Clacking sound from Cylinder 4 - 1999 2WD 3.4L

Hello all,

first time poster and don’t know jack about cars so go east on me.

Truck is 1999 2WD 3.4L V6, 230k miles. For a couple weeks I’ve been getting a clacking sound from the engine; this past weekend I changed my oil and it didn’t improve. With the engine running I can feel the plug terminal on the valve cover for cylinder 4 shaking in time with the sound; all other terminals were secure and didn’t vibrate.

The sound starts as soon as the engine starts, is noticeable while idling, more noticeable below 30 mph, and isn’t noticeable over 30mph.

I have not yet inspected the spark plugs or tried changing them. No check engine light but I haven’t checked if it’s throwing any codes.

any thoughts or advice for diagnosis would be appreciated!

 

Not to go west on you but are you talking about the 2nd cylinder on the driver side spark plug tube?

 

That’s the one. Middle cylinder on the driver’s side. I actually looked at it with my brother this afternoon and we noticed the coil (or whatever the top bit is that sits on top of the valve cover) is actually moving, pulsing up and down by about a mm as the cylinder fires. He said he thinks it could be a valve clearance issue or a bad spark plug seal. I don’t know what either of those mean but I’m looking into it lol

 

That is super weird, and makes very little sense unless the spark plug is loose enough to be letting cylinder pressure through the threads. Can you check? It would not be valve related.

 

Yeah I'll check it out and get back to you, I actually have new plugs coming in the mail since I don't know when the previous owner last swapped them. His hunch about the valves was just based on the sound, before we noticed the ignition coil jiggling around.

 

Agreed
and easy fix

 

Hey so I got new Denso dual-electrode plugs in the mail. Currently working on the truck. The plug boot and tube for the problem cylinder was caked in carbon and soot, I pulled the plugs and they not OEM single-electrode so someone did the plugs at some point before I bought the truck.

I can’t get the new plug to thread at all. Won’t bite even a little. I’ve done 4 plugs already and had no trouble with them. I’m thinking the last person do do the plugs cross-threaded or stripped the plug hole and that’s how I’m losing compression/exhaust up through the plug boot and and valv cover.

not sure what my options are if I can’t get the plug to thread.

 

not huge deal.......just as long as you have clearance to use something like this

$15 Spark Plug Thread Repair Kit, 14mm Cylinder Head Rethreaded Kit Repair Tools Gasoline Engine M14x1.25 Inserts and M16x1.25 Tap Kit

https://www.amazon.com/Cylinder-Ret...=&hvlocphy=9052405&hvtargid=pla-1951094768068

now i didnt research exactly what SP thread size you have, but you get the idea

 

Sounds like you found the issue!
I'd probably try what Control Car sent you

 

Update: Truck is running, leaving this here for others with similar issues:

First thing I tried was a thread chaser, which looks like a tap but is designed to “shape up” existing threads if they’re mildly damaged or have grime in them, rather than cut new threads.

After using the chaser with anti-seize paste I tried screwing in a new spark plug without any anti-seize paste, since there should have been plenty from the chaser. The plug came back out with anti-seize all the way up the threads, which indicated it was inserted all th way into the hole but didn’t catch a thread, so the hole was completely stripped.

next I purchased a 14mm spark plug thread repair kit from autozone for about $15. It came with a tap and inserts of different depths. I covered the tap in grease to catch metal shavings and used a ratchet to slowly retap new threads in the plug hole, backing it out periodically. I fished a skinny hose into the cylinder to vacuum out any shavings that fell in, there was a pile about the size of a dime sitting on the piston surface. Was able to vacuum it up easily.

threaded the new spark plug into the insert with AS paste, used red loctite on the outside of the insert, and screwed that into the newly re-threaded plug hole. Let the loctite set for 12 hours. Truck runs fine!

my only concern is the quality of the repair kit, I’ve seen others reference kits that cost $150+ so I’m a little nervous about how cheap I went. If it fails I’ll take it to a machine shop. Wish me luck!

 

Well done!

 

EXCELLENT!!

great step vacuuming as well
Kudos!

 

Update: I drove around the neighborhood for about 15 minutes, got it up to temp, and everything was good. Running smooth, no noises.

This morning I got on the freeway and got up to about 55mph. The engine started running rough and the check engine light came on. I pulled over and put on my headlamp (this was about 5:30am) and opened the hood. Noticed a strong burnt smell, I checked the spark plug boots and all looked normal; noticed some light smoke, looked for the source and I noticed a drip fresh oil on the valve cover (maybe below the valve cover, it was dark and I was stressed) but somewhere toward the rear of the engine on the driver's side.

Immediately took the truck home, it ran rough all the way back, even while idling, but the check engine light didn't come back on. Didn't have time to look at it any further, had to catch a train to work.

Plan is to:
1. Double-check all hoses, wire harnesses, spark plug wire layout to make sure I put everything back correctly after changing the plugs
2. Remove the new spark plugs and check electrodes for damage, check electrode gaps, they're brand new so hopefully it's easy to tell
3. Then inspect the valve cover seal for oil leaks; replace cover gaskets if necessary
4. Replace spark plug tube seals, PCV grommet and PCV valve
5. Replace air filter

Obviously with it running rough it could definitely be an electrical issue related to the spark plugs I just replaced, but the burning oil was suspect. As a newbie to doing my own work I feel defeated, I was really careful to do the spark plug change by the book and even called my mechanic to run through it with him verbally. If I go through the above steps and still can't get it running right I'll take it in to the shop.

 

Well crap

Check out the tossed code 1st
If the same as b4, that’s your starting point

don’t worry about VC leaking, unless HUGE, will not toss CE lite. Save that for another time.

guessing that burning smell just might be the same wollered out SP thread.

PCV and grommet good idea/fairly inexpensive

get everyone that newly popped code

U GOT THIS

 

@ControlCar Wanted to circle back and update you on this since you were so encouraging!

After i got that misfire, I ended up replacing the VC gaskets, mostly because when I pulled out the original plugs, a couple of them were badly oil-fouled and had oil sitting in the bottom of the plug tube so i figured my SP tube seals were leaking.

I pulled off the airbox and intake plenums, disconnected all the vacuum hoses, etc. broke a hose because they were so brittle but was able to find one at a dealership and replace.

Pulled the valve covers, got them cleaned up; buckets and cams looked okay, some weird wear patterns on some of the cam lobes but no sludge or metal sparkles in there. Still kicking myself for forgetting to take photos while i had the VCs off.

Installed new spark plug tube seals and vc gaskets. Didn't mess with resealing the half moons or cam caps, was already feeling in over my head so left them alone.

Valve covers and intake went back on with FIPG in recommended spots, new spark plugs went back in, installed new NGK brand wires on driver's side and got all the vacuum lines and throttle cables hooked back up.

Truck has run perfectly fine ever since! I eventually did get those codes read and they were for a misfire; haven't thrown a CE light since.

thanks for your support, i went into this having never touched a wrench and couldn't have told you what a spark plug looks like so this was a big deal for me!

 

Awesome job!!!

always good to help anyone that listens and willing to wrench/get dirty