: Weird knocking when coasting 20-30mph with light pedal; almost like car is "slurring"



stevenriz
05-06-13, 01:22 PM
With 130k, I have a weird nose like a light "knock" or as I call it, slurring when driving 20-30mph with light pedal. Just like when coasting. Weird. When I let off or step on it to downshift, the knock goes away... Bad gas? I use regular... Timing problem?

josephdav01
05-06-13, 01:42 PM
With 130k, I have a weird nose like a light "knock" or as I call it, slurring when driving 20-30mph with light pedal. Just like when coasting. Weird. When I let off or step on it to downshift, the knock goes away... Bad gas? I use regular... Timing problem?

I had knocking at 80k and I was using regular. I know u can use regular but my caddy didn't like it. I switched to premium and now I have 101,000 miles on my car and haven't heard the knocking since.

EChas3
05-06-13, 07:57 PM
Steve - If you aren't using Top Tier gas, that would be the first change I'd recommend. If that's not convenient, consider adding some Techron and/or Throttle-body cleaning. If it persists, Try mid-grade or premium.

You could just go to premium and then work backwards, but under those conditions, I doubt you'd really be doing any harm. (I have heard that noise on those rare occasions when I burn crappy E10+.)

stevenriz
05-07-13, 11:54 AM
Hey guys. Thanks for the tips. I'll try premium and see what happens. What will it cost me, an extra $2/tankfull? I'm also thinking about the about the plugs that are still original. Could old plugs cause this do you think? Should I replace them? Next tankful will be premium. I normally use Mobil.

EChas3
05-07-13, 08:40 PM
Exxon Mobil is Top Tier. Unless your car has close to 100,000 miles, I wouldn't recommend plugs. If you do change them, use OEM. N* is fussy about plugs.

Living in MA, you might be in an area with a crappy gas formulation. Is it all E10?

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http://pure-gas.org/

MoistCabbage
05-08-13, 12:40 AM
IF this is knock/detonation...

If the engine has just started doing this, then the problem is not 87 octane, and masking the problem with higher octane won't fix the problem.

Have you pulled codes?

When was the last time the engine saw some WOT?

What happens when the engine is under load? Knock usually doesn't occur under light throttle.

stevenriz
05-08-13, 09:37 AM
Lost my post... Retyping...

I exclusively use Mobil. Not always high test, mostly regular. WOT? Wide Open Throttle? every once in a while I do it but not often.

This knocking does NOT occur under load. Only when coasting under light load at about 20-30mph. I am noticing now that there is a quick knock between shifts.

I will bring it in and see what the dealer tells me :|

I will report back what the resolution is!!

stevenriz
05-08-13, 11:41 AM
To answer another question, it is all E10 here in the Northeast I believe. I am only looking at the plugs for misfiring due to age. They may not work that way. Not sure.

Ludacrisvp
05-08-13, 12:09 PM
Well your plugs should have been changed at 100k using only OEM plugs as the N* is very picky about its plugs.

EChas3
05-08-13, 07:24 PM
I wonder if this occasional noise is related to the VVT? I sure hope it's not piston slap.

stevenriz
05-09-13, 10:03 AM
What is VVT? variable valve timing?

curtc
05-09-13, 11:08 AM
What is VVT? variable valve timing?

Yes.

Akatate
05-09-13, 08:40 PM
OP, I am having a similiar problem just recently with my '06 STS V6. I have just hit 80,000 miles. At cold start, primarily, low RPMs or cruising at higher speeds but only (like you said) when I lightly press the gas, I hear a knocking/slurring sound and a choking acceleration. Almost like having bad gas.

When I floor it, no problems what so ever. But especially when I am leaving my neighborhood in the morning, anytime I slow down and start to accelerate, it knocks and gets choked up a little.

I was thinking either fuel filter, injector or spark plugs. I changed the Air filter and am changing the fuel filter in the morning, but after reading this forum, I have little hope of this resolving the issue.

If anyone has any suggestions, I would greatly appreciate it. Ive only had the car since September, 2012, and I would hate for this to turn into a major problem bc this car is a dream.

EChas3
05-09-13, 10:30 PM
Akatate,

Your experience is very different than mine. I've never heard what I've described when the car is cold or within 15 minutes of cold. When I have heard it, it's on the way back to work after lunch. The engine is essentially warm, but maybe not quite hot.

I've never noticed any affect on performance, hence no concerns on my part.

Make sure the oil level isn't low, it affects the VVT. Have you had your car on a code reader? The V6's often log valve timing sensor codes.

Ludacrisvp
05-10-13, 08:35 AM
Also keep in mind the V6 lacks a low oil level sensor so actually open the hood and check it, so don't rely on an idiot light that doesn't exist.

MoistCabbage
05-10-13, 09:32 AM
so actually open the hood and check it, so don't rely on an idiot lightREGARDLESS of weather or not the car has an oil level sensor, you still need to check the oil manually. The message isn't triggered until the oil level is 2 quarts low.

Akatate
05-10-13, 10:17 AM
Ok, thx. I'll check it. My oil life % says 50 but I realize this doesn't indicate lvl.

Ludacrisvp
05-10-13, 11:12 AM
Ok, thx. I'll check it. My oil life % says 50 but I realize this doesn't indicate lvl.

Which is why you should manually check it regularly as there isn't a level indication inside the car, and only a low oil message for 2qts low in the V8.


