Knocking after intake removal

[Axianator]

Can't believe I'm posting in this section, but here's the story.

On Wednesday night, I decided to remove my upper intake for some plug gap measurements and valve cover cleaning (TB coolant line bypass was also performed while the intake was off). I was slow and careful during removal and installation but still ended up with a stumbling idle after reinstallation. Figuring a vacuum leak was to blame, I double checked my connections again this afternoon and noticed that the EGR-to-intake bolts weren't fully threaded into their holes, resulting in a teeny gap between the EGR and intake which created a vaccum leak. I tightened everything up and the stumbling idle was fixed. I let the car sit at idle for a few mintues before I left for my test drive, thinking that everything was golden. Right?

Wrong.

After a few minutes of a seemingly perfect idle (and no more stumbling around 400-600rpms like the night before), the stumbling returned right as I was about to leave. The engine would never completely stall, but it wouldn't hold an idle, either. I decided to shut to engine off and give it a few seconds before I restarted.

That's when it happened.

All of the sudden, as I restart the engine, I hear a strange knocking sound that wasn't present just a minute ago. The best description I can give is that it sounds as though something is rattling around inside the block and is not unlike the sound of a completely failed cam tensioner or chain. The sound is RPM-matching and will very rarely fade away and come back after I rev the engine. I've always heard a significantly softer version of this sound since I owned my SHO (sdpatt and I noticed it after my 60k in '02) but it's never been this loud or noticeable.

Regardless, I'm both stumped and very concerned. The engine was idling quietly one minute and making noises the next. I welcome any and all suggestions or ideas as to what could be causing this sound. The sound is present as soon as you start the car, is with you through-out the rev range and is concurrent with engine speed. It's pretty loud and, to the casual observer, can be heard from both the top and bottom of the engine.

Based on various searches I've performed, I've read the following may be possible:

- rod bearings or wrist pin failure
- loose spark plug that was not fully tightened
- bad or low octane gas
- hardened carbon deposits or other foreign material in the cylinder
- bad water pump or accesory bearing(s) or bolts
- other misc. things like a loose bolt, etc.

It should be noted that aside from the sound, the engine idles perfectly now. My rod bearings shouldn't be a concern since they were changed 10k and 6 months ago by TexanTony himself. Oil level is good although it'll need changing within a few hundred miles. Engine is otherwise perfectly healthy (sdpatt and Tony can attest to this) and is fed Castrol GTX 10w-30 with a Motorcraft FL-400S filter every 3k miles. The only plugs that were touched the night before were the front three (gap was measured and adjusted, plugs reinstalled) and the wires stayed on the coil pack. I am using 87 octane gas with this tank, but I've already put 100 trouble-free miles on this tank and I can't believe that the low octane would cause a sudden and unexplained knock like I'm hearing.

Any ideas what would cause a seemingly-fixed idle to start stumbling and then produce a sudden and consistent knocking sound?

 

[SHOman24v]

I would check to see if your intake is grounded, my friend had a problem were the car would stall. Every time we took the intake off it ran good for a while, then went back to acting up. He ended thinking it was a cam sensor, changed that and it did nothing. It was him not properly grounding his intake. I would make sure that the crossover bolts are tightned. Hope that this may help.

 

[Axianator]

Thanks for the help, SHOman. Unfortunately, I've double-checked and triple-checked all the connections that I can think of on the top of the engine and everything (grounds included) seems ok. I should also note that, aside from the knocking noise itself, the engine idles perfectly and does not seem to exhibit any other problems.

To help aid others in diagnosing my problem, I made a little clip of the SHO tonight. The clip is an .mp3 file (about 602kb in size) and can be downloaded here:

http://hosting.superhighoutput.com/axianator/audio/sho_knock.mp3

For the first 30 seconds, you'll here the engine start and idle with the microphone at hood level, right next to the drivers door. From 0:30-0:45 I take the microphone down near ground level and give it two quick revs. The final 5 seconds hear the mic taken back to hood level right before the engine is shut off. All recording was done by me with my person in the driver's seat, holding the microphone just outside the open drivers window. The hood was also closed during the entire recording, if that gives you any clue as to how loud the noise is.

Sometime this weekend, I plan on briefly running the engine with the accessory belt off, just to make sure that none of the front-end items are to blame for the noise. If the sound is still present after that test, then I'll try to obtain a mechanic's stethoscope and listen all around the engine and see if I can't pinpoint the source of the noise.

Again, any ideas or suggestions are welcome.

 

[SHOman24v]

WTF, it sounds like there is a bolt somewere in the engine.....

 

[AutoSHO]

Adam, I IMed you a few ideas that came to mind listening to that.

 

[DethSHO]

My car sounds similar

My engine is making the same noise, hence my post here:

http://www.shoforum.com/showthread.php?t=28178

It sounded like the cam, so we took off the valve covers today, and they looked fine... any other ideas?

 

[Racer X]

You think maybe you threw a shim? It doesn't sound like a spun bearing, I've done that once or twice on other cars (none of my Tauruses, knock on wood), and it didn't sound anything like that.

 

[SHOman24v]

You think maybe you threw a shim? It doesn't sound like a spun bearing, I've done that once or twice on other cars (none of my Tauruses, knock on wood), and it didn't sound anything like that.

Is that even possible?

