Drilled a hole in my intake manifold today

[JamSKahler]

Yeah, I know.

So to start off, my Jeep has been functioning terribly over the past year or so.

It's had an ongoing issue where it won't idle and I have to apply gas + brake at the same time to keep it alive, which I thought was from a clog in the catalytic converter.

I want to say that there was some kind of clog in the intake manifold instead. Here's why. On cylinder #1, before I drilled holes, today I found a couple of cracks in the manifold which looked exactly like they had been created *by* vacuum pressure itself. There had been a leak and large enough vacuum pressure from the cylinder to actually pull straight through the plastic at it's weakest areas.

So I figured, well ok let's see what happens when I drilled a hole right there. Just where those cracks we're at.

Sure enough, my car now idles like new.

Now all I have to do is figure out what's going on with the engine. Just this morning, before drilling, the car developed a consistent "hitting" sound louder at low rpms that is same as the speed of the engine. Mechanical hitting sound, like something bad. Piston hitting something or some kind of mechanical issue w/ explosions opposing engine momentum.

Anybody have any idea what could be the cause? Sometimes during acceleration the pop will occur louder at times, like something randomly hitting something else harder. Definitely sounds... bad. It is completely consistent, does not "disappear".

(Edit: Also, I don't think it's possible anything got into the cylinders through the cracks - the first ones were way too small for anything to get in there)

 

[Sephiroth]

You have successfully created a vacuum leak, check your long term fuel trim, you're probably running lean I would have tried an IAC before drilling your manifold, it's probably sticking and choking the engine at idle, now you need a new intake, the knock could be rocker arm, do you have a cel? Any missfiring cilinders?

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[JamSKahler]

I wanna say I needed a new intake manifold from the get go. On that cylinder, there were indentations leading to cracks only an excessively high vacuum pressure could create.

As far as IAC goes I still need to check it - I'm not exactly sure where it is but I know I at least cleaned the sensor for it. It does still respond slowly to throttle (delay) so it could be an additional cause here.

(Where do I find IAC?)

Also had knock sensor codes before drilling the hole, haven't noticed any additional issues. I think I had p301 as well.

Also knock is percussing loudly through intake manifold on that side and sound can be localized there

Starting to think. Any possible / likely first go-to places for engine damage from excessive vacuum pressure in a cylinder? I'm still not at all sure what could have gotten stuck in my manifold

Also starting to wonder if indentations were caused after cracks instead of before...

 

[tjkj2002]

You can not have excessive vacuum on a naturally aspirated engine.

 

[JamSKahler]

Ok. So what's caused holes on *only one* of the ports on my intake(aside from me)? That's the part I'm trying to figure out. The holes are nearest to the engine. I'm not sure if antifreeze is a reasonable option, simply because I've been using mostly water after having had a head gasket-like issue in the past.

All I know is that my car idles smoothly now (aside from the sounds) after creating this leak and seems to run much better. It will actually idle at 7000 rpm now, and it feels like *all* cylinders are firing. The gas mileage has decreased a bit more though. Was at 10 mpg before, now down to 8-9.

Edit: Could gasoline erode the plastic away? Say if that cylinder were regularly misfiring

 

[JamSKahler]

Um here's a theory if anybody wants to think it over. Not sure if plausible, but it kind of connects the dots at least.

Say the exhaust valve in cylinder 1 stuck shut. Over time unburned gasoline throws back into intake and erodes plastic, making it thin enough for vacuum pressure created from intake stroke to crack it.

And then something something rocker arms creating popping noise due to stuck exhaust valve. (Btw this sound resonates loudly in manifold, like a hollow repetitive popping sound.)

(?)

 

[Sephiroth]

Take the valve covers off and make sure everything seems ok in there, no broken or lose parts you should not be able to move anything be hand, the IAC is located at the trhottle body under the position censor make sure it's port is clean and you could test it by screwing in the plunger and put it back in, idle should be higher and slowly get back to normal. normal idle is at about 600rpm in your case about 700 with that leak. Vacuum is not likely to break anything, the engine would have stalled before causing any damage.

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[tjkj2002]

Ok. So what's caused holes on *only one* of the ports on my intake(aside from me)? That's the part I'm trying to figure out. The holes are nearest to the engine. I'm not sure if antifreeze is a reasonable option, simply because I've been using mostly water after having had a head gasket-like issue in the past.

All I know is that my car idles smoothly now (aside from the sounds) after creating this leak and seems to run much better. It will actually idle at 7000 rpm now, and it feels like *all* cylinders are firing. The gas mileage has decreased a bit more though. Was at 10 mpg before, now down to 8-9.

Edit: Could gasoline erode the plastic away? Say if that cylinder were regularly misfiring

In bold is a dead give away to the issue.

Only 1 way the intake got "stress cracks" and that is from to much heat.