Post by PatM on May 20, 2005 12:51:48 GMT -5
Hi All---
A friend has an 87 4wd with a TBI 305. It presently has something on the order of 120k miles on it, and recently has begun running badly. It is stallish, and surges in neutral or park at idle (revs, then drops off, then revs again...). It stumbles badly off idle and at mid throttle, but once up and going seems to run fairly smoothly.
It has new plugs, cap, rotor and wires. There don't appear to be any vacuum leaks.
Now the part that throws me-- It seems that there is something amiss with the ECU. It shows no check engine light at startup, and attempting to scan the computer with either my code scanner or the paperclip-to-ground technique brought no response (no flashing code 12 with the ignition on and engine off with the paperclip, and something along the lines of 'the computer is not responding' from the scanner). I tried re-seating the connectors to the ECU, this changed nothing.
Can the ECU fail partially, but still run the engine? I haven't really had any occasion to deal with an ECU and am thus pretty clueless as to how they go bad. How interchangeable are they- are the GM computers from that time period pretty much the same and tailored to the specific engine/vehicle by the PROM, or are there different versions? In other words, if I try to come up with another one to swap in, what are my options? The exact computer in the truck, or something that may have come from another car or truck that I can swap the PROM into?
Any help and/or troubleshooting suggestions would be appreciated.
Thanks
-Pat
A friend has an 87 4wd with a TBI 305. It presently has something on the order of 120k miles on it, and recently has begun running badly. It is stallish, and surges in neutral or park at idle (revs, then drops off, then revs again...). It stumbles badly off idle and at mid throttle, but once up and going seems to run fairly smoothly.
It has new plugs, cap, rotor and wires. There don't appear to be any vacuum leaks.
Now the part that throws me-- It seems that there is something amiss with the ECU. It shows no check engine light at startup, and attempting to scan the computer with either my code scanner or the paperclip-to-ground technique brought no response (no flashing code 12 with the ignition on and engine off with the paperclip, and something along the lines of 'the computer is not responding' from the scanner). I tried re-seating the connectors to the ECU, this changed nothing.
Can the ECU fail partially, but still run the engine? I haven't really had any occasion to deal with an ECU and am thus pretty clueless as to how they go bad. How interchangeable are they- are the GM computers from that time period pretty much the same and tailored to the specific engine/vehicle by the PROM, or are there different versions? In other words, if I try to come up with another one to swap in, what are my options? The exact computer in the truck, or something that may have come from another car or truck that I can swap the PROM into?
Any help and/or troubleshooting suggestions would be appreciated.
Thanks
-Pat
