A fun game for all the family: Name That Air Leak

casm · **Joined:** Sun Jan 29, 2006 5:05 pm **Posts:** 694

There's an air leak under acceleration that's been driving me crazy for a few weeks, and I'm hoping that someone can help with locating it. So far, all efforts to track it down have resulted in nothing of any use.

Symptoms: very evident sound of an air leak under acceleration, becoming noticeable at around 2000rpm. Seems to be dependent on throttle position, and sounds as though it is directly in front of the driver. The pitch is fairly constant, though the volume increases or decreases with the amount of accelerator being used.

There is a full Weeks kit installed. So far, there have been no evident cracks or poor seals around the intake plumbing up to the manifold on the driver's side. Have not yet pulled the manifold adapter to check that the RTV is still making a good seal. Does not appear to be weather-dependent as I first noticed this at freezing temperatures, but it was 80°F out today and the same symptoms were still occurring.

It is happening with the radio on or off, so it's not alternator whine seeping through.

Any ideas? At this point only the manifold adapter hasn't been inspected, and while I'm not ruling it out I'd just like to know if there're any other possibilities I might want to check out as I don't want to risk potentially removing it to check the RTV only to find that it was OK, then reassemble it only to possibly not get it properly re-sealed.

GordnadoCRD · **Posted:** Thu Mar 22, 2018 9:56 pm

Check the MAP sensor, that it hasn't loosened and begun leaking there (or broken off and is leaking through)

detach the weeks adapter that is bolted to the intake, from the rubber hose piece that connects it to the elbow. Remove the whole assembly from there to the CAC, and inspect for leaks, especially at the clamp points.

Check the CAC for leaks along the area where the plastic ends are clamped to the header plates. (soapy water check)

Also, It could possibly be a vacuum leak. Check the metal tube for cracks. Check the vacuum hose from there to the brake booster. Check the brake booster for leaks, and the line that leads from there across the upper firewall to the turbo stuff.

casm · **Joined:** Sun Jan 29, 2006 5:05 pm **Posts:** 694

GordnadoCRD wrote:

Check the MAP sensor, that it hasn't loosened and begun leaking there (or broken off and is leaking through)

Yep, that one's solid. It's only been on there about two months and the problem's been happening longer than that - if anything, this one is sealing down better than the old one was.

Quote:

detach the weeks adapter that is bolted to the intake, from the rubber hose piece that connects it to the elbow. Remove the whole assembly from there to the CAC, and inspect for leaks, especially at the clamp points.

Did that as well. Nothing seemed to be amiss.

Quote:

Check the CAC for leaks along the area where the plastic ends are clamped to the header plates. (soapy water check)

That would benefit from a re-check. It was OK as best I could tell when I checked it before, but I didn't do the soapy water test.

Quote:

Also, It could possibly be a vacuum leak.

This is kinda what I'm leaning towards. More:

Quote:

Check the metal tube for cracks. Check the vacuum hose from there to the brake booster. Check the brake booster for leaks, and the line that leads from there across the upper firewall to the turbo stuff.

Those weren't inspected as thoroughly. I'll go back and double-check them hopefully this weekend.

hopp · **Joined:** Wed Sep 20, 2017 3:11 pm **Posts:** 38

I see you have the weeks kit. Did you make sure intercooler hoses are engaged up to the indexed stops on the CAC? When I installed my kit there was a bit too much oil on the inside surface of the hoses and they slipped down causing an air leak under boost at 2k+.

WWDiesel · **Posted:** Fri Mar 23, 2018 10:29 am

Quote:

Have not yet pulled the manifold adapter to check that the RTV is still making a good seal.

Most likely! :roll:

And a leaking or loose boost hose usually will just blow off connection!

casm · **Joined:** Sun Jan 29, 2006 5:05 pm **Posts:** 694

Just spent an hour going over everything and tightening stuff down. The air leak seems to be gone (for now), but, since I took the nuke-it-from-low-orbit approach and checked / retightened everything, it's not 100% clear as to what was actually causing it. Throttle response is noticeably improved, however, and soot at cold startup seemed reduced.

The finger is currently pointed vaguely in the direction of the 10mm nuts holding the manifold adapter to the manifold; the ones nearest the engine had backed out slightly. However, I also loosened and re-tightened a number of clamps, re-seated vacuum lines just to be sure, etc., so it could have been down to any one or a combination of factors.

For my future reference:

hopp wrote:

I see you have the weeks kit. Did you make sure intercooler hoses are engaged up to the indexed stops on the CAC? When I installed my kit there was a bit too much oil on the inside surface of the hoses and they slipped down causing an air leak under boost at 2k+.

