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

[David Cooley]

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...  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.  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.
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.


> -----Original Message-----
> From: diy_efi-bounces at diy-efi.org 
> [mailto:diy_efi-bounces at diy-efi.org] On Behalf Of Phil Lamovie
> Sent: Monday, May 30, 2005 2:32 PM
> To: diy_efi at diy-efi.org
> Subject: [Diy_efi] Re: open loop maps MAY cause damage. 
> 
> 
> It is important to understand why narrow band closed loop is used.
> 
> The answer is only catalytic converters.
> 
> There was a time back in the last century when 99% of all EFI 
> systems were made by Robert Bosch GMBH. Yes I know about the 
> US systems that came and went in a blink.
> 
> The first was D Jetronic, it used sets of breaker points to 
> fire the injectors was entirely linear electronics and as 
> Bosch had not yet manufactured the O2 sensor had none fitted.
> 
> They were supplied to about 30 different manufacturers world 
> wide who used them on all their sporty / upmarket models.
> 
> Imagine what would have happened when the world found out 
> that the Queen of England's Rolls Royce had dropped it's 
> lunch because it was running that dangerous open loop.
> 
> Then we discovered that poisoning the planet can ruin your weekend.
> So some bright spark came up with an oxidizing and reducing 
> catalyst fitted after the engine exhaust manifold.
> 
> This cannot work without that rich/lean switching that takes 
> place at a center A/F of 14.7 that meant there was now a need 
> to make a sensor that detects the crossing point b/w richer 
> and leaner than
> 14.7
> 
> The use of O2 for global map correction is usually (and most 
> sensibly) limited to prevent engine damage caused by a faulty 
> sensor. That is regardless of the sensors output the 
> correction cannot exceed a few percent either way, sometimes 
> systems will have a greater capacity to go richer as the fuel 
> is paid for by the customer and warranties by the factory.
> 
> Just because you see BLM tables doesn't mean that the ECU 
> accepts all values between 0 and FF and calculates the fuel 
> accordingly. There are hard coded limits on acceptable values 
> of every sensor or input the ECU sees.
> 
> How the ECU deals with "wild" values is not just an 
> engineering issue. When I did some work for one of the Big US 
> OEMs I was shocked when I was told that my Failure Mode 
> Strategies had to be signed off by the marketing dept. as if 
> they would know what to do.
> 
> Well they do know a lot about customers and warranties and 
> made me not use the check engine light more times than I care 
> to remember.
> 
> Learning about Engine Management by partially reverse 
> engineering a product that suits only a very small segment of 
> the market can result in all sorts of funny ideas most of 
> which are harmless. Not all but most.
> 
> Inferring that something "works" because some business sells 
> it is the reason that snake oil is made in the quantities that it is.
> 
> cogito ergo zoom,
> 
> Phil
> 
> 
> 
> 
> 
> 
> 
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