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Hi Guys,
Its my first thread on the forums.
I’m in Australia and have a Holden Commodore VZ SV6.
It is a GM LY7 3.6L V6 190KW engine with VVT on both intake and exhaust.
I have a bit of a sluggish performance issue and have replaced a few items to resolve the issue and also due to age of them/condition/maintenance interval.
Spark Plugs replaced
Fuel Filter replaced
Fresh engine oil (i do this every 7,500-10,000km)
Throttle Body removed and thoroughly cleaned
2 Intake hoses replaced (had splits)
EVAP Solenoid replaced (was leaking)
02 Sensors replacedI have a couple of issues, the biggest being the car runs really sluggish once warmed up, if i get in the car, start it and drive off, it runs pretty near perfect till it starts to warm up.
When its running sluggish it requires the throttle to be pushed down a bit further to really go and and light foot driving feels worse than my partners 4 cylinder.
If i try to take off at lights or speeding up onto the highway/freeway/motorway it runs sluggish then will rev higher up then roar off.
If i WOT the car picks up and takes off, obviously doing this all the time is not a good idea.
My fuel consumption due to this has suffered somewhat.
I noticed when checking stuff over the other day, the intake camshaft position sensor actuator solenoid on bank 2 (passenger side) is leaking oil around its seal.
As a matter of caution i am going to replace the solenoid and seal mentioned above.
I have been taking some logs of OBD data via my Android phone using a Bluetooth OBD2 adaptor.
I have attached some Excel spreadsheets of recent data log runs.
The one thing i have noticed, bank 2 fuel trims look to be a little off and for the most part bank 1 runs fine.
I have tried to do a log for TPS sweep, but it looks fine from the readings.
Also to note, when at lights you can feel the car going from a ok-idle to a pretty rough idle however the RPMs don’t appear to move that much and via OBD only show around a 5-20RPM fluctuation.
Hoping someone can give some further suggestions?
Thanks.
EDIT:
Just also, i’ve gone through all of the performance issue testing on this and many others including testing coil packs (this was before i could see fuel trims) and checking for vaccum leaks, etc.
I also forgot to mention, the reason i was checking TPS also, i am having an odd issue mainly when either suddenly accelerating or slowly down suddenly from high speed (eg. from freeway/highway/motorway) where the RPMs will stay up in the high range, as if my foot was on the pedal.
From what i have read this issue is commonly either TPS, which since my car is fly-by-wire its all contained in the 1 costly throttle body unit.
Also read this could be a CAM sensor issue?
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Interesting – Post Cat O2 Sensor Readings https://www.dropbox.com/s/tgplomygq95p7hl/trackLog-2014-Mar-04_21-33-46.pdf
What about the thought of running a compression test? A cylinder power balance test may mean the cylinders are equal but maybe they’re all equally worn.
Have you tried unplugging the MAF and driving it to see what happens? (Yes, I know the CEL will illuminate, etc but it’s for test purposes only.)
Since things like an exhaust restriction have been mentioned, what about the possibility of transmission slippage due to aged fluid, hardened seals inside the transmission, etc?
I’m assuming this has an automatic.[quote=”Bluesnut” post=90245]What about the thought of running a compression test? A cylinder power balance test may mean the cylinders are equal but maybe they’re all equally worn.
Have you tried unplugging the MAF and driving it to see what happens? (Yes, I know the CEL will illuminate, etc but it’s for test purposes only.)
Since things like an exhaust restriction have been mentioned, what about the possibility of transmission slippage due to aged fluid, hardened seals inside the transmission, etc?
I’m assuming this has an automatic.[/quote]Yes this is an automatic.
As above, the transmission was rebuilt 23,000km ago and was in today for its 20,000km interval service.
Got the car back today from the transmission specialist after the service, he advised there is nothing mechanically or otherwise wrong with the transmission.
He advised the issues occurring are engine or sensor/electrical/ECU related.
