V6 Mystery Power Problem

[daniel_c_dc]

Hi guys, I've been working on a problem with my VT for a while now. I've searched the forums and the net, and can't find a problem exactly like it.

When accelerating with very light throttle, and the car up shifts into third at about 50km/h, there is a rumbling noise coming from the exhaust.
When this rumbling occurs, there is almost no power and you can barely gain speed (1-2 km/h a second). This lasts for 3-5 seconds typically, and goes back to normal, but the throttle 'jumps' to another stage if you change the throttle position during the rumbling. It feels like the car is either being starved of fuel, or the exhaust is clogged/faulty.
In an effort to solve the rumbling and other problems I've had, I have had the Transmission, leads and plugs, rear main seal, gaskets, fuel pump, radiator hose, ECU, BCM and starter motor changed.
The only thing that hasn't been touched that my mechanic has suggested it could be is the coil packs.

The only modifications to the car performance wise has been the exhaust system (pacemaker extractors, 2.5 all the way through, and the standard cat converter) and a K+N panel filter.
The exhaust was installed by a notable exhaust shop on Port Road, and cost me $1100 fitted. The car has just under 200,000 kms on it.

Has anyone experienced anything similar, or has any ideas, I'm all ears!
I've spent just under $5k trying to fix things on my car in the last 12 months, and money doesn't grow on trees as we all know!

Thanks,

Daniel

 

[Cashman_309]

Search "Throttle Position Sensor" and "TPS"

 

[daniel_c_dc]

Thanks for the help mate.
I'll get my mechanic to check it tomorrow, but wouldn't there be an error code present if it was malfunctioning?
Cheers

 

[som]

For my money your mechanic has hit it on the nose.These things are notorious for chewing through coils.You are far better off replacing the pack(3 coils + DFI module),rather than replacing individual coils.Insulating your plug leads helps them to last longer but at the end of the day they're working pretty hard.Don't know where you are but Bursons Spares have them for (I think)$365.On line ex Ebay or Holmart I'm pretty sure that you'll find a "genuine" coil pack from $200-$250.If you say "three hundred dollars" very quickly it doesn't sound so much.Good luck

 

[daniel_c_dc]

Appreciate the write up mate, Coils was his next option, that cat convertor itself as an outside guess, but I'd probably hear the rattling of something loose if the cat was buggered!
The pricing was really helpful too, thankyou!
Probably replace both the Coils and TPS at this point, I'll be sure to update if I come to any solutions tomorrow!

 

[Mick1988]

Have you cleaned the throttle body and replaced the throttle position sensor?

 

[daniel_c_dc]

Haven't yet, will be looking at doing that tomorrow

 

[KAL SPL]

Maf sensor

 

[Mick1988]

I can sell you a DFI module with 3 coil packs out of a VX which drove perfectly from Perth to Bunbury for $70 inc postage if you want a set.

 

[lout]

did you oil the k&N filter if yes probably MAF sensor
otherwise sounds like TPS to me
coils usually act up worse when loaded like going up a steep hill or towing