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VT Commodore underload problems

danielwoodward15

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Im having trouble with my commodore whenever the car is under load or on a slight incline while driving the car starts to jerk.
I have tested the car by putting it under load as in holding down the break and flat foot accelerating to see what the car does and if it misses which
it didnt at all although i can hear buzzing coming from the fuel pump.

I believe it may be the fuel pump which is causing it but not 100% but it doesnt seem to be the plugs or leads.
 

Brett_jjj

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One of the main causes of these cars misfiring or otherwise running crook under load is crook plugs, plug leads and/or one or more of the 3 ignition coils is faulty. If the plugs and leads are 12 months old or more, replace them as they dont last long on these EFI cars with the heaps high voltages they run in the ignition systems, not like the old days where a set of leads would last for years.
These fuel pumps rarely loose pressure, they mostly either work or dont work. You can get the fuel pressure checked at a mechanics fairly cheap to confirm the serviceability of the fuel pump if you have any doubts about it.. Has the fuel filter been changed recently. It may be half blocked if it hasnt been changed for a while. Because these filtes are tucked up under the rear of the car in front of the fuel tank, a lot of people seem to forget about changing them.
 
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danielwoodward15

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I have replace the leads but not plugs the engine has only done about 125000ks but i can hear a loud buzzing coming from the fuel pump it also takes a couple of seconds to start and struggles to start sometimes but once the car is started and you turn the car off and back on there wont be any troubles start few ticks and it starts as a vt normally should its only when u leave the car for afew min it struggles
 

Brett_jjj

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Fuel filter?? Has it been changed regularly?? If its half blocked, it will cause the fuel pump to run noisily as it will put a lot of extra load on the pump. It can also cause the car to not start properly and run crook. If you think it might be the fuel pump itself, then get the fuel pressure checked to confirm it, and if it is, replace it.
 

666-GMH

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I had my car serviced at Ultratune, on the way home, this happened. Took it back the next day, took him for a drive and he said it was missing, he replaced the ignition leads and fixed it perfectly.
2000km's later, it started again.

take note of your rev's when it does it.
Mine only did it at ~60-90km/h in 4th gear at like 1500rpm. roll until you get down to that speed then just hit your foot on the accelerater and it will start doing it?
 

som

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I'd do all of the previous suggestions.Plugs should be replaced every 40,000km,leads 80'000km but that's if you're using the best (Genuine) and if your leads have been insulated. Fuel filter should be replaced at 40,000,I think....They're all fairly inexpensive regular service items. Coils will usually last more than 125,000km but not if they've been mated to plugs or leads that are below their best.Then they will last for a very short time because they are working too hard. Just check the size of the plug gap (you could almost park a truck in there) and see how far it has to send a very strong spark. So at the end of the day you replace fuel filter,plugs and leads.If that hasn't fixed it then you replace the coil pack (again go genuine,check the prices on ebay) Lastly if you still have a problem then you can look at the fuel pump which although your car's only travelled 125,000km the pump is still 12 years old. Sounds like a lot of work but except for the fuel pump you won't even get your hands dirty if you have a clean engine bay. Good luck mate.Cars...Gotta Love Em
 

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Spark plug leads should be tested first and only need to be replaced if their resistance is too high or the insulation is damaged. This is articulated in several workshop manuals for various model Commodores with the same ignition system. They are not intended to be a regular service item like fuel filters, spark plugs etc but by all means if people want to spend money for no reason then go ahead.
If they get too hot the insulation can be damaged. Their resistance will also increase over time however I have not witnessed this over a time frame as short as 12 months. The leads on my VY are original and I have measured the resistance each service that calls for new spark plugs and it has hardly changed, infact not by more than the error or repeatability you'd expect from a digital multimeter. Spark plug leads have a max. recommended resistance and unless the resistance is higher than this then it's not going to damage the coil packs. Each coil fires 2 spark plugs at a time (waste spark) and you'll find that if you take one spark plug lead off the other plug on that coil will still fire so a spark plug lead going from 5000 ohms to 6000 ohms when the service max is 17,000 ohms is going to make stuff all difference.
see post http://forums.justcommodores.com.au...2002-2004/199406-problem-vy-acceleration.html
 

som

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I'm sure that everything you've quoted is spot on wortus cos I do have a bit of a reputation for over servicing so I'll happily retract the "80'000km replace leads as a general service item".I'll still be doing it (old habits die hard) and unless Daniel has fitted genuine leads and has tested them as you've suggested,in his case I'd still replace them.Let'say though that he doesn't.If he ends up having to buy a coil pack there are a number of on line suppliers of genuine packs that will supply genuine plugs and leads for very little cost when included with the purchase of the coil pack.It's worth checking on ebay.
 

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I'm sure that everything you've quoted is spot on wortus cos I do have a bit of a reputation for over servicing so I'll happily retract the "80'000km replace leads as a general service item".I'll still be doing it (old habits die hard) and unless Daniel has fitted genuine leads and has tested them as you've suggested,in his case I'd still replace them.Let'say though that he doesn't.If he ends up having to buy a coil pack there are a number of on line suppliers of genuine packs that will supply genuine plugs and leads for very little cost when included with the purchase of the coil pack.It's worth checking on ebay.

I suppose if they are cheap enough with the coil packs you may as well buy them. I haven't had to replace any coil packs and I've owned 2 x V6 Commodores since 1998. The only ignition parts I've had fail is a crank angle sensor and a single spark plug lead on my VN and in that instance I just grabbed a spare lead the same length that came off a VT and was still OK and it never played up after it was fitted and the car was sold like that.
 

som

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That's unreal.I'm not complaining though I've only replaced one coil pack but that was to save me replacing my transmission ,ages ago,which everyone told me was r/s.....430,000km of reliable motoring so far,Even when you include all of the other sensors etc that I've replaced, pretty cheap I reckon..
 
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