Hi everyone,

I've noticed my Fit seems to "bog down" with the A/C on. Acceleration drops dramatically (fine without the A/C), RPMs fluctuate occasionally at stop lights, and things like that.

I recently replaced the spark plugs, air filter, oil & filter, and ran some fuel system cleaner through it because I had to do a couple of long drives for work. While changing the plugs I ended up changing the coils as well because they were pretty beat up when I got in there. Everything runs great without the A/C on, but everything gets real lethargic as soon as I turn that knob.

Does anyone have any experience with this that can recommend other items for me to check?

 

What you're describing is normal behavior. The GD3 doesn't exactly have gobs of power available, and when you turn on the A/C, a fair amount of that power is siphoned to run the compressor.

When I had my GD3/5MT, if I were about to merge on the freeway, I'd turn the A/C off, accelerate, and then turn the A/C only after I was up to speed.

 

Yep, that's normal behavior for small displacement / low-power engines. It doesn't help that you have an automatic transmission. You could "fix" the issue, but it won't be cheap.

 

This is not normal, especially if was not present before work done
There should be no idle fluctuating with A/C on (only at 1st blower speed the idle will drop to normal when a/c cycles off)
What brand name of coils/plugs did you use?
Have you made sure that the there were no debris, pits of carbon deposits around the plug holes (all above items will cause plug gasket not to seat properly and the plug will undo itself and leak out)

 

I wish I had more to suggest than remove the plugs and coils, inspect and reinstall. I can tell you I read your post because I got on here to post a about the difference in performance when it gets warm and humid here in the midwest for anyone's thoughts. But with awesome responses that sum up to 'it's a shitty car, get over it', why bother. For the past few months, my acceleration has been crap - mainly when it gets warm and humid. I'm doing the same maintenance you just did. My next thought was if I need to be looking at the o2 sensors. Hopefully, Doctor J or someone else will have some insight to offer.

 

Now that you mention it, it does seem to be more pronounced when it's hot and/or humid out.

It was actually present before the routine maintenance was done. I just mentioned those things so that people would know what has already been done recently. I should have been more clear on that. My apologies.

It sounds like this is normal and I'm just noticing it because of the heat and humidity over the summer here in the midwest. Thanks to everyone for your replies.

 

If it was present before, then it's just the Fit normal. Mine has been lethargic with AC on since it was brand new. As someone mentioned above, I switch it off if I need an extra boost to merge onto an interstate or something like that.

 

I WILL RECOMMEND doing net step only if spark plugs same type/brand as original and coils are genuine Honda (while Hitachi 053 coil is a best alternative these coils are having wider tolerances for QC acceptance).
Borrow the scanner that sows live data and read the MAP values under following condition:
1) ECT above 78C, accessories off, idle in neutral (or park)
2) same as above, idling in drive (AT only), D+ brake
3) same as 1 A/C on, compressor engaged, fans running
4) same as 3 ., D+Brake
For best results try doing it during "g00d" and "bad" days; post data to the forum
I'll scan and post my data as well.
high MAP reading (weak vacuum) combined with higher fuel consumption may indicate abnormal valve clearances, leaking exhaust valves or exhaust back pressure.
Also, I notice that when A/C is on (fans are on) the engine temperature stays LOWER than when A/c is off and it is hot outside (so the fans are off until the ECT reads about 94 to 96 degrees C)

 

We bought our Fit new in 2008. Since day one it has hated two things...it's own A/C compressor and hot weather.

Here's my theory...
1. An A/C compressor takes roughly the same power to turn regardless of car. Let's say it takes 10 hp to turn the compressor. In a 300 hp car you now have 290. Not noticeable. In a 100 hp car (accounting for losing some power due to age) it's taking 10% of your power. Noticeable.
2. Lets say that hot air takes away 10% of your available power (my time slips and data logs on other cars show it's that much or more). On the 290 hp car (a/c running) you now have 269 hp. Still a good running car. On the other hand, a Fit is now down to 81 hp.

Heat and the A/C compressor has turned the low power car into a way underpowered car. Add an automatic transmission for 20-25% parasitic loss and you're down to ATV power level.

As for the idle quality, the A/C compressor adds additional stress on the motor. It's literally having to give up horsepower at idle to turn an additional accessory. The ECU is designed to compensate by adding throttle input. It will open the throttle body slightly more so that the motor has more air to help create power in order to maintain the same or slightly higher idle speed.