Stay away from shotgunning the sensors or something electrical. Stick to the basics. You stated that you checked the vacuum but were not specific on checking for an exhaust restriction. The catalytic converter is only one suspect for this. You could also have a muffler that’s clogged, or a pipe that has collapsed internally. When looking for exhaust restrictions, don’t limit yourself to just one component. Do the vacuum test and see what you come up with.
Don’t rule out the basics. Engine mechanical is often overlooked. Doing a compression test really can’t hurt and might reveal a problem. I don’t think swapping injectors around is going to tell you much. If you had an injector issue I would think that would cause a misfire, not a general engine performance issue. Also check the engines mechanical timing. If there are issues here it can also cause performance problems. This may involve an exploratory to check the condition of the components and also the timing marks.
I would be looking for something general across the board like a mechanical issue of some kind. I wouldn’t start looking for electronic causes until I had exhausted all possibilities with mechanical.
Keep us posted.
[quote=”Bluesnut” post=90245]
Have you tried unplugging the MAF and driving it to see what happens? (Yes, I know the CEL will illuminate, etc but it’s for test purposes only.)[/quote]Disconnected the MAF this morning for my drive to work.
No SVS or Check Powertrain (equiv to CEL for my car) light showed up, but readings via OBD did show the MAF reading to now be 0 g/s.
The car seemed to drive exactly the same as when it was connected.
[quote=”EricTheCarGuy” post=90295]You stated that you checked the vacuum but were not specific on checking for an exhaust restriction. The catalytic converter is only one suspect for this. You could also have a muffler that’s clogged, or a pipe that has collapsed internally. When looking for exhaust restrictions, don’t limit yourself to just one component. Do the vacuum test and see what you come up with.[/quote]
When i did the vacuum tests prior, i also checked for typical signs of exhaust restrictions, but was not focusing purely on that.
One of the signs of exhaust restrictions would be loss/drop of engine vacuum?
I used your video to determine for that when checking vacuum, at 2000 RPM constant, the revs stay around 12-13PSI vaccum.I’ll go through and check again and see what i get, i have to replace some suspension bits and pieces on the weekend so i might even pull out the pre-cat O2 sensors and then test.
[quote=”EricTheCarGuy” post=90295]
Doing a compression test really can’t hurt and might reveal a problem.[/quote]I’ll try and get this done on the weekend if possible.
[quote=”EricTheCarGuy” post=90295]
Also check the engines mechanical timing. If there are issues here it can also cause performance problems. This may involve an exploratory to check the condition of the components and also the timing marks.[/quote]From reading workshop manuals, the only way to check the timing and the timing marks requires pulling off the front timing cover to get to where the chains are, which requires pulling all accessories off the front of the engine to even get to the cover. Such as http://i28.photobucket.com/albums/c243/mccabe1100/DSCF7841-1.jpg
[quote=”EricTheCarGuy” post=90295]Stay away from shotgunning the sensors or something electrical. Stick to the basics. [/quote]
Also to add, the reason i am looking for something electrical is because of how revs are sticking when the accelerator pedal is not pressed in, with the transmission specialist confirming the transmission is 100% what else could cause if not electrical?
I don’t think timing would cause the revs to stick? Such as if on the freeway and accelerate hard (not that i typically would) the revs can stick up higher above 3000RPM for a while until i tap the accelerator again.
The revs sticking can occur either before the transmission shifts at which is causes a harsh shift or after it, as if i’m still trying to accelerate.
This to me seems like it could either be a TPS or throttle pedal sensor issue.
My car uses fly by wire/electronic throttle control, so no seperate TPS i can replace or test with as its all contained within the one throttle body assembly and a electronic accelerator/throttle pedal sensor.
By the issues i am having, i assuming right up my issue is a combination of 2 or more things failing.
I may be able to get a hold of another throttle body to test with.
EDIT:
After thinking a little and reading your comment about brakes i thought of another issue.
For a little while now, i’ve seemingly had a little more travel in the brake pedal when trying to brake and requires a bit more foot to stop (i tend to brake early anyway so it hasn’t been a big issue).
