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Discussion Starter #1 (Edited)
BC update

I now have just over 125k miles on the BC update A stock 2008 LS. The mods include activating the cruise control, replacing the steering wheel to the SS stile with the extra buttons for cruise & radio controls.
Fe5 shocks & struts and a new Front 05 SS sway bar, Thanks to eBay and ZZ parts. New forged Al LCAs and the new intermediate steering shaft. That was a pita. Also installed new AC stock 41-103 iridium plugs and both O2 sensors (Denzo 234-4066 rear & 234-4668 front) air filter and sprayed the mass air flow sensor.
Changed the oil & filter using Mobile 1 5W-20 and replaced the original cabin air filter/ mushroom farm.
All this when EBay delivered the BC from Florida back to TX where it was originally titled
Since then I have changed the oil & filters once both engine and cabin.

After my second oil & filter change I had the P0303 code pop up within 500 miles. As a recall I played swap plugs, injectors and finally cleaned the MAss air flow sensor before the code cleared and provided another 5k miles.
Oil is now 70% and that P0303 is popping every 2nd or 3rd tank of fuel. Averaging 33-34mpg.

Now time to brake out the TechII and see if and how many misfires are actually happening
I checked an still have the original O2 sensors along with a new pair of Densos And that second set of Moog sway bar bushings. My miss order. I read you needed 2 and the listing said one per box so, I ordered 2 boxes and received 2 per box.
@$7.00 It was just the same to keep them as to pay shipping back.

Also it’s time for new tires. RF is showing the wear bars on the stock 195/R65 Toyos.
I still have a complete SS cobalt rear Axel with rotors, calibers, and the SS E-brake assembly and SS rear Coils.
Remember it is set up for 5 lug and I have the 08 LS 4 lug setup and still have the stock LS front coils.

So there you are enjoying running around @ 70 mph getting 32-34 mpg and enjoying the MP3s from the replaced front speakers.

Time to do a little PM deciding if stock 15” or new 16” or a set of SS 18” wheels and 4 new 5lug hubs or....
Work on my Geronimo. Still need to do some smoothing on it’s ruffled feathers.
 

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Discussion Starter #2 (Edited)
@Coby7
Looked today at RF tire. It’s pretty much gone. Wear bars are clearly showing. Both rear tires have very good tread.
LF tire is a good used tire.
Thinking on installing 5 Lug hubs and 18” SS wheels. This would force new front rotors also.
Now I have that SS rear with brakes. But still no proportioning valve and I have not installed or have the ABS.
So a little background on installing the ABS and how it is on the Cobalt. 2 front an 1 rear servos or all 4 wheels???
Or
Just getting 5 lug rotors and drums

18” tires ~$125 X 4
5 hubs ~ $40-$50 x 4

5 lug rotors & drums ~ $20 x 4

I still have one odd 15” steel wheel stock hubcap does not like.
Toyo 195/65 15 ~$75 ea

And I still enjoyed tooling around not the stock (as received) Tokyo’s.
 

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ABS system uses sensors at all 4 wheels. The proportioning valve is not and absolute necessity if you don't have ABS. It's just that rotors bite a little better than drums and may take some getting used to. If you find the rear locks up too often then you will have to get one.
 

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Discussion Starter #4
@Coby7
Took the Tech II out today and pulled up the errors (P0300) and looked at the count.
Cylinder 1 -2
Cylinder 2 -5
Cylinder 3 -12,000
Cylinder 4 -4

Pulled up the misfire graph and misfires on cylinder 3 stop generating above about 1200RPM
No other errors
Fuel trim 0 to 2
Front O2 sensor moving up and down ~0 to ~.500
Rear not moving but about .700 - .850

Checked fuel injector and cylinder balance and all injectors and coils respond pretty much the same when I disable one.
Instant rpm drop then engine returns to ~ 90% prior RPM. On re-enabling, there is a sudden increase in RPM for ~3 sec then RPM returns to pre-test value. This is on the fuel injectors and coils. That is if I had indeed accessed the tests properly.

Base RPM command 550RPM engine speed 750RPM plus or minus 20 rpm
No other codes

So, I will play swap parts between cylinder 2&3, clean the mass air flow sensor and check the oil level. It’s been ~3,000 miles since oil change and oil at ~75% using Mobil1

On another note. I pulled up my radio info and logged radio 25775626 calibration 4
I do this in prep to install a Malibu radio UUI option. It’s a Panasonic with a USB port on the front on the lower Right corner & mini jack on lower left. If I would have thought about it, I might pick up the vicm (sp) with Bluetooth and the BlondStar mirror/mic. Not interested in BlondStar just the Bootooth for wife’s phone.

---------- Post added at 03:23 AM ---------- Previous post was at 03:18 AM ----------

ABS system uses sensors at all 4 wheels. The proportioning valve is not and absolute necessity if you don't have ABS. It's just that rotors bite a little better than drums and may take some getting used to. If you find the rear locks up too often then you will have to get one.
4 sensors yes without a question. But, I have not checked, is there 3 hydro lines (LF,RF,R) or 4 lines. I do know of some ABS systems with 3 and others with 4.
 

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Always 4 with T/C
 

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Discussion Starter #6
Thanks @Coby7
Swapped plugs & coils between cylinders 2 & 3. No joy!
Still gendering misfires on cylinder 3...
Next I will try injector swap or ..... ?
Leaking injector o-ring or dirty injector? Will dirty throttle body cause just 1 cylinder misfire? Does not seem likely.
Leaking intake port/ bad gasket/o-ring?
Remember both O2 sensors new & I still have old ones & a new set.


Also looked and saw the 6 brake lines into the p valve telling me more amount the 4 wheel ABS.
By adding the 4 hubs with sensors I suspect I would need the body wiring to the 4 corners.
I would be surprised if they were there on a non ABS LS.
Connecting the ABS pump assembly should not be a large problem taking it from an ABS Cobalt & its p valve.
 

