Need Help Diagnosing Cylinder Misfire

Hello TW, I am in a bad spot right now. I have a '97 taco w/ a 3.4L v6 with a TRD supercharger (added aftermarket) and I am experiencing misfires on all of my cylinders and I cannot figure out what is causing it.

I just got my engine put back together after replacing the knock sensors and wiring harness. While I had it apart I replaced the intake, plenum, and throttle body gaskets, spark plugs and plug wires. Cleaned all the surfaces. I followed instruction that I found through different forums and youtube to take it apart and put everything back together torqueing everything to spec.

When I started it up I could automatically hear/feal that the engine was misfiring and after a couple minutes it threw these codes as well as had each code a second time but Pending:

P0300 (misfiring cylinder problem)
P0301 (cylinder 1)
P0302 (cylinder 2)
P0303 (cylinder 3)
P0304 (cylinder 4)
P0305 (cylinder 5)
P0306 (cylinder 6)

I checked that all the hoses were connected and didn't notice any signs of leaks, all plug wires are in the right order, I even put the old plugs and wires back on it with no change.

What should I do and where should I start?

 

Ran fine before? You didn't mix up water hose to heat the throttle body with the vacuum hose? (vacuum hose that comes off the back of each side of intake runner)

 

Or if you have an EGR you didn’t mixup the coolant and vacuum hose to the EGR valve to the supercharger?

 

Truck ran great before I took it apart. I have checked all hoses and they are all in the right place. I took pictures beforehand to make sure I didn't mix up any hoses.

 

I would double check all connectors and especially all grounds.

 

Still dealing with this issue, found out that I had a bad O2 sensor and one of my fuel injectors was actually bad so I have replaced both of those things. Put all new O-rings and grommets on all injectors. I have replaced a couple hoses that were starting to crack a little bit, all connectors are good and grounds are clean.

The next thing I am going to do is take it all back apart and put gasket sealer on the intake and plenum gaskets to make sure it's not being caused by a leak there, and ohm test the new knock sensors and harness to make sure they are working the way that they should.

One other issue I am seeing is that my short term fuel trim is too high, sitting at about 19.5% at idle and then when accelerating it looks more normal running as low as -4.1%

If the gasket sealer doesn't do the trick then I am going to take it in to the mechanic because I have no other ideas

 

The fuel trim is really lean. I would suspect a vacuum leak for sure. Especially since it levels out when accelerating. Did you make sure to torque the intake bolts? Or at least start in the middle when tightening and work your way toward the ends evenly.

If you tightened in an odd sequence the intake could be sucking in air. I would think that would be a pretty audible noise though.

 

That's what a couple buddies of mine said as well. It does seem lie a vacuum leak. Just happened to find those other things not working correctly either. I could not find the torque sequence for the manifold when I did it the first time but I did start out in the middle and work my way out and there has been no audible noise or area where I had carb cleaner sucked in.

I found a FSM online but it doesn't give a specific torque sequence for the intake manifold. So I guess I will do the same inside out method.

 

I’m curious, does the truck actually stay running? Or does it die right away?

if every cylinder is misfiring that’s kind of crazy if it stays running.

have you tried clearing the codes? Do they all come back?

another easy thing to check is the Mass airflow sensor. If you have a buddy with a similar truck you might be able to swap MAF sensors with him and see if it does anything.

 

The truck still runs, and I can drive it. While it runs it surges a bit and isn't smooth. My short term fuel trim is lower and idles around -0.8% to 10ish %

Haven't been able to check the MAF, I did clean it. While looking at live data it seems that it is running a bit on the high side.

I got it back together today and put gasket sealer on the intake and plenum gaskets to make sure that there wasn't a vacuum leak from there.

I have cleared the codes a couple times and they do end up coming back. After getting it back together today I drove it and the codes I am getting have slightly changed. I am seeing:

P0300 (misfiring cylinder problem)
P0301 (cylinder 1)
P0303 (cylinder 3)
P0305 (cylinder 5)

and these ones as pending, which I am not exactly sure what that means.

P0300 (misfiring cylinder problem)
P0301 (cylinder 1)
P0302 (cylinder 2)
P0303 (cylinder 3)
P0304 (cylinder 4)
P0305 (cylinder 5)
P0306 (cylinder 6)

 

Stupid question but have you checked all plug wires for burs where they could jump fire? I had a similar issue on my 99’ took it to several people and they all said vacuum leak vacuum leak vacuum leak even with the P0301 misfire code. One of my dads mechanic buddies came out, popped the hood and said change your wires.. instantly ram like new.

 

I could take a closer look at them, but they are new oem wires. When it first started to happen I even changed the plugs and wires back to the old set and it didn't change anything.

 

Gotcha. Seems strange it worked then didn’t work. Which is what mine did , mine was jumping fire in the head right before the wire connected to the plug.

 

Can’t see the spark because of the flash but it was all the way at the bottom. Good luck buddy!

 

I have pulled all the plugs and tested the spark with the engine running and didn't see any other sparking happening.

 

Thanks for the idea! I am really grasping at straws at this point. Planning to take it in to the mechanic in the morning.

 

I wish I could help ya but I’m not a mechanic lol. Wish you the best.

 

I’m not sure with yours being the v6 if the plugs install the same way but it’s always possible

 

This is my first toyota and the setup is the first I have seen with three coil packs and no distributor. It has been a learning experience.

 

My first yota as well. We will learn as we go bro. Keep at it.