Petrol 1.4 acceleration with aircon on

J

JonathanB

Member
Hi All,

I've had my 1.4 SE now for a couple of years and absolutely love it. However, I've always been bugged by its poor acceleration from rest if the aircon is on. Its particularly dangerous when entering fast moving roundabouts. There is little reaction to throttle input for about a second then the engine bumbles between 1500rpm and 2000rpm for a few more seconds before the car decides its time to move. Several times now I've almost fallen prey to other vehicles on the roundabout. Also, pulling away on slight inclines, particularly if there is more than one person in the car, almost stalls the engine. It just doesn't want to build the revs. I've also noticed quite a lot of 'pinking', the metallic sounding pinging noise, when accelerating in 2nd gear, even on the flat. I've tried normal unleaded, Ultimate and Optimax without difference. Two different Audi garages have said "the car feels like anyother 1.4 petrol A2" and everything is within normal parameters. Unfortunately, I've never driven another A2 so have nothing to compare with. Has anybody else had a similar experience?

When I was having a repeater module replaced, the Audi Roadside guy told me as much as 30% of torque can be lost when aircon is on and a firmware update might improve things. The Audi garages weren't interested.

I've been thinking of getting AMDtechnik to run it on the rolling road to check it out, maybe even get the ECU remapped to smooth things out.

Cheers

Jonathan
 
Hi Jonathan, welcome to the A2oc
I drive a TDi so have no first hand experience on the way performance is affected by aircon on the 1.4 petrol but i'm surprised how much it affects your car. I'm also surprised you get a lot of 'pinking' which makes me wonder if you have a faulty knock sensor or other engine management system problem which may be contributing to the lack of acceleration.
The A2 aircon system is one of the most efficient around and I would guess it absorbs around 7 or 8 bhp on full load and not 22+ bhp (30% of 75bhp)
Hopefully some of our petrol engine members will comment on the way aircon affects performance.
A rolling road check will only provide a full load power curve. This won't really give the full picture regarding your problem of poor mid range acceleration so before spending your money on a dyno test and rechip, make sure you can try before you buy. I think the AMD charge around £500 for the 1.4 petrol mods which gives an extra 10 bhp but probably little improvement at 2000rpm.

Cheers Spike
 
Spike's right, there are little gains in the lower rpm on the normally aspirated 1.4 A2 engine, the gains are mainly seen at the higher rpm's.
It's this reason most VAG tuners don't offer solutions as the gains are minimal sometimes. It can be good in combination with other upgrades though and give better driveability.
 
We have had two petrol A2s and have never noticed this, according to the figures it should be faster to 10mph than the diesel but will lose out from then on - I have driven three petrol 1.4s (one was the demonstrator) and a loan diesel 1.4 and all felt about the same off the mark. No hesitation from rest at all.

Never felt I needed to make allowances for the A2 being slow although I did not drive it that often - was the wife's car.

As an indication it should be faster off the mark than a 1.6 Focus!

Looks like something is wrong somewhere.
 
my 2p worth

Although I have the FSi, in this heat with a/c on, it is noticeably slower. Also from a stand still, if I don't give it more revs, I hear a knocking sound from the motor, a bit like heavy "pinking".
Since modern petrols run so lean, and it's fine in winter, I do not think I have any fault to worry about. Also I reckon I'm 4 mpg worse off.
 
Thanks Guys,

Maybe I'll go back to my local Audi garage and badger them to do a bit more than look for diagnostic alarms, which to date have given the car a full bill of health. Now that the car is out of warranty they'll perhaps be a little more enthusiastic to find faults and charge me a hefty sum for replacement parts plus labour!

The Audi roadside assist guy was referring to torque, not power. At low engine revs/low power, where there isn't much torque capability, a bit more parasitic torque from aircon has quite a marked effect. At higher engine revs/higher power, the parasitic torque is dwarfed by engine torque and is not really an issue.

Cheers

Jonathan
 
Hi, i have a A2 TDI and i think it is also noticeable, however our 19 TDI beetle was exactly the same (when it wasn't in the garage)

I think it's just such a big power drain that it has an effect.

if i drive along in third gear for example with a little acceleration, switch the AC on, and it feels like im almost touching the brake slightly. Cruise in fifth apply AC and watch the speed dip, or apply more throttle and watch the MPG take a dive.

