Whistling sound from engine bay

[burch]

Hey Everyone -

Recently finished my first VOD job (coolant leak), and now when driving the car, I now hear a whistle sound (think a quiet tea kettle) from the engine compartment area. Here are the details:

1. Whistling only happens when car is not in Park or Neutral.
2. Whistling only happens when accelerating. The noise subsides when I release the accelerator to maintain speed.
3. There is no fuel smell, and no visible (or tactile) leak on any of the Fuel Distributor connectors.
4. When reassembling, I used all new crush washers and torqued to spec.
5. Absolutely no liquid drips of any type have been seen.

My initial thought is that it has to be fuel system related, due to the timing of the whistle. And while I have not discovered any fuel smell, again, I can't replicate this with a stationary vehicle, so driving, stopping, popping the trunk and sniffing may be ineffective for a small vapor type leak.

Any thoughts? I've got extra crush washers, so I may start with replacing and retorquing each connection to the distributor one by one.

Thanks!

[Bitsyncmaster]

It's Probably a vacuum leak. Most common is the W pipe but that normally whistles at idle. Check all your vacuum hoses for good connection. Hope it's not the mating of the intake to engine leak.

[DMCVegas]

Is your idle surging a lot?

[Jonathan]

Here's another vacuum connection unique to automatic transmissions for you to check. I assume your car is an auto since you mentioned park and neutral.

http://store.delorean.com/p-8926-vacuum-modulator.aspx

It connects back at the engine through this long vacuum line shown as item 26, 27, and 28 on this diagram:

http://store.delorean.com/c-293-4-5-6-computermodulator.aspx

[PJ Grady Inc.]

I agree with Dave that it sounds like a vacuum leak. The crush washers are for fuel and not vacuum except for one on the cold start pipe mtg bolt. Did you replace all of the o-rings and made sure they were of the correct size? If so perhaps one of the six intake o-rings dropped out of position. Spray a little WD40 on the head/intake interfaces to see if the whistle goes away temporarily. If it does it means the intake will need to come back off!
Rob

[sdg3205]

My money is on the paper W-pipe gaskets being poop.

[DavidProehl]

Given that you just did a VOD job, +1 on the vacuum leak. If that isn't it, take a look at your pulleys. I had a pulley that would usually only squeal/whistle at higher RPMs.

Just thinking it might also be possible this is unrelated to the work you did (though unlikely).

[burch]

It's Probably a vacuum leak. Most common is the W pipe but that normally whistles at idle. Check all your vacuum hoses for good connection. Hope it's not the mating of the intake to engine leak.

I think you're right, Dave. I checked the connections and reseated the large vacuum lines at the back of the Intake Manifold, and the sound went from "noticeable" to "barely perceptible". Thanks!

[burch]

Wow, thanks for all the quick responses!


My money is on the paper W-pipe gaskets being poop.

They looked relatively new. PO did a water pump job about 2 years ago, based on the lack of wear and deterioration, these appear to have been changed then. I've seen a couple spots where it is suggested to seal these with "The Right Stuff" as well, is that recommended?

Rob - That's a great tip. I'm going to verify that the W pipe is torqued properly (believe it is), and if there is any perceptible whistle after that, it's spray time :)

[burch]

Is your idle surging a lot?

Did seem to be surging more when cold, now that I've readjusted the lines, I'll let the car cool back off and check that again tonight.

[PJ Grady Inc.]

Wow, thanks for all the quick responses!



They looked relatively new. PO did a water pump job about 2 years ago, based on the lack of wear and deterioration, these appear to have been changed then. I've seen a couple spots where it is suggested to seal these with "The Right Stuff" as well, is that recommended?

Rob - That's a great tip. I'm going to verify that the W pipe is torqued properly (believe it is), and if there is any perceptible whistle after that, it's spray time :)

"The right stuff" is the wrong stuff in my opinion for anything you hope to ever take apart again. Ron Ferguson's new(er) engine and auto trans. were assembled using it. It had an AT pan leak and to try to save the pan we would have had to pull the trans-axle so it was cheaper for us to force the pan off but destroyed it in the process. His air sensor housing was also assembled with it and had leakage issues. We could not pry it apart with a chisel so it had to be reinstalled as is or we would have had to replace it as well. If you want to make something almost unserviceable IMHO then "the right stuff" is for you. Blue Hylomar is a better choice for paper gaskets or a thin coating of conventional red or blue hi temp silicone on each gasket surface can also be more safely employed. I'm glad for you that it appears to have been a simple hose connection. Vacuum leaks are common with PVR motors and require extra attention when reassembling things.
Rob

[sdg3205]

The paper gaskets don't seem to like being reused. If you took everything apart for your VOD job and reused the paper gaskets, that may be source of some of the noise.

