2004 Tundra 3.4 Engine Manual Transmission (power problem)

First indications was the engine appeared to be stalling out, from a stop as well as highway speed. Changed inline fuel filter and air filter and problem remains. No codes or check engine light and my mechanic was unable to find the problem through codes or driving with computer attached.

Additional information: Problem only started after approximately 45 minutes of drive time. Changed coils and wires, electrical relays for fuel pump and injectors. Problem remained.

Change the ECU yesterday, test drove for five hours no problem. Second day after the ECU change with about 2 hour of drive time and problem returns, as described above.

This time I was able to notice that when there was a reduction of speed (like the clutch was pushed in) engine RPM would not increase or decrease. This leads me to think a pending transmission failure but not a clutch failure.

Any thoughts would be helpful

 

4.7L or 3.4L? There is no 3.7 in these trucks. But I can't tell if you fudged the 3 or the 7 on your "3.7L" in the subject.

 

Thanks for the help. Need to give the right information to get the right answer.

Best regards and thanks again.

 

Before you throw money and parts at it, give us the specifics of your vehicle, concise description of symptoms and what codes it is throwing

 

No worries, but I do have questions.

Just for shits and giggles ...

Any check engine light, either solid or flashing, at any point?

Have you checked the level, color, and smell of your transmission fluid?

What is the status of your spark plugs currently and coil packs? If you've replaced, can you get me a brand/model number on each?

I feel like squirrely problems like this usually end up being electrical gremlins. Bad ground. Pinched wire (like the one to the fuel pump). That kind of stuff.

 

Guys thanks for helping. No check engine light and no codes. I have not checked transmission fluid. In fact on a manual transmission I don't know how to do a proper fluid check.

Ignition wires are Duralast PN 9266, coils are NAPA brand PN IC223CB.

I agree that it sounds very much like an electrical issue; that is way the fuel pump, injector relays and ECU where changed. My understanding of a electric problem causing a reduction of power, or a feeling of an engine stall, there would be a reduction of MPH (which there is) and a reduction of Engine RPM, (which there isn't). At this point when there is an event in third gear, 3000 RPM, 40 MPH; there is a power lost causing the truck to slow but no decrease in RPM.

 

Do you have any way to monitor voltage, and fuel pressure? That could definitively answer the question about what's going on. Are you watching for voltage fluctuation while it's happening?

Buuuut... I just had another thought.

I would tell you, "huh, it's really weird it worked for 15 miles after swapping the ECU!" but ... it's not.

To test my theory, which I'll explain in a sec along with telling you what I'm guessing the problem is, do this: Go remove your negative battery cable, specifically, for 15 minutes. Then reattach, and go drive around. Is the issue gone?

Why did that one symptom raise an eyebrow for me? And why am I surprised your mech may not have thought anything of it?

When you remove power from the ECU (or replace the ECU for that matter, because the replacement was powered off), the ECU conveniently forgets the parameters within which it was running. it takes anywhere from 5-10 minutes to 5-10 days before relearn is complete and new params are saved.

So what's my thought here?

Your ECU uses your MAF to measure volume of air entering the intake so it has an idea how much fuel to spray into the cylinder.
Your ECU uses your upstream O2 to measure the composition of combustion after ignition happens, and if rich or lean, it adjusts the fuel trims up or down over time.

When you clear your ECU (power off for 10-15+ mins), the ECU resets to baseline "known-good" specs and runs with those until it gets a chance to relearn. Which, if it's happening in 45 minutes after you swapped the ECU, makes sense.

But ... say it maps what it things is right, but your upstream O2 sensor is giving bad info about combustion? Or your MAF sensor is giving bad info about the volume of air? Your engine is going to run rich, lean, or misfire potentially to the point it won't get logged as an error, and generally feel like shit.

Now, you may be able to use a scanner to check your long term fuel trims "LTFT" to see if they're totally whack. That could tell you something weird is going on where the ECU is confused.

What would I do?

Well, I've got a good OBDII tool that would help me dig in and monitor voltages for my O2 sensors, and check my LTFT and STFT (short term) to see what the ECU is doing for fuel. That could tip my opinion on which it was.

I also have a digital multimeter, and the process to test resistance at the MAF to see if it's bad is really straightforward, and I have a can of CRC MAF Cleaner, which I'd have used a long time ago to clean my MAF. If you're one of the unfortunate souls who bought into the scam of oiled air filters, or the K&N "hot air intake" kits, your MAF and throttle body maybe caked up with oil and dirt, as happens with those specific things frequently.

But I'll also tell you:

This could be a bad coil pack causing misfire; while store brand coils are absolute eff'n garbage compared to OEM, if the problem was there before and after coil pack swap, they're not the issue (pro tip: I'd swap OEM back in! They fire hotter/stronger than aftermarket.)

This could also be your fuel pump crapping out. But the "45 minutes on new ECU" kinda debunks that theory, as would forcing a re-learn (removing neg batt cable) for 10-15, and if the engine runs generally good for the next 20-60 minutes, fuel pumps don't just magically get nice after battery disco.

Anyway, that's a goddamn wall of text, sorry. But that's where my brain is at on this one.

• Cheap test first: Give the negative battery a disco for 10-15 and report back.
• You should get a can of MAF cleaner if you don't already have one, and give it a shot; if you have a DMM and need instructions on how to test MAF (and ar comfy with a DMM), let me know.
• I would check (or post a pic) of your throttle body so we can see if it's caked
• If you're running an oiled filter or K&N style intake, let us know, don't be ashamed, I'm not a fan but quite a few on here run them all the same, they do buy a nominal amount of low-end torque.