I just finished building my truck, '59 Chev cab on '89 K2500 4WD chassis. We can't get the engine to run quite right. Anybody have any experience with OBD1 systems? I'm not a pro mechanic, I'm a carpenter. I have a good friend, George, helping on this who is a pro, but he rarely works on anything but stock vehicles, so he's not sure about the effect the mods have on the computer system.
Here's the deal: Engine is rebuilt from '89 350 that had about 70,000 miles on it run on propane. It was extremely clean inside. I re-did everything but the valves, they seemed too clean to mess with. Non-stock items are (1) Holley #502-6 670 cfm throttle body, stock intake holes bored out to 2" to match the TBI. (2) Crane cam P/N 114112 (very mild), with new lifters. (3) JBA Tri-y headers with 3" exhaust. The transmission is manual Muncie HD 4 spd.
The O2 sensor fitting was located about 6" from the head on the #7 tube, but we moved it to just aft of the final collector, just ahead of the cat. It's not heated. The reason for the move was that the system was having trouble staying in closed loop, plus we thought it would get a better reading on all 8 cylinders. It stays in closed loop better.
On cold start, it runs, but not smoothly, I usually have to feather the throttle to keep it running. When it goes into closed loop, it will idle okay. When driving, it runs fairly strong, but has some hesitation on acceleration. Steady running seems pretty good, but there's a noticeable sag when you step on it. I'm not looking for neck snapping power, just a little passing power. It takes awhile to recover power.
Snap-On scanner says it is usually running lean. We tried adding resistance to the coolant temp circuit and got the apparent temp down to about 140 degrees. Some improvement, but not even what you would expect from a bone stock motor.
Valves are set at zero lash. George fiddled with that for a while and thought it sounded better that way. Crane says 1/2 to full turn beyond zero. Any thoughts?
We haven't been able to check fuel pressure yet, but the injectors appear to be putting out plenty of fuel.
Timing is set at 4 degrees advanced (unplugged), just because it seemed happier that way.
One other thing we weren't sure about is how the speed sensor interacts with the computer. I just have it connected direct since I can't use the original speedo to buffer the signal.
Any suggestions would be appreciated. I'm sure some of you guys have some good ideas. Merry Christmas and have a Happy New Year.
Don
Here's the deal: Engine is rebuilt from '89 350 that had about 70,000 miles on it run on propane. It was extremely clean inside. I re-did everything but the valves, they seemed too clean to mess with. Non-stock items are (1) Holley #502-6 670 cfm throttle body, stock intake holes bored out to 2" to match the TBI. (2) Crane cam P/N 114112 (very mild), with new lifters. (3) JBA Tri-y headers with 3" exhaust. The transmission is manual Muncie HD 4 spd.
The O2 sensor fitting was located about 6" from the head on the #7 tube, but we moved it to just aft of the final collector, just ahead of the cat. It's not heated. The reason for the move was that the system was having trouble staying in closed loop, plus we thought it would get a better reading on all 8 cylinders. It stays in closed loop better.
On cold start, it runs, but not smoothly, I usually have to feather the throttle to keep it running. When it goes into closed loop, it will idle okay. When driving, it runs fairly strong, but has some hesitation on acceleration. Steady running seems pretty good, but there's a noticeable sag when you step on it. I'm not looking for neck snapping power, just a little passing power. It takes awhile to recover power.
Snap-On scanner says it is usually running lean. We tried adding resistance to the coolant temp circuit and got the apparent temp down to about 140 degrees. Some improvement, but not even what you would expect from a bone stock motor.
Valves are set at zero lash. George fiddled with that for a while and thought it sounded better that way. Crane says 1/2 to full turn beyond zero. Any thoughts?
We haven't been able to check fuel pressure yet, but the injectors appear to be putting out plenty of fuel.
Timing is set at 4 degrees advanced (unplugged), just because it seemed happier that way.
One other thing we weren't sure about is how the speed sensor interacts with the computer. I just have it connected direct since I can't use the original speedo to buffer the signal.
Any suggestions would be appreciated. I'm sure some of you guys have some good ideas. Merry Christmas and have a Happy New Year.
Don