| Author | Message | ||
     Brian Brown (Rtiqulatendisco) New Member Username: Rtiqulatendisco Post Number: 38 Registered: 01-2004 |
I recently replaced my Alt due to bearing problems and was hoping that it would fix my tach from jumping from 0 to 4000 RPM. Seems ok at idle but goes nuts at highway speed. All wires at the Alt are tight. What's next to look at? Thanks | ||
| Will Tillery (Will) Senior Member Username: Will Post Number: 376 Registered: 11-2002 |
Are you experiencing actual loss in power? Was the alternator new? Thanks | ||
| Chris Browne (Chris_browne) Senior Member Username: Chris_browne Post Number: 689 Registered: 02-2003 |
The tach feed wire might be shorting on something | ||
| Sergei Rodionov (Uzbad) Senior Member Username: Uzbad Post Number: 366 Registered: 08-2003 |
got one of them rebuilt alt , have you? you can check for belt slipping, who knows. | ||
| Justin Miller (Evil_j) New Member Username: Evil_j Post Number: 2 Registered: 03-2004 |
I had the same thing when I replaced the Alternator in mine, tach bouncing. I had it bench tested and all and it passed. Check all wires making sure they were tight and not shorting out, belt wasnt slipping. It turned out that the alternator wasn't rebuilt very well and had an internal short. | ||
| Rob Caulfield (Wrldky) Member Username: Wrldky Post Number: 119 Registered: 02-2003 |
Brian, Are you having loss of power like Will asked? Did you route the serpentine correctly? | ||
| Brian Brown (Rtiqulatendisco) New Member Username: Rtiqulatendisco Post Number: 39 Registered: 01-2004 |
There is no loss of power. The alt was rebuilt with all new brushes, bearings, and voltage reg. Haven't checked the belt but when I got the radiator flushed out yesterday, the guy said that the fan clutch was a little wierd. Something about some oil leaking but he left it at that. When I put the belt back on, it seemed just as tight as when it was removed. | ||
| Joe Still (Discojoe) New Member Username: Discojoe Post Number: 2 Registered: 03-2004 |
Sounds like you got screwed on the rebuild just like I did. On second or third try most of us either get a Bosch rebuilt (80% sucess first try) or pay $600 for the new Marelli. Bad rebuilts have got to be close to number one complaint on D1 IMO. I got my Bosch rebuild from Nathan(still took two trys but Nathan made it right immediately) BOL | ||
| Brian Brown (Rtiqulatendisco) Member Username: Rtiqulatendisco Post Number: 42 Registered: 01-2004 |
Found a vacuum hose loose/off at the rear of the plenum. Now it idles just fine. At highway speeds that damn thing spends most of the time at O and jumps up to 3000rpm once every 8-10 minutes. Will, I did notice some loss of power today...what do you think? | ||
| Robert Sublett (Rubisco98) Senior Member Username: Rubisco98 Post Number: 1175 Registered: 04-2002 |
$600 for the new Marelli. Just go with a Mean Green for about half of that. | ||
| Will Tillery (Will) Senior Member Username: Will Post Number: 381 Registered: 11-2002 |
Brian its pointing towards a rebuild issue. It happens ALL THE TIME.. I have seen this issue hammered into the ground. I have never checked on the mean green as Robert suggested but I can get new ones for around 330.00 or so. I had the same thing happen on my truck over a year ago. | ||
| Brian Brown (Rtiqulatendisco) Member Username: Rtiqulatendisco Post Number: 44 Registered: 01-2004 |
What is the problem with rebuilding an alt? It's not that hard is it? You just clean and replace all the parts and it should be as good as new...I hoped. I'll be calling the shop today. | ||
| Brian Brown (Rtiqulatendisco) Member Username: Rtiqulatendisco Post Number: 45 Registered: 01-2004 |
One more question. If the truck is running and the alt is supplying the correct current, why would the problem be the Alt? How is the tach related directly to the Alt? Thanks | ||
| Sergei Rodionov (Uzbad) Senior Member Username: Uzbad Post Number: 370 Registered: 08-2003 |
Brian - there is wee wire (one of 3) that goes from alternator, thats how tach does read input. I.e your tachometer really measures rotation of alternator, not of engine. | ||
| Brian Brown (Rtiqulatendisco) Member Username: Rtiqulatendisco Post Number: 46 Registered: 01-2004 |
If I recall, there were 2 wires that I had to reconnect to the Alt and one wire running across the back side but I never had to disconnect it. Does that sound right for a Marelli? Thanks for all the help. | ||
| Sergei Rodionov (Uzbad) Senior Member Username: Uzbad Post Number: 371 Registered: 08-2003 |
Personally i cant remember right now, as i ripped out my alternator about 2 months ago, after stock one started to drop dead. Replaced it with mean green and truck is happy as pig in ..  I'll check manual, but to my recollection there were 3 wires - ground one, positive charging line and third one from the back, that was only one that you could actually disconnect (rest you had to unbolt/cut). Tiny white one - thats the one to tach. Its very unlikely for tach itself to die or for this wire to become heavily corroded to cause such jumping. So its either connection of that wire (not tight/contact isnt clean blah blah) or, most likely, rebuilt alt. While rebuilding of physical charged isnt big deal (face it - its mere magneto), i think some bits stock one that control charging are very fragile and easily haunted. I second Rober - for about 350$ you can buy alternator with twice of amperage, so your dual batteries/deep cycle batteries wont kill your alternator | ||
| Geoff 93 RRC (Geoff) Senior Member Username: Geoff Post Number: 300 Registered: 11-2002 |
Sounds like a loose connection for the tach wire or a short in it. Otherwise you can buy a digital multimeter for about $20 at Home Depot or an auto parts store and test the charging system. Set it to measure the voltage (not amps) and test the output of the alternator by putting a probe on the output post (+) and the other on the alternator housing. Should read around 14.4 volts at fast idle. Next put it on the battery + and - posts and you should get less than .5 v drop. If you see a large drop between the alt and battery you can also test the + and - paths individually for resistance using voltage drop. This will tell you which path is causing the drop. Put a probe on the alt output (+) and the + batt post. Should see a drop (positive or negative reading on the multimeter depending on which way around you have the probes) of .5 v or less. The neg path is between the alt housing and - post on batt. Should see about .2 v drop, but .5 is acceptable. |