Got used to it now

Emm
 
I've also noticed that the car feels much more sprightly when cold, even with aircon on. Presumably the engine mapping is different until normal operating temperature is reached at which point the engine is dialled back a bit. On a long journey, when the car is hot, if I go through a town with a bit of stop/start it is quite difficult to acheive smooth driving. Yet town driving first thing in the morning is fine.
 
yep,my FSI's been sluggish in this heat,made worse by the fact I had to put cheap **** ESSO petrol in the other day,really is running like a pig at the moment.:mad:
 
My 1.8 Zafira also suffers like this with the AC on, sometimes so bad that I switch the AC off on certain roads. My Golf TDi was fine, as is the A2. Diesels usually produce more torque than petrols, and usually lower down in the power band. That's why it's more noticeable on petrol engined cars of low cubic capacity. (Yank tanks and large 3.0l plus petrols usually don't suffer from this)
 
That's interesting what you say about the condenser switching off momentarily to provide full power to the wheels. I would expect to notice some difference when pulling away on a light throttle compared to full throttle. I don't. If, at rest, I fully depress the accelerator, the revs barely rise above 1500rpm for a few seconds. Bite the clutch and the revs drop to 1000 at which point the car crawls away. Basically, when pulling away from rest the engine just refuses to respond to throttle inputs when aircon is on. Once underway, things improve although I'm always aware of the aircons influence especially on inclines.

If I try to pull away from rest on an incline, irrespective of throttle input, I have to switch off the aircon to avoid serious engine knocking or even stall.
 
jon, I have the 1.6FSI and also notice the problem. Is so frustrating, and usually happens while at the lights, next to some smug looking spotty teenager in his ten year old 1.2L vauxhaul corsa, who proceeds to burn rubber in your face.

Could seriously do with a good solution to this problem, as I've always got the air con on(I feel the heat/cold a lot, and need to regulate it pretty often).

If anyone has any bright ideas, please put us out of our misery :confused:

Could we possibly add some extra engine cooling jibjobs or something...anything...arrrghhhh
 
Hi Jon, I've had my 1.4 Petrol for 4yrs now and I drive congestion charge zone stop-start traffic. I kind of understand what you're saying, but I believe it has as much to do with your driving style as the annoying electronic throttle. A prove is hold rev at 2k rpm in neutral, left foot break and rev drop ~200rpm for no reason. Traffic light grand prix is common for central london, so I have plenty of experience in fast get away. Very often at the lights, car is rev'ed to 2.5k, wait for light then clutch, 3/4 throttle, 2nd gear, 35mph, pick my lane and straight to 5th gear, cruise.

The throttle doesn't response well for the first 1.5 inch of travel, getting to 1.5k - 2k rpm is difficult because of the electronic throttle, after 2k, it is much easier to hold at any rev in neutral. And the engine doesn't have much juice under 2k. I've mastered the technique to adjust my right foot for the speed I need. It helps to avoid 'pinking' because trying to engage the clutch at <1.5krpm then accelerate is certainly not good enough for hill start or full on AC.

The engine idle speed is about 800rpm in winter with climate on. It is about 1k in the summer when AC needs more than '4 bars'. What you lose really is torque and not power. So I use my well trained right foot to adjust my get away engine speed according to how hard the AC is working. 2.5k is usually good. Despite all that, the car does cruise along at 30mph in 5th in a rather civilised petrol way :)

and finally, V-power makes a noticable improvement in responsiveness and tesco 95 makes the car happy at 70mph+
 
ULP said:
So, in reality I suspect the A/C in an A2, and most cars, will take about 7.5bhp from the engine throughout the rev range and probably about 7-10lb/ft of torque once again throughout the rev range. Factor this in with an already noticable decrease in performance in this weather (as air becomes less-dense so the combustion process becomes less efficient). You probably notice that in order to get a smooth pull-away from a standing start you need to give it a few more berries ;)
Click to expand...

ULP,

With colder ambient temperatures you will get more air into the combustion chambers, not less. That's why a turbo has an intercooler. However, the engine will take longer to reach it's optimum temperature.

RAB
 
I don't /did'nt read the thread, maybe you know it:
The newer models have a different engine-control-unit, wich will shut off the aircon when accelerating at maximum gas. And there is also a new version of the air-cooler radiater control unit... because the old version could cause a (Audi known) problem..
 
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