98 1st gen Taco misfiring #3 & #4 cyls

Hi all. New guy here. 98 Taco 3.4 V6 290k miles.
Relatively capable w/tools but bonehead capable as well.

Engine recently started misfiring and had #4 & random misfire readings... so pulled #4 plug and center diode totally burned down...
swapped in new

$18 denso k16tr11 spark plugs, pack of 4

denso k16tr11 plugs but still misfired. old plugs showed high temp stains @porcelain to thread connection...

so replaced original coils and problem got worse, misfiring w/a backfire and now reading misfire at 3&4...

Have also had a sort of high pitched whine for a bit from intake (note: K&N filter had fallen off briefly a while back so pulled tube to check throttle body. sprayed w/TB cleaner not realizing it might drip and crud up inner workings as recently noticed on timmy toolman intake plenum vid)

about to order gaskets and injectors thinking fuel injectors may be cause but am curious to linked cylinders misfiring together maybe not being coincidental. Had also previously replaced SP wires a couple years back...

Hoping to solve asap for minimal cost... also hoping backfire wasn't sign of internal damage.

Going to invest in compression tester and see if it's worth a deep dive...

plan on changing injectors, intake & TB gaskets, VC gaskets while accessible, and cleaning throttle body. maybe new plug wires.

Any input would be greatly appreciated!

Thanks!

 

Current codes are P0303/P0304?

 

If P0172 pops……that might very well be injectors

 

Yes, current codes P0303/P0304/& random misfire detected...

Forgot to mention that when this first started and since there has been a noticable vibration...

Just checked SP wires and it seems they were a bit loose @ connection to coils.... recrimped ends and have tighter connection to coils... seems to have moments of running slightly better/smoother but quickly back to rough w/vibration...

seems new plug wires might be a good next step...?

 

Agreed with new wires

after the crimping fix…..codes still?

 

Here are old plugs... 2,4,6 all seem to show more wear and higher temp... also seem to be burning richer... due to less spark? Seeming likely poor signal/power from coils...?

 

You can measure the resistance of your injectors, and on the driver's side you can actually access the wires without having to do anything else. I think. It's been around 25K - 30K miles since I replaced mine.

The injector should measure around 14 ohms when measured across it with the engine turned off. 15 ohms is suspect, more than required replacing the injector. I can't recall but I think one must pull the plug off of the injector to get a correct reading.

 

Code was still there so cleared codes and ran it for a bit... very rough at low rpms idling but smooth out a bit near 1800-2000 rpm... no codes or chk eng light yet but not running better.
Have some new denso wires on the way a couple days out...

 

I would use the double tipped OE equivalent for the 5VZ from what I have read here from seasoned V6 members

 

I lied. Sorry, don't know what I was thinking.

 

Had a similar issue with my 98 when I got her... the prior repair involved taking the upper intake off and they tech used a fiber gasket and it sucked through. I think that that whine you are hearing is a vacuum leak. Look at your upper to lower intake connection and see if you see metal or fibre. There is a reason why Toyota uses a 3 peice metal intake gasket and this is it.

 

great idea^^^
Brake cleaner test (the bad flammable stuff)
While engine running, spray BC on top of engine
If RPM’s change, there is your vacuum leak