Misfire no CEL 5VZ, running out of solutions.

TW, ive got a intermittent (and very annoying) misfire on my 5VZ (312k mi) that has been an absolute nuisance. I get a wobble on startup then it goes away when warm. Then when the engine is under load the power delivery isint smooth accelerating and on the highway in top gear its really pronounced and shakes the whole truck i presume thats when TC is in full lockup and can feel the most. Heres the list of items ive addressed or replaced:

- New (6) NGK dual tip plugs (none of old plugs came out washed)
- New denso coils
- New TE66 blue leads
- Compression tested good, avg 195 psi across all with △ no more than 15 between all cyls
- MAF cleaned
- New (6) denso injectors from Motorwest and gaskets
- Vacuum lines are all in relatively good condition

Im running out of solutions here, what gives? what more do i need to do?

all of this without a single CEL which not to mention i cant even check it if i did get one because its a 96' and shorting the te1 + e1 doesn't work for smack.

 

Have you checked your fuel pressure? If that's good, then it might be worth checking the crankshaft position sensor and camshaft position sensor.

 

have you put a computer on it yet or do you have one?

 

Ignition System Issues
These are the most common:

• Failing ignition coil (especially on coils that serve two cylinders—waste spark systems).
  
  
• Worn or cracked spark plug wires – especially under heat or load.
  
  
• Old or fouled spark plugs – even if they "look" okay, carbon tracking or internal resistance can cause problems.
  
  
• Loose or corroded connections at the coil or plugs.
  

Fuel Delivery Problems
Intermittent fuel delivery = intermittent misfire.

• Dirty or clogged fuel injector – often shows up on a single cylinder.
  
  
• Weak fuel pump or pressure regulator – more likely to affect multiple cylinders under load.
  
  
• Bad injector wiring or ECU signal – check for continuity or signal with a noid light.
  

Vacuum or Air Intake Leaks
If it’s running lean, misfires follow.

• Leaky intake manifold gasket – common on older 5VZs.
  
  
• Cracked or brittle vacuum hoses – check around the throttle body and EGR.
  
  
• MAF sensor issues – dirty or failing MAFs can throw off fuel metering.
  

️ Sensor-Related Causes
Intermittent signals = intermittent combustion.

• Crankshaft or camshaft position sensor – when they start to fail, they often cause random or intermittent misfires.
  
  
• O2 sensors – especially upstream sensors; if they're lazy or slow, they can skew fuel trims.
  

Mechanical Problems
Less common but serious.

• Burnt valves or low compression in one cylinder – shows up in a single-cylinder misfire.
  
  
• Timing belt issues – if it's slightly off (like one tooth), it can cause rough running and misfires, especially at certain RPMs.
  

️ Diagnosis Tips

• Scan for codes – even if the CEL isn’t on, stored codes might point to a cylinder.
  
  
• Use a timing light or scan tool to watch for dropout in ignition.
  
  
• Spray carb cleaner around intake while idling to test for vacuum leaks.
  
  
• Swap components (coil, plug, wire) from one cylinder to another to see if the misfire follows.
  

 

really need to get a computer on it...

 

1. Motor Mounts (especially the driver's side)

• A wobble at cold start that smooths out warm often points to collapsed or cracked motor mounts, which settle once the engine warms and smooths.
  
  
• Under load, the engine torques, and if the mounts are shot, it’ll shake the chassis hard, especially when torque converter locks.
  
  
• These symptoms mimic a drivetrain misfire. Worth checking!
  

2. Torque Converter / Transmission Lockup Issue

• Since you feel it strongest in top gear at highway speed, converter lockup shudder is very plausible.
  
  
• If the torque converter clutch (TCC) is slipping, chattering, or trying to engage erratically, it can feel just like a misfire.
  
  
• Solution: A fluid flush (if it hasn’t been done recently), or possibly a failing TCC solenoid.
  
  
• Do a stall test or drive with OD off and see if the shake changes.
  

3. O2 Sensors (Lazy Upstream)

• Even if they aren’t throwing codes, an aging upstream O2 can cause rich/lean hesitation, especially under load.
  
  
• On warm-up, if you’re rich/lean hunting, the cold stumble makes sense.
  
  
• Solution: Try logging STFT/LTFT at idle and under load. If trims go wild, you’ve found your culprit.
  

4. Exhaust Leak at the Manifold

• If there's a leak pre-O2 sensor, it can throw fuel trims off and mimic a misfire.
  
  
• Also can explain cold stumble + highway shudder under load as AFR gets skewed.
  

5. Harmonic Balancer

• Not common, but if the rubber ring is separating, it can cause a visible engine shake that feels like a misfire—especially at startup and cruise.
  
  
• Check for wobble at idle when watching the pulley.
  

Bonus Weird One: ECU Capacitor Failing

• Some early 5VZ ECUs (especially pre-2000s) have been known to act flaky when caps start leaking.
  
  
• Not common but can cause load misfires, random trim issues, and intermittent ignition cut.
  

What I’d Do Next

1. Inspect mounts for cracks, especially the driver's side (look while power-braking in D with hood open).
   
   
2. Drive with O/D OFF and see if the shaking disappears—this isolates the TC.
   
   
3. Log fuel trims and O2 voltages with a scan tool (especially under acceleration).
   
   
4. Look for manifold exhaust leaks (cold start ticking or use soapy water test).
   
   
5. Check harmonic balancer for visible wobble at idle.
   
   

 

No, its pre OBD 2

 

Cold start misfires that go away are typically headgaskets leaking very slowly.

It mists coolant into the cylinder after running and all night it fills with mist, then on fire up, it stumbles.

A borescope into the cylinders after a hot run or pressurizing can sometimes spot this

 

I would run thru the free or close to free tests I pasted above before firing the parts cannon. Would just cost you some time. Good YouTube's on testing most of that stuff for free or near free money wise.

 

what would he be looking for in the scope? steam cleaning?

 

That was my first assumption. Per the previous owner the HG was replaced on both banks less than 100k ago, and if not that the heads are probably cracked. But the compression test coming out good and none of the cyls being washed might point towards a fuel/spark issue. Last thing left is probably the fuel tank pump

 

Dribbles or a fine mist on the camera.

5VZ's are known for it.

Another possibility is a valve issue. Compression never tells the whole story, cameras can show a lot.