Trying to fix an illusive problem that has had my Ty disabled for a couple of weeks. Its running rich enough to foul plugs in a couple of miles. Idle is'nt any worse than normal. Not able to get a clean enough data stream at ALDL to get reliable readings with Diacom. A Snap-on scanner will not link up at all. Scoping the data line shows a lot of garbage on the waveform- the pulses are there, ~5v.with RF on the waveform, making me think this is the cause of erratic readings with Diacom. Here's a recap of what's done so far:
1. New CR42TS , Autolite wires, and Accel cap/rotor. Fowled out in ~50 miles.
Changed out above to NGK's, MSD wires and cap: no difference
2 Tried 2 new ECMs and one new Memcal- no difference
3. New MAT sensor- no difference
4. Ran new grounds from top post of (new) Optima to sheet metal in front of battery and
to grounding strap on firewall- no difference.
5. Replaced ground terminals on wires connecting to back of block and manifold bolt under alternator- likewise.
6. Checked and tightened grounds in cab, as indicated in svc. manual
Timing is ok. Fuel pressure is 38# with vac disconnected. (thought it was ~42)
Checked pinouts of ECM, other than the garbage refered to earlier seem ok.
I know there is no magic button I can press and make it all well again, but obviously I'm overlooking something- keep coming back to a ground problem; in that with key-on, I'm reading anywhere from 10 to 50 millivolts or more from battery terminal to ground at ALDL, ECM box and its associated grounds, and to other areas that should be ground. At one point, reading was negative (!) 140 MV at ECM can. Go figure...
Does anyone see a pattern here? The guy helping me runs a garage and does this stuff for a living, and is a thorough diagnostician. Me, I track down errant electrons in all sorts of equipment and also ran a garage in the distant past. We're both dazed and confused at this point, and sure could stand some fresh ideas.
Thanks (humbly).... Cornell
1. New CR42TS , Autolite wires, and Accel cap/rotor. Fowled out in ~50 miles.
Changed out above to NGK's, MSD wires and cap: no difference
2 Tried 2 new ECMs and one new Memcal- no difference
3. New MAT sensor- no difference
4. Ran new grounds from top post of (new) Optima to sheet metal in front of battery and
to grounding strap on firewall- no difference.
5. Replaced ground terminals on wires connecting to back of block and manifold bolt under alternator- likewise.
6. Checked and tightened grounds in cab, as indicated in svc. manual
Timing is ok. Fuel pressure is 38# with vac disconnected. (thought it was ~42)
Checked pinouts of ECM, other than the garbage refered to earlier seem ok.
I know there is no magic button I can press and make it all well again, but obviously I'm overlooking something- keep coming back to a ground problem; in that with key-on, I'm reading anywhere from 10 to 50 millivolts or more from battery terminal to ground at ALDL, ECM box and its associated grounds, and to other areas that should be ground. At one point, reading was negative (!) 140 MV at ECM can. Go figure...
Does anyone see a pattern here? The guy helping me runs a garage and does this stuff for a living, and is a thorough diagnostician. Me, I track down errant electrons in all sorts of equipment and also ran a garage in the distant past. We're both dazed and confused at this point, and sure could stand some fresh ideas.
Thanks (humbly).... Cornell
