Contour Enthusiasts Group Archives Forums Modifications 3.0L Duratec ?Help tracking down the stuttering problem....Long...

Hey DemonSVT I just ordered it so don't worry I won't ask any more. Just making sure that I will get use out of it.

I changed the MAF yesterday. It changed the way it acted, but didn't help any. Seems to almost have made the situation worse.
Those of you with the 2000 SVTs. I think if your problem is the same as mine then the SAFC will work. Good luck and keep me posted.
I have a new plan that I am going to try soon to see what happens. I'll post the results later.

warmonger

I was pointing at Warmonger actually...

However you fit the description too...

OH MY JESUS -- I tested out your theory WarMonger: There is ------NO------ stutter when the engine is cold. I started the car and let her warm up only for 15 seconds for oil pressure - then I went out on the road. No stutter below full secondary open. Once she got up to operating temp, I got the stutter back. I t was SO nice being able to cruise in 4rth and 5th gear especially and be able to acclerate a little without nasty bucking. I tested this 3 times today. Engine cold = no stutter or as your tests indicate, no stutter below 80 degrees. Since this stutter is a lean-misfire condition until full secondary-open fuel enrichment mode -- couldnt this be fixed by a prom adjustment? You also mentioned some additional electronics? This is a major breakthrough for all of us who have this problem . TtYs.

What I am thinking is:

You have no stutter when the engine is cold because the ECU is still running in closed loop mode... It runs a preset fuel/spark table which is probably alittle rich for protection. This is good for you guys. But once the car is up to temp, it goes into open loop mode and starts trying to run at a perfect a/f ratio. This is where you guys are having troubles.

By making your car think it is not upto temp yet, your car is continually in closed loop mode, and you dont get the stutter.

I dont think its good for your car to always think its cold, so I hope this is just a temporary solution for your problems.

my .o2.

No one is actually running their car with the "tricked" temperature sensor other than as a verification of concept.
We needed to duplicate the situation on more than one car.

The pcm richens the AF ratio when the car is cool to prevent driveability issues. When the coolant and intake temperatures warm up enough, the pcm ceases to richen the AF ratio and the stuttering begins to happen.


Demon:

Boy do I have something Good in the works right now!
I found some goodies that should work really well to tune my car. Once I try it out I will post the results. I believe its much better than the SAFC.
(that's why I'm waiting)

warmonger

Better than digital quality retunability???

I'm listening...

DemonSVT: Hello. Question for you - This Apexi S-AFC can actually richen the air/fuel ratio below IRMC opening point to avoid this lean-misfire condition we are experiencing? Trying to dig up more info here. Also interested in seeing what WarMonger is waiting on to alleviate this as well. Thanks!

The S-AFC has 8 indiviual rpm settings (you choose) & interpolates between them.

It also has a high & low throttle setting feature & interpolates between them as well. (WOT - Part throttle - You pick the Throttle %'s too)

All digital accuracy! (not analog dials/pots - ever heard a scratchy volume knob on a radio - How do you know "exactly" what volume level it's at too?)

DemonSVT -- Thanks for the quick low-down on the Apexi unit. With all the info we are discovering so far, it leads me to a hypothetical conjecture -- The reason why some svt's get horrible drivability below IRMC opening with cracked secondaries is that you are allowing more air into the engine via the additional suction from the 2 other valves (via the cracked butterflies). This additional oxygen exacerbates the engine's running on the verge of dangerous lean (fuel economy? Torq?) and causes lean-misfires (too much oxygen, not enough fuel) ie the problems other svt's/v6's have had with cracked secondaries. Let me know what all of you think on that one. That Apexi unit looks like an extremely good avenue to cure this lean-misfire condition in any case or, perhaps, a custom chip that does run the engine so frigging lean below IRMC open (closed loop). Hey WarMonger (anyone really, but warmonger especially), Ill be looking for your additional updates when you post 'em. TtEl.