Ecomodding my winter beater: a unicorn no-rust (*) 2000 Chevrolet Metro 1.0 5-spd

[MetroMPG]

I'm going to experiment with the coolant sensor signal to dial in a "spoofed" coolant temperature.

Shown in the pic above is a 0-5K potentiometer variable resistor and a simple on/off switch. The car's coolant temperature sensor has highest resistance when cold, with values similar to this plot:




Adding my circuit in parallel with the sensor will cause the ECU see a lower resistance when the pot is turned to a lower resistance setting.

Fellow EM member mjspiess did a similar mod (with a single value resistor) and documented the effect in his '95 Metro.

Jump forward to 0:50 to see the change in idle speed and GPH fuel consumption as he repeatedly turns his circuit on / off...

https://www.youtube.com/watch?v=d4le76QUvFY

[Daox]

So, you plan on using this to short cut the cold start / high idle situation? Do you have to constantly mess with the potentiometer while things warm up?

[MetroMPG]

I'm not too worried about high idle, because I don't idle.

What I'm hoping to learn is whether there's significant fuel enrichment above idle (ie. while driving) when the engine is cold.

I'm wondering if a valid test is to rev it to, say 2k RPM while cold and monitor GPH with the mod active vs. not active.

[MetroMPG]

So the switch/potentiometer on the coolant temp sensor works as expected!



But does it actually DO anything useful in terms of MPG?

I monitored fuel consumption (GPH) using this method on a cold engine:

- Starting FWT = ~35 F
- holding engine RPM steady at 2k RPM
- check GPH value
- activate mod so FWT value is ~160 F
- check GPH value
- toggle the mod on/off several times

From what I could see, there was no change in the GPH reading.

I was talking to Tim about this. I forgot that the ScanGauge doesn't read fuel consumption directly from injector pulses. It's estimating it from air consumption. And if I keep the RPM steady, the air consumption isn't changing.

So really I needed to be using an MPGuino for the test.

It's definitely having some effect: if I let the (cold) engine go to idle when the mod is switched on (spoof the computer to think it's warm), it stumbles and dies. The mod cancels fuel enrichment (how much??) and fast idle.

[arcosine]

I did that on my saturn a few years ago, well maybe 10, but it was running too rich when cold, open loop. The diode on the map sensor also helped. I put another themistor ( temp sensor) in series with it on the head , and maybe a resistor or diode in parallel with that.

[MetroMPG]

68 MPG US fill-up this week = 3.4 L/100 km.



But 2/3 of that tank includes summer weather driving before I put the MPGiata on the road (last fill was Aug 1st). And it was summer fuel, too.


Looks like mid-winter tanks last year were around 50 MPG = 4.7 L/100 km. We'll see what this winter brings.

[MetroMPG]

A kid in a Civic pulled up beside me in a parking lot today, declared my car looked 'sick', and asked if I minded if he took a picture.

He was chuckling (to his passengers) as he asked, clearly taken with the coroplast on it - massive air dam, kammback and whèel discs. Possibly not as much impressed as amused (I'm not delusional!).

While he was snapping away, it occurred to me the Metro is probably older than he is, so I asked if he knew what it was. Nope! So i also got to impress him with details about the engine.

He chuckled, thanked me and drove off. I'm sure the car is being made fun of on instabook or facechat as we speak!

[Piotrsko]

The rice kids are always looking for that last little bit of unique edge in either handling or power. When racing a 10th second decides the winner. They obviously saw some potential in your mods. Then they saw the driver which I believe was the funny part. Old people don't race (much).

[MetroMPG]

Two items to update:

1) Sport exhaust upgrade!



(I didn't look to see if the Metro is on its original muffler, as the Firefly was until relateively recently.)

I noticed earlier this winter that the car had quite a nice (to my ear) sound to the exhaust that I didn't remember from last year. An exhaust note that reminded me of old, old engines (like this one Model A in town, and some old 4-cylinder boat motors).

Then I noticed it was getting a bit louder. I had a quick look for leaks and couldn't find one, so I think the baffles inside the muffler itself may be going. Fun!

2) Too light in the back = easy FWD oversteer on snow?


(Flickr photo: Greg Gjerdingen)

I've taken a couple of highway trips (80-90 km/h = 50~55 mph) recently on snow-covered roads, and was SHOCKED at how loose the back of the car is. It'll oversteer at the slightest steering input. I've had the back end start to come around at constant throttle/speed in a gentle sweeping curve.

And it's got snow tires with lots of tread on all 4 corners.

I double-checked tire pressure - normal. I don't believe I have an alignment problem - car tracks true, rolls forever, no unusual tire wear.

At first I thought: maybe my kammback is the problem -- generating lift? But the Firefly had the same aero mods on, and it never behaved like this. The biggest difference between the two cars is a lot more weight stripped out of the Metro, all of it from behind the front seats. But I'm sure I haven't taken more than 100 lbs out. Is it possible that little weight change on the rear tires can make that much of a difference?

Anybody ever experience this kind of behavior in a FWD car? I'm going to try adding weight in the back next time I head out on snowy roads and see if it helps.

[freebeard]

I don't know about the FWD, but one particular 1954 International pickup truck was really loose in the rear without some load in the bed. Have you put it on a scale to get the front/rear axle weights?