Metrompg.com mailbag: do the OBD2 Suzukiclone ECU's lower MPG compared to pre-OBD2?

[MetroMPG]

Rec'd this message...

Everyone tells me to stick with 89 to 95 metros because the computers were changed to make them more powerful/less fuel effecient in 96 and above. Can I change the co mputer? if so which one...I know there are several. Thanks

I've heard this before, but I don't buy it.

There's even a similar statement at Wikipedia, which has no citation:

1996 - OBD-II (On-Board Diagnostics, Second generation) is added to Metro models, at a cost of some fuel efficiency.

The engine specs, power wise, are identical across the board except for the XFi. So there goes the "more power" angle.

The biggest difference is that the 95 and up cars were about 200 lbs heavier than the previous models. That alone would lead to approximately 4% lower fuel economy in city driving, according to the EPA's rule of thumb.

[LibbyMetro]

do you happen to know of any ride differences in the newer (1996 and up) metro's than the older ones? I have a 1993 and it rides pretty rough , even with the decent suspension, and I was wondering anyone had owned both generations , and could distinguish the two in that area for me , thanks

[MetroMPG]

Can you explain what you mean by "rides rough"? You mean the suspension is stiff? Transmits bumps & road noise?

Both the pre- and post-1995 models have similar 4-wheel independent suspension. Cars equipped with anti-roll bars will tend to have a firmer ride (and will transmit more harshness to the car).

On top of that, the older cars with 12 inch wheels/tires may be more affected by road impacts than the 13 inch tires (particularly the 155/80/13's which will have more sidewall flex).

My '98 is the firmest riding of the 3 models I've driven (also a '93 Swift 1.3 SOHC, '92 Metro), even when the tire pressure is set at OEM specs.

[LibbyMetro]

i run the 155/80/13 as well, yeah the stiffness, and road noise is what im talking , if newer models were less harsh in those areas I would think about upgrading from the 93 , to a newer model, but if the newer arent any better, I'd look at possibly getting a civic vx, i wont get into the 60 mpg range , but 50's pretty easy.

[Coyote X]

From what I can see from cutting and messing around on these cars is the engine is the same other than an update to a better computer that is more tolerant of not having a perfect engine. The old obd1 computer had a fuel table and a spark table but no trim tables. So the newer computer can make up for an injector that is slowly getting clogged or a dirty air filter or any other maintenance type of issue without going out of tune. The old ones had to rely on the fuel table and the O2 sensor to keep it right with no way to adjust the fuel table over time.

The obd2 cars are heavier and have heavier tires so I think that is where all the difference in mileage is. You should edit the wikipedia entry and put the proper info in there

It would be an interesting experiment to try to see what the difference in mileage is between the 145/12 tire and the stock 13 incher. The reduction in engine rpm might not offset the extra load from spinning heavier tires maybe.

To correct the speedo to do the experiment is easy:

The speedometer drive plastic gear with 18 teeth is the same on all(fixed on diff.).The differents are only on speedometer driven plastic gear
speedometer ratio (faster) 18 x 16(brown) for wheels 14" (GT,GTi)
speedometer ratio (slow) 18 x 17(white)for wheels 13" (GA,GL,GLX,GS)
speedometer ratio (slower)18 x 18 (yellow/beige) for wheels 12"

[MetroMPG]

Thanks for the input Coyote. You do know your stuff, and I'm much more inclined to believe what you say vs. some anonymous wikipedia editor.

So the people asking about swapping mk2/3 sensors/computers into mk4/5 cars have it backwards. They should be looking at putting a mk4/5 system into a mk2/3 car.

[DAN]

the new one is better but you can mess with the old one