Possible vacuum leak?

[Zach0112]

So, I've been reading through here and Gagt and I think I may have a vacuum leak. I have a low rpm surge, below 1800ish rpm) that gives a trailer hitching feeling going up hills. While driving easing into the gas it seems low on power and when you hit 2000 rpms the engine note completely changes. Not just because it's spinning faster, but almost sounds like it smooths out or something. You can feel it pull so much more right when you hit 2000-2100. Kinda like a boost of power. While I had my hood open tonight I could hear a Sucking sound. At first I thought it was my wai, but on further inspection I noticed it was coming from the passenger side. So I started working the throttle and the Sucking sound would get louder, louder than my wai I think even. Sounds like it behind my ps pump and just to the rear a bit. Can't really see down there, but are there hoses or anything? I sprayed starter fluid down there with out a change in engine sound. Seriously sounds like I have a filter tucked in behind my pump, it's that loud. I'm also getting 27-28 mpg with the 3.4 with spirited driving. It's strange if it were a vacuum leak that I'd still be getting this.

[sleepyalero]

If your rpms jump up and down and you feel it on slight incline. It could be a bad torque coverter. I had the same issue. Sounds like you have a vac leak as well... and no hoses over there really.

[Zach0112]

Idk where it was or who posted it (he's one of the better known guys here like you, Chris, Mike and so on), but he hadan idea on checking the torque convertor in a way. set cruise at 55 put just a small amount of pressure on the gas, turn cruise off, hit the brakes just hard enough for the torque convertor to unlock, if it jumped up a couple hundred rpm that was good. Can't remember exactly why, but my car did as he described. I know I have a small amount of weeping taking place on both sides of the limg, but wouldn't the air get sucked in just under the Uim? Thanks on the hose part, never really had much off the pass side of the engine to get a good look.

[sleepyalero]

Kinda sounds like a LIM leak. But I honestly dont know.

When I had the rpm issue. After I swapped tranny it never did it again. So I assume it was indeed a torque converter

[a.graham52]

My 3400 had a plugged vaccum port on the rear passenger side of the upper intake . If the cap came off or is rotten, there's your leak.

[Zach0112]

It may in fact be a torque convertor issue, but it does it in a gears. I guess you could say it feels like a miss. I'll hook a vacuum gauge up this after noon to see what I pull and how steady it is. Supposed to be right around 20 I think.

[Zach0112]

Graham, I had suspected that also. I know when you touch it your fingers turn black. It's beginning to get on the rotten side. I'll pull that cap off and stick my finger over it to see if it changes.

[sleepyalero]

You know what. I conpletely forgot about that little port..... haha my bad.

Yeah the TC mine usually only did at 30+mph.

My cars vac gauge sits about 18-20

[Zach0112]

Pressure tested cooling system. Held 15 psi for ten minutes. Stuck the lil rubber cap on vacuum gun held vacuum good. Still have to check engine vacuum though.

[sleepyalero]

Let us know.

[Zach0112]

On the way home from school I was paying attention to when it would start Surging and you had it right on the money with 30 mph. I'll get back with vacuum readings within the hour. Gonna try idle, just above where it runs a lil rough and I'll say at about 3k.

[sleepyalero]

So when it surges does the rpms go up and down about 600 rpm or so then back down along with the whole car. Can you feel it and does it go... vroom vroom vroom vroom

[Zach0112]

When it surges it normally only jumps 1-200 rpms & 300 tops I'm guessing. When I did that check I told you about earlier with tapping the brakes, then it will jump the 600 or so rpms. Yes, I can feel the car go vroom vroom vroom and more so on steep hills. With high load low rpm scenarios. Did the vacuum test. Idle the needle shakes like crazy between 18 and 19. Needle looks like a blur almost. When I hit the rough spot (about 2200) the gauge reads just a lil higher, but continues shaking as described. I set up screen mirroring with my phone and laptop so I could see the tach while under the hood and brought it to 3k. At 3k needle is rock solid at 20. The exhaust does make a faint poof sound every couple seconds and it affects my rpms about 100 rpms. Watched this on the tech ll. It isn't showing any misfires while this happens.

[sleepyalero]

Sounds like a misfire. But you def probably have a bad TC unfortunately...

Sounds like you might have a vac leak to somewhere from going off the gauge... but vac leaks are hard to find

[Zach0112]

I was hoping it wasn't a torque convertor lol. Maybe one of these days I can get the tech ll and go for a cruise and watch what the tc does. But yeah the sound I hear is like a loud whooshing and my wai is nowhere near as loud as it used to be. Maybe due to this new noise masking it? It's coming from somewhere on the passenger side just not sure where. Sounds like it's somewhere around the Schrader valve.

[Zach0112]

I'm sure you understood me, but to clarify, when I said the rpms jump anywhere between 1-300 that's cruising or a hill. When they jump up 600 that me tapping the brakes lightly to unlock the tc. I've run it in 3rd up the hills and it still does it, but definitely not as noticeable. I'm assuming because the rpms are up. If I go balls out and drive the car hard I don't have issues with Surging. Nice smooth gear changes and it doesn't miss a beat. It's like the Surging issue is only low rpm based.

[Garnetdawn]

My car was doing that last week for like a day and suddenly stopped I was thinking it was the torque converter but it hasn't done it since so i forgot about it till i read this.

[Zach0112]

Probably is tc. I dunno. If it makes any difference I have a whole lotta oil in the upper intake. When I did vac test I saw oil where the brake booster connects and so I stuck a qtip into the nipple and it's gooey oil.

[sleepyalero]

yeah I know what you meant. it only happens on slight inclines or bigger.. and only with slight throttle.

as for oil in the in the UIM. that's normal. that is from the PCV.

[Zach0112]

Yup, car does it exactly when yours did. Well, that sucks I'll just have to put up with it. With the oil I know it'd come from the pcv just didn't realize that much I guess. Now just to figure out what's causing my vac to jump around. Could it be an Uim gasket leaking? I sprayed carb cleaner around it with out a change in sound