3.8l VT hesitation / misfire under light load when warm

[Dazzy74]

could possibly be TPS, this can definitely cause rough idle, idling low and high if it is worn etc… nothing to lose, cheap part to replace.

 

[Lex]

but i did spy some coolant in he valley at the back.

So, the lim gaskets need replacing.
This would be where the extra air is getting in.
replace the lim gaskets & take it from there. While in there take notice of the pcv.

 

[Reuben Campbell]

could possibly be TPS, this can definitely cause rough idle, idling low and high if it is worn etc… nothing to lose, cheap part to replace.

Thanks Dazzy74 & Lex

Ive got to the point now where I'm just going to start replacing parts. Ive done all the trouble shooting I can do with my skillset.
Cheapest first.
So tomorrows shopping list

Lower intake manifold gaskets - to stop the coolant weeping (https://www.repco.com.au/parts-serv...ket-ms3841/p/A9687608?kwSearch=intake gaskets) is this the one you mean?
PCV valve

then
Throttle position sensor
Cam angle sensor
IAC sensor
fuel pressure regulator

If thats no good / no success
Coils
DPI
Oxygen sensors
crank angle sensor (due to increased difficulty getting out)

Then after that im running out of ideas
maybe the carbon canister under the fuel tank?

then maybe set fire to it.....

 

[Lex]

Thanks Dazzy74 & Lex

Ive got to the point now where I'm just going to start replacing parts. Ive done all the trouble shooting I can do with my skillset.
Cheapest first.
So tomorrows shopping list

Lower intake manifold gaskets - to stop the coolant weeping (https://www.repco.com.au/parts-service/intake-exhaust/manifold-gaskets/permaseal-manifold-gasket-ms3841/p/A9687608?kwSearch=intake gaskets) is this the one you mean?
PCV valve

then
Throttle position sensor
Cam angle sensor
IAC sensor
fuel pressure regulator

If thats no good / no success
Coils
DPI
Oxygen sensors
crank angle sensor (due to increased difficulty getting out)

Then after that im running out of ideas
maybe the carbon canister under the fuel tank?

then maybe set fire to it.....

What model vt do you have?
I'm not sure about seals that go at the end of the lim?
I can see that 1 pair is for s1. Not sure if the lowest one is s2.?

Last year l got a lim gaskets from repco. Cheap set, l broke every gasket.
I had a set of used Mace metal manifold gaskets stting on the wall, so l used them.

PERFORMANCE LOWER INTAKE MANIFOLD GASKET KIT FOR HOLDEN COMMODORE VT VX VY L67 S/C 3.8L V6

Our quality aluminium gaskets to suit Holden vehicles fitted with Ecotec L36 and L67 Supercharged 3.8L V6 engines, will prevent leakage and last a lifetime.

www.maceengineering.com.au

If you use repco or the mace gaskets that l have linked to, you will still need plenum & plenum lid gaskets.
If you've got s2, just checked again the mace gaskets are for s2.

 

[vc commodore]

Replace the spark plugs....Those puppies cause all sorts of issues when they get on....

 

[Reuben Campbell]

Replace the spark plugs....Those puppies cause all sorts of issues when they get on....

They were only done 500km ago. NGK units. Shouldn't need to do them yet!.
When i go to the shop, ill buy a service kit anyways so that I have stock at home.

What model vt do you have?

2001 Series II VT Wagon.

Ill double check to make sure that I get the right ones - and make sure that I get a complete upper set.

Ill take my VIN down with me to - that usually ensures you get the right parts.

 

[Reuben Campbell]

Updates
The bolts in the valley, some were milky, so some water has been mixing in with the oil, but not enough to notice it seems.

The black grime on the inside of the plenum, feels gritty. Hope thats just carbon, and not sand.....

Have just got the bolts out, and going to get the tensioner off tomorrow morning, before heading to perth again for a quick job.
Whilst im there,

Is it worth putting one of those rebuild kits through the injectors while they are out?
(https://www.repco.com.au/parts-serv...rk748/p/A9502198?kwSearch=injector repair kit) like this?

And since Ive got to get the top tensioner off as well, Im going to replace this as it was worn already and I was avoiding replacing it.
Its funny, it only throws belts when it rains and I go over a bump.
Is the steel pipe that connects to the thermostat, is that pressed in?

I bought a PCV valve to replace what I have since I'm there anyways, and to replace it later is a mission.

 

[Lex]

Is the steel pipe that connects to the thermostat, is that pressed in?

No. It has a oring on the thermostat end. Both heater pipes have the oring. If you go to holden for them, l think they charge @$20.00 each.

I took my pipes to where l buy my bearings. Got them for $1.00 or less?

l also got the oring for the pcv at the same supplier.

Have you ever had the injectors replaced or serviced? If not, It may be a good idea to put the kit through them?

Clean the plenum & inlet manifold runners.

Once its clean, l lift the lid on the plenum once every year or 2. Usually just needs a wipe with a rag.
Don't let the crap be baked on for 20 years.

Good luck with repairs.

Like to know how the repairs go?

 

[Reuben Campbell]

so, just got everything back together and took it for a test run.

no dice - still playing up.
its def running better and smoother, but its still doing the 'half-a-miss' thing when accelerating.
Runs fine at idle.

about to try the 'spray flammable stuff' at the gaskets and flanges to see if that improves anything, but im not hopeful as it runs fine at idle.

couldn't do anything with the injectors.
every store I rang didn't stock them. No o-rings, no kits.
the best I got was an offer of 3 injectors from two different stores - and no guarantee that the stock levels were correct.

In the gasket set i got, the seals between the plenum and runners were o-rings rather than a standard gasket.
Unfortunately, my engine doesn't have the groves for these type of o-ring gaskets.
I had to reuse the existing steel flat gasket.

next thing is to try and find any more vacuum leaks, and maybe glue up with No2 aviation gasket glue between the plenum and runners.

 

[Reuben Campbell]

so sprayed brake cleaner around anything i could get to - No changes that i could find, but i wasn't expecting anything as its idling fine.

Slow ,controlled acceleration everything seems to be fine.
Only when you give it a foot-full does it do its miss thing.

rechecked the coils - they seem to be fine.

Could be an injector, but then if it was failing, then it should be missing all the time, especially at high revs, which they do not.

Going to glue up the plenum to the runners this morning - just have to do some window repairs on the house first...