I've got a 94 LT-1 coupe that I had the fuel pump replaced on about 2,000 miles ago. Car starts and runs perfectly. I mention the pump, because I'm not sure, but it may be part of my mystery noise.

Once every 5 times or so, after the car has set overnight, I start it and right after it starts I hear this bizarre noise. It sounds like its coming from the passenger side of the car, but its really hard to pinpoint. The noise is difficult to describe, but for lack of a better description it sounds a bit like the noise a straw makes when you are trying to suck up the last liquid in a glass. Kind of a gurgling noise. Almost like a fuel line with air or something in it. It makes the noise for about 3 or 4 seconds and then it stops and all is well after that. Again, the car starts perfectly and runs great during this. It has happended with 3/4 of a tank of gas and with 1/4 of a tank, so the amount of fuel doesn't seem to be an issue. Anybody have any idea what this could be? :confused:

 

hm. I have heard that same sound... and I think it's to do with the climate control... but not sure.

anyone else???

 

Interesting idea. I do turn off the air con before parking the car in the garage at night, so maybe something doesn't get purged from the system or maybe some fluid doesn't clear or or something until its started again.

Jeff

 

On early C4's a lot of cars had a problem with the fuel line pulsating upon cold startup that caused a hammering noise a lot like what you are describing. GM added an in line dampener to correct the problem sometime before 1990. Obviously your car came with this dampener, but maybe it went bad or for some other reason you are getting these pulsations.

 

I hear this same noise from time to time and it sounds pretty much exactly as you described. I don't have climate control and always turn off the A/C before I park. I always thought it was fuel pump related, but what do I know... :crazy:

 

:iagree: :iagree:

This is a common problem on cold starts. Mine does this also.

 

This is the great thing about this forum. I post a question that I figure no one on the planet will have a clue about and lo and behold I have several guys jump in and relate that they have the same situation. Nice to know that its unlikely to be a major problem and that others have it too. I think I'll talk with my mechanic about the fuel line dampener you mentioned and see if he is aware of that. Will post back if I get any further information.

Thanks!

 

I just thought of something else. The "dampener" I mentioned in my original post is actually a 2nd dampener located in the fuel return line and was added in 1987. There is another dampener between the fuel pump and the hard fuel pump supply line in the tank that even the early C4's are equipped with. The Delco fuel pump replacement kit comes with a short piece of 3/8" hose that can be used ILO the dampener, the bonus being that it will hold fuel pressure better than the dampener because the dampener is not clamped on the ends. The drawback is that you can get pulsations like the ones you are describing.

 

Sure sounds like that may be the situation, particularly since the noise started after the installation of the new pump. Its not a big deal since it only happens ocassionally and only on cold start, but it is good to know that its unlikely to be a situation where damage would occur or I would have some sort of failure. Thanks for the info!

 

And the answer is...........the ASR ABS system running its pre-check right behind you. Sometimes it's more noticable than others. I hear mine more when it's a little low on brake fluid or the pads are about worn out. Normal sound, and nothing to worry about. You might even here it if your ABS or ASR kicks in, though my car is so loud now, I don't hear the "normal" things much anymore. I am taking this is a sound you hear right AFTER you start the car and not the whirling noise from the fuel pump right BEFORE startup.

 

You won't hear the ABS pump do its cycle until you begin to move. Not sure of the exact speed, but I believe it's set to do its brief cycling at like 2 or 3 mph. So, if this sound is happening before you begin moving, then it is *not* the ABS pump (which, by the way, is in the compartment directly behind the driver's seat).

Granted the ABS system is functioning normally, you will hear this sound everytime after start up, and it should sound the same each time.

Lastly ... the ABS is not related to the ASR system.


[Modified by SkunkCar, 4:43 AM 7/23/2003]

 

The ABS is not related to the ASR?

Then why does the ABS system pump whenever I hit a big enough hole on acceloration?

the gurgle is definately in the right side, dash. or at least that's where I hear it... and on mine, is is VERY inconsistant... I can go MONTHS without hearing it once... then it will do it 2 or 3 times... once, my AC programmer flashed.

 

[QUOTE]And the answer is...........the ASR ABS system running its pre-check right behind you. Sometimes it's more noticable than others.

Nope, that's not it. I know what that sounds like and that happens once the car in motion. This noise happens right after the car is started and before it is ever put in gear.

