[Diy_efi] Re: open loop maps MAY cause damage.

[J Creech]

> The old analog systems also ran overly rich.  The new systems are run with
> base maps that are near perfect on a brand new engine with no wear, at
> exactly 72 Degrees farhenheit, and 29.97 inches of mercury barometric
> pressure...

...... for the "middle of the Bell Curve" engines. Fueling is too rich for one end of the curve, too 
lean for the other end. Case in point: the "Knocking that wasn't" on '98 and later Dodge Truck V8s. 
The majority of people owning these trucks didn't have any problems, and the people on the "rich" 
end of the bell curve had no problems (due to pre-ignition). But those few who happened to have a 
"lean" engine........

Of course, DC initially took the typical German Corporate stance (patterned after BMW Motorrad) 
"There is NO problem - go about your business". VE vill tell YOU ven dere ist der problem........

> As the engine wears, and there is less friction, then parts
> move easier, valves and seats wear in and air flow increases slightly, fuel
> pumps wear, injectors build up deposits that reduce flow etc, and the O2
> makes long term corrections to fuel trims to compensate.

You're forgetting that, as these mechanical parts wear past their "break-in", the pumping efficiency 
starts to go *downhill* - i.e., you're going to run *richer*, according to the base fuel map.

True, injectors may build up deposits, but fuels these days DON'T have as much crud in them, and 
with all the "programming" the American Consumer is subjected to, getting someone to put the 
occasional fuel injector cleaner in his tank every 3 or 4 fill-ups isn't a big deal.

When I worked for an un-named retailer, injector cleaner moved faster than oil (11+ years ago). I 
would order something along the lines of 10cs/week for EACH name-brand variety, probably 25cs/week 
for the "house brand". I can hardly believe that trend has gone downward, with the price of 
gasoline, and Johnny Consumer wanting to keep his 11.297518mpg SUV running at its "peak" (gotta get 
more mileage, dontcha know!).

>Remove those fuel
> trims and the O2, and it's not just making it Cat unfriendly... You now have
> an engine that can be dangerously lean under load and can cause engine
> damage.  MOST ecu's, when they go to limp mode due to a failed O2, run
> overly rich by default and reduce timing in an effort to protect the engine.

Nah, they do it in an effort to make the engine run so poorly, you *have* to take it into your local 
Dealer. Yes, the base maps are good enough, if you didn't have a "problem", you'd just continue to 
drive it until it quit - some 150k miles later or so.

Long-term fuel trims are just a "neat idea" some engineer came up with. One of those "Well, since 
we've got to put this O2 sensor in anyways to pass emissions, we might as well do some GOOD with 
it."

I happen to have a late model ('04) fuel-injected motorcycle, that has a 2-way cat, and NO oxygen 
sensor (though for the life of me I have no idea why - it has a 32-bit ECU, why not close the 
loop?). So, you're telling me that I'm straddling a missile (complete with explosive payload!) every 
time I fire it up & run down the road. 13k miles so far, and it's YET to grenade............ 
(perhaps I should bail out now?)

Oh, and usually when you're in actual "Limp Home" mode, the computer is probably toasted. Likely, if 
it's shut off, the vehicle won't re-start.

> The leaded fuel export cals use richer base maps than the standard US smog
> cals so the engine running lean after thousands of miles of use is not an
> issue.
>
>>
>>
>> It is important to understand why narrow band closed loop is used.
>>
>> The answer is only catalytic converters.