Hey guys I have a question.  I wanted to know if I am trying to tune my 1994 1500 TBI, do i need to do it via a chip or have the computer reprogrammed?

I am stuck between a rock and a hard place because I am having timing problems and I was told my MAP sensor is out of wack (too much air in manifold).  Also, should I purchase a bigger TBI unit or use the one that I have?  The engine has a bigger CAM (442,443) bored 30 over & hedders.  I was told the truck is running too lean.  

I am all ears to suggestions.  Thanks!   

TBI engines don't allow for much change to the engine configuration before you get into fueling problems. These systems and many later TPI systems indirectly measure air flow through the engine by a formula that takes sensor data of air temp, Engine temp, manifold pressure (vacuum), throttle position, RPM, transmission gear, and mixture ratio off the O2 sensor. 

You typically get into two issues with these designs when making mods to the engine. The first is changes, especially camshaft changes, that upset the previously described relationships to the point where the sensor input data to the computer no longer matches the data relationships used in the fueling and timing maps. To a small extent the O2 sensor will overcome these problems but it is design limited to about a 10% range of authority. This also leads into the second issue which is total airflow, the fuel map is only designed to cover the expected CFM range of operating conditions. Modifications that not only change relationships mentioned above but also increase total air flow capacity such as more cam timing  and lift but also include manifold, throttle body, exhaust improvements, and head or port changes that allow more air through the engine can take the fueling requirement beyond the end of the fuel map.

So this is a problem of both the relationships expected by the computer from the sensors and one of total mass flow that goes beyond the factory fuel map. The solution is a new PROM that is programmed for these new relationships. Check this out and there are many others make custom chips: http://www.fastchip.com/

A larger throttle body such as the Holley 502-7 can be used if your going to higher RPMs or a larger displacement engine. The stock TBI flows about about 440 cfm where as the big Holley and also the TBI from the 454 flow about 670 cfm.

You probably don't need a new MAP sensor.

Any modification that changes either the relationships of manifold  vacuum to throttle position or total mass flow through the engine requires a new chip, so you need to plan the engine get that data to the chip guy. Any further changes will require another new chip so try to this once as chips are rather pricey.

A variable pressure regulator can be installed to provide some additional fuel trim capability, but don't try to use it to simply richen the mixtre with a proper chip as increased pressure alone doesn't cover all the contingencies.

Bogie  

Thanx Bogie i am trying to decide which company is the best. I also wanted to ask what should i do because when the truck is runnung idling it runs hot even without a load on the motor now should i chalk this up to it runnin lean or should i look deeper int to the matter. Now on the tbi unit issue is it more cost effective to go witht the 454, the holley, or send my unit to turbo city i am on a budget and cant afford the mistakes so i am tryin to nail it on the first trip. Thanx in advance  

Running hot can be an issue of a new engine on an old radiator which no longer has the flow capacity required to cool the engine. Things to look for are proper water pump, sertpentine pump rotate backwards relative to V-belt pumps so having the right one is critical. Same goes for the fan if youre running a pump driven fan.

Given that budgets seldom allow for getting into unanticipated problems, I'd forget the 454 TBI and go with either a new Holley or with Turbo City both have good reputations.

Fastchip is an excellent source of custom chips. http://www.fastchip.com/

Bogie