2003 4.7L limited misfire hell

Hi all,

first post here looking for some help. Been dealing with a p0305 misfire code for some time. Bought the truck last year so once the code came up I figured might as well replace plugs injectors and coils while I’m dinking around. Put her all back together, started getting a p0301 misfire code. Checked compression on the 1 and 5 cylinder and we’re good. Continuity on the injector clips was fine. Didn’t understand why the misfire code would switch, but started swapping parts around to see if I bought a dud (all denso btw). Same p0301. might bite me in the butt later, but pulled the ecm fuse and restarted. Back to p0305. At this point I’m out of easy options that I can think of. I think it’s useful to mention that the previous owner installed new dual cats as I’ve seen some threads mention misfires down the road after doing the same? All those issues seemed to be solved by replacing injectors or coil packs. Sorry for the wall of text but I think it’s should all be pertinent. Any help is appreciated thanks for reading!

 

I mean, if you bought your Denso parts on fleaBay or scAmazon you may've gotten counterfeits. They're rampant at those sites.

The traditional way to do this without the fucking semi-auto-parts-cannon at the problem is to simply move the coil pack on the misfiring cylinder to the cylinder next to it, and swap the plug on the misfiring cylinder to the other cylinder next door, so you distribute the sparking bits to two different cylinders, and monitor for another misfire. If the misfire is still there, sparks aren't your problem.

Understand: EFI engines need air, fuel, spark (metered) Misfires are caused by a limited variety of things...

• Bad spark
• Air/vacuum problems (or air metering)
• Fuel delivery
• Timing problems

Given you replaced all the sparky bits, and it's persisting, we can rest assured it's probably not spark.

Given it's on one and sometimes two cylinders, not one entire bank... and you replaced all the injectors, we can safely say it's probably not fuel delivery.

That leaves us with air/vacuum problems and timing. And I'm suspecting timing without knowing any better, because it's persistently on a cylinder and sometimes on another cylinder.

The timing is an engine killer on these Tundras with the V8. You MUST replace the timing belt with a new OEM/Aisin brand belt every 90k or 9yrs. If you decide you're smarter than Toyota and use an off-brand or get counterfeit product, you need to reduce that time-to-change considerably, like maybe half of what Toyota recommends (if you use OEM or the Aisin kit, no problem going 10yr/100k).

So I ask you:

• Last time timing belt was done?
• Have you verified timing before throwing all the fucking money/parts at your engine?
• Have you at least inspected the belt to see if maybe a mouse, an acorn, or something else got in there and made it jump a tooth, which would cause these symptoms?

Don't get me wrong. Your issue could be as simple as your intake gasket is fucked on bank 1, and you're getting extra air on cylinders 1 and 5 periodically. Gaskets fail, and getting extra air pulled into those cylinders would cause a misfire on a single cylinder. If you've had the intake off recently, and you didn't inspect or replace the gaskets (as you should, when you take the intake off, and trust me, you don't want to use aftermarket gaskets, we can share horror stories with pictures), sure, that could possibly be the issue. But my gut is telling me you need to be validating your timing my dude.

 

Appreciate the input. Before buying anything I swapped out the injectors coils and plugs and was able to alleviate the issue after cleaning injectors and replacing them. New parts (oem and not from Amazon) back on, issues started back up. When bought I checked timing and was fine, belts seemed relatively new. However, I haven’t replaced it in the year I’ve owned it. Will check timing and update with status. Thanks.

 

Is this misfire easily duplicated? For example whenever the engine is running the misfire is guaranteed to occur or does it only happen under certain conditions as in cold start, under load etc.?

 

Update: Solved.

Timing is fine; belt is fine but probably will replace soon. Got my hands on a fancy diag that can read your trucks dreams and shit to get a live misfire data (was relying on an ultra gauge, which may have given confusing code sequences beforehand). Only cylinder 1 shows anything. Swapped the coils and the misfire jumped to three. I think i stated above hastily about replacing parts and it may come across ambiguous, but to clarify i only swapped the coil packs that had the rubber boots break when removing (3) so original parts remained. At this point I think I'm just not smart enough to take two identical parts that are in my hands and make sure they actually switch.

And yes, the misfire was easily duplicated and constant at idle, higher rev, cold, warm, etc. As should be evident for a faulty ignition coil.