Sub and Amp affecting fuel economy??

ZenArcher · Postby **ZenArcher** » Fri Oct 06, 2006 6:25 pm

This is a strange one. But a while back I did a lot of work on my MX over a weekend. Then after a while I started getting bad fuel economy. I know fuel guages are only a guide, but the way I look at it is that the guage will react the same each time. that is it might say 1/2 full but in reality be 2/3rds full, but it will do it consistently.

Anyway, after I had the 1.8 upgrade, I was still getting 400+ K's per tank full around town driving. I live in Canberra where most roads are 80kph except around housing areas. But I live very close to one of the main highways in Canberra so drive 60kph for about 1/2 a kilometre and it is 10 minutes of constant 80kph right to my work carpark at the AIS. Which is great.

OK, after all the work I did, which included installing a second amp and 6 inch bazooka tube subwoofer, spark plug change, oil change, cleaning the throttle body, after my next tank full of fuel, my total range dropped to 275k's per tank. Not happy.

So, a few days ago I took the sub out and the extra amp, which I mounted together on a MDF board so that it can be taken out as one unit. Since then I have been getting much better fuel economy like it was a month or 2 ago before I installed the sub.

Is it possible that the second amp and sub were drawing too much current away from the coils and hence not getting a decent fuel burn in the engine? The battery is a pretty decent and expensive gel cell sealed battery and the alternator is also working fine. It's not like the sub and amp weighed lots, not much really, so I didn't think it would be a weight issue.

Any ideas anyone?

Adam_NAclubman · Postby **Adam_NAclubman** » Fri Oct 06, 2006 8:02 pm

No idea

But is this you?

http://www.youtube.com/watch?v=atCF5kyR ... ed&search=

Russellb · Postby **Russellb** » Fri Oct 06, 2006 8:41 pm

Doesn't make Sense :shock:

I have two amps and a 12In SUB and my economy is great ( about 450 round town short runs Dickson to Belconnen and over 550 o the HWY Mania and back )
I dont think the small extra load on the ALT would cause the fuel Economy to Go through the roof like that

ZenArcher · Postby **ZenArcher** » Fri Oct 06, 2006 8:53 pm

Adam_NAclubman

No, absolutely NOT ME.

Russellb
Yeah, I know it doesn't make sense, but that is what has happened. I don't know why, it just has. My wiring isn't dodgy in anyway at all. I have always been brought up with the attitude of \"if you are going to do something, then do it right the first time\". I can't explain it and it doesn't make sense.

Alf · Postby **Alf** » Fri Oct 06, 2006 10:54 pm

ZenArcher wrote:Is it possible that the second amp and sub were drawing too much current away from the coils and hence not getting a decent fuel burn in the engine? The battery is a pretty decent and expensive gel cell sealed battery and the alternator is also working fine. It's not like the sub and amp weighed lots, not much really, so I didn't think it would be a weight issue.

Any ideas anyone?

OK here's one from left field. The bogun/chav amp/subwoofer combo is drawing enough current that it's reducing the voltage at the fuel level sender and you're seeing it look like empty way before it is. Have you noticed anything else unusual like your fuel tank now only takes 25 litres to fill?

Cheers,
Alf

ZenArcher · Postby **ZenArcher** » Fri Oct 06, 2006 11:30 pm

No, still takes the same amount of fuel to fill up when the guage reads empty.

bruce · Postby **bruce** » Sat Oct 07, 2006 1:26 pm

But man, are you getting more BASS :lol:

Me · Postby Me » Sun Oct 08, 2006 1:51 am

in theory yes if the voltage is dropped and extra weight. but i dont notice any difference in the fuel consumption after my sound system installation.

some sounddomainers claim (an old post from sounddomain.com) they suffer bad fuel economical problem after putting in a huge sub box.

Postby **Okibi** » Sun Oct 08, 2006 3:51 pm

The more you amplify, the more power the amp draws, the greater the load on your alternator, the less power the engine has to put to the ground, or the more fuel youâ€™ll use to drive the same speed.

AJ · Postby AJ » Sun Oct 08, 2006 5:18 pm

toss that pi$$weak 55 amp alternator out & bang a 90 amp one in, you'll be fine then, & added benefit of longer battery life..........i assume you've done the right thing & used the appropriate relays with your amps

Alf · Postby **Alf** » Sun Oct 08, 2006 10:50 pm

Okibi wrote:The more you amplify, the more power the amp draws, the greater the load on your alternator, the less power the engine has to put to the ground, or the more fuel youâ€™ll use to drive the same speed.

Yeah but even AJ's 90 amp alternator is only going to supply a little over a kilowatt, drawing, say, 2kW from the engine if it's HUGELY inefficient. A couple of kW ain't gonna make a30% difference in fuel economy.

I'm still betting on lowered voltage affecting some sensor (O2, AFM, etc) or maybe the ECU itself. I'd at least measure the voltages with & without the panel rattler running, to eliminate this potential cause of the problem.

Cheers,
Alf

AJ · Postby AJ » Mon Oct 09, 2006 7:46 am

yep, i'm with Alf, the amps & sub are sucking all the grunt out of the electrical system & a power drop to the ECU is causing the problems, hence my suggestion to up the alternator

ZenArcher · Postby **ZenArcher** » Mon Oct 09, 2006 9:10 pm

Thanks for the help everyone.

As you may have noticed, I have now installed a Wolf 3D V4 computer. Going to have a play with it when I get the time. David (Mx5 Mania) showed me some stuff and also if I stuff up, it is easy to just re-upload a working map.

I noticed there is a voltage compensation area with the programming, so maybe I can look at that a bit closer.

Just have to sort out the idle up with A/C and fast idle cold start first.

If anyone is willing to share maps or send me one that I can look at to work out the differences I need for cold start, (see other post) that would be great.