Yes i needed some input here. I recently finished putting a motor in my 94 chevy pick-up i bored it 30 over put in a beefier bumpstick as recommended by my engine builder, and had the heads redone. i got it to fire up but i am having trouble timing it. I have had it 8,10 and 12 degrees timing and the truck tends to stumble and want to cut off but, only at low rpms if i put the screws to it i can light up the tires for a block. I have a pro-billet dist. with a msd coil, msd wires and a set of rapid fire plugs, any help would be greatly appreciated  

I had this problem with a toyota that I rebuilt. I was one tooth retarded on the timing. I wasn't careful when I put the cam in and got it back one tooth. It runs better when you get on it because of the advance. I'd double check your crank to cam alignment.  

This was originally a computer controlled Electronic Throttle Body Fuel Injected truck with swirl port heads.

Your modifications require closer questions. Is the distributor for an EFI engine? Did you retain the TBI? Are the emissions functional? What is the cam?

Assuming you kept the TBI, then you needed to use the MSD Pro-Billet distributor 8366. If you didn't use the EFI compatible distributor, and kept the TBI, you're in a heap of trouble as the computer needs that distributor for an RPM reference. Also, the computer controls spark advance including the base setting, the proper set up is 0 degrees. 

The cam has a big impact as cam timing directly affects throttle position against power loading which changes the relationship of intake manifold vacuum to throttle position and engine RPM. There are sensors that read barometric pressure and temperature, engine temperature, manifold vacuum, throttle position, RPM, selected transmission gear and road speed. This information is passed to the computer that crunches it through an a bunch of equations to derive a reference number. Then a comparator takes that number and looks across a fuel map and ignition advance table to determine the proper amount of fuel for the computed air flow requirement and commands an advance rate to the distributor.

You have shocked this system, as with the changed cam the sensor data no longer correlates correctly with the fuel map and advance table. What's surprising is that it runs at all let alone just a bit weird.

You need to get a custom chip made that reflects the changes made to the engine to get sensor inputs back in line with the fuel map and advance table. See these people:

http://www.fastchip.com/

http://www.hypertech-inc.com/

http://www.superchips.com/

http://www.kcspeed.com/

http://www.jetchip.com/

Bogie

Hey Bogie i am sorry yes i did retain the tbi system and it already has superchip that i had cut a local speed shop . Someone told me maybe i am one tooth off on my distributor. Could that be a solution i had the engine built and the cam has a lot more and a litle more duration it is a mellings cam and it was computer friendly so i am at a impass and cant get over the hump any help is appreciated.  

Could i do this at the distributor? I am trying to avoid pulling the motor apart thanx.  

There's always the possibility that the chip isn't right. I try to deal directly with the chip vendor rather than go through a shop, part of that I suppose is the growing lack of speed shops in the Northwest.

There really is no such thing as a TBI computer friendly cam, other than what came from GM in the first place. TBI is a MAP (Manifold Absolute Pressure) system as are some TPI systems as deferentiated from MAF (Mass Air Flow) systems. The latter use a heated wire of sprung door to measure air mass passing into the intake. MAP systems use throttle position, engine RPM, road speed, transmission gear, air temp, and manifold vacuum sensors to compute mass air flow rather than the MAF system of direct measurement. So it's pretty easy to get a MAP system screwed up with poor or missing sensor data as a result of changes to the engine.

The MAP system is very intolerant of changes. Anything much beyond headers and a CAT back requires careful reprogramming to get the sensor data squared away with what the engine needs from the fuel and ignition curve maps. GM truck cams are very mild with .050 lift durations measuring around 180-190 degrees and much less than .400 inch lift. So it doesn't take much of a cam to alter the engine's operating characteristics, thus sensor data, to something that's way off compared to what the equations in the computer are telling it the engine needs for fuel and advance.

Being a gear tooth off on the distributor should be a problem, within some dimensional reason that can be compensated for by twisting the cap till the rotor and cap achive the proper relationship for the cylinder being fired. Best way to check this without tearing everything apart is to pull the left rocker cover and all the spark plugs. Pull the crank around with a breaker bar and socket in the clockwise direction when standing in front. Watch the number one cylinder's valves, when you have both closed, your coming up on compression. Put a small screw driver thru the sparkplug hole to feel for TDC. When you get there, the damper's timing marks should be on 0 degrees or TDC what ever your's says and the rotor should align with the cap terminal for number 1. This should get you close enough that the engine will light off and you can use a timing light to make the final adjustment to 0 degrees with the tan wire removed from the distributor for this adjustment, so the computer can't put an advance signal into the timing while making this adjustment.

