twostep

You laid out the details of the test but what was the results? Does it vibrate with the OD on and off? TC locked and unlocked?

When you say "loss of power" does the engine speed slow?

manvstaco

I could not get it to start acting up during my test with OD disabled and the TC locked up yesterday when I floored it on a strait away. The gas pedal did not vibrate, and the RPMs exceeded that of when it acts up on the freeway trying to go 60mph+ with the OD locked up.
If it was a fuel delivery issue wouldn't it have the problem only during higher RPMs? I can mash it around in a low gear high rpms no problem noticed, but it wants to fall on it's face on the highway with the TC and OD enabled.
There is no PCM, no cold start circuit, no TCU, this is all with toggle switches on the dash. I have all day to work on this problem just running out of ideas..

Just a thought... I never had these problems before i swapped out my alternator a month ago, i did have a voltage spike of 18v for a minute or two before I was able to adjust the voltage regulator properly. idk if it could've damaged the fuel cut off solenoid but just throwing that idea out there.. I get a solid 14v at all times, can see the voltmeter needle move up and down a little(+/- 1 volt) with the blinkers on.

BHD

So it will hit the governor in all gears, including Neutral, but OD?

manvstaco

So far I only seem to be having this stumbling problem while driving, I can't get it to do it in park or Neutral
Sooooo, I made a video to help us diagnose the problem, wth is going on here?
Pay close attention to 10:20-10:35 when I tried exceeding 60mph, this is when I'm losing power and it feels like the gas pedal is trying to fight me, no noticeable black smoke when it happens, lose all boost during it, fuel pressure never went below 5-6psi while driving, 7psi at idle
start-8:20 driving through town 35-40 mph
8:22 exceeded 60mph with TC locked and OD disabled,
8:50 downshifted going 60mph(no worries)
9:45 entered Hwy
10:20-10:35 tried exceeding 60mph(problem time)
10:35-11:45 cruising 50-55mph
11:45-11:55 OD on, TC disabled, tried to see if I could go faster than 60mph with different results, same problem observed
13:15 exit freeway
13:15-end 30mph driving through town

BHD

Sounds like you have narrowed the problem down to only when the OD is on. Have you dropped the tranny pan? I am no auto trans guru or fan, but if the OD planetary is starting to fail that may be your drivability issue.

manvstaco

BHD, so you think that overdrive could be the problem even though the video only shows the throttle cable going crazy at 10:20-10:35 and not the entire engine? Wouldn't the whole engine be bucking around if OD is seizing up on me? I just tried it again, I lose boost during this event every time. Goes down from 20 to 0 psi once i try to exceed 60mph
my buddy is telling me that it look like the governor might be trying to shut it down in the video and to gut the FSS?

BHD

Hmmm. Good point. Once again I am no auto transmission wizard, I have ruined my fair share of juiceboxes and tossed them away in favor of a handshaker, pulling the trans pan and looking for big metal flakes will tell you if the OD is on the way out. Gutting the FSS would be an easier, less expensive, and less messy way to eliminate another possible issue though. Seems odd that it won't act up unless the OD is engaged.

Alec

I hope that I have read your posts correctly; here is a summary of what I understand to be happening.

When you are in OD and try to exceed 60mph, you suffer a rough loss of power.

While the loss of power is experienced, there is decent fuel supply pressure (I assume you are measuring fuel pressure between the filter and the injection pump inlet), no black smoke, and diminished manifold pressure.

This indicates that the pump is defueling.

Looking at the video, it appears that the pump is defueling because the accelerator linkage is moving away from the fueling position.

Disconnect your TV cable from the accelerator linkage, tie the TV cable off at ~3/4 of full acceleration, and test the vehicle.

I do not think that there is anything wrong with the engine or fuel delivery system. Nor do I think the transmission is "binding" and loading down the engine in any way (boost & smoke would go up were this the case). I think that something is causing the accelerator linkage to be pulled toward deceleration, and there is nothing in the injection pump that could do that. This leads me to the TV cable (or some very strange linkage problem).

Angry Johnny

Well, process of elimination is an excellent way to diagnose the area of concern. You have narrowed it down to where it only does this in O/D. Pull the pan, if your problem was somewhere else there would be problems in other ranges as well.

manvstaco

I think I found the problem. I'll know once I replace the transfercase that just exploded on me when I was trying to exceed 60 mph lol
You guys thinks it was the transfercase causing all these problems or just a new issue?
Does anyone have a replacement they would like to sell?
this was the 241dld

twostep

Wait, so there is more to this story than just the 47RH trans... So you have a second gen (driver side drop) TC and front axle as well? Meaning no lock outs on the hubs?

mknittle

I would like to know more about this truck.

oliver foster

The first sentence in the first post states that he has a '93 Suburban with a Cummins swap...

twostep

Yes, but he says '91 cummins with a 47rh. No mention of 4x4 but even if it did I think most of us would assume NP205 and KP60.

lock-out or non lock-out hubs is important to know if the front DS is involved in this mystery.

BHD

The plot thickens.