VY 3.8 v6 running on 4 cylinders

[jambo58]

My car sounds like tractor without any power. It seems to be running on 4 cylinders and making some rather loud knocking noises with the roughest idle ive experienced. the car struggles to make 80km/h and is going through a bit of fuel.

I have taken it to 3 different mechanics to determine the cause of the issue - each with their own opinion.

1- fuel system - pump and injectiion... Checked out OK

2- Ignition system - checked out ok

3- Blown pistons - not confirmed because they will need to take apart the cam & head etc

If its a total rebuild required im looking at $2k . am i better of just doing away with engine without digging deeper into the pocket and fit a recon for around $1200k?

[wortus]

Has it been compression tested? This will tell you if a cylinder has a fault such as a hole in the piston, stuffed rings or damaged valves.

[jambo58]

yes it has been compression tested but the mechanic said the only way to narrow it down for sure is to visually inspect it.

- looking at $100/hr in labor to diagnose and the most likely out come will be a suggestion to have engine replaced.

[wortus]

I assume all of the spark plug leads have been checked to make sure their resistance is in spec or not open circuited?
I'm sure there are places that would have some sort of optical fibre device to look at the pistons through the spark plug holes? How many K's has this engine got on it and has it been flogged?
If they put some form of camera down the spark plug holes and the piston tops were fine then its either valves or rings and to isolate rings you just put oil in the cylinder and re test the compreression, if it goes up heaps its the rings if it doesn't change then it's a valve. Then you take off the rocker cover and check for damaged valve train on that cylinder.

[delcowizzid]

are the 2 dead cylinders on the one coilpack the middle coil is bad for dieing

[Skooby]

I find it hard to believe that three different mechanics can't find what's wrong with it?

It shouldn't take them longer than an hour to diagnose it anyways, probably a cheaper option that getting a reco engine, even at their $100 an hour rate.

[colgf]

What were the conditions that brought on this defect. Were you thrashing the motor , did it have enough oil , Radiator water , - Is there oil in with the radiator water, could be a cracked head, or blown head gasket. V6's dont just die in cylinders without a reason , either was overheated lack of radiator water or thrashed due to overrevving , lack of engine oil. If you were driving normally with no warning lights then it just started to run rough , my guess would be an ignition problem or timing or fuel injectors . Did you fill up with fuel from a servo that isnt your normal supply. You have to retrace your movements & actions prior to the fault developing. Something out of the ordinary you did to bring on the fault.

[jambo58]

Thanks for your posts and pointers guides..

assume all of the spark plug leads have been checked to make sure their resistance is in spec or not open circuited?

Yes all tested and working

I find it hard to believe that three different mechanics can't find what's wrong with it?

believe me, its frustrating. i am getting another professional opinion tomorrow

What were the conditions that brought on this defect. Were you thrashing the motor , did it have enough oil , Radiator water , - Is there oil in with the radiator water, could be a cracked head, or blown head gasket. V6's dont just die in cylinders without a reason , either was overheated lack of radiator water or thrashed due to overrevving , lack of engine oil. If you were driving normally with no warning lights then it just started to run rough , my guess would be an ignition problem or timing or fuel injectors . Did you fill up with fuel from a servo that isnt your normal supply. You have to retrace your movements & actions prior to the fault developing. Something out of the ordinary you did to bring on the fault.

I am a family man and this vehicle definitely has not been thrashed, my Fiance being the main driver, is not really that type of driver.

But i will check for oil in the radiator and the gasket. there is no warning lights and the service computer at the workshop does not read one error what so ever...

The fault developed one after noon the next day after i filled up (100km). i do use multiple servos though.

The morning i was driving to work was fine. Then when ive left work, it started and idled fine. after being in stop start traffic for 15mins it started to rough idle but still had power. once i got onto a straight uphill run the power started to decrease and the shuddering+knocking developed, i pulled over to check the ignition leads, all good, oil level was fine too.. anyway i got backed in and very gently idled home at 40km an hour.

i thought it may have been dodgy fuel so ive put some fuel into it from a different vendor but the problem is just getting worse.

are the 2 dead cylinders on the one coilpack the middle coil is bad for dieing

The two cylinders are on different coil packs.


The last mechanic has a theory that there was not enough lubrication getting to the left hand rear cylinders/pistons (where the problem seems to be) this would have caused them to seize and crack or something.

the current engine has 150k kms on it.

Will post back tomorrow with updates.. thanks again!

[JazzyJezza77]

vacume testing is great for stuff like this refer How to Use and Interpret a Vacuum Gauge i used to tune my v8 vl with a vacume guage never ran better

[wortus]

You said the fuel system was OK? Has actual fuel pressure been checked as opposed to just fuel flow? I friend of mine had rough idle on his VS and he simply checked fuel flow but it turned out to be fuel pressure, he replaced the pump and it was OK. If you haven't then try replacing the fuel filter you may have got a tank of crap, did you fill it with E10? While E10 is fine to use as a fuel ethanol is a solvent and may have disloged some gunk in your tank which has then got through your pump and blocked the filter? You may also have water in the tank? It can be removed by either using E10 or some metho in the fuel as water is soluable in ethanol/methanol and will pass through your system.
Also if the pump and filter are OK check your fuel pressure regulator which is on the fuel rail at the motor, it regulates the flow back to the tank to maintain the proper pressure.
As I said you can look at the pistons with fibre optic devices through the spark plug holes and compression test to determine if it's rings or valves. These motors are fairly bullet proof if not thrashed or run out of oil, coolant etc. Coolant must always be 50% otherewise it can boil around the valve area and casue damage and you have to be sure there's no trapped air however if this has happened the damage is done and may need a new head(s).
Has the crank angle sensor been looked at to make sur eit is not damaged or anything like that? Also electrical connections to the coil packs, injectors etc, the motor wasn't degreased or anything like that, solvents etc onto electrical wires and connections?

[colgf]

Hmmm- After reading that extra info I am now thinking its Crank Angle Sensor/or wiring to it , or Fuel Pressure regulator. How long since you changed your fuel filter??? You may have picked up a load of crap in that fuel fillup. How was the Temp gauge when you were idling in traffic???

[jambo58]

Well after 4 mechanics i finally have A straight answer.
Turned out to be a clogged fuel filter and low pressure fuel pump that was 'checked and tested' by the 3 prior workshops . What's worse is that one of those work shops actually fitted the fuel pump hose and filter about 2 months ago. They had also dialled into the ecu to increase the fuel flow. There's a few other dodgy actions taken that left me ripped off but I won't mention it here. The car is still at the shop so I will update once I get it back.

[wortus]

I understood that fuel flow and pressure on VN's are set and maintained by mechanical means ie a pump that runs of 12 volts at a constant speed and a mechanical regulator. Do you mean they somehow changed the pulse width of the injector or something like that? After my VN fuel pump broke on a long weekend and the only 2nd hand one I could get crapped out the next day and a $250 towing bill I'd be changing the fuel pump every 100,000km even if it was OK as there only about $100 from Holden these days.
Fuel filter may have blocked from a load of dirty fuel or using E10 as ethanol can dissolve deposits in the tank.