drove 15 miles, filled tank, still have 3/4 of a tank left on that process.
PCV valve.

 

Why not Toy WS trans fluid? Did it do this surging before you began tinkering?

 

Yes I think it did it since I got it.

I did a lot of reading about Toyota WS and Valvoline, which is WS also. I like Valvoline products and think they are very good. And read a lot of Toyota owners saying they had better experiences with Valvoline Extended protection than the Toyota WS. Like the transmission shifted smoother. And it's cheaper too.

 

How are you determining the correct level for the trans fluid?

 

With the check plug out while running, and up to temperature, using an infrared thermometer on the bottom front of the pan, at 100 F which is about 110 F inside. Then open the check plug and let it drain until it is a smaller stream, then close it while it is a small stream. Oh, and all this after making sure that the truck is completely level.

 

When I checked codes previously, there were none. Yesterday I got this one:

2013 TOYOTA Tundra 4.6L V8
5TFUM5F18DX046255
Odometer: 121,900 miles

Startability Malfunction

 P1604 indicates that the vehicle has detected a starting issue, such as a hard start or
engine stall.

It can frequently be accidentally triggered if the key (or push button) has been held in
start too long or released before the engine has fully started.

It can also be triggered if the fuel level is too low.

If this code persists, and the cases above can be ruled out, prioritize the fixes listed in
this report.

 CLEANED MASS AIR FLOW SENSOR
 REPLACED ENGINE AIR FILTER
 REPLACED BATTERY
 REPAIRED BATTERY
 REPLACED STARTER MOTOR
 REPAIRED STARTER MOTOR
 REPLACED STARTER MOTOR CABLE

© BlueDriver 2024 Page 1 of 3
Code Definition

1 Possible Cause

47 Frequently Reported Fixes

P1604 Repair Report - 2013 TOYOTA Tundra 4.6L V8
 REPAIRED STARTER MOTOR CABLE
 REPLACED STARTER MOTOR CONNECTOR
 REPAIRED STARTER MOTOR CONNECTOR
 REPLACED STARTER MOTOR WIRING HARNESS
 REPAIRED STARTER MOTOR WIRING HARNESS
 REPLACED ENGINE IMMOBILIZER SYSTEM
 REPAIRED ENGINE IMMOBILIZER SYSTEM
 REPLACED SPARK PLUG
 REPLACED DIRECT IGNITION COIL (IGNITION COIL)
 REPLACED IGNITION COIL CONNECTOR
 REPAIRED IGNITION COIL CONNECTOR
 REPLACED IGNITION COIL WIRING HARNESS
 REPAIRED IGNITION COIL WIRING HARNESS
 REPLACED FUEL INJECTOR
 CLEANED FUEL INJECTOR
 REPLACED FUEL INJECTOR CONNECTOR
 REPAIRED FUEL INJECTOR CONNECTOR
 REPLACED FUEL INJECTOR WIRING HARNESS
 REPLACED FUEL PRESSURE REGULATOR
 REPLACED FUEL PUMP
 REPLACED FUEL PUMP CONNECTOR
 REPAIRED FUEL PUMP CONNECTOR
 REPLACED FUEL PUMP WIRING HARNESS
 REPAIRED FUEL PUMP WIRING HARNESS
 REPLACED FUEL PUMP CONTROL MODULE
 REPAIRED FUEL PUMP CONTROL MODULE
 REPLACED FUEL LINE
 REPLACED FUEL TANK
 CLEANED FUEL SYSTEM
 REPLACED FUEL
 REPLACED VAPOR CANISTER PURGE SOLENOID VALVE ASSEMBLY
 REPLACED VAPOR CANISTER PURGE SOLENOID VALVE ASSEMBLY CONNECTOR

© BlueDriver 2024 Page 2 of 3

P1604 Repair Report - 2013 TOYOTA Tundra 4.6L V8
 REPAIRED VAPOR CANISTER PURGE SOLENOID VALVE ASSEMBLY CONNECTOR
 REPLACED VAPOR CANISTER PURGE SOLENOID VALVE ASSEMBLY WIRING HARNESS
 REPAIRED VAPOR CANISTER PURGE SOLENOID VALVE ASSEMBLY WIRING HARNESS
 REPLACED EVAPORATIVE EMISSIONS SYSTEM LINES
 REPLACED MASS AIR FLOW SENSOR
 REPLACED MASS AIR FLOW SENSOR CONNECTOR
 REPAIRED MASS AIR FLOW SENSOR CONNECTOR
 REPLACED FUEL FILTER

 

I searched and read this forum about P1604 and found one post where it was solved with Denso camshaft and crankshaft position sensors.

