Highway RPMs seem high?
 

Hi there, first off my sig is my mods. Truck pulls fine around town and seems like the tranny isn't slipping.. I get on the highway, doing 100 km/h (60 mph I think?) my truck is seeing 2400 RPM consistently ! I can verify it is in O/D as it will go in and out and I have to pedal it to get it into O/D so I can do 100.. I have an A518, 3.54 gears as far as I know, and this seems obnoxiously high.. Any advice or anyone else seeing these kind of rpms?

1:1 (3rd) ratio with your size tires you should be running 2169rpms at 100km/h.
.69 (OD for the a518) you should be turning 1496.

Bad torque converter maybe?

Something's off for sure. Getting on the pedal should kick it down to 3rd (1:1) not up into OD. :humm:

FWIW, I think you are due for a governor spring before you do anything else.

Truck fuels past 3500.. I can free rev to 4K (not that I do) but I have verified at more than one stoplight that it will fuel up top . Anyway to check the TQ? I'm doing a fluid/filter change as we speak and am going to turn up the line pressure and tighten the bands..

I would say your tach is wrong.

I'm pretty sure my tach is on.. Prior to my throttle rod and high idle shaft removed, it free idle to 2800 or so. The only thing I can think of is that either a) the TQ fins are bent/melted from PO causing a false higher stall speed, or b) the PO changed gears to 4:10s.

Even with 4.10s your rpms should be about 1800.
You can check ratios using this calculator at the bottom of the page : Engine RPM Calculator

My 92 at 55mph runs at about 1650-1700 RPM on a factory tach. 235/85R16 tires and 3.55 gears.

Any sure fire way to check rpms besides another tach? I don't think it could be out almost 1000 rpm, but then again it does spin off the alternator..

---AutoMerged DoublePost---

Well, I changed the fluid, filter, adjusted the bands on the tranny and bumped the line pressure a bit and now it seems to run 2300 or so. There were very very few metal shavings in the pan, and the fluid was in tip-top shape.

I can, your taking it off the alternator instead of the crank shaft. Gas car and a timing light is how I did it in the good ol days. Used the gasser for a reference and pointed the timing light at the diesel.

Is your tach compatible with the factory tach harness? I have mine wired into there and it works great.

It's an autometer diesel specific tach, I'm going to see if I can get BD diesel to read my idle rpms while I'm at dyno days so I can calibrate it. May try moving around the probe too and see if that makes a difference.

On my tach I had to adjust it up abit to get it where I thought idle was. On the hwy it seems pretty correct. Untill its in od then it seems to read really low, but I have 3.07's lol

A little update, I dynoed the truck at bd dyno days, with the mods in my sig the dyno showed 205 horse .. Sound on par with my sig? Don't think so. I'm thinking the TQ is pooched.. Can anyone recommend a good quality TQ that won't totally break the bank? Not on the best budget unfortunately!