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2009 CTS Base 3.6 VVT
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Discussion Starter #1
I have 2009 CTS base with the 3.6 VVT.

Today, out of the blue, after driving for 20 minutes without issue, sitting at stop light for 20-30 seconds, the engine speed increased by 200 rpm from its normal 660 rpm. After work it did the same thing within 5 minutes of startup after being parked for 8+ hours. Got on the highway for 15 minutes and then got off, normal 660 rpm idle, and then it did it at the first stop light after idling ok for about 20-30 seconds.

The other thing I noticed, is at the lower rpms, a more rpm-dependent whine. Above 1500-2000 rpm it's probably getting washed out by the engine noise. This also seems to be new. Not sure it's connected to the subtle rpm increase.

Found no fault codes with my OBDII reader.

Both issues are noticed whether I have the A/C compressor on or off. For the record, changed my oil about 100 miles ago. In the past 6 months, I changed the #6 and #2 coilpacks due to consistent misfiring. Due to rainy weather, a lot more water on the roads than usual but I can't imagine that the car hadn't experienced that in the last six months.

Any ideas what the increased idle and noise could be? Or how to diagnose them?
 

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2011 CTS Coupe Premium
Orlando - We take orphans
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First question is whether the RPM increase is being commanded. I'd use a GM scan tool to monitor the commanded idle speed. If no change then does the manifold pressure drop. I wonder if something like the evaporative emissions solenoid is triggering and has a hose missing (but just one possibility). What we need to find is what is changing and that requires instrumentation. I suspect that Torque Pro ($5 plus a smart phone or tab and a $12 BT dongle) could do that.

BTW can your code reader monitor engine parameters or just read codes ?
 

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08 CTS DI
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Check to see if there are any pending codes, there may be one coming that hasn't met all of the parameters necessary to set yet. Years went by before I ever noticed my scan tool had that function let alone before I ever used it. Not all have it and it can be very helpful in the event of a hard fault that renders the motor inoperable before a code sets. The whine you are hearing makes me suspicious of the alternator, but it can come from just about anything under the hood with bearings. Vacuum leaks can cause an idle change, but it would be immediate at every startup and the computer would try and counter it by closing the throttle until the desired rpm was reached and if it could not reach it, a code would likely be set.

It could be associated with the A/C also since usually there is a subroutine in programming that kicks the rpm up a little when the compressor cycles on and for some reason it is more noticeable now than before.
 

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'09 CTS DI FE1 Luxury
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How's the battery? The PCM can command a faster idle when it senses that the charging system isn't keeping up with demand. Possibly a failing alternator if the battery is good. Monitoring the voltage on the DIC could provide some clues as to whether this could be the problem or not. It could be many other things as well but unless the pcm commanded the idle increase, a problem will set a code eventually.
 

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2009 CTS Base 3.6 VVT
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Discussion Starter #5
Thanks all for the suggestions.


I was imprecise in my description of the code reader - I am using a dongle and Torque Pro.

So, the car has been sitting for 4 hours and engine down to 150-160 deg.
I started it up and immediately heard the this lower pitched whining at the lower rpms.
A/C and control panel are OFF.
Idle didn't stay on startup for more than 10 seconds or so.
Then it settled to about 550 rpm. 18.0% throttle. About 15 in Hg vacuum. 183 deg.
5 minutes later. 670 rpm. 19.0% throttle. didn't catch the vacuum.
The whining seemed to stop more suddenly rather than fading away.
2 more minutes. 550 rpm. 18.0% throttle. 15.0 in Hg vacuum.
Then I "goosed" it a few times.
After it settled, and this is weird, because the car is parked. Parked. Hasn't moved since 4:30 pm.
Every 10-20 seconds, I see the speedometer bounce to 7 mph and settle back.
The rpms were a bit in unison with it - hunting between 550 rpm and 660 rpm, sometimes going to 700 rpm.
And then slowly over a minute or so the hunting and speedo bounce faded, and settled at the 650-ish rpm.

There are no faults or pending faults.

What could cause the bouncing speedo?

So, I need to monitor/evaluate:
-voltage (DIC or maybe a parameter in Torque)
-commanded rpm value
-battery condition

I do have a CTEK MXS 5.0 battery tender that has "rejuvenation" cycles - maybe I should take it through that?

Other suggestions?
 

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08 CTS DI
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Interesting and more suspicious of a charging system problem. I believe the speedo signal passes through the BCM, when it doesn't see the voltages it expects on the supply side things definitely start to go wrong. Since alternator output is computer controlled, you may be seeing fluctuations that are the result of PCM commands to the alternator in an effort to achieve a specific voltage, or in response to fluctuating output. There's no reason the speedo needle should move after startup if the car is not moving and it all may be a false reading. Check the rpm and speedo against the scan read out and see if the blip registers on the scan gauges as well.
 

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'09 CTS DI FE1 Luxury
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The bouncing speedo is worrisome. No good ideas. Hopefully something simple.
If no battery tester, check the resting voltage with a Multi-Meter (MM) or DIC. It should be 12v+ on DIC, 12.5v+ at battery terminals. Try to determine how old the battery is.
Check the charging voltage with a MM or DIC. It should be 14.5V+ immediately after starting.
I wouldn't desulfate charge the battery until determining it's health. It shouldn't hurt to charge the battery overnight on a low amp (~2A) setting.
 