Both appeared to be clamped correctly at both ends, and indexed as intended. No splits that I could find, but I do plan on replacing them with silicone hoses at some point. Holding off on doing them until after I can get the Provent that's sitting here installed.

WWDiesel wrote:

Quote:

Have not yet pulled the manifold adapter to check that the RTV is still making a good seal.

Most likely! :roll:

And a leaking or loose boost hose usually will just blow off connection!

Entirely possible. Decided to not go the whole hog and yank the adapter as I don't have the gasket on hand, but given the backed-out nuts it's a definite suspect. Going to drive it for a few days and see if anything changes; if it does, that will be my first port of call.

casm · **Joined:** Sun Jan 29, 2006 5:05 pm **Posts:** 694

Ugh. The air leak is back, and it appears to be getting worse. Symptoms are more or less the same, but it's becoming more audible.

I'm beginning to wonder if this isn't an early sign of brake booster failure: it seems as though more pedal pressure is being required to bring the KJ down to a stop than I remember it needing, but I'm also not sure if I'm talking myself into believing there's a problem there when there isn't.

Here's what I'm proposing, and could use some comments on this.

1) Replace the check valve, grommet, and vacuum line to the manifold. Would want to do that anyway if the booster needs replacement, and they're easy to take care of.

2) If that doesn't work, replace the booster. This looks like a giant pain because this KJ has ABS and, per the FSM, would require a DRB tool to cycle the ABS pump for bleeding.

My main question is whether or not the booster can be replaced without having to open up the brake hydraulics, which would also answer the issue of whether or not I'd need a DRB to bleed them. However, anything else that might be useful to know would be appreciated if it could be passed on to me.

apardo001 · **Posted:** Mon Apr 09, 2018 7:12 pm

casm wrote:

1) Replace the check valve, grommet, and vacuum line to the manifold. Would want to do that anyway if the booster needs replacement, and they're easy to take care of.

2) If that doesn't work, replace the booster. This looks like a giant pain because this KJ has ABS and, per the FSM, would require a DRB tool to cycle the ABS pump for bleeding.

CRDs don't have vacuum line to the manifold, we have a vacuum pump attached to the engine block below the CP3 pump. There are procedures to test the brake booster, like turning off the engine and counting how many times you need to depress the brake pedal before it feels rock solid.

Also, a vacuum leak sound would be constant at all times while engine is running, meanwhile an air leak (caused by boost pressure) would be absent at idle and high under acceleration.

I suggest looking at the intercooler, cracks on plastic or failed seals to the aluminium body, try soapy water as suggested before.

apardo001 · **Posted:** Mon Apr 09, 2018 7:16 pm

casm wrote:

My main question is whether or not the booster can be replaced without having to open up the brake hydraulics, which would also answer the issue of whether or not I'd need a DRB to bleed them. However, anything else that might be useful to know would be appreciated if it could be passed on to me.

Brake bleed procedure calls for use of scanner, but not necessarily a DRB3, other brands with access to ABS module can trigger this procedure.

casm · **Joined:** Sun Jan 29, 2006 5:05 pm **Posts:** 694

Just noticed something that had completely escaped my notice earlier: this only happens with the KJ in gear.

In Park or Neutral, there is no air leak sound. In any other gear (including reverse), there is.

Any ideas? I am stumped.

GordnadoCRD · **Posted:** Mon Apr 16, 2018 1:04 am

If the sound is independent of whether or not your foot is on the brake, then perhaps it's not an air leak you hear, but the sound of a failing hydraulic system.

casm · **Joined:** Sun Jan 29, 2006 5:05 pm **Posts:** 694

GordnadoCRD wrote:

If the sound is independent of whether or not your foot is on the brake, then perhaps it's not an air leak you hear, but the sound of a failing hydraulic system.

Doesn't seem to be - I changed the brake fluid a couple of weekends ago and brought it up to the correct level. It hasn't moved from there.

Did notice one interesting thing last night: moving the direction of the cabin air a) takes 5-6 seconds for the change to happen and b) sends the air to the wrong places as it switches between modes. Not sure if this is normal or not, but figured it might be worth mentioning.

Oh, and to clarify my earlier comment re: the sound only being there with the Jeep in gear: that's correct, but it only happens while in motion (e.g., the engine is under load). This is making it really difficult to track down.

GordnadoCRD · **Posted:** Wed Apr 18, 2018 1:51 pm

That's why the last question. Was thinking transmission rather than brakes.

