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

vsd

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My VT Commodore runs very rough until warmed up. Once warmed up it performs perfectly, and will start and run smoothly for the rest of the day. The issue consistently (and only) presents itself after a long cool-down period i.e. overnight.

Both the mechanic and the auto-mechanics I have taken the vehicle to cannot diagnose what is happening. They've had the car for 6 weeks between them!

What they have done:

- Replaced spark plugs and leads
- Replaced coil packs
- Fault codes produced are apparently (meaningless). These seem to primarily relate only to the secondary issue of very very rough running.
- The auto electrician has progressively swapped "all" the components from a donar car onto my car. He is now at the point where he believes it is NOT an electrical issue.
- They've had the Holden dealer mechanic over and he is also unable to assist.
- A few weeks prior to the issue arising the mechanic replaced the crank sensor (for a different issue that is fixed now i.e. car would turn-over but not start).
- The mechanic suggested taking it to a dyna-tune shop down the road... would that help?

More detail of symptoms...

The car, from dead cold, starts easily. It idles rough but as soon as any load is put on, the engine runs very roughly. The maximum speed is only about 15-20 km and the car cannot get up any hills. As soon as the car warms up (after about 6-10 minutes) it runs perfectly.

Is there a way to identify whether it is electrical or mechanical?
I'm not an expert but would be greatful for some options that I could suggest to the mechanic (who it seems has almost given up).

Thanks
 

slowandlow

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sound like the choke is f'd the way its acting.... (not professional opinion :D). possibly your injectors r sucking air, and when it warms up, maybee it seals better then?????? small gasket leak??? try looking into the auto choke (having a brain fade, cant think what unit does this a.t.m.), if you have a user manual. be wary of mechanics telling you warning lights are meaningless. it means that they cant be farked, or are useless dumbos, and have no idea. i recently had this situation with my engine warning light. the repco mechanic (hallam) told me it was faulty and nothing wrong... i eventually got codes myself, diagnosed biggest possibilities, and fixed it fine.

DONT GIVE UP ON IT.......
 

vsd

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Hey thanks slowandlow, yeah some good options there. The mechanic said he noticed a slight manifold gasket leak when the car was cold but he reckoned that would not be related. I wondered whether this leak may have been throwing some sensor of track?
 

Brett_jjj

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Ive had a very similar problem happen with my VSV6 a while back.When the car had been sitting for 24 hours or more,it would misfire and shake when first started, and it seemed to only run on a few cylinders for 30 seconds or so,then the misfiring cylinders would pick up and start firing,and it would then run smooth like it should.It only did this after sitting for 24 hours or more though,once it had been started for the day,it would start up perfectly every time,until it sat again for 24 hours or more.I tried everything,plugs,leads, coils etc,looked for leaking injectors and whatnot,nothing fixed it.Then I had an error code come up to show that the purge cannister solenoid was faulty,after replacing this solenoid,which was $120 from holden!!!,the misfiring when cold stopped.I dont know how it was causing it,but when it stopped it from doing it,it sure suprised me,its the last thing I would have thought would cause this to happen.It might be worth your while checking it out,or swapping it for another solenoid to see if it fixes it.
 

vsd

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Yeah - that sounds exactly like the same symptoms!!! Thanks heaps for posting, I'll run this past the guys.
 

vsd

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

The mechanic (Rick) is wondering whether there could be a hairline crack in the cylinder head, which is resulting in antifreeze getting into the cylinder (when cold, and causing the rough cold running). He said he could put a product into the radiator to try and seal it up?

What do you guys think?
 

graham7773

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Not wanting to contradict a "mechanic" but the VT V6 does have a purge canister solenoid! It is remote mounted in the line/pipe that runs from the canister to under the throttle body. One wire runs from the solenoid to the EFI relay and the other wire goes to PCM terminal C4. The solenoid controls vapour flow to the inlet manifold. Hope this helps
 

vsd

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Thanks for the quick reply graham7773 - I'll let you know how things go.
 

Wherry951

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I have a problem with my VT V6 manual where you drive it and it just will not pull away fast, the first 30 seconds are powerless and if you put your foot down it tends to kinda jolt and in a way bunny hop very lightly. But it doesn't stop that much when warmed up, i have to give it alot of revs to pull away fast or it wont have the power to take off fast. My mechanic reckons its the injectors, might be similar with you? He says over the years they just get dirty and just don't work, so take out your injectors, clean them and they come up like new, might fix the problem. I'm going to do that soon, as well as a full service and see if the problem fixes itself
 
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