Hissing sound from open tube after knock sensor repair, causing misfires

Hello, Can someone help me understand if there is a hose, or missing "plug" on my engine...please see picture below. Working on the car today, and had a lot of the air intake components off to fix a knock sensor. I thought it all went back together well...but I'm getting misfiring error codes, and there is hissing sound from the open tube shown in the center of the picture below. I can find no extra hoses...so not sure what I forgot to connect to this port. Or where a plug has "disappeared" to... Is this supposed to be an open tube? Many Thanks for all help!!

 

I believe that’s the nipple for the molded vacuum hose to the power brake booster. Zoom out so we can also see the master brake cylinder.

 

Yes, that's it! Thank you!! The hose from the brake booster had curled up and was "hiding" behind it on the firewall.... I reconnected it, but the engine is still running terribly. Surges on startup, and then runs very rough with what I call "loping".... Is it possible that there is still a massive amount of air in the fuel lines and it needs to work it's way out?? I'm hesitant to keep running the engine with the "check engine" light flashing at me. Do I need to bleed the fuel system of air? Not sure how to do that .....Thanks very much for the help!

 

Pull the negative battery cable. Leave it off for 10 minutes. Then re-start.

You just had a pretty big vacuum leak with that disco'd. Doing the above will force the engine to re-learn. Let it idle for 5-10 minutes after starting.

Did you do ANY other maintenance recently related to intake, like cleaning the throttle body or other?

 

First, Thanks Again for the help! It is much appreciated! Problem persists..... I left the negative cable off for one hour, restarted and the engine is still loping, and threatening to stall, with check engine light flashing. Also is "reving" too high
before quickly settling down to a low-rev loping mode. The engine work I did was to change the knock sensor harness (rodent damage, of course....). No other engine work done, I did have to remove the throttle body of course, but didn't adjust it in any way. ?Throttle plate in wrong position....I did note that the replacement harness (from RockAuto) was a bit different than the OEM...the wire colors were reversed in the short and long segments of the harness. Is it possible that putting the knock sensor harness with the left and right sides reversed is causing the issue?? Thanks!

 

Check engine flashing ... read codes, I'm assuming you're misfiring. The codes will point to your likely problem.

Revving high can = vacuum leak. You sure you didn't reattach a vacuum hose backwards or into wrong ports?

 

My partner in this adventure (adult son) is coming by this afternoon to read the error codes...The knock sensor replacement job we did was not easy ...so I'm hoping that one or more folks on this forum can help me understand whether installing that harness incorrectly could account for the problem.,,ie: I don't want to have take everything apart again unless I really have to...Thanks for the help!

 

Knowing the codes will help identify the issue.

Knock sensor code will have the truck running in limp mode - at least it had my truck in limp mode when I triggered a knock sensor code twice in the last couple of years, though I'm not sure why it threw the code still. I need to look into that.

If it's a misfire code as I'm suspecting, hopefully knowing if it's random, or on a specific cylinder will help. You may want to re-check coil pack harnesses are clipped on, no bent pins. But I've got my suspicions it's vavuum/intake related.

 

Understand...sounds good. I'll report back when I have the engine codes and we will double check for vacuum leaks! Thank you!

 

Be sure to check and make sure you didn't accidentally swap two adjacent vacuum hoses also.

I believe most of our trucks, if original OEM hood on it, have a sticker with vacuum hose routing pasted under the hood from the factory.

Also, in this thread, around the 4th or 5th paragraph, note the link to the field service manual. Download it. Give it a look over while you wait, check for vacuum hose routing info there. You'll also find diagnostics info in there.

 

Finally got the little device hooked up to read the error codes: P0300 (random multiple cylinder misfirings detected) and P0301 (Cylinder 1) and P0302 (Cylinder 2) misfiring. We did a little more sleuthing, and thought we heard a hissing sound near the throttle body.... consistent with suggestions in this thread pointing towards a vacuum leak. Not having a smoke/vacuum detection system we reached for a can of starter fluid, and nervously sprayed it around the throttle body (and elsewhere, to make this a legitimate, controlled experiment)...and there was a clear, and reproducible increase in the engine speed when the area in the back of the throttle body was sprayed. So, I'm ordering a new throttle body gasket, and we'll do a careful inspection of all the vacuum hoses while we change the gasket. Anything else I should be doing/ordering? Thanks again for all the thoughtful comments...your help (and time) is greatly appreciated!!

 

Nothing else can personally think of but I’m not super familiar with the V6es on these trucks. I take leak/vacuum leak made the most sense given the symptoms. Sounds like you’re on the right path. Let us know how it pans out!

 

Another thing to think about, did you replace the intake manifold gaskets when you had it off? That's a classic sign of bad intake manifold gaskets if the TB gasket doesn't fix it completely.

 

How would you know?

 

Follow-up on this problem, which persists. We changed the throttle body gasket, and it did not solve the problem. And we did change the intake manifold gasket when re-assembling. All bolts torqued to spec. We can hear a hissing sound, but can't identify the presumed vacuum leak. We sprayed started fluid on all vacuum hoses/connectors...no change in engine speed. However, when we spray starter fluid on the two hoses connected to the throttle body...or in the area right behind/below the throttle body, we hear a clear, and reproducible increase in engine speed. We don't understand this, however, because I believe these hoses are for water/coolant,,,,and do indeed led to the thermostat housing. Why would spraying starter fluid on them give an increase in engine speed??? So, stumped at this point...still have flashing check engine light, and engine is loping and threatening to stall... Any ideas?? Thanks for all help!!

 

Israel - where are you located? Maybe another member can come over and take a look with fresh set of eyes. The hissing sound indicates a vacuum leak. Perhaps you pinched a gasket during install or perhaps you left off another hose?

 

New Problem--Brakes! To review, we finally found the vacuum leak that was throwing codes tusing a smoke testing device...turned out to be a poor 0-ring seal on 1 of the ignition coils...cleaned off some dirt and engine runs perfectly! But....We are now having a new problem with the brakes... squishy sound when applying them, and they are very "grabby"... come to a sudden halt instead of usual slow deceleration. We didn't touch the brakes, EXCEPT for introducing "smoke" from the diagnostic machine into the brake booster vacuum line...towards the manifold, of course. Could residual smoke sucked into the booster after we reconnected have damaged the booster??? I can't think of any other reason for the brakes suddenly grabbing.... Thanks again to the good folks on this very helpful forum!

 

If coils seals are holding pressure or vacuum you may have a broken or loose spark plug.