Engine/Transmission (1998.5 - 2002) Bucking when lugged below 1200 rpm

[claykelly]

Okay, all in one night I installed my 4" exhaust, 275's, and a new VP-44 from Industrial Injection. Since then, I can't load down or lug the engine below say... 1100-1200 rpm without it bucking. Of course once the bucking starts it only gets worse as the drivetrain wraps up. Doesn't seem to be throttle related since as soon as I notice the slightest bit of bucking I can floor it and it won't pull out of it. Sometimes if I "tickle" the throttle and give it just enough to control the bucking until the rpms come up to around 1300 or so it will come out of it. Usually with very light load as in normal driving around town, turning a corner and accelerating in 3rd or even in 5th at about 40mph. Driveability is bad now, I have to "hot rod" it everywhere I go. Everything else in the rpm range runs perfect, just won't lug down like it used to before the repairs/upgrades were made.



Any ideas or where to start??



Oh, new lift pump, boost pump, and fuel filters where installed before the repairs were made.

 

[JL penner]

Not an expert, but I would guess your clutch can't handle the power.

just my . 02

 

[ToolManTimTaylor]

General rule of thumb is that lugging is just bad period. You are creating alot higher egt (High fuel high boost low rpm) for one and 2 that is extreemly hard on the drivetrain as a whole. The nature of an inline six is to produce tremendous ammounts of torque down low and theese engines are no exception whatsoever. Lugging is 1400 rpm and under and that leaves alot of time between firing inpulses that acts like a hammer drill on u-joints, input shafts and output for that matter and those reverberations are then transmitted thru the frame and that is what you feel. Especially now you have some nicer enhancements to the fuel delivery and exit departments.

 

[tgee]

Just a theory, the stock engine is rated max torque at around 1600 rpm, thats where, between fuel and air, and scavaging, the engine is at its most efficient operating area. Does it black smoke when you lug it that low?

 

[RustyJC]

Solution - downshift!!!



Rusty

 

[claykelly]

No black smoke down low, or anytime really that I can notice.



Clutch holds fine in all gears... so far.



This isn't lugging as in pulling a load and working it, just lower rpm casual driving, very little throttle, in traffic, etc. , etc.



I guess my main concern is that it didn't do it before. So..... is there a problem somewhere or is this just a side affect of the mods I've done so far. If so, I might undo whatever mod caused it, as I'm not too happy with the result.



I haven't got the TST box installed yet, so now I'm concerned that it may make the problem worse.



Dl5treez, are you saying you have more of a problem with bigger nozzles? Anyone else confirm this?

 

[ToolManTimTaylor]

This isn't lugging as in pulling a load and working it, just lower rpm casual driving, very little throttle, in traffic, etc. , etc.

Exactly "Lugging" isn't working the truck hard but rather it's moreso bogging it down unnessecarily loaded or not at all. And yes bigger injectors will make that more pronounce.

 

[mgoncalves]

Did you go with the standard rebuild pump or the hot rod version?



My new pump made my known bad apps, extremely noticeable. I had a small skip in my throttle on the lower end of the range, could hardly notice it with the stock pump. The hot rod pump is very throttle sensitive, and I was having a hard time driving it down low also. A new apps cured it for me.



If you can't figure out what's going on, call Brady, he'll point you in the right direction.



By the way, my truck does not buck at all in those conditions, that's with Brady's stage three's, so I think you definetely have a problem somewhere. I drive around 12-1400 rpm's much more now with the new pump, it really broadened up the low end on my truck.



Matt

 

[claykelly]

My symptoms are exactly as Dl5treez described, to the letter almost. I spoke to Brady at Industrial Injection and he too thought the APPS was possibly flaky. When my VP was dying I put a scanner on it and checked the APPS and it seemed okay to me, nice and smooth/linear. Also the fact that when the bucking just starts, if I throttle into it, it usually won't go away, indicates to me it's not the APPS. It's like the engine just can't run that low anymore. Brady also suggested air in the lines and/or transfer tube to injector mating problems, but it runs so good everywhere else I'm stumped.



Supposedly the TST box does some wicked fueling down low, so do you think this will make the problem worse... . or better?

 

[Oil Burner]

Clay,

any updates? i am getting the same thing now and I never noticed it before.

 

[claykelly]

No, no solution as of yet, it completely quit for a day or at least it seemed to, so I know something must be up other than just the larger injectors.



If and when I find a solution, I'll let you know. Anyone else have any ideas?

 

[jcarew]

Lugging our engines is probably the worst form of abuse that you could do to it. shift!!!!! or buy an automatic and it will do it for you.

 

[RonaldLarson]

I had it too.

Put on a fuel pressure guage, and saw almost no pressure when lugging occured. Put on an after market lift pump, problem solved. I have injectors, box, 4 inch and boost elbow. The stock pump could not keep up, and it bucked. I put on the pump featured in a TDR back issue from '04, built by Stanadyne. Have yet to see under 6 PSI under heavy loads: idle or cruising, 18 PSI .

Ron

 

[Tcolesanti]

Mine also started bucking down low with the addition of the injectors and continued when I switched from the VA box to the Edge Comp. I don't consider lugging to be at a certain RPM on all CTD's but mine I can run down to about 1250rpm, much below that it will buck a bit if I am going up a slight grade. At 1400rpm I am already over 20psi of boost and at 1650rpm I have already crested 30psi of boost, on 1x5 (tow mode for me). Hope this helps.

 

[OTRPU]

Even an automatic isn't a cure all. My TransCommander wouldn't drop out of OD when coming to a stop. Somthing's gotta give, either the engine has to turn over or the rear end is gonna hop. Cost me two yokes, third yoke is spreading again, a couple sets of u-joints and beat the u-joint bearing straps til distorted. Lotsa people puttin in parts, nobody finding the solution to the problem. Finally got ATS to fix the TransCommander so it would downshift sooner. They're supposed to be ordering me in a new yoke to have replaced sometime passing through. Hope things hold together til then. Good grief.



Cheer,

Steve J