[Bitsyncmaster]

The paper gaskets don't seem to like being reused. If you took everything apart for your VOD job and reused the paper gaskets, that may be source of some of the noise.

I ended up cutting my own gaskets from black gasket paper. That will move your mixture unit a little so you have to loosen the two bolts on the brackets toward the back, tighten the front and then tighten those two bolts. You may also have to adjust your idle screws.

I used a hard gasket sealer on one side and the other side left dry. So you can take it apart many times if you like.

[john 05141]

Funny, I have the same sound I think.
It can be heard but not loud, sounds almost like a turbo.

I have a stick shift model.

But Ihave something that combines to it: When I drive at a steady speed, no matter in which gear or at what speed, just steady, the engine is not running properly, and gives very small shocks. When I step on it it will accelerate without shocks.
I was told my engine's setting is too poor. And this would be why the engine whistles??

I had a new warm up regulator built in and since it does nut run as it should be.

Jan.

[DMCVegas]

Did seem to be surging more when cold, now that I've readjusted the lines, I'll let the car cool back off and check that again tonight.

The answer is: λ

(in case anyone can't tell, that's Greek for Lambda)

Like all managed fuel systems, proper function is dependent upon a tightly-sealed air intake system. It needs this for proper fuel metering to try and constantly achieve that perfect fuel mixture. Which of course leads to ideal economy and emissions. Anyways... As stated, in order to know how much fuel to dispense, the entire system must know exactly how much air is coming into the engine. EFI uses a MAF sensor to measure airflow, and K-Jetronic uses a metering plate. As more air comes in, it pushes against the plate, and that tells the Fuel Distributor to send more gasoline to the injectors to match that ideal ratio. The entire system is designed for this to work in harmony (specific mechanical functions however are for another thread).

And then what we have is a little add-on called the LAMBDA system. It has an Oxygen Sensor in the exhaust to measure the amount of O2 present, and can perform fine-tuning to help reach that perfect 14.7:1 Air/Fuel ratio as close as possible.

So what happens when you have a vacuum leak?

When you have a vacuum leak, un-metered air is entering into the engine and the K-Jetronic cannot account for it. Worse yet is the LAMBDA system which is oblivious to this and will still try and tune the system which results in some wacky behavior. LAMBDA itself is meant to be a continuous circle of adjustment between lean and rich fuel mixtures. Normally it's just a tiny amount that you wouldn't notice. But with a vacuum leak your engine will have wild, erratic idle as the LAMBDA and Idle Speed ECUs unknowingly fight one another.

Excess air comes into the engine through a vacuum leak. LAMBDA sees the high O2 content and enriches the mixture to lower it->Now the engine is being fed MORE fuel to match that air, so it's RPMs jump above 775+!->The Idle Speed ECU is engaged, so it starves the engine of air to drop them back down-> The lack of air now causes a rich condition so LAMBDA further reduces the amount of fuel being fed into the engine->This causes the RPMs to fall below 775±-> This starves the engine so it stumbles->The Idle Speed ECU freaks out and pops the ISM open to rapidly increase RPMs back to 775+->The addition of all this additional air as the RPMs climb results in a lean condition->LAMBDA sees the high O2 content and enriches the mixture to lower it->Now the engine is being fed MORE fuel to match that air, so it's RPMs jump above 775+!->The Idle Speed ECU is engaged, so it starves the engine of air to drop them back down-> The lack of air now causes a rich condition so LAMBDA further reduces the amount of fuel being fed into the engine->This causes the RPMs to fall below 775±-> This starves the engine so it stumbles->The Idle Speed ECU freaks out and pops the ISM open to rapidly increase RPMs back to 775+->The addition of all this additional air as the RPMs climb results in a lean condition->LAMBDA sees the high O2 content and enriches the mixture->Now the engine is being fed MORE fuel to match that air, so it's RPMs jump....

And this just goes on and on. All because of a vacuum leak. I'd never heard of the trick to spray WD-40 to try and block the leak to see if that cures it. That's a good one. Normally it's been the slightly more dangerous spray little squirts of starter fluid around areas to see if that causes a sudden surge in engine idle. If it does when you spray a particular place, well, you found where the leak is.

Whenever you work around something that involves sealing passages. Be it O-Rings or Gaskets, you should just go ahead and replace them no matter how good they look. (The rare exception are gaskets that are purposefully reusable, but I've only ever seen those on transmission pans.)



Funny, I have the same sound I think.
It can be heard but not loud, sounds almost like a turbo.

I have a stick shift model.

But Ihave something that combines to it: When I drive at a steady speed, no matter in which gear or at what speed, just steady, the engine is not running properly, and gives very small shocks. When I step on it it will accelerate without shocks.
I was told my engine's setting is too poor. And this would be why the engine whistles??

I had a new warm up regulator built in and since it does nut run as it should be.

Jan.

