2,000 rpm fluctuation at 55 mph

[treerxjon]

My 97 7.3L engine seems to go to pretty high rpm prior to shifting and once I reach 55 mph will go up and down about 2,000 rpm. It’s almost like having a Jake brake set itself for about three seconds and then off for a few seconds, Jake again for three, off again for few.
My brother thinks this could be the low pressure oil pump not pushing the injectors sufficiently? I’ve got 280,000 miles on her, I’d like to keep her on the road for a while longer.
Please help! Thank you.

 

[greenskeeper]

post a video of the problem

LPOP feeds the HPOP which supplies the injectors, I doubt it's that.

is the truck an automatic?

What happens when you manually shift gears as you accelerate? Will it hold each gear?

 

[treerxjon]

I’ll do that, but won’t be able to till this weekend.

It is an automatic, with a newly rebuilt trans, less than 1,000 miles on it. It holds gears but shifts late at high rpm’s. It’s holding gear at 55 too, but the rpm’s just cut back and forth about 2,000. Literally similar to a Jake.

Thank you for your help man. I’m shade tree at best and greatly appreciate it. Will work on that video this weekend sir.

Have a good one.

 

[greenskeeper]

was the issue present with the old transmission or something new?

 

[treerxjon]

I don’t remember it being there before. My truck has been down for several years, basically since the transmission was replaced. When I pulled her off the road it was not doing this, mechanically it drove well. I pulled it off the road because my suspension had pretty well rotted out. Just finished rebuilding everything from the hanger brackets down to the ground, which has taken me about 4 years to do.

I made three videos. One showing the dash when the truck is being started and the delay of the oil pressure kicking up. Another showing the tack as she comes up to about 60 mph and holds speed while the engine speed kicks up and down. Another video showing the tack jumping around while I hold the truck at 35 mph but I can’t seem to download videos to this site?

It’s almost like there is something off with the torque converter?

I greatly appreciate the help. This isn’t something I can afford to just go and get done. I need my truck back but am pretty limited on the finance end of things.

If anyone knows the secret about downloading videos from an iPhone to this site, please let me know the trick? I’m a chainsaw jockey, not a tech person.

Thank you!

 

[greenskeeper]

upload to youtube and link the videos in a post

The TC is locked by the PCM grounding the signal wire from the transmission. If that wire or signal isn't constant, it wouldn't stay locked at higher speeds.

Did you try manually shifting through the gears?

Sounds like something is wrong with the new transmission or the install.

 

[trackspeeder]

If there is an electrical issue with the tranny it should be throwing a fault code. Scan it and see what shows up.