Vx Automatic - kickdown stutter/ sluggish at low revs

[ebm_wiggy]

okay i just moved this post from this websites' Pub - "ask the ex holden techician" as i think this is a better place for me to find the cause of my commodore's problem, without wasting money replacing perfectly good components.

DESCRIPTON OF PERFORMANCE summary:

: when the car is being driven normally and for example approaching a gentle incline say for example on the motor way, the car seems to take lonGer than it should to kick down. when it finally does kick down it jumps straight back UP into the gear it was in prior to kick down. it will do this until either the road levels out or i put my boot into it. this actually feels like the cars is missing!

HISTORY:

i thought i may save some money by asking the top-gun's first. i am not against mechanics but you may understand why i am asking here and not going to another one as first point of call.

i have had a VX v6 commodore Acclaim for several years now. a while back i did a head gasket so after a week in the mechanics getting heads machined and new radiator installed i was driving it home & after about 15 mins travelling when my Dash "electrical" warning light came on. i pulled over, turned off the ignition and rang the mechanic. he said not to worry but drop it back in asap. (i had never seen this light come on before this point in time ever).

i started the engine and drove it home. the light came back on about 15 minutes into what was now 2nd leg of my trip.

i also noticed a power / kickdown stutter. i assumed it was a limp-mode thing which would go away after we fixed this electrical fault.

upon a revisit the next day, the mechanic said he had the 'oxygen sensor' fault show up in his diagnositc equipment which he simply re-set. he saw the fault at this re-visit show up again several times so he re-set it and said everything was fine but we should put a new oxygen sensor in soon.

i purchased a new Ox sensor and fitted it myself , i also disconnected the battery and a few minutes later reconnected it to re-set limp mode if it was a factor, and went for a drive. and the car was much better but still not perfect. the warning light no longer comes on at all however...

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see DESCRIPTON OF PERFORMANCE" at top of this post for my current situation.
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the car has no issue with performance if i am heavy footed but it has to be very obvious. the car seems to be worse with this kickdown stutter as it gets hotter.

just as a side note, after i first noticed this kickdown problem i checked my transmission oil level which was very low & very dark coloured. this was not the case before i took the car to the mechanics as i check the fluids regularly. obviosly i can see no reason why the transmission would need to be drained to do my engine's head repair but i filled it to normal level with new oil.

i am not an expert on automatic transmissions so i can not diagnose if that is part of my problem but to me it rather feels like a power problem to me and that the auto simply does not have a chance to select the appropriate gear to match this engines power at critical points in the rev range, or rather revs it has been designed to change gears at that no longer are in accordance with the power / control module?

i am inclined to think that i should firstly put new spark plugs in however the current ones look fine and are factory specificaton. i would consider plug leads but normally they display symptoms at high revs not lower revs?

it all just seems a bit suss to me... what do you reckon?

[Tree cutter]

The reason you would have been low on trans fluid is because the trans fluid runs into an oil cooler in the bottom of your radiator so some fluid would have been lost when the radiator was changed. Your mechanic should have checked the trans fluid level and topped it up as necessary.
The surging problem does sound like spark plugs. i have heard of spark plugs being damaged from being in contact with coolant after a head gasket has blown or a head has cracked. The coolant can leave a coating on the spark plugs so they do not spark properly.
It was probably coolant that damaged your oxygen sensor when you blew the head gasket because coolant would have been blown out through your exhaust when the gasket went.
Put a new set of spark plugs in her and it should be right. I dont think there is anything else that could have been damaged from a blown head gasket.

[kego]

^^^^ what he said but go and change you tranny fluid because you said it was black and that means you have cooked it and then you just filled it up again.so new tranny fluid,new tranny filter and new leads and plugs and see who that goes mate.

hope that helps.

thanks matthew

[ebm_wiggy]

thanks lads i appreciate that. it is encouraging to get such sensible responses like this.

i will do the leads and plugs tomorrow as you both say and also the transmission oil and filter which does make very good sense.

i will be making a friendly phone call to my mechanic next week i think... just to put him in the picture.

[BIG-EV]

if ur gonna do ya tranny fluid change make sure u clean the whole pan of the fine black/grey sludge (if any) as these are metel fillings... also to keep ur fluid nice and red install a tranny cooler. pwr sells a kit on ebay for 130$

[ebm_wiggy]

progress update...

1) i dumped the old oil and cleaned the fines from the pan. (heaps of black sludge as you say) then refilled her and then
2) fitted new spark plugs (factory spec) and a new set of plug leads
3) just out of curiosity i then checked all fuel injectors were all within spec (ohms) which proved satisfactory
4) treated 1/2 full tank of fuel with injector cleaner.

i am glad to say that it has been running fine for over 1 week now. thanks lads.

[kego]

glad to help mate.

[another_gold_vtII]

ebm wiggy, same thing happened to me
blew the head gasket back in Nov/Dec 09, after repair, all seemed well until last week.

going up an incline, engine revving below 2 grand, the trans starts to thump.
slight increases to throttle make no difference, have to put the boot in or manually throw back to third.

trans oil was fine and plentiful,
replaced the spark plugs and a new set of leads and trans is operately perfectly.

I was worried i would be up for a big $ rebuild.