stock programming on modified engine question..
Thread Starter
Race Director
Joined: Nov 2000
Posts: 17,103
Likes: 39
From: stop the fun suckers
stock programming on modified engine question..
How is it possible for a 383 with a bigger cam to run rich at idle with the stock chip in place?!? I'm curious.. i set my pcmforless chip out to be reprogrammed and jsut for giggles i put the stock cip in a used datamaster to log it idleing... just like the PCMforless chip.. it ran RICH! 89 Sterm counts with the lterm at 108.. weird huh? could it be because the MAP is way off from the factory settings for idle? BTW: 1993 lt1 -speed density..
I check the plugs and the look good.. lightish grey-brown.. bizzaro huh.. I hope the when the new chip arrives it fixes this probelm..
Oh and lastly.. anyone with a pre- 1993 car using datamaster.. does datamaster indicate the car is in park when you have it in park (under gear selected) or does it say unknown..
thanks! :cheers:
I check the plugs and the look good.. lightish grey-brown.. bizzaro huh.. I hope the when the new chip arrives it fixes this probelm..
Oh and lastly.. anyone with a pre- 1993 car using datamaster.. does datamaster indicate the car is in park when you have it in park (under gear selected) or does it say unknown..
thanks! :cheers:
Safety Car
Joined: May 1999
Posts: 3,651
Likes: 5
From: Atlantis
Cruise-In I Veteran
Re: stock programming on modified engine question.. (BluByU)
My guess is gonna be the 383 with the bigger cam is running LESS manifold vacumn than the stock engine. Less = more....
Less manifold vacumn to a MAP system means the throttle is opened more.
More throttle opening= more fuel flow.
Less vacumn = less vacumn at the FP = more fuel pressure.
Make sense?
Less manifold vacumn to a MAP system means the throttle is opened more.
More throttle opening= more fuel flow.
Less vacumn = less vacumn at the FP = more fuel pressure.
Make sense?
Le Mans Master
Joined: Jan 2003
Posts: 8,596
Likes: 19
From: Portland Oregon
Re: stock programming on modified engine question.. (BluByU)
Did you also change out the injectors? If the stock or modified prom is not programmed with the correct injector constant it will also run rich. But the main reason is as VetteNutJim states, having a larger cam and more displacement has changed the VE. The idle MAP values are now different so the ECM looks at a different part of the table now for idle fuel. Instead of maybe idling at 30 kPA its idling at 55 to 60, therefore the ECM thinks its idling at a much higher load value and is adding fuel. Then of course the O2 sensors sees a rich value so the ECM compensates with the low fuel trim numbers.