 

You did it correct for the most part on the fluid level. I’ve seen using an IR gun on the back of the pan is more accurate. I’d suggest adding a pint of fluid in your trans. A whole quart extra maybe a touch too much.

Cam n crank sensors you can test there resistance to see if they’re good or not, but getting to the crank sensor, you may as well replace it.

 

Thanks. The back of the pan was always cooler by far when I was reading it. So if I waited until the back of the pan was 100 F, then the internal fluid would be hotter than it was when I closed the plug. If hotter, and fluids expand when hotter, then it would drain more out than what I did, which would leave me with less fluid in the pan than what I did.

 

This may be a stupid suggestion, but have you tried turning your HVAC system off? (No A/C and no Defrost)

I have a 4th gen 4Runner that had an extremely similar issue when the A/C was slightly overfilled. Under higher engine load, the compressor would overpressure the system, and cycle on and off quickly like that.

Give it a try and see if the issue goes away completely with the HVAC off.

-Rob

 

I would agree with @RivMan, AC puts a load on the engine.
On another note if you mean surging going up a hill, this is normal as transmission hunts for the most appropriate gear for the best fuel economy, which will cause it to downshift and go into higher rpm then drop to lower gears when the ECU thinks the road has flattened out and it detects additional load and it'll downshifts into lower gears surging into higher rpms and it will continuously do this cycle. This is my understanding of your issue.

Heavy acceleration it's common for it to drop 2 gears and have the engine surge into higher rpms then drop as necessary.

Your best bet going up a hill is to pick a gear 3 or 4 and take the mpg penalty into the higher rpms until the road levels out.

 

That is not a stupid question. No, I have not tried that. Will do. Thanks!

 

OK, good to know, but it doesn't seem like it is changing gears. I've paid attention to gear changes now because I was wondering if it had to do with the transmission. Gear changes feel different. This seems like only engine related. But I could be wrong. And when it does happen, it's every second or so, surge, back off, surge, back off. Rhythmic. And will do that on the same slope hill, maybe 4-5 cycles.
Thanks!

 

Sounds like gear hunting. On a hill set it in 3rd or 4th gear, see if it surges

 

Do you have a pedal commander or throttle control module hooked up by chance?

 

OK thanks, will do!

 

Not that I know of but I just got the truck in Feb. I guess I would have seen some control for that on the dash. There is nothing but stock stuff on dash and steering wheel.

 

This is the video that I used as reference for how to check the temperature of the ATF and how to get the correct level using the check plug drain.

He compares the temperature outside of the pan measured with an IR gun with the temperature inside of the pan measured with a scanner.

He says that the inside temp should be 104-113 and that the IR outside of the pan will read about 5 degrees lower.

He points the IR gun at the middle of the pan.

So, I took all of this into consideration, and I figured that I wanted to error on the side of having just a little more fluid in the pan.

So I pointed the IR gun at the front of the pan, and when it reached 100 degrees, I opened the check valve. At this point, the middle of the pan was probably a few degrees lower. Which means that the inside temp of the fluid was probably about 100 to 102, just a little lower than the range of 104-113.

Because, at a lower temperature, the fluid is more condensed. Therefore, I'm leaving more fluid in the pan by stopping at a lower temperature than if I left it go higher, which would cause the fluid to expand, and more of it to flow out the check valve.

I saw videos and read other people saying that when you open the check valve, it will drain a strong stream then it will change to a smaller stream, and to close the check valve while it is still draining a small stream, rather than wait until it is dripping slowly.

So that is what I did, because I wanted to error on the side of a little more fluid in the pan.

Am I thinking correctly?

https://youtu.be/TH90IJSgg2M?si=0oFPvFKsLOtBDvrL&t=317

 

I don't see anything about you pinning the cooler thermostat open while servicing the trans...Does your truck have a trans oil cooler?

 

Car care nut channel can show you a good way to do it all properly.

 

Yes I did that. Do you want to see my entire procedure?

See attached.

 

Ok thanks!