 

the gurgle is definately in the right side, dash. or at least that's where I hear it... and on mine, is is VERY inconsistant... I can go MONTHS without hearing it once... then it will do it 2 or 3 times... once, my AC programmer flashed.[/QUOTE]

YES, that's EXACTLY what I'm talking about! Interesting that several of us are aware of the sound, but seems to be a couple of options on what it might be. It really is more of a "gurgle" than anything else. You can almost invision water running somewhere.

 

The ABS system is a completely separate system than the ASR. I'm fairly new to the mechanical end of things, so I'll do my best to explain what I've discovered so far. As I understand it, the ABS system monitors the rotation speed of the wheels via sensors that hook into the bearing hubs, and when one wheel appears to be stopped, brake fluid pressure to that wheel is lessened in an effort to unlock the "supposedly locked up" wheel (due to too much brake input). In other words, the point is to keep all four wheels rotating under excessive brake pedal pressure which would, otherwise, cause skidding.

I have not read the theory of ASR in the factory manual (I should do so when I get home tonight -- the service manuals are *great* at covering that kind of stuff), but from looking at the mechanical end of things under the hood of my '96 car, it appears this system is designed to reduce throttle input when the rear tires lose traction. I'm thinking this because in looking at the ASR unit under the hood (driver side, above battery, about a foot in and back from the firewall -- black casing marked "ASR"), it has cables that run to throttle body ... why else, other than to control throttle input? :cool:

Now, as to why your ABS kicks in when you hit a hole under acceleration? Don't know, though I've heard of this happening before. In fact, an autocross buddy of mine who has a '91 coupe complained just the other day about how his ABS will kick in momentarily on occasion when he hits some rough sections on a road. This could probably be its own separate topic :D

 

I'm thinking it's got to be a/c related, in particular perhaps freon in the system is making noise upon initial circulation :confused:

This may sound way out in left field, but my garage refridgerator at home (you know, that place where all the beer is kept :cheers: ) makes a gurgling sound whenever the door has just been closed. I've always imagined it was freon (or whatever medium is being used to cool incoming air) that was making the gurgling sound ... I wonder if the same issue is at work in my garage as in your car? :crazy:

 

Okay. Now that we've determined he knows it's not this. I'm wondering what it is? :rolleyes:

As far as this statement is concerned Yes it is.

The ASR system has control of three different things. Depending on conditions it can:

1. Reverse the throttle
2. Cut timing- limiting power there as well
3. APPLY REAR BRAKE/s to the wheel/s that are slipping. (it does this through the ABS system by computer.)

Or it can do all three or any combination of the above.

 

I was not aware that the ASR system was related to ABS in that sense. I stand corrected. Though ... it seems odd that an "anti-lock" system would "apply" braking in any sense. That's counterintuitive. Wouldn't ya think an "anti-lock" system would only work to lessen braking effort, and not to *apply* brakes? (as would be the case if ASR is using ABS to apply braking action)

Thanks for the correction.

 

I'm thinking it's got to be a/c related, in particular perhaps freon in the system is making noise upon initial circulation :confused:

This may sound way out in left field, but my garage refridgerator at home (you know, that place where all the beer is kept :cheers: ) makes a gurgling sound whenever the door has just been closed. I've always imagined it was freon (or whatever medium is being used to cool incoming air) that was making the gurgling sound ... I wonder if the same issue is at work in my garage as in your car? :crazy: [/QUOTE]

The more we discuss this, the more I think in is probably AC related. I wonder if my habit of turning off the climate control just before parking it for the night is partially the culprit. Maybe not giving the system time to continue whatever process its in at the moment causes some sort of bubbles, or fluid flow, or something that needs to rectify itself on next startup. Next time it does it I'm going to see if I can quickly turn on the AC and "interrupt" the noise.

 

Well as you know, when you apply your brakes and the ABS sensors sense the wheel is locking up, then the ABS takes over and (for lack of a better word) pulse the brakes. The ABS has complete control of the brakes as long as you keep your foot to the floor. That's why you don't want to "pump" the brakes of an ABS car. The system won't work. It's this same pulsing action of the ABS that the ASR uses when it senses the rear wheels spinning. Oh, and though there are other sensors involved, the ASR uses the ABS's wheel sensors to detect the back ones are moving faster than the fronts. Rears are spinning.