On an older vehicle, the throttle body is likely dirty from engine blow by over tons of miles. So, when the ECU tells the throttle body to open more, it does, but the total airflow is likely less due to the dirty throttle body.

In short, if your car idles rougher when the A/C compressor is on, first thing to check is the throttle body. It probably needs to be cleaned.

If your car is down on power when the A/C is on and it's hot outside, it's normal. Just much more pronounced in a low power car.

 

If the A/C charge is high it will take a lot more power to get it turning,, FWIW my GD shuts the AC compressor off at WOT.. These small R134 systems require real gauges the self service cans are for generating AC service business.. My BMW is like +- 1/5 oz of charge to be in the optimum zone, and you can tell when you run it..

 

MAP readings with ECT at 91 C (a/c off)
Idle in park 26kPa
Idle in drive 33kPa
(STFT 1.6 LTFT 0.8)
I'll do it today with a/c on.

 

Thanks for the added input and keeping the discussion going. I talked a couple of weeks ago with a local shop that are honda/toyota specialists who took some time to help me make some decisions about what service to tackle over the next few months. This sluggishness along with an occasional struggle to start leads me to think plugs and coils. I brought up the valve clearance check, and the shop recommended holding off on something big like that until it's still happening in the fall/winter. I've never had a car that reacted to weather changes like this one has. At this point, I'm just glad it's not in my head - at least totally.

 

Every car is different but, like I said above, ours from day one has performed poorly with the A/C on during hot days. It just saps what little power the car has.

Ours has new coils, plugs, and has been religiously maintained. Valves have been adjusted three times and they are nearing time for the fourth.

 

No probs!
In theory humid or dry air should not have effect of on combustion in computer controlled engine (MAP sensor measures density of air inside of the manifold with correction provided by air intake temperature sensor and barometer sensor).
Moisture affects secondary ignition components (old cracked coil boots) especially if outside temperature allows condensation inside of spark plug wells (94 Mazda Protege and Ford escort issue); this produces rough running engine until it warms up.
Other issues such as short of secondary coil voltage to its primary circuit or built-in igniter failure (Coil On Plug) is caused by high operating temperature; second defect causes occasional violent jerk in idle speed.
Third issue is a weaker spark which is caused by oxidation of the coil output point, spring or opening in resistor. This can be fixed by cleaning of affected components (discussed before) or gaping the plug to smaller gap (I don't like doing any of these things, because they are temporary).

 

MAP reading (with ECT at 82 degrees C):
Idle: 38 kPa
D+brake 49 to 50 kPa (blower at 2nd speed)
STFT -.8 LTFT-1.6

 

I just got that same feeling i get in my chest when my kid asks for help with her algebra homework after reading that. If you find time to translate the data to small words for non-sciencey wrench turner, I'd love to hear what you found.

I had to fill up and pulled in a QT that offered no-ethanol gas, so I paid the extra nickel a gallon just to see. I also put in new plugs. I was going to wait until I got a full set of new coils, but I'm impatient and needed to play with my car. There was a noticeable difference on the rolling hills at highway speeds with the no-ethanol. This is my third fill-up since doing the plugs. Bottom line seems to be when the humidity and temp are up, the performance is going to lag as the old girl ages. Just like me.

Coils are still going to happen, though. Starting is taking few cranks more to happen most morning.

 

MAP sensor indicates engine load. It also related to the engine vacuum.
Healthy engines tend to generate higher vacuum compared to the ones not in the top shape (for whatever reasons)
I could use the reading from the MAP sensor to see if engine has to struggle to meet certain power demands.
For example, few other members will post their numbers, read from live data scanner: MAP reading with A/C on near sea level and the engine is warmed up (80 degrees C or higher)
Someone will get 55 kPa and someone will get 45 . So in theory, someone who got higher number had more out of tune engine than other, especially if MAP reads high as well on idle with a/c off (like 30 kPa instead of 26)

 

Just my 2 cents, but it looks like you've figured this out...

Rock auto is trustworthy and reliable and good prices with OEM available.
Amazon is cheap but usually aftermarket and is at your own risk.
If I cant find what I'm looking for on those two, I resort to hondapartsnow. Guaranteed OEM but you'll have to pay the price. They're a go-to for misc items like brackets, clips, bolts, cowl stuff, etc.

what a good time to be alive.

 

I've always called the A/C switch the turbo button, because it's the only way to get the car to accelerate.