VT rough idle, slight miss IDEAS!!??

[wrx884]

how much did u pay 4 the scan tool? assuming its not a tech 2 and will b like the snap on type which dont go in depth like the tech 2? if so ud b better off going 2 an auto elec and using their scan tool. should only charge u $60 4 it. but if they got a tech 2 even better.

 

[aveugotone]

yeah, well it wasn't expensive just one with a labscope n that to make life easier, but as long as i can see sensor data and trouble codes im happy...

 

[2DIE]

Out of curiosity do you have a after market exhaust on it?

My VT sounded perfect until I put a 2.5" cat back on it, at low RPM its not pushing out enough exhaust gasses and it has been put down to the pulses changing. It doesnt put out enough gasses for a constant note thats why it sounds like a miss every now and then from the rear.

 

[TI3VOM]

It might be that you have a 3.9L engine, and we have a 3.8L version lol
You might want to change that.

 

[aveugotone]

haha yeah i reckon must be the 3.9 stroker, lol... um yeah bud it does have 2.5 catback but it is definatly missing, and using way too much fuel, gonna do a trip tomoro on the highway to see how much its using and whether it is just the stop and start sh*t....

 

[Mick1988]

How is your fuel pressure. My fuel pump in the wagon is on it's way out and I can tell when it's struggling to keep its pressure because I get a slight miss.

 

[aveugotone]

42 psi under load and idle perfect, might do flow test on it tho....

 

[evil_monkey]

if you are still having issues, back in the day i had the same kind of symptoms and spent big bucks trying to have it sorted, ended up beeing a vacuum leak, theres a hose attached to the throttle body called the purge hose few cm's long and 10 bucks, myne had hair line cracks in it, check all your vacuum

 

[BlackoutSteve]

Was this problem ever fixed?
I also have an intermittent stumble at idle that is non-existent on some days and frequent on others. It also occasionally happens during light throttle cruise ~2000 rpm.
Engine is a VT V6/SC (L67)
It lasts about half to one second and does it 2, 3 or 4 times in a row. Almost exactly like the ignition is cut and quickly reconnected again.
Hot, cold, A/C on or off, lights on or off, drive, park or neutral, all makes no difference.
No missing at all under heavy acceleration so I've ruled out weak ignition (plugs, leads, coil etc). I had a coil pack fail previously and the symptoms were purely moderate to heavy throttle. Leads are new GM and ~2 years old and new plugs gapped to ~1mm.
This issue is mainly idle.

I just swapped the fuel pump relay in case it's momentarily breaking power to the pump (apparently failing pump relays are common) , but I haven't yet driven it to see if that's the fix.

Can the OP update the outcome of this thread or anyone else chime in with ideas on what to check?
I'm thinking a sensor or connection.
Thanks.

 

[BlackoutSteve]

Not the fuel pump relay.
Yesterday.. Perfect. Not one hint of it happening.
Today.. Worst it's been and went as far as stalling the engine at the lights and left the Engine Warning light illuminated.