Hard to say. It might be a couple of things. Do you have the surging idle problem?



"The right stuff" is the wrong stuff in my opinion for anything you hope to ever take apart again.

Yeah, but that stuff works wonders on cars you decide to flip and don't care about. For anyone that's never used this stuff, it's like using Line-X bed liner to seal something that you either don't plan on going back in for several years, or ever again. I've used it many times before, and it only failed me once. It didn't like rubber hoses, nor HSMO on the old Jag for that stupid 3-way hose. Which you know what? Quick side note. I fully believe that everyone should work on an XJ40 at least once in their life. It makes the DeLorean and the PRV look like a lawnmower... You think the PRV has a Valley Of Death to go through to replace a water pump? The AJ6's is settled down within the 4th circle of hell.

[PJ Grady Inc.]

Robert (DMC Vegas) said;
"And this just goes on and on. All because of a vacuum leak. I'd never heard of the trick to spray WD-40 to try and block the leak to see if that cures it. That's a good one. Normally it's been the slightly more dangerous spray little squirts of starter fluid around areas to see if that causes a sudden surge in engine idle. If it does when you spray a particular place, well, you found where the leak is."


The old trick I heard back in my Chevy dealership years was to use "brakleen" for checking for vacuum leaks. However when trying this on the o-ring sealed PVR I soon learned that it would sneak past the o-rings and give you a false positive for a vacuum leak while simultaneously trying to asphyxiate you with highly toxic fumes. So you learn to adapt when you decide you want to go on living a while longer. Hence I switched to a slightly more viscous and way less toxic fluid years ago and am happy to report most mornings I still remember my name when I get out of bed...at least on the good days! Starter fluid...now that's advanced. No need for a nightcap if you've been sniffing burnt starter fluid fumes all day but the next AM must be a killer;)
Rob

[DMCVegas]

The old trick I heard back in my Chevy dealership years was to use "brakleen" for checking for vacuum leaks. However when trying this on the o-ring sealed PVR I soon learned that it would sneak past the o-rings and give you a false positive for a vacuum leak while simultaneously trying to asphyxiate you with highly toxic fumes. So you learn to adapt when you decide you want to go on living a while longer. Hence I switched to a slightly more viscous and way less toxic fluid years ago and am happy to report most mornings I still remember my name when I get out of bed...at least on the good days! Starter fluid...now that's advanced. No need for a nightcap if you've been sniffing burnt starter fluid fumes all day but the next AM must be a killer;)
Rob

My worst memory was being bent-over to replace the baffle in the fuel tank. When it was ¾ full. And I had no nitrile gloves. Nothing like waking up the next morning groggy with an intense migraine, lower back pain, and burning hands from dipping them in raw gasoline. Plus I had the bonus smell of fuel that I couldn't get away from which just kept me in nauseating pain.

I cannot imagine using Brakleen to test for leaks! I still remember my first brake job where I used that stuff. Turns out it's under a much higher pressure than your normal aresol, and sprays in a direct stream too! I did not know this. Suffice to say, I quickly learned.

Brakeleen: It not only safely cleans asbestos and grime, but it also provides one of life's tender little lessons to make sure you don't ignore the safety warnings...like if the warning label tells you to wear safety glasses, it's not merely a suggestion.

http://www.bogley.com/forum/attachment.php?attachmentid=70086

[PJ Grady Inc.]

My worst memory was being bent-over to replace the baffle in the fuel tank. When it was ¾ full. And I had no nitrile gloves. Nothing like waking up the next morning groggy with an intense migraine, lower back pain, and burning hands from dipping them in raw gasoline. Plus I had the bonus smell of fuel that I couldn't get away from which just kept me in nauseating pain.

I cannot imagine using Brakleen to test for leaks! I still remember my first brake job where I used that stuff. Turns out it's under a much higher pressure than your normal aresol, and sprays in a direct stream too! I did not know this. Suffice to say, I quickly learned.

Brakeleen: It not only safely cleans asbestos and grime, but it also provides one of life's tender little lessons to make sure you don't ignore the safety warnings...like if the warning label tells you to wear safety glasses, it's not merely a suggestion.

http://www.bogley.com/forum/attachment.php?attachmentid=70086

THAT AIN'T NOTHIN! Back in the day (transporting a brandy new customers POS back up from the Williamsburg DOA event in '94) I found myself doing the same thing in the breakdown lane with my back to I-95 and the semi's blowing past at 80 MPH. I think they were having a contest to see which one could get closest to my rear end without technically hitting it. "Hey Weezer look at that A-hole in the breakdown lane with one o dem Deeelorin's. Let's see if we kin razzle em a tad heh heeee!!! Yup....thooose were the days my friend...those were the days.
Woke up totally shell-shocked the next day but oh the memories...what was I saying just then?
Rob