REGARDLESS of weather or not the car has an oil level sensor, you still need to check the oil manually. The message isn't triggered until the oil level is 2 quarts low.
I agree completely, I do check mine on a regular basis as with the 02 DTS Deville I was using about a quart every 1200 - 1500 miles (125k on the car at the time).
On the 08 STS V8 I haven't seen it budge.

EChas3
05-10-13, 07:37 PM
They finally got the Northstar right for the XLR, SRX & STS.

stevenriz
06-04-13, 03:43 PM
The dealer checked it out and saw nothing. No codes and couldn't replicate the issue. I had since started using middle grade fuel. I also had the high pressure power steering hose replaced since I was going through a quart a month. Was that something I could have done myself? also had the cooling system flushed and new thermostat put in at the same time. So I guess I keep the thing for a little longer!

EChas3
06-04-13, 07:33 PM
The power steering hose can be hard.

Guy.Seminerio
06-04-13, 09:21 PM
The 2005 sts sae 100 has an actual oil life monitor, not based on some algorithm that reads your driving habits and estimates.

Aurora5000
06-23-13, 02:42 PM
I use mid grade and NEVER use ethanol..

MoistCabbage
06-23-13, 07:54 PM
The 2005 sts sae 100 has an actual oil life monitor, not based on some algorithm that reads your driving habits and estimates.

SAE 100?

What kind of sensor can test oils ability to lubricate?

Guy.Seminerio
06-23-13, 09:40 PM
Oil life. How much oil you have left. Search the 2005 STS SAE 100.

Ludacrisvp
06-23-13, 09:49 PM
SAE 100?

If only they would have made that one.
Headlight and foglight setup was a nice set of LEDs.
Likely is what was the proto type for the escalade platinum LED lighting. Also the instrument cluster used appears to also have been an early attempt at the CUE system.

EChas3
06-23-13, 10:16 PM
From what I saw, there was no trunk space. :)

The OLM works just fine.

MoistCabbage
06-24-13, 01:11 AM
Deleted.

Guy.Seminerio
06-24-13, 01:31 PM
You can have the trunk space. Ill take the sae 100.

Ludacrisvp
06-24-13, 01:36 PM
You can have the trunk space. Ill take the sae 100.
My sentiments exactly.

1harleyman
06-24-13, 06:06 PM
I have the same issue with my '06 STS, code came up as throttle body needing cleaned, did that but havent driven it much since, but what little i did it seamed to help so far.

jasonjsimon
07-02-13, 09:47 PM
With 130k, I have a weird nose like a light "knock" or as I call it, slurring when driving 20-30mph with light pedal. Just like when coasting. Weird. When I let off or step on it to downshift, the knock goes away... Bad gas? I use regular... Timing problem?

I have this exact problem with my 05 V8 with 145k. My symptoms are exactly as you've described. Gas is crap in Utah. Regular is 85 octane. My question is, how soon should I see an improvement in the knocking if I start using premium?

EChas3
07-02-13, 10:44 PM
I'm not convinced there's anything wrong. The Northstar isn't the quietest engine, especially since they added VVT.

If you haven't been using Top Tier gas, you'll need a throttle body cleaning before long. If you do, two tanks of premium is more than enough.

Make sure to have the your codes read to be certain you havn't had un-noticed ignition issues. You're at the right time to start needing a xoil or two.

jasonjsimon
07-03-13, 11:56 AM
I'm not convinced there's anything wrong. The Northstar isn't the quietest engine, especially since they added VVT.

If you haven't been using Top Tier gas, you'll need a throttle body cleaning before long. If you do, two tanks of premium is more than enough.

Make sure to have the your codes read to be certain you havn't had un-noticed ignition issues. You're at the right time to start needing a xoil or two.

Thanks for the response. I will clean the throttle body and try a couple tanks of premium. I haven't got any codes right now, so I don't know of any other ignition issues.
What are the symptoms of a bad coil?

EChas3
07-04-13, 12:29 AM
A coil going bad may cause an occasional miss or loss of power when hot (especially a 'heat soak' situation) or when cold & damp. Hard starts and other symptoms will usually set an engine light, but not always.

If there really is anything wrong, the noise will get worse. I'd be surprised if it's anything major on these V8's. No worries!

KRSTS
07-04-13, 09:29 AM
A bad or failing coil pack will cause a misfire which will normally throw a code and illuminate the check engine light.

fredolan
12-18-13, 08:41 AM
I just posted this in the knocking thread.

I had the problem with "knocking" whenever I used less than premium fuel (I know, I know, its in my head. . . but it wasnt). I only use 93 octane. This problem was noticed when I first bought the car in 2006 when it had about 40-50k on it. It now has 211k and I just started to hear this knocking again despite the high octane fuel. It is very subtle and most people probably wouldnt notice it. It only "knocks" when there is a very slight pressure placed on the accellerator. In "accelleratio" it does not "knock" at all. I will probably have it looked at and then post what I find. I am hoping to drive this car for another 100k. . . .I hope. It has been an excellent vehicle all around.

Also, I had plugs replaced recently (I have never used anything but OEM) and am very particular about oil level. Only use Mobile 1 oil and change it religiously. I doubt these are related. It has gotten very cold out in Michigan recently. . . .
For me this "knock" seems to come and go. I'll re-post if I get any answers. Regards, Bob