The fluids about 20,000km old, this was changed when i got new brake pads and rotors a year or so back from a mechanic.
I’ve done checks around the brake booster vacuum hose that hooks upto the intake, i was thinking could there be a vacuum leak within the brake booster or master cylinder which causes both softer brake pedal and engine sluggish?
If i am off my rocker, please let me know, i’m just getting sick of these issues and really don’t have the cash to fork out to pay a mechanic to again tell me “nothing is wrong”.
Well today, after changing over some suspension stuff (and fixing a clunk i had, woohoo) i removed the pre-cat o2 sensors.
Unfortunately, due to lack of ALL automotive accessories/parts stores around my area NONE of them have any vacuum gauges nor even sell them to test with.
When starting the car up with the o2 sensors out, you could hear the rough idle more (and also obviously the exhaust).
The sound it gives almost sounds like a miss, but its really hard to confirm.
Idle stayed exactly the same as prior to removal of the o2 sensors, it made absolutely no difference at all.
Was not able to drive the car much at all however, trying to move the car with the o2 sensors out was worse than leaving them in, the car would barely move at all without reving very high, so i reversed in and out of the drive way.
Put the o2 sensors back in to continue other tests.
Using OBD2 scan, i did see, when going through the rev range when driving nice and calmly the vacuum does die down relatively easily and without pushing the car a tonne i seem to max at around 3200rpm.
I also noticed, the post-cat o2 sensor reading differences between bank 1 and bank 2 for when bank 1 reads 0.7~, bank 2 reads about 0.4~.
I’m going to order a vacuum gauge off eBay or so and then check exhaust back pressure to be certain, i’ll keep checking
Unfortunately nothing further with this issue.
I ended up taking it to a mechanic who had it for a day and a half and could feel the issues i reported but no reason for solution.
So i’m absolutely no further at getting this sorted out.
I managed to locate a auto parts store who can order in a fuel pressure tester, so will test this and report back.
Wonder if i can get any more suggestions for what and how to test?
After spending $110 on diagnosis and not getting any answers, reluctant to take it back to another mechanic.
The issue seems to be more so at low rpm and acceleration, if i WOT the car roars off..
Well.. cause i was bored and not doing anything on my birthday, i treated myself and replaced the injectors, after confirming the fuel pressure was perfect both at idle and at 2000-3000rpm.
The old injectors pretty much broke trying to remove them out of the fuel rail and the o-ring’s i had to remove out of the rail later.
The old injectors were quite dirty and no wonder there was an issue!
After putting the new injectors in and driving the car around.. both the rough idle and hesitation seem to be pretty much gone!
There is still however some small performance issue there, i’ll be giving the spark plugs a quick clean tomorrow in hopes its just carbon build up from running lean….
Just a bit of an update guys.
Seems Eric was on the right track being a mechanical type issue.
Turns out, despite the compression tests being fine and no major overheating the head gasket is blown and/or a cracked head.
Randomly 2 weeks ago, during a short drive to the shops, the car completely overheated, to the point the ECU cut the engine off for ‘Overheat protection’.
After then checking the coolant reservoir stick, i could see oil in the coolant.
Managed to limp the car to the closest mechanic after hours when it was cool.
They came back a few hours later advising definitely confirming oil is getting into the coolant and so is exhaust gases, which is causing the cooling system to pressurize extremely quickly, cause a random quick overheat.
Due to the car being quad overhead cam, and also the age and KM, the mechanic has advised against just replacing the head gasket, due to it being costly and also may be cracked heads, etc.
Both myself and the mechanic called around places for an engine with lowish km.
I was able to find an engine with 105,000km less than my current engine, and for $2000 flat (incld delivery to the workshop), the mechanic was only able to find 1 for $3000, so i saved myself $1000 by looking myself.
Currently awaiting the mechanic to undertake the engine swap for me for $2000 (so $4000 all up incl engine), including replacing the water pump, all hoses, engine mounts, thermostat, etc
I’ll update the thread once this is all done.
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