Bucking under load

JSPulliam21

JSPulliam21

We Don't Rent Pigs
Joined
Apr 8, 2007
Messages
228
Here is a video of my truck a couple of weeks ago at a truck pull. You can hear the bucking/missing/flubbering several times. It started doing it around 2800 - 3000 rpms, and I had to keep it just below 2800. What the crap is going on? It does this at 3200 consistently, and intermittently between 2000 and 2800. Maybe this will help you see my problem.
http://video.competitiondiesel.com/video/93ee04ab-efa5-4e7b-b793-996201761a26.htm
(the vid may not be up right now, but it should be soon)
 
By pump, I assume you mean P-pump. I have a 98.5, and I forgot to specify that in my sig.
 
Two serious diesel mechanics that I have been dealing with say that the pump is slipping timing. Today we hooked up a code scanner and drove the truck to check sensors while the "event" was happening, and everything checked out. We put an APPS on it, and that did not solve it. The only thing that is left is the pump. I guess I will just keep running it until it throws a code or dies. Thanks for all of the help guys!
 
Are you the same bigblue from dtr? If so, I saw that you were dealing with a failing IP recently. Did it give any symptoms like this? What symptoms did you experience, and what makes you think it is the IP for sure? I want to continue my learning about diagnostics, and if I have some reasoning behind your diagnosis I can understand why it is the way it is better. Thanks!
 
Yup. I am one and the same. Mine never gave any symptoms at all other than for 3 or 4 dynos in a row I went from 496hp to 451hp. The pump had 136k on it and had been tapped for 110k so it was just getting weak. I replaced the pump and the power feels like it's come back. A dyno will tell for sure though.
 
VP's are notorious for getting lazy and doing all sorts of wonky stuff before they crap out. You using the stock lift pump?
 
Okay, scratch that Idea, how old is you IP and what electronics are you using
 
I am not sure how old the IP is, but the previous owner said that it had been replaced. By electronics I assume you mean electronic fueling. I do not have anything, but I occasionally borrow my friend's Smarty. The PO said he had an EZ on it, though.
 
BgBlDodge said:
Yup. I am one and the same. Mine never gave any symptoms at all other than for 3 or 4 dynos in a row I went from 496hp to 451hp. The pump had 136k on it and had been tapped for 110k so it was just getting weak. I replaced the pump and the power feels like it's come back. A dyno will tell for sure though.
Click to expand...

Let me be the first to predict 499/999 for your next run :hehe:
 
JSPulliam21 said:
I am not sure how old the IP is, but the previous owner said that it had been replaced. By electronics I assume you mean electronic fueling. I do not have anything, but I occasionally borrow my friend's Smarty. The PO said he had an EZ on it, though.
Click to expand...

You running a boost fooler of any kind?
 
But it does it with the Smarty, which does boost fooling. Also, the defueling I have felt on other trucks just feels like it falls on it's face. No bucking or jerking, just a smooth slow reduction in power as the rpms continue to climb. This bucking is very violent.
 
The other day I took the electrical connector off of the VP to check the wiring and pins. The pins and connector looked clean and straight, and the wiring looked unmolested and solid. So, I put some dielectric grease in the pin sockets, like I do with any electrical connector, and plugged it back up. Today, I decided to see if it would buck and carry on. I could not induce the bucking and flubbering at all, and I reamed it hard past redline in every gear or about 10 miles. It revved clean and smooth all the way to 3500 rpm's where it defueled smoothly, like it should, and stayed there. I wonder, if one of the pin sockets in the plug is loose, and a certain rpm's the pin or connector vibrates and breaks the connection intermittently. If so, then the dielectric grease took up the slack. Any thoughts on this diagnosis? Good and bad are welcome, as always! I will continue testing, and update you guys as I learn new things.
 
You must log in or register to reply here.
Back
Top