[Gmecm] Strange effect while trying to tune my GM-EFIed beast

Sat Aug 26 00:13:11 UTC 2006

I am impressed that your mother lets you fiddle with her car. My wife 
won't even let me touch hers.

Don

David Allen wrote:

>  Tomas, since the effect is so profound, probably the error is something obvious if you just happen to focus on it.  For instance, I had a car that needed a little more canking fuel to get it started when cold.  I intended to modify the cold-engine cranking fuel pulse-width.  The car started perfect cold and hot, but there was a temperature range when it would NOT start.  My mother discovered this (it was her car) and I had to drive into town to get it started.  Using clear-flood mode got it going in a cloud of black smoke!  
>  After farting around with it, I noticed 2 cells in the table (which I had not intended to modify) were off by a factor of 10!  I must have "bumped the mouse" and accidentally edited these cells.  Correcting this fixed it.
>  Look at your tables in "graph view" and see if there are any strange peaks, valleys or cutoffs. Anything major wrong should show up.
>  Do you save each old calibration?   So you can therefore "go back" and undo the changes?  I've got about 7 calibrations where I tweaked on different aspects of my turbo motor. This has saved me hours of work on more than one occation!
>  Which model Bimmer have you got?  (used to work at an independant BMW / Mercedes shop)
>Later,
>David
>
>----- Original Message ----- 
>From: "Tomas J. Sokorai Sch." <tsokorai at minimania.org>
>To: <gmecm at diy-efi.org>
>Sent: Friday, August 25, 2006 5:56 PM
>Subject: Re: [Gmecm] Strange effect while trying to tune my GM-EFIed beast
>
>
>  
>
>>On Friday 25 August 2006 18:17, David Allen wrote:
>>    
>>
>>>  What was the last set of modifications you mention?
>>>      
>>>
>>Uhh ... hard to remember... I'm a bit "non-methodic" when doing table & 
>>consts. changes: sometimes I get into a "change everything" frenzy  :)
>>The main were a bit more of fuel (VE lower and upper tables) and a bit more of 
>>advance. I also played a bit with the DFCO parameters, but I only increased 
>>the RPM threshold, because before that I was getting engine stalls on 
>>downshifts on long decels (manual tranny).
>>The strange thing is that before my last modification session, the engine ran 
>>at any RPM, but very anemic at high RPMs.
>>
>>    
>>
>>>  Have you scoped the "reference" signal from the DIS module to the ECM? Is
>>>it faltering away over 2000 RPM? What kind of crank trigger are you using? 
>>>      
>>>
>>I'm using a "frankenstein-sensor" ;) it is a VR sensor from the TDC diagnostic 
>>setup BMW put on these old k-jetronic engines, but the signal was too low, so 
>>I modified the sensor a bit stacking three NdBFe magnets on the back to get a 
>>higher signal level.
>>
>>    
>>
>>>Could it be gaining resistance as it warms up?  If it's a VR sensor
>>>(magnetic pin with a coil winding) then the signal is usually dirtier at
>>>high-revs. Anything interfering with it would be worse when hot (more coil
>>>resistance) and at high-revs (dirtier signal). Have you verified the
>>>polarity of the crank trigger coil with relation to the DIS module? To
>>>      
>>>
>>I checked the polarity very early on my adaption phase: with the switched 
>>polarity, it barely runs at any RPM :)
>>
>>    
>>
>>>isolate tuning versus hardware causes, you could replace the temp sensor
>>>with a fixed resistor.  This resistor would give a low "temperature"
>>>reading which corresponds to the actual engine temperature reange where the
>>>engine performs properly.  If the engine runs right when fully warned up so
>>>long as the ECM is being told it is not warmed up, then it is a tuning or
>>>code issue.  If  the problem persists, then it is a hardware issue and not
>>>a tuning issue. Hope this helps!
>>>      
>>>
>>Thanks!.
>>I'm getting the feeling it is a too big advance, but the strange thing is that 
>>instead of knock or backfire, I get a complete missfire and even an exhaust 
>>bang! 
>>I don't think it is the crank sensor because before my last changes it was 
>>running more or less smooth at any RPM. 
>>Now I need to narrow down exactly *what* in my modification-fest gave me that 
>>result.
>>
>>Well... it was fun trying to drive the car across the whole city with a 2000 
>>RPM limit ;) 
>>
>>-- 
>>Tomas J. Sokorai Sch.
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>>
>>    
>>
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>  
>

-- 
Don Sauman
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