Very Rough Running when cold - Mechanic and Auto electrician can't diagnose

[l1ck3r]

sounds to me like either your mechanic could be right and you could only hope not, my best guess without looking at the vehicle in question would be the 'TEMP' sensor or the 'AIR TEMP' sensor playing up if it is only when it is cold starts... gather the info needed to self test the 'PCM' and record and google the code or codes, '12' means system pass but is always the first code and each code will repeat 3times before the next is displayed.. tho in reality if it is the 'TEMP' sensor it may or may not come up as a fault code (temp and air temp sensors are under the altenator on my vr but not sure on the vt) hope this helps to solve your problem...

 

[Wherry951]

Yeah well i'm gonna change my fuel filter on the service, dunno about fuel pump. I'll get it looked at if it persists after the filter is changed and injectors are cleaned. Might be your problem, might not

 

[db_notso]

lack of power on cold start ?
like stuck in higher gear than should be, no misfire, just wont accelerate easily
as if in a manual you selected four instead of two?

either leaking injectors over long period when cold (common)
or could be sticking tourque converter clutch......(un-common only cold but is like stuck in higher gear)

as for a crack head there is a dodgy test you can do yourself

remove plugs when cold
place a coolant pressure tester on cooling system
pump it up to pressure
let sit and see if pressure is lost
keep pumping it up and let it drop a few times
unplug all your injectors at injectors
get someone to hold a clean piece of a4 paper on each side of motor covering spark plug holes (or tape them there at least watch holes on both sides while cranking)
get third person to crank motor over

if coolant on paper cracked head or leaking head gasket (are to be only cold but could be leaking compression into coolant then excess pressure simply coming out resevoir of coolant)

sugest you post these useless codes maybe misunderstood by the person reading them...
or check codes yourself
https://forums.justcommodores.com.au/threads/checking-error-codes-vt-vx.23665
and post them up then we will talk more maybe......

 

[Brett_jjj]

Ok - the mechanic has got back to me and advised that the commodore VT does not have a purge canister solenoid. :-(

I have a VT V6 engine sitting on a stand, and its got the purge cannister solenoid on it in the exact same place as my VS one,at the back of the motor.It looks like its the exact same solenoid too.Id avoid that mechanic.

 

[wortus]

The purge solenoid is only meant to operate (open) under certain conditions which are basically when the engine is at operating temperature and the car is being driven above a certain speed. If it's stuck open then the engine will suck from the fuel tank vapour cannister all the time.

You could try locating this tube from the solenoid into the inlet manifold and putting some kind of clamp over it to see if it fixes the problem. If it fixe dit I would take the solenoid out and see if it's coil has continuity and if it is trying to operate with 12 volts applied to the coil. If may just be blocked with some gunk keeping it partially open so you may be able to clean it shoudl that be the case.

 

[vsd]

Hey thanks guys for the suggestions.

An update of where things are at.

The mechanic is trying to track down a "loan" purge canister valve to try the option mentioned above.

Meanwhile he has also done the 'cracked head test', (thanks db_notso) and found no issue... I will check with him whether he did the coolant on paper trick.

Regarding the fault codes... The mechanic sent the car down to an auto-sparky to do all the testing of the "electrics" so I doubt the fault codes are available.

The mechanic said the next step would be to try putting the car on a dyna-tune machine (a different business down the road).

Watch this space...

 

[vsd]

btw I will suggest that he try your idea wortus re purge canister - thanks.

 

[db_notso]

dyno tune?
very expensive measure for a rough idle cold....
they will load the car up in gear on the dyno to find out if its one cyclinder playing up or not
that and swapping parts and redyno is main benefit they'll get here

fyi unplugging the coolant temp sensor will default its reading to 92 degrees....... and hence wont run full power but shouldnt be rough

the paper trick is a backyard method of testing for coolant leaking into cylinders.... he may have better methods he used...

i need to know those codes for more help without seeing car....maybe stop in and jot them down?

 

[vsd]

Thanks db_notso it may take a while to get the fault codes sorry. Although I am pretty sure the auto-sparky did check them?? It's a bit delicate putting too much pressure on the guys (mechanic and auto-sparky) as they have said they wont charge for their time as they have not solved the problem (which is good of them).

I like the idea of unplugging the coolant temp sensor...does that fool the car into thinking it is running warm?

One other thing... the mechanic said there is a hairline crack in the exhaust manifold - although he also said that this should not be causing the rough idle when cold issue. What do you think?

 

[acarmody]

One other thing... the mechanic said there is a hairline crack in the exhaust manifold - although he also said that this should not be causing the rough idle when cold issue. What do you think?

Nah it will have a bit of a ticking sound but that's about it.