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Stuttering, flatspot and backfiring on takeoff

Dannal

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I have a 96 VS V6 wagon. I have recently replaced the air filter, fuel filter, plugs and leads. A problem started to develop as a flat spot upon takeoff but has now gotten considerably worse over a period of about a month. If I put the foot down (especially when it is cold) it missed really badly, backfires a few times and eventually takes off while continuing to misfire. When I am doing a reasonable speed and I plant the foot again, it kicks back a gear or two and takes off like a rocket without a problem.

Any ideas people???

Cheers!:yeah:
 

wortus

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I would be checking the spark plug leads for excessive resistance and make sure there isn't a cracked spark plug. Other than that check the throttle position sensor.
 

Brett_jjj

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If the plugs and leads show to be ok try replacing your coils one at a time with a spare coil and then drive it eacch time and see if it still happens.You can check the coils with a multimeter but Ive seen coils show up as ok on a multimeter but still cause problems similar to yours.If one coil is defective I think its best to replace all 3 as they seem to loose their performance over time which results in longer cranking time when starting,bad fuel economy and loss of performance.I replaced mine and couldnt believe the difference.They would have saved me heaps in fuel bills alone.
 

hako

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I'd check the coolant temp sensor which tells the ECU that the engine is cold and needs extra fuel till it warms up...if the ECU thinks the engine is hot (when it's cold) it will deliver a lean mixture designed for a hot engine and this can result in a flat spot when cold. There is a test for the sensor in the Gregorys manual. Another thing is that you may have dislodged the air temp sensor located on the air filter housing....or maybe knocked a vacuum line off around the throttle body. Finally runs a fault code test - you never know what it may turn up.
http://forums.justcommodores.com.au...22307-checking-error-codes-vr-vs-revised.html
Good Luck.
 

Dannal

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Thanks for your replies everyone. I took it to a mate of a mate who used to be one of GMH's head mechanics. He diagnosed that the problem is most probably the plugs and/or leads. That is what I initially thought however I replaced both of these mere months ago. I just purchased genuine leads which didn't do anything so I will be off to buy new plugs in the morning.

I won't be around for a few days to give you guys an update on the situation but as soon as I get a chance I will let you know how it went.

Cheers again everyone!:yeah:
 

Dannal

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Well I replaced the leads and with genuine leads but it didn't do a thing. It is actually still deteriorating rather badly. I also just purchased 6 new plugs and will throw them in tomorrow morning when the engine is cold.

Will keep you updated.
 

wantd_1

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i am getting this exact same problem wit my vr calais, constantly sputtering, flatspot wen take off, and missing more thn johnny howard trying to play cricket.....

i am also keen to know how u go, i just sent her in 2 weeks ago for a major serice : leads, plugs, filters, etc n ****...

thinking bout:
1. cleaning out throttle body.
2. replacing and or cleaning injecters.
3. coils, replacing...

plz let me know how u go.

thanx

MIKE.
 

Dannal

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I have now replaced the plugs and leads and it hasn't done a damn thing. About 3 months ago I got some quality throttle body cleaner and went crazy with it. I also put a few doses of injector cleaner through the tank too. Next week I am going back to the mechanic who has a spare working coil pack for me to try. If that isn't the problem then I am afraid that I might have to have a tantrum!

@Mike - I will post again and let you know how I go after trying the other coil pack.
 
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