If this doesn't do it then your going to have to assume that the IAC is miss adjusted or failed or one of the other sensors has failed, or the chip doesn't have the right codes in it to relate sensor data to the fuel and advance map.

Bogie

You brought up some good points as i recall the chip i have now was for the stock cam and at that time i only had headers and tbi spacers so you think that i am going to need to have a new one made the cam in there now has 215 degrees of duration and 424 and 434 lift i was told by comp cams that 218 is my max so i think i am safe there. I had a friend of mine (more experience i thought) time it with a light and i found that it ran better when i timed by hand and sound so if you were in my shoes what would you do first, second etc. I am anxiously trying to get this done as i have a interest in building me a new project so i am all ears. Thanx again.

I think you're getting into semantics with Comp Cams; they mean one thing, you mean something else, they sound similar but aren't really the same.

When Comp says that 218 (@.050") is your max; they don't mean your stock chip is good till you hit that number. What they mean is that 218 is as far as you can push TBI MAP technology sensors and get any data that is useful for the computer to use for finding the engine's requirements on the fuel and advance maps. That's not the same thing as blowing a chip to model sensor inputs of engine conditions up to that point.

MAP systems are rather specific and TBI is more so than TPI. The factory cams on TBI engines are very mild, even the 305s that were put into Camaros and Firebirds. Those engines have timing that varies from about 170 to 190 degrees @ .050 lift. When you go beyond 190 degrees duration, add lift over .35 inch, install 1.6 ratio rockers, you also need to have a custom chip as now the relationships of manifold vacuum is changing (going down) to throttle posiiton (staying the same or going up) to RPM  (going up) have significantly changed. Idle vaccum has dropped from say 18 to 22 inches to 14-18 inches. The program on the chip doesn't know anything about why the vacuum dropped only that it has. It now wants to fuel the engine for a partially open throttle condiiton at cruise RPMs but that's not what the engine is doing, it's ideling. So the computed fuel requirement for operating conditions is incorrect and this continues throughout the rev and load range. A new chip seeks to put the new sensor relationships back into alignment with the operating condition of the engine. Generally for every change that affects power by 10% a chip needs to be made for those changes.

Above 218 degrees of cam duration the manifold vacuum has dropped so low that the vacuum and other sensor signals are falling into what engineers call the "Noise Level" that's where the sensor discrimination is no longer large enough between data points for the computer to make sense of one signal compared to nearby signals which maybe close in value but represent significant differences in operating requirements. To run a hotter cam than that requires that you go to the aftermarket, such as Howell, to get sensors that offer sufficient signal discrimination. These get really expensive really fast. So 218 degrees is about it as wild as you can absolutly go with cam timing for a TBI MAP injected engine using factory sensors. (The LT-4 HOT cam will work with computer changes and factory sensors but that's as good as it gets and its unlikely to SMOG, but it will run fairly well.) But up to that limit, you need a new chip for any change that adds or removes more than 10% to power developed with the previous engine and chip configuration. Anytime after the engine is built and a new chip blown for it, if you make another 10% of greater change to air flow thus power through the engine, you have to blow a new chip. So you want to plan where you're going with changes and do everything once as these chips are pretty expensive, usuall 3 to 5 hundred dollars. It gets worse with OBD II and up systems.

Bogie

This link will hopefully explain how to verify the alignment. No you dont have to disassemble the engine. You pull the timing cover off to access the crank/cam gears. if you need to adjust you can pop offthe gear from the cam to slip the chain off. You would adjust the crank to cam alignment and reinstall the chain & gear.

http://www.gmhightechperformance.com/tech/0506htp_degree/

Ok then Bogie i get it now so i will call jet chip and give them my mods and see what they say. You really opened my eyes on this one i am hoping to make in the 300s with hp you think i can do it? So i will keep you up to date on what happens