Rough Running 350

Shoestringmechanic · June 27, 2008

(This is Shoestringmechanics wife, he does not type, and too old to learn now, he says) I bought a 1998 4X4 GMC pickup with a 305 in it, knowing that the engine was blown up. I had a 350 ready to drop into my commercial fishing boat if I had a break down. I had replaced the heads with ones that used a caburator for using in my boat. Upon buying the truck I removed those heads and put the original ones back on and it was back as a motor ready for a vechicle. I put it in the truck, it started and run but it was a rough run. We read up about this model of truck and changes that have been made in the last few years that make adjustments and repairs by a shadetree mechanic a thing of the past. On this site we read about the scanner for setting the timeing and the crank. I was lucky I had a friend who had one. He set the timing at 0, and relearned the crank setting, and it runs some better. But it is still not running right, and slow to responding to acceleration, but runs better at higher speeds. Some people have mentioned that the computer may still think it has a 305 in it and not the 350. Could this be the problem? One said we could locate another truck with the same option codes with a 350 and order a new computer with that VIN # and it would fix the problem. Is this illegal? I don't want any jail time please. Some say we need to take to a dealership, but we are thinking that could really be costly, like the fellow with nerves of steel with the "misfiring chevy". Fishing is the pits this year, I appreciate any help you guys can give.

98silvz71 · June 27, 2008

(This is Shoestringmechanics wife, he does not type, and too old to learn now, he says) I bought a 1998 4X4 GMC pickup with a 305 in it, knowing that the engine was blown up. I had a 350 ready to drop into my commercial fishing boat if I had a break down. I had replaced the heads with ones that used a caburator for using in my boat. Upon buying the truck I removed those heads and put the original ones back on and it was back as a motor ready for a vechicle. I put it in the truck, it started and run but it was a rough run. We read up about this model of truck and changes that have been made in the last few years that make adjustments and repairs by a shadetree mechanic a thing of the past. On this site we read about the scanner for setting the timeing and the crank. I was lucky I had a friend who had one. He set the timing at 0, and relearned the crank setting, and it runs some better. But it is still not running right, and slow to responding to acceleration, but runs better at higher speeds. Some people have mentioned that the computer may still think it has a 305 in it and not the 350. Could this be the problem? One said we could locate another truck with the same option codes with a 350 and order a new computer with that VIN # and it would fix the problem. Is this illegal? I don't want any jail time please. Some say we need to take to a dealership, but we are thinking that could really be costly, like the fellow with nerves of steel with the "misfiring chevy". Fishing is the pits this year, I appreciate any help you guys can give.

I'm pretty sure its the same computer that runs the 4.3, 5.0, and 5.7Ls. How long have you let it run because I was told that it could learn how to run up to a 383 stroker with no problems. Is it throwing any codes perhaps? You might have left a sensor off like a 02 sensor and it can't learn to fuel the engine if one of those is bad.

Shoestringmechanic · June 28, 2008

(This is Shoestringmechanics wife, he does not type, and too old to learn now, he says) I bought a 1998 4X4 GMC pickup with a 305 in it, knowing that the engine was blown up. I had a 350 ready to drop into my commercial fishing boat if I had a break down. I had replaced the heads with ones that used a caburator for using in my boat. Upon buying the truck I removed those heads and put the original ones back on and it was back as a motor ready for a vechicle. I put it in the truck, it started and run but it was a rough run. We read up about this model of truck and changes that have been made in the last few years that make adjustments and repairs by a shadetree mechanic a thing of the past. On this site we read about the scanner for setting the timeing and the crank. I was lucky I had a friend who had one. He set the timing at 0, and relearned the crank setting, and it runs some better. But it is still not running right, and slow to responding to acceleration, but runs better at higher speeds. Some people have mentioned that the computer may still think it has a 305 in it and not the 350. Could this be the problem? One said we could locate another truck with the same option codes with a 350 and order a new computer with that VIN # and it would fix the problem. Is this illegal? I don't want any jail time please. Some say we need to take to a dealership, but we are thinking that could really be costly, like the fellow with nerves of steel with the "misfiring chevy". Fishing is the pits this year, I appreciate any help you guys can give.

I'm pretty sure its the same computer that runs the 4.3, 5.0, and 5.7Ls. How long have you let it run because I was told that it could learn how to run up to a 383 stroker with no problems. Is it throwing any codes perhaps? You might have left a sensor off like a 02 sensor and it can't learn to fuel the engine if one of those is bad.

You may be on to something 98silvz71, we went ahead and licensed and insured it so we could put a few miles on it and to see how it would do driving it more than a mile at the time. It seems to be doing better the more he runs it, it has set up for a while. I remember when the friend had the tool on it he said there were 2 codes on it. As he told what each were, hubby remembered that he had unhooked something along that line. Maybe we should give it a few days and get him to check for them again. They shouldn't show up again, and if they do he will know what to look for. Thanks so much for answering, if you have any more ideas all are welcome. Thanks!