Firstly - I’m a bit embarrassed to be writing this after having benefited so much from the information found on this site in the past and never having contributed, but here it goes;
I'm struggling to pinpoint a problem with performance / mpg on my 3.0l MV6 auto. When accelerating normally (e.g. not uphill and not putting my foot down :p) the car seems to accelerate much more slowly than it has done in the past. The rev counter seems to indicate that the engine responds as it always has, but the power eventually put to the road seems lacking.
A bit more detail;
The car only inches forward/backward only ever so slowly when put into D from N. On a slight incline the car will remain stationary until power is applied – on a steeper incline (Sheffield – lots of hills!) the car will tend to roll backwards (annoying!).
The car idles at approx 700 revs and seems to idle fairly smoothly – perhaps ever so slightly lumpy occasionally – according to the good chaps as the (quite respectable/trusted, non-VX) garage this is ‘normal’ (I’m not convinced).
Speeding off at junctions / from standstill is much more ‘civilised’ now – not at all the way I like it for those rush-hour / small gap moments
. Likewise, suddenly accelerating (from any speed) seems to be difficult – the revs are happy jumping approx 400-500 revs or so, but power only follows afterwards in a way that makes it difficult to see off the odd gimp in an escort who is determine to screw you in that soon-to-merge outside lane. Sure I could floor it, but I hate doing that regularly.
When accelerating, the engine speed might jump 500 revs before the actual road speed begins to catch up. In a similar manner, when transitioning from a level piece of road to an incline, the engine speed will tend to stay the same (whilst keeping my foot in the same position
, whilst the road speed might drop 7mph or so.
Changing from 3rd to 4th gear usually happens around 50mph – because I try to drive sensibly (fuel prices and all that!) the revs usually drop down to around 1800 at this point. More recently, however, the revs drop only slightly at this point, perhaps to 2200. Driving on the M180 today, the lockup didn’t seem to want to engage (assuming this gearbox/torque convertor does have a lock-up in gears 3 and 4?) – accelerating (smoothly) from 70 – 80 mph causes the rpm’s to jump up from 2500 to just under 3000 and stay there whilst the road speed catches up slowly.
While keeping a constant speed (or accelerating very slowly) up an incline, the rev counter seems to ‘twiddle’ slightly (as opposed to remaining steady, dropping, or going up). It’s probably only about 10 revs up/down or so and hardly distinguishable, but you spend enough time with a car and you pick up these things
. The engine sound seems to mirror this (bear in mind I’m the only one who can see/hear this – it is VERY slight).
Overall MPG seems to be suffering - especially at lower speeds / accelerating smoothly (and slowly!), I seem to be getting around 10mpg (until 12-20mph -ish?). Motorway mpg seems about 5mpg down on normal at around 28-30 average, instead of 35 average.
Overall the gear changes are as smooth and consistent as I've ever known them (but then, I bought the car with 93k on the clock).
I’ve had the car at a gearbox specialist – and by specialist I mean they are a garage who ONLY deals with gearbox problems. They checked the fluid level/quality, hooked up some sort of diagnostic tool, and took the car out for a drive (well, I was in the passenger seat – the guy pegged it as fast as he could up a street and listened to the gear changes/strange noises). Overall he said it sounded fine – good even, although there was one slow change while he was flooring it. The diagnostic tool revealed no transmission error codes, although it did show a code 31 Engine speed (Present RPM) sensor no signal. I had my regular garage (who does the work I just don’t have time for or REALLY don’t feel like doing :p) swap out the sensor, although looking at the receipt just now it mentions a ‘crank angle sensor’ (which I imagine is the same?). While it has made the engine idle better (still not perfect for my liking) it has done nothing to improve overall performance. (Oh pooh - after further reading I realise its quite typical to show this error if the engine is not running! I do wish the search function would return more than 15 results though
)
Other (potentially relevant) work done recently includes new rocker gaskets (and covers – grr), timing belt, serpentine belt, oil filter/oil, spark plugs, coolant. Bits still outstanding include cleaning the breathers – I doubt the garage gave the lot a clean when they put on the new rocker covers, and an air filter.
I’m not an experienced mechanic by any stretch of the imagination, but am comfortable taking apart anything I have the tools for – it was all a lot easier with the car I had before the Omega though :p.
Any help is very much appreciated. I would to find a garage around here that I can give my car to and be assured that I would get it back fixed, but like so many, it seems to have to look further afield to get some real answers from those who are so much more knowledgeable
.
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Topic: Performance and MPG not up to scratch / autobox (Read 4549 times)