WWDiesel · **Posted:** Wed Apr 18, 2018 2:32 pm

casm wrote:

GordnadoCRD wrote:

If the sound is independent of whether or not your foot is on the brake, then perhaps it's not an air leak you hear, but the sound of a failing hydraulic system.

Doesn't seem to be - I changed the brake fluid a couple of weekends ago and brought it up to the correct level. It hasn't moved from there.

Did notice one interesting thing last night: moving the direction of the cabin air a) takes 5-6 seconds for the change to happen and b) sends the air to the wrong places as it switches between modes. Not sure if this is normal or not, but figured it might be worth mentioning.

Oh, and to clarify my earlier comment re: the sound only being there with the Jeep in gear: that's correct, but it only happens while in motion (e.g., the engine is under load). This is making it really difficult to track down.

All this could be indicative of a bad vacuum leak somewhere in the system.
You could try clamping off each of the vacuum supply hoses one at a time and see if it makes any difference in the noise you are hearing.
But be very careful if you disrupt the vacuum going to the brake booster. :wink:

casm · **Joined:** Sun Jan 29, 2006 5:05 pm **Posts:** 694

GordnadoCRD wrote:

That's why the last question. Was thinking transmission rather than brakes.

Gotcha. Apologies; I think I was still semi-fixated on the brake booster.

At this point, I'm really out of ideas. There don't appear to be any transmission leaks, so unless it's something else in that general vicinity that I haven't found, I don't know what it might be.

What's really puzzling is how it happens under load, but not in park or neutral. I can see how that might suggest transmission, but... I just don't know what it might be related to that.

casm · **Joined:** Sun Jan 29, 2006 5:05 pm **Posts:** 694

WWDiesel wrote:

All this could be indicative of a bad vacuum leak somewhere in the system.
You could try clamping off each of the vacuum supply hoses one at a time and see if it makes any difference in the noise you are hearing.
But be very careful if you disrupt the vacuum going to the brake booster. :wink:

I am leaning towards vacuum leak, but where is the question. Point taken re: clamping off the lines and seeing what happens.

This is a case where I'm really trying to avoid throwing parts at it.

GordnadoCRD · **Posted:** Thu Apr 19, 2018 9:53 pm

You can definitely test the vacuum hoses and system by blocking off sections. If it's transmission, it's happening internally, so not really able to test from outside.

If you completely pinch off and disconnect the vacuum line (cap the metal line from the pump) it should hold vacuum in that system. If not, there is a leak... perhaps several.

casm · **Joined:** Sun Jan 29, 2006 5:05 pm **Posts:** 694

GordnadoCRD wrote:

You can definitely test the vacuum hoses and system by blocking off sections. If it's transmission, it's happening internally, so not really able to test from outside.

Fair enough. Manual transmissions are in my comfort zone... But automatics are filled with voodoo and

Quote:

If you completely pinch off and disconnect the vacuum line (cap the metal line from the pump) it should hold vacuum in that system. If not, there is a leak... perhaps several.

Pulled the main one to the booster check valve and got a nice little vacuum pop. Repeated this after repressurising the booster and clamping the line; pressure was held. Got similare results when pulling the smaller secondary line from the booster check valve running over to what I think is a vacuum reservoir over on the passenger side.

Discovered that the Help! section at Autozone does not have a check valve with fittings for both lines on the check valve body - or, at least, the store I went to didn't. I'd be willing to replace that and the grommet just to see what happens, but need to find a valve that can handle both lines first.

I did order a replacement intake adapter gasket, which should be here in a few days. Hopefully that will nail it, though smoke testing with smouldering cardboard around that area didn't show anything obvious.

GordnadoCRD · **Posted:** Fri Apr 20, 2018 8:52 pm

well, without seeing it and hearing it for myself, I have no idea where to look.

What did you do to piss her off so bad? Cheap out on the honeymoon? Forget to get her an anniversary gift?

casm · **Joined:** Sun Jan 29, 2006 5:05 pm **Posts:** 694

GordnadoCRD wrote:

well, without seeing it and hearing it for myself, I have no idea where to look.

Oh, believe me, that's understood. Don't mean to sound unappreciative for the help; I completely get what it's like to try to track down an issue by keyboard from great distance. If I'm sounding frustrated right now, it's with the Jeep, not you (or anyone else here).

Quote:

What did you do to piss her off so bad? Cheap out on the honeymoon? Forget to get her an anniversary gift?

Yeah, I don't get it either. This has been one of the most needy vehicles I've ever owned, and it's not even close to living up to the promise of what it should be. I'm going to keep plugging away at it for the time being, but there's only so much I'm willing to put up with.

A fun game for all the family: Name That Air Leak

Who is online