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2009 CTS Base 3.6 VVT
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Discussion Starter #8
So maybe the whine is from the alternator and so is the voltage fluctuation.
The Torque app speed gage was definitely bouncing at the same time the dash speedo was bouncing.
Of course, it could be my mind playing tricks on me but when I had the hood open trying to isolate the whine, I swear I caught a whiff of the classic over-heated electrical component smell but very subtle. Just don't remember smelling that when I was changing the oil.
 

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So maybe the whine is from the alternator and so is the voltage fluctuation.
...classic over-heated electrical component smell but very subtle...
That's telling, and since the computer is sealed the likely culprit would be the alternator. Try to get close enough to it at some point when it's safe for a good smell test. This is something you want to replace before a complete failure if it is the culprit, because previous threads suggests it can take out the BCM along with it and that may be why you are seeing signs of electrical abnormalities.
 

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2009 CTS Base 3.6 VVT
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Discussion Starter #10
This morning, did some cold measurements.

From the DIC:
Pre-start 12.0v
Post-start 14.6v RPM 1300
near end of high idle 14.5v RPM 720 130 deg
5 minutes 14.5v RPM 550 167 deg
did some goosing
10-12 minutes 14.4v RPM 560 203 deg

Never did the speedo bounce.
Never heard the whine.

It's as if the issue has disappeared.

Battery: can't find the actual installation date but the newest date on a sticker is from April 2015 so I'm thinking it was installed in late 2015 or early 2016. (I bought the car in October 2016.)
 

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**2014 CTS4 Sport Wagon-Luxury**
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do you know the type, brand and warranty of the installed battery???...I mention this as I acquired a Ford F150 this year and found paperwork for a top of the line Interstate battery installed at Firestone but under the hood I saw that it had been replaced with a 2 year warranty (2 years were up March of this year) Interstate as a warranty item from Firestone...

I have a friend who bought a 2006 GTO with a brand new TOTL AC Delco battery...he let it go flat and instead of charging it up or using the warranty, replaced it with the cheapest replacement from O'Reilly Auto...it went dead in a year and just outside warranty...you guessed it...he replaced with another cheap battery and it too went out after a year...he is looking at his 3rd replacement battery in almost 4 years and I mentioned he could get a better battery and use his Deltran Battery Tender Plus when he's not driving the GTO but what do I know... ;)

good luck with your ride...

Bill
 

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2011 CTS Coupe Premium
Orlando - We take orphans
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Back in the day I had both a JC Penny and a K-Mart "lifetime" battery ($99 AFAIR). Would last about three years so about every 18 months was replacing batteries. Since kept those cars a few decades did get my monies worth. Now I just buy AGMs and those seem to last 7-8 years.
 

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2011 CTS Coupe FE3, 2003 Thunderbird, Gone 2013 ATS, 02 Deville
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I think your alternator is going BAD. Have someone check the output of the Alt. and check the Battery.
 

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2011 CTS Coupe Premium
Orlando - We take orphans
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Also the speedo bounce may be indicative. When slowing down to a stop, the computer goes into something called DFCO (deceleration fuel cut off). Despite the name the action is to hold the throttle open a little bit (the 19% vs 18% or is that the pedal (TPS - throttle position sensor) rather than the actual butterfly position ?) for emissions control.

BTW when an alternator goes to a high charge rate they often whine but should be visible in the voltage.

Torque Pro is great for displaying parameters and generally saves trips as a .csv file.
 

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2009 CTS Base 3.6 VVT
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Discussion Starter #17
Thanks everyone for the continued suggestions. I too now think it's the alternator. Not sure why it's intermittent though but I guess that's just good luck for me - I have a little more time to replace it. About $200 with a lifetime warranty and $17 for a new serpentine belt (seems like the original). It seems like the R&R are pretty straightforward - maybe 2 hours for someone like me.

The battery I have today is an ACDelco Professional 42. I think about 3 years old. Here in North Texas, lead-acids only last 3-4 years even if they are the top model in a make. Most of the time they just die without warning.
 

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2009 CTS Base 3.6 VVT
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Discussion Starter #18
A new twist...

This morning had heavier whining right after start up. Just as exiting the driveway, the DIC displayed "service power steering". Had noticeable loss of steering assist.

Voltages were ranging with the engine rpm and never came up to the normal 14.5v post-start value. Higher off-idle rpms had about 13.1v and idle was about 12.2v.

Checked for DTCs with Torque and nothing was thrown or pending.

What does all this mean? What are next steps for diagnosis?
 

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2011 CTS Coupe FE3, 2003 Thunderbird, Gone 2013 ATS, 02 Deville
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You will need to spend $$$ to have it fixed. Take it to a mechanic and have the battery and charging system checked. No one can fix it over the internet.
 

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2011 CTS Coupe Premium
Orlando - We take orphans
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Check the power steering fluid. When they get low, will draw air into the system and whine. Can usually feel a vibration in the steering wheel. May have a leak. "DIC displayed "service power steering"" that should have set a code in history at least. Torque may not see that & need a GM scanner.
 
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