Can cylinder misfire be cause by insufficient clamping between plenum and manifold?

Okay -- this may be far fetched but I will ask.

After performing a cylinder leakdown test and general checking of spark plugs (to find a source of oil loss/burning), I am getting the engine codes for misfiring of cylinders 1 and 2. The engine runs but is mildly shaking. I decided not to drive the truck until I resolve the codes.

All the spark plugs and the ignition coils were in good condition. The spark plugs were changed when I replaced my head gaskets about 7-8 months ago. There is no oil residue on the spark plugs.

However, one thing happened during the reassembly after the leakdown test: As I was unaware I had just broken my torque wrench, I was overtightening one of the hex bolts that attach the intake manifold to the plenum and I broke it. I guess the spring in the torque wrench broke after the previously fastened one of these bolts.





I haven't had a chance to extract the broken part out and get a new bolt so I just reassembled the intake using the 3 remaining hex bolts and the two nuts, one at each end.

Could the lack of clamping force between the intake manifold and the plenum be leaking air, which in turn is causing a lower compression and the cylinder misfiring?

 

It could be a vacuum leak, but it will not effect compression if the valves are sealing as they should.

The vacuum leak would also cause poor idle and shaking.

 

But you wouldn't say this would cause misfire ?

 

I just checked my OBDII again -- in addition to the misfire codes, I am also getting

P0441 -- Evaporative Emission System Incorrect Purge Flow
P0455 -- Evaporative Emission System Leak Detected (large leak)

Could those be caused by the missing bolt between the manifold and the plenum ?

 

Not trying to sound like a Search Nazi, but there are 20 threads that have P0441 in the title; 2 that have P0455 in the title.

Jimmyh did a nice job of covering both in post #4 of this thread:

https://www.tacomaworld.com/threads/p0441-and-p0455-in-2005-v6-help-plz.383001/

 

I know but I'm trying to relate it to my relatively odd circumstance, which is a possible leak due to a bolt missing and wether that causes a loss in vacuum and these codes. Or how I introduced the condition by merely lifting the intake manifold to reach the spark plugs.

 

evap system codes being thrown have nothing to do with that. The system does a pressure test of the charcoal caniser and tank every so often when its off.... if it doesn't hold pressure it throws a code.

 

I disconnected the battery to reset the codes and wasn't getting them after.

 

Update: I have found it's two spark plugs that are causing the misfires. I did it by moving them around.

At first the OBDII was saying cylinders 1 and 2 were misfiring. So I took both the coils and plugs (as I wasn't sure if it was one or the other) from the said positions and put them in 3 and 4. Reset the codes by disconnecting the battery, got an updated reading -- showing 3 and 4 were misfiring. I was onto something...

So now, still not knowing if it was the coils or the plugs or both, I switched just the coils in positions 3 and 4 with 5 and 6 respectively. Reset the codes, got the reading, still showing 3 and 4 misfiring. Then I switched the plugs from 3 and 4 to 5 and 6, and got corresponding error codes, meaning it was the plugs.

But I changed the plugs with iridium ones less than a year ago when I was doing my head gaskets. The mystery is, how did I damage them while I was checking for oil residue and doing my cylinder leakdown test?

The only thing that comes to mind is that they may have gotten wet as it was raining and got shorted when I put them back in. Is that a likely scenario?

 

No.

 

No getting the plugs wet isn't the issue.

You may have bumped the tip and knocked the iridium off ( iridium is very hard, but brittle ) or changed the gap.

 

I believe that Torque Lite will reset OBD codes - It's a free Android APP. Saves you the grief of pulling the ground strap off the battery.

 

Is there any way to test this and find out exactly what happened? I'd be willing to ship the plugs to get them diagnosed. Cause it's bugging me

 

It will be obvious if the tip is damaged, compared to an unbroke one.

 

All the 6 of them look the same. No difference in the ones that the test indicates are broken.

I will know for sure when I replace them.

 

It could be a cracked glass insulator.

Any damage to the tips should be visible and or detected by checking the air gap.

 

Get rid of the Iridiums and install a set of copper plugs. That would be cheaper/quicker than shipping plugs to whoever for analysis.

 

If the manifold is loose you're probably running those cylinders lean. There's unmetered air getting in.

Fix that before you waste time chasing other issues.

 

1GR hates expensive crap, so Iridium plugs are not needed,
Get cheap Denso from dealer and you will be fine. Also get better torque wrench when working on engine.

 

I'm with this guy. Unless you are running a super charger, get those iridium plugs out of there. Go back to factory. They are cheap to replace. You will have to change them every 30k. But will run better.
As for that plenum bolt....whether it is the cause of this problem or not....GET IT FIXED! It will eventually cause issues that will be costly down the road. P0455? Check your gas cap. Is it a locking one or and aftermarket one? Throw it in the trash. Get a factory cap.