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You may have a bit of carbon build-up on the exhaust valve causing it not to seat properly. You may be due for a good seafoam cleaning before you burn that valve. If you do a compression test and it shows up low on cylinder 3, then you'd know for sure but don't panic.

Doing the ABS swap is a project for sure, good luck.
 

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Discussion Starter #8
Ok
I could see that (sticky or leaking exhaust valve) can do a max pressure and differential/leak down test.

Just looked at TechII live misfire graph. No misfires over 1000 RPM. With engine at operating temp. At idle I am seeing cylinder 3 ramp up from zero to ~ 50 counts over 6-10 sec. then it drops straight down to zero for about 2 sec and then starts to ramp up again.
The max value of the graph does not look to be max value available.
Just a simple saw tooth graph with a 10% dead spot between the ramps.

Will try to do pressure test today.
Again this is @125,000 miles on engine
 

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Discussion Starter #9 (Edited)
Swapped cylinders 2 & 3 fuel injectors and cleaned the MAF sensor. Let’s see if any change now. Last P0300 happened alter 130miles

I looks like the T-body has never been cleaned. I don’t think that is an issue though.
If this does not work, I will do the cylinder pressure diagnostics.
 

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the spray. since you are literally spraying it into the throttle body. i had a misfire in my durango which it helped. but i have ran it through my cobalt i think 4 times within the past year. car runs smoother afterwards everytime. i got the car for 900 with 200k miles on it. and it wasnt maintained that well. so i have used both. but i stand behind that shit because it works great.
 

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Just make sure you stay away from the butterfly hinge. There's a sealing lubricant at the pivot point you do not want to wash out or you could get moister on the throttle position sensor wipers. I would try one in the tank first.
 

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No, but it will clean carbon buildup on valves and top of the pistons. If 1966tbird has a small camera he could insert in the spark plug hole when he does the compression test it might show any buildup.
 

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Discussion Starter #16 (Edited)
Thanks all
Sorry my camera took a powder had a nice boar scope with a 180 degree tip that would inspect the valves via the spark plug hole.
It will be replaced so I can show images.
In the mean time.
Replaced the cam chain tensioner and managed to retrieve all of the original flat faced cam chain tensioner with the “hump” style.
I also replaced the valve cover gaskets.
I could not tell if I had actuated the tensioner or not so I removed, disassembled, armed, and reinstalled. And gave it a smart tap again.
Fired it up and heard about 30ms (at most) of valve clatter. Then smooth clean engine.
Oil at 60%.
Picked up a can of sea foam thinking it was spray......NOT.....it was 16 oz so...I dumped it into the 12 gal of fuel ... @Coby7...thanks for the suggestion above....
I will drive this tank of fuel out and report back..

While there, the AC has not been working as well as it should. Hooked up the AC gauges and added 12oz of R134...temp came down to 42F
It’s been 2yr as of this coming Aug. so this was anticipated and not out of line...noticed green dye on the low pressure side. Just a squirt’s worth you might get when disconnecting from the service port. No signs of die on any other fitting or line.

Things to do.
Sea foam Spray....maybe
Image piston top, valve tops, valve guides.....camera on order... I must get this fixed quickly because of the other engines I work on. Log the cylinder pressures.
Try the Malibu radio with the USB port on the front. Option UU1 ??? Wondering what speaker options to enable.
 

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Discussion Starter #17
Now down to 1/4 tank of fuel from fill up & a full 16oz can of Seafoam. I received only one P0300 code. Mileage and power seem great since new cam chain tensioner was installed. Still no images... I have made progress changing out the 3 belly skin panels on the Geronimo.

This is under the 3rd row of seats and shows the tube frame of the 1955 Piper. This is the center of the 3 .025” thick skin panels I’m replacing. Piper actually calls them fairings since they are not structural and we’re originaly fabric.
 

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Discussion Starter #18
Been busy working on the Geronimo and running the tank of fuel with the Seafoam treatment. No codes for the first 3/4-7/8 tank of fuel
Gettng @34 mpg.
Now topped off the tank with ~ 12 gal and poo, 200 miles in, P0303.
@Coby7
No updates on compression or images yet..it’s on the list.
I Still have original and new O2 sensors and the O2 sensors installed have only 12k miles. TechII does show misfires on cylinder 3

Now showing @60% oil change on Mobil1 with new oil & filter on hand....air filter looks clean & new

This P0300 / P0303 is getting to be a pain.
 

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Discussion Starter #19
Picked up both Seafoam fuel treatment & spray. Planning on another set of 120mile jaunts out to work on the Geronimo.
Also
Had the nasty misfire on a 2005 sable 24valve V6 DOHC @ 100k miles. After replacing all 6 coils, plugs it was still throwing random misfires on the outside cylinders....easy to get to. So, fresh front O2 sensors 100k mi is not out of line. Then it starts throwing lean on both front & rear banks. Along with misfire on cylinder 6 and random misfire and lean on both front & rear....
this said vacuum leak. Turned out to be broken hose on PCV valve. With one test drive cycle, all IM Ready monitors set except for evap. That should clean on second drive cycle from a cold start.

Now, if I can ID this Cobalt’s P0303, P0300.
Let’s see if the Seafoam works or not.
 

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Discussion Starter #20 (Edited)
Found a cracked/ split hose on the valve cover to plenum. While attempting to remove it, the entire hose barb came off of the plenum in one piece. A good cleaning, removing all of the rough edges and a good bead of 5 min JB Weld and a new hose fixed that problem.

@Coby7
Wondering if the potential leak passed the mass air flow sensor is enough to trigger the P0303?
 
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