Quote Originally Posted by steveo View Post
hey.. so wait a minute here

if you disconnect the alternator and it runs better, and your BLMs become correct, the first place you need to jump is that it could be but a bad rectifier and/or regulator causing fluctuations in voltage, which totally screws everything.

questions:

- what happens if you say run jumper cables from another running vehicle, running off its alternator, while yours is disconnected?
- is this an internally regulated alternator, or external? are you sure?
- is your alternator bracket painted? are the bolts coated?
- do you perhaps have an oscilliscope or a friend that owns one....?

afaik any gm ecm should operate correctly from probably 10.5 volts to 15 volts. just because the voltage is ok on a dc multimeter doesn't mean it's clean enough.
I thought this too! The alternator on the truck was original and had 180,00 miles on it. So I bought a rebuilt alternator from NAPA which is a single wire internal regulator alternator. The bracket is non painted. Still same problem. So I decided to eliminate the wiring. I hooked the output wire directly to the postive post of the battery. I disconnected the single excite wire (brown wire) and went directly to the postive post of the battery. I then ran a ground wire directly from the alternator case to the negative post of the battery. Same problem. The motor will idle but not smoothly and it surges badly above idle. When all this started (truck would not crank had to use starting fluid) then would run, I went to the fuel pump checked pressure and it was 10# at the TBI. So I decided to put in a new fuel pump ( a new AC DELCO) this pump showed a little more pressure 11#. Yes I was smart enough to cut a trap door in the bed so I won't have to drop that 36 Gal tank again. My friend says why don't you just get another truck, well I can't afford another truck, I burn wood and use the truck in the woods, I am the 2nd owner had this truck 20yrs, it's been a good one, and frankly I am not going to let this beat me!!! G.S.