p0300 and many other misfire codes, extensive troubleshooting, no dice.

A few weeks ago I purchased an 04 sequoia with 220k. Test drive was fine, I noticed it lacked power up top but coming from early vortecs, that seemed normal-ish to me. Aside from the driver side manifold leak, everything checked out. It was almost empty so I stopped and got gas and drove it home. A few days down the road I noticed it popped a CEL. Pulled out the scanner, p0300, 1, 2, 4, 6, 8. Pretty sure 5 was in there at some point. Cleared the codes, tossed some heet and it went away. And then came back. I've been down the rabbit hole since.
First thing I did was change the plugs (some of them were loose.. and copper ngk's that didnt look too good) to denso's and figured that would be the fix. Nope. I replaced the Amazon coils with Densos (ouch, a bit pricey but buy once, cry once, right?). Didn't fix it.
I replaced the fuel filter. No change. Drove it until it was a 1/4 tank and then jumped the fuel pump and completely emptyed the tank at the filter input. Put in a fresh tank of gas. Still no change. Swapped out the crank angle sensor. From what I could see, the wiring looked ok.
I sprayed everywhere around the intake manifold and throttle body and pretty much every vac connection with carb cleaner to listen for an idle bump. Nothing.
So I cleaned the MAF. Still not getting anywhere. Throttle body was fairly clean, intake filter element was brand new.
I towed my corvette on a uhaul trailer this weekend and that was a very rough adventure. Thats a max weight of 5300lbs and some of the gentler hills were a challenge, basically anything that wasn't as flat as kansas. Thank God for no steep ones. Zero top end and some serious vibration above 65.
Anyways, earlier today while watching the live misfires on my autel with some roughish idle, it was getting pretty hot so I flipped the AC. I noticed if I turned on the ac, the misfires all went to zero and held zero. Perhaps the extra pulse width with the increased load smoothed everything out? So I got hopeful and checked the fuel pressure. Rock solid @ 42 at idle and free rev, little change. The o2 voltage graphs logged look like they are switching properly and both upstream and downstream appear to be functioning properly.
I guess next I will be checking the mechanical timing and then compression testing. PO claimed to change the belt 10k miles ago and had the aisin sticker. Perhaps it's a tooth off?
Any input would be appreciated as I'm new to this platform, but very experienced mechanically. I've been working on vehicles for 20 years, multiple engine pulls and rebuilds etc.

 

Double check your crank sensor wires are not damaged from the belt. Many times when the timing belt is replaced, this wiring gets routed wrong and gets damaged by the belt rubbing against it. It can be hard to see so check it twice.

 

Misfire being the result of improper ignition, timing, fuel, or air, and knowing what you did with air already, clipping that crank position harness could impact the fuel pump circuit indeed, though measuring consistent 42 at the rail makes me skeptical it's a fuel delivery problem. Don't get me wrong, it's worth checking that harness to confirm it was properly routed since clipping the harness by the belt is such an issue.

I agree, timing is the next thing I'd be verifying if this was my vehicle, and I think it should be the next step. For shits n giggles I'd also be using some CRC MAF cleaner to clean the MAF, I assume you also checked the existing MAF per the FSM to confirm it's within spec at ambient temp, just to confirm metered air is fine. And it sounds like all O2 are fine, and when you checked the harnesses, they haven't been cut/spliced and show no damage?

 

Given new to you vehicle and +200K miles, compression test would be good to have regardless.

Given you have the Autel, what are your MAF, IAT(intake air), Coolant Temp and LT(long term)/ST(short term) fuel trims....at idle.

 

Hope this guy replies. I hate when we never hear the results of troubleshooting.

 

Lol thank you for the replies. I have to work too but will be back at it this evening. If the crank angle sensor wiring is damaged it would be damaged inside the loom, no outside visual damage. I'll check it out too.

 

Looks like the mechanical timing is off two teeth on each cam. Compression was good, 181-190. Ordered up all the aisin kit (no way I'm resetting that and not changing out everything) and other associated items. Long weekend coming up to knock this out.

 

That’ll do it!

 

Ding ding ding. We have a winner.

The 'doesn't misfire under load' was the deal-sealer for me, I'm glad you noticed that symptom. Reminded me of this guy (long ass read), who has the VVTi version of the 4.7, and a step he forgot when doing cam seals led to a condition where his timing was slightly off. IIRC, if he gave it a little gas, misfires would disappear.

 

Damn. I hope that's not my issue. Those timing cover bolts are so corroded so I can't remove and get a full visual and I've had this issue right along thinking it's either water in the gas or a fuel pump on the way out.

Although my issue only comes and goes, so hopefully not.

 

It's amazing how much better everything runs in proper mechanical time. Also replaced the radiator, noticed some small leaking. Appreciate all the replies. Now to tackle this front lower oil pan leak..

 

You sure it's the pan, and not something leaking from above?

Not trying to ask a stupid question, we find much more often that the valve covers are leaking from above, down around everything, far more often than the pan is leaking. I can only think of one member on here who had a pan leak, I believe it was @FirstGenVol but I may be mis-remembering.

 

Wasn't me.

 

Well damn. I know I saw someone on here saying they had a pan leak. And it's not that you stripped the threads on your oil pan, is it? Or was that the trans pan?

Oil pan leaks seem to be super unusual in the 2UZ unless someone else took it off previously for some reason.