1990 Engine swap Help?

[rpreston]

This will be long and windy but here goes. Have 1990 Silverado shortbed 4x4 w/5 speed manual, A/C and Cruise control. Recently replaced tired 305 with rebuilt 350 longblock from Mid-Atlantic (not sure of year, but requested 1990). Used everything from old 305 on new engine except exhaust manifolds (rear cylinders off by about a 16th of on inch). Put in 350 knock sensor and replaced oxygen sensor (was getting 44 codes). Have not put 350 injectors in the TBI yet. Here's the problem. Would not hardly run at all with 305 chip. Bought new 350 chip from local Chevy dealer. Runs better and is now drivable, but not nearly right. Starts great but idles rough hot or cold. Will shut off at a stop, occasionally, if you don't quickly tap the throttle. Bogs down so badly till it warms up that you can't drive it. Has bad hesitation thru all gears, but if you hold your foot steady on the throttle in 1st, 2nd or 3rd it will suddenly take off good after hesitating for awhile. Can constantly feel it hesitating in 4th and you cannot put it in 5th (overdrive) till reaching 55 or 60 MPH, and then you better be on level ground. Still has the constant hesitation in 5th and standing on the throttle does nothing and you must downshift on the slightest upgrade. Uses gas to the point you can almost watch gauge drop (No fuel leaks). Engine itself seems good. Hasn't used a drop of oil in 500 miles. Timing was set OK (TDC) but when I tried to double check it after putting in new chip, engine would quickly stall and I would get 42 codes. Out of curiosty, watched with timing light while it was idling (with bypass connected) and the timing mark was all over the place. I'm not real convinced dealer sold me the right chip (P/N 16167287). I no longer get shift indicator lights except when I step on the gas at about 55 MPH. Does anyone have any ideas? The dealer says the ECM I have (P/N 1227747) will work with either 305 or 350 with auto or manual trans but my local parts guys system (Car Craft) says the 350 with manual trans uses ECM P/N 1228747 and possibly a different pigtail. Does anyone know who's right? Can anyone tell me if the new chip I have is the right one? Any other ideas? Money is funny and I need some answers or ideas before doing any wholesale replacements...

[broughy84]

don't know about the chips, but i would say that part of the problem is going to be the injectors the 350 is gonna want more fuel.

[rpreston]

Thanks. You may be right about the injectors causing a problem. I'm just not sure how much of a problem considering how much gas it's using right now. It's really running terrible...

[383chevyZ71]

The 305 and 350 have different lb/hour rating on the injectors. You will want to either get a throttle body off a 350 or buy the 350 injectors as that is the only difference in the throttle body. I don't really know about the different #'s on the computer. You might want to recheck for correct part on the chip though. I had a friend who swapped his 4.3 for a 350 not long ago, he had a standard transmission and the dealer sold him a chip for an automatic and his truck wouldn't run right. and would barely do 55 mph. If you don't have the right chip and have to get a different one you might think about getting a high performance chip as they a less sensitive to other modifications as well.

[rpreston]

Thanks. I was pretty sure I was going to have to get the right injectors at some point, I just wasn't sure if that could be the cause of the problems. I wouldn't have expected them to cause this severe of a problem, but I guess you never know... From what I've found so far, apparently either one of the ECM's will work. Very interesting about your friends experience. It sounds very similar to what I have going on...The parts guy at the dealer isn't very helpful. He's pretty old school and doesn't seem to have a lot of knowledge or experience with the different chips and such. I've been trying to research the chip P/N on the web but have had no luck so far. The only info on it I've been able to find is that it diffinently is for a 350 and the correct model year, but the different sources I've seen list only the engine and don't list the tranny type or any other info. Doe's anyone know of a web site where you can plug in all the trucks info and get the correct GM part number? The aftermarket chip may be the best alternative. I just wish I knew for sure that it would take care of the problem before parting with the cash then finding out something else is wrong...