Im stumped yet again! The VS has a missfire that i noticed on idle. i put my hand near the tail pipe, it idles smooth but occasionally and sharply pops/ puffs/ stutters, wateva you want to call it. There are no error codes logged. I have tried 3 different coil packs and DFI's, 3 different lead sets, 3 different ECU's, 2 sets of plugs, checked exhaust for leaks, and intake pipe for leaks AND did the injector disconnection test (injectors are new anyway). NO LUCK! still the same.. Driving along, it doesn't obviously/ clearly missfire as such.. just feels a little underpowered, and power band is not very linear. It sort of seems like a timing issue, but they are electronically controlled right? Only things i can think of is fuel system? blocked fuel filter- but its only 4000km old?? Could it be my motor giving up the ghost?
i have the same problem, ive also replaced dfi, coils, plugs ,leads, done all filters etc. i do know my auto is fried and i wonder if it has any impact on it? does it slowly loose coolant? maybe a stuffed intake gasket. ive checked the bolts on the intake manifold on mine and made sure there tight (they were) but you can still see a little oil buildup around em so maybe stuffed gaskets there? have you rplaced the CAS?
All that stuff has been done either very recently, or within the past 6 months. Would the CAS cause a problem like this? i havent touched that since ive had the car. how much would i be looking at to replace that?
right now i'm more concerned with the quickly dying auto. last time i replaced the CAS on the VN it cost me $110 but thats here in NZ, sure it must be cheaper overthere?
160$ installed CAS and your car would stall if it was////might be on way out but if ur car hasnt stalled id be lookin at somthing else
im thinking cracked vacuum hoses.. maybe check and replace the hoses round the TB, i know with mine bottom hose that leads to the rear purge valve is shot at one end and keeps comming loose.. its really teh only thing i cant see listed as replaced.
thats not a bad idea, i have noticed on the VS that if i boot it with the aircon on it starts to change which ports it blows out of which works of the vacuum which does indicate a vacuum leak somewhere. i've checked many hoses but being unable to find my vacuum leak this far.
i noticed you said that your injectors are new...so that obviously means they have been installed recently. did you use all new o-rings and lube them properly before installation? if an o-ring has perished or worse, fallen off during installation, then that would allow a slow leak of pressure under idle causing a misfire, but wouldnt misfire to much under load. its a long shot, but you've checked almost everything else...
mine does the same thing, drops to the floor when i boot it, i believe its a problem round the vacuum ball area, cbf pulling the guards off to check it, but when i install the bezzles and foggies, i'll check it out then. i;ve really only heard of it being the plastic nozzle that has cracked or broken off.. not a big problem to fix, but just a lil time consuming really.
i have looked around there but couldn't see or hear anything, i'm going to try and block off the little vacuum hose (by the T fitting behind the motor) going to the vacuum ball and see if the problem goes away i think.
To find the offending cylinder, simply disconnect the connectors on the injectors one at a time. When you pull the connector off, the engine idle should instantaneously change, as there is no fuel being input by the injector. The only exception to this will be the cylinder that is not working correctly - As it is already playing up, disconnecting the injector signal wont make a difference. When you disconnect this one, the idle wont change. That will tell you which cylinder it is. Now, if you have one, put a 12V light bulb into the connector. Its only a light bulb so theres no polarity ie doesnt matter positive and negative. The bulb should flash indicating a signal at the connector. If you dont have a 12V bulb handy, you could try using a multimeter, although im not sure if it will pick up the pulsing properly. If the bulb flashes, there is signal at the injector. If theres no flashing, problem is signal getting to the injector. You can then go from there. When you do find the cylinder that is playing up, remove its spark plug. When you clean the injectors crud can work its way through when you remove them and will stick to the electrodes on the spark plug. This will stop the spark plug sparking and the cylinder wont fire properly. Simply cleaning the plug will fix the problem if that is your problem. Good luck, let us know how you go.
A mate has given me another possible cause for the miss! could it be a blown head gasket between two cylinders? sounds logical to me? possibilities???
Or a burnt/leaking exhaust valve, or worn compression rings (although if it is not blowing smoke - oil rings - the compresion rings are usually still good). A compression test will tell you which of the three.
A compression test wont tell you what rings or valves are leaking.A compression test only measures the amount of pressure inside the combustion chamber.A cylinder leakage test is what will help you determine where your leak is,By applying compressed air into a cylinder you can see if it is leaking out the exhaust (ie exhaust valve) or out the throttle body or carbi (ie inlet valve) or out of the sump (ie rings).To me i have come acroos many commodore V6's where they idle roughly but dont seem to miss and also drive differently to other commodores.Does your engine ping?
Compression test WILL tell you if the rings or valves are leaking. Compression test all cylinders. On the dead cyl (or if all are low do it to all) take out the plug and pour a little oil into the cylinder. Raised compression indicates rings, same compression indicates valves or upper cyl problem.
Well explain to me how a compression test with a compression gauge is going to tell me whether the inlet or exhaust valves or the compression rings are leaking???
G'day Kruptd, Oil tends to help the Rings seal, and so, increases the [Apparent] Compression BUT doesn't change the compression when it is the Valves. WHY? I have no idea, but use this on my Bikes.
If it's a blown head gasket it will miss fire all the time and may use coolant. Bubbles in the radiator......
