Tach acts funny and possibly a bad gas pedal "switch"?

[MOBS]

My 96's tach needle will bounce a little and sometimes fall to 0 if I accelerate full throttle from a dead stop(this has not happened in a long time since alot of sensor and electrical parts replaced). (this next comment is a current/everyday occurrence)When going up and down hills on the highway, it will sometimes show a lower rpm than expected(about 1k lower), and during that time if I remove foot from pedal, the engine will ofcourse go back to idling as normal(which is at 1000rpm) but the tach will show 0 at idle, then at say 2500rpm it will show 1500....think it's the tach internals?

Also, when slowly easing down pedal from dead start, truck will accelerate then fall back to idle with pedal down just a tad then when pedal goes a bit further down it REALLY takes off. I may have to check another forum for this, but I'm thinking it's a bad spot in the accelerator "switch"(electronic gas pedal).

It's a '96 6.5, do we have anyone here that's any more knowledgeable on diesels than me?(which isn't saying much)

Thanks.

 

[Aloicious]

I replied breifly in the other thread about the tach, it sounds like some kind of malfunction with the cluster, especially if it periodically drops to zero for no reason, likely a short or corrosion or something.

as far as the other issue goes, the diesels are a whole different beast. I've never even touched a 6.5L so I can't help too much, but here's my '96 GMT400 wiring schematics, and there are some diesel ones in there, maybe something can help out: http://www.gmtruckcentral.com/wiringdiagrams/1996.html

 

[MOBS]

The 3rd big problem I'm having(from researching I'm led to believe it's sensor related), since my pedal is normally around that dead spot when cruising(without a load), my truck won't enter OD until I'm going way over the speed limit(half throttle, which is JUST clear of dead spot). I've read that the 3 sensors that can cause OD not engaging are: VSS(vehicle speed sensor), ESS(engine speed sensor/RPM sensor/crank trigger), and the TPS(throttle position sensor....located on pedal). I'm going to go ahead and replace all 3 of those and see what happens, since they're all relatively cheap. Actually, work truck doesn't need VSS(sensor on tail of tranny), but another truck I have does.

I'll post back with what it does and if it helps....or worse, hurts, haha....my luck lately.

 

[Aloicious]

the VSS does more than just provide a speedometer signal, it'll do all sorts of things in the PCM, so even if you don't need the readout correct at the cluster, thats a sensor you want to read correctly at the PCM at least.

 

[DRAGGIN95]

The alternator provides the tach signal on 6.5TD I found that out after my alt died on my 96 dually, right before it totally quit my tach was acting crazy and not reading right, when I changed it I also upgraded to an AD 244.

 

[MOBS]

Duuude, that just made complete sense. When I went to town earlier, my tach was messing up and at the same time, my batt gauge was showing 14 at city driving speed but was going doing to the 1/4 mark when hitting hwy speed. This is the first time it's done that, so maybe my alt IS ready to go out....or I'm just "cluster f***ed" <---

Thanks to the both of you, I will replace alt....then test all 3 sensors to see if pcm signal wires are outputting within tolerance.