 

[Porkchop]

Throwing a shim is possible as I have seen it with my own eyes. Doesn't happen that often but it does happen. Don't know exactly why though - thats the sucky part

 

[SHOspazz92]

Oh that sound is So HAUNTING, thats EXACTLY What my SHO sounded like when we spun a rod bearing....*shivers*

 

[revhardSHO]

So could it be a failing cam tensioner?

You could try running a cylinder balance test, just for more info.

 

[Bizzy]

Adam, stupid things to think about here.....

Are all the bolts in place and tight? Could anything have dropped down inside the intake ports while the intake was off? Did you take the valve covers off? If so, are they tight?

The sound is so familiar to me. Fred and I were discussing this past weekend my 3.2 swap and I had a racket very similar. It was the cam tensioner IIRC that wasn't all the way tightened down and that was what was making all the racket. I think my cam covers were on but not tightened all the way down also and that enhanced the noise. Or at least that was discussed. I was so freaked and tired that my memory is not so good on that one.

I think you'd be wise to pull the intake again as well as the cam covers and check those things out. I'll point Fred in this direction also so he can hear the audio clip.

 

[Axianator]

Guten idea on the tensioners, Beth. It's entirely possible that I've either ejected a shim or have some type of cam/tensioner problem. Chris (AutoSHO) and a few others have suggested that it might be exhaust-related, since my lack of a tight EGR was the cause of my initial vacuum leak the night of the intake removal. I felt all around the EGR pipe last night, however, and could not feel or notice anything out of the ordinary, eg. no leaks, cracks, etc. I also removed the front three spark plugs that I had been playing with the night of the intake removal and checked them again - all were fine with electrodes and insulators in place.

A quick rundown once more of what happened "the night of":
- Upper intake was removed, lower ports covered
- TB and IAC coolant line bypass mod performed
- front three plugs were removed, checked and reinstalled
- Upper intake was reinstalled with newly-bypassed TB lines
- Engine would not hold an idle, would stumble around 600rpms
- Vacuum leak assumed, could not find it that night

The next afternoon, the following happened:
- Teeny EGR vaccum leak was found to be the cause of stumbling idle
- EGR-to-intake bolts were fully tightened, EGR completely sealed
- With the EGR leak fixed, the engine would now idle perfectly
- Engine was ran for at least two minutes upon restart with no problems
- Towards end of test, the car started stumbling again (not sure why) but would not stall
- Engine was shut off after 5-10 seconds of this behavior
- Upon restart, the knocking sound appeared and has not gone away since

At this point, I'm guessing that the sound has to be coming from somewhere in the rotating assembly. The sound remains consistent with RPM and seems to be occurring with every revolution of the crank. I'm leaning towards the valvetrain, though it's possible that a wrist pin or the rod bearings are also to blame. I'd hope that it as something simple like a loose bolt/item that I've missed or perhaps an exhaust leak somewhere, but those things aren't looking likely at this point. I just pray that it's not either of the last two items I mentioned earlier (wrist pin or rod bearings), as I will not be a happy man if that case.

The search continues on ...

Many thanks for the thoughts thus far. Keep 'em coming.

 

[Axianator]

Just a little update for everyone.

The car is currently sitting in the garage of TexanTony with a nearly-***** engine. He informed me that he tore down both the top and bottom-ends of the engine but that he has yet to find anything - all of the valve shims were intact and within spec, the cams and (AFAIK) the tensioners/chains looked good, and all of the rod bearings were in place, not spun and looking "beautiful".

Knowing now that it's not a thrown shim or a spun bearing, we're both really scratching our heads on this one. The search for the sound continues on Mr. Tony's part, but I'd like to help him out in the search as much as possible.

What are everyone's thoughts? Any ideas on other areas we could check, keeping in mind the clip I posted earlier?

 

[revhardSHO]

Perhaps some dirt or pebbles fell into the lower intake runners as you were removing the upper intake? Did the plug wells look clean before you removed the plugs? Same thing could of happened there...

 

[Axianator]

The only plug wells that saw any kind of exposure were the front three, and they were all were free of oil and dirt, save a lil' grit in the #4 well. I took each plug out one-at-a-time and covered each hole with it's respective plug boot to prevent anything from entering the cylinder bore. The fact that the car ran perfectly (eg. like it did before I even touched the engine) after the intake was reinstalled and my EGR vaccum leak was fixed leads me to believe that the problem isn't a foreign object in the crankcase.

 

[CheckerSHO]

im not real sure about the vaccum/coolant line arrangment near the throttle body...and this seems a little off the wall i know...but is it possible that a coolant line got hooked up to the intake somehow and that sound is a mild hydrolocking situation? Im guessing the person that tore the engine down would have seen signs of this by now but i figured i'd get it out anyways

 

[biker889]

any update on this problem? My car has the SAME problem and i cannot figure it out. Except my car isnt as loud. Does your car still have power, mine has decent top end, but the low end isnt great.

 

[Axianator]

Sorry, man, but there won't be an update until Mr. Tony returns from his vacation a couple of weeks from now. Also unfortunate is the fact that the sound was still present even after he buttoned everything up last week (this, after a full inspection of the top and bottom-ends of the car - no ejected shims, no damaged cams, no failed tensionsers, no spun bearings, and no obvious anomolies). The next step is to tear back into the engine and keep digging until we find something. Our current suspicions are that either a failed valvetrain component (eg. a broken valve spring or failed keeper/guide) or a bad wrist pin are to blame at this point.

I'll keep everyone updated as further events warrant.

 

[DHMag]

Adam, it sounds awfully close to a stuck valve or unseated valve seat.