vinny

Howdy,

Just drove the new(to me) truck home from VT...

All the way home,with my Caravan on the dolley behind me,the truck was doing a sort of chugging/jumping at idle,in gear,while moving. I mean really violently at times too. I could make it happen at will...
Almost like a race car with a huge cam in it...

Doesn't do it in reverse...stops if you stop dead...only while moving very slowly at idle. If you completely let off the brakes and let the truck pick-up a little speed it smooths out. It was kind of a pain going through the tollbooths with it doing that. :I

I noticed today,after unloading the truck,and with no dolley behind it,you would have to work to get it to do it. By that I mean try to keep the truck at a very slow speed while idleing.

Also,once the truck was empty today,I decided to (ahem) test all the mods that have been done to it...wheee! My what a lot of smoke...I'm thinkin' NO one behind me is going to be happy...anymore.
But...when I slowed back down(took a little bit) the truck seemed like it was loaded-up or something...idled rough for a second,almost like it was missing...then seemed to sorta' smooth-out,and began to idle normally.

Kinda' spooked me...

Do POD's do this? Modified fuel pin?

Would a bad motor mount make the truck jump around? I don't hear any twisting/clunking when "killing mosquito's".

Thanks for any idea's...

Vinny

ChrisLib

I don`t know if it`s the same thing but on my truck I adjusted the smoke screw to lessen the amount of off idle fueling wich cleared up the low speed hazing but once in a while it`ll do a sorta chug thing right off idle. I have reurned the smoke screw to where it was and it went away, but the haze came back so I re-adjusted it to get rid of the haze. I live with it, doesnt bother me at all.

wannadiesel

I think it's the idle speed. If it doesn't creep too bad at idle, turn the idle speed up a little. That's one of the many benefits of a stick, you can set the idle pretty much wherever you like. I'm at 800 RPM, but I'm thinking of speeding mine up a little. It's kinda lumpy when the A/C compressor kicks in.

The POD's really don't give a clean burn at idle, and the slower you idle it the worse it is.

vinny

Thanks Wanna,

It seems to be idling around 700rpms or so...I'll try that first...

And...it does seem to be PO'in the people around me in traffic... maybe that'll help.

I'll also check the smoke screw...

Vinny

Nuttymopar

Also check your center bearing underneath. I heard that you don't really need to take it to a shop but just slam it off and slam if on with something that fits over the drive shaft. You did find the new one in the back I assume.

My brother would say that he could see my rear end (truck's) shake a little when taking off from the driveway. This is why I think it may be suspension related but not really sure, other then I thought the idle was low when it left, around 700.

Please keep me posted.

Thanks.

SoTexRattler

I'm with WannaDiesel.. 700rpm's is a TAD too low for in-gear idle. Mine's too low right now too and it makes it tend to lurch/lope in gear when the gov starts hunting with my A/C on. It is also very embarrasing to have the mighty Cummins repeatedly die when gently goosing it to back off of the lift at the tire shop.
Try crank it up a tad and see if it doesn't lessen the lurching.


Keith

vinny

Seems I was a little off with the idle...it was around 750 in-gear to start...

That put it around 800 or so in neutral...

Well,I turned 'er up and now it's a little over 800 in gear,and 900 in neutral...and it makes no difference except the shaking seems worse.

The "chugging"seems worse because at that idle speed there's more power available...I'm holding 'er against the brake now,so when I let off the brake it has more momentum...I swear the passenger seat shakes back and forth at least a couple inches...like the forks on a harley at idle.

Also it feels like I'm holding 'er against "high idle" when I put it in gear...and going back and forth between gears sounds BAD...shifting from drive to reverse loads/unloads/loads the suspension with an unhealthy sound.

Any other idea's I can try?

When driving it I've noticed if I let it roll-out on it's own without hittin' the fuel pedal it'll clear-up by 900-1000 rpm's.

If I press the pedal it will chug until it's over 11-1200 rpm's before it smooth's out.

For now I'm going back to a lower idle,and try whatever else you guy's come-up with...could it be a broken motor mount,bad center bearing,or loose spring packs in the back? Could it be in the drivetrain?

Thanks in advance...

Vinny

Nuttymopar

You are right with the 'Holding it against the brakes' feel. Idle was better around 750 or so (in gear). Have someone watch the truck from underneath to see if the rear end is flexing or not as you start to take off giving it a small amount of power. Also check the center bearing height to see if it is either too far out with the spacers. The pinion angle must be the same as what is coming out of the transfer case and the angle going into the rear end. Doesn't matter if the driveshaft is straight or not, it is the angle of the 2 pinions that matters. Check rear spring pack to make sure the little bolts that hold the springs together have not loosened up. Transfer mounts looked ok but old but they were tight. Replace center carrier bearing. I am not sure if it needs to be pressed on or not, I hear large socket would do the trick to press it on. Put a load in the back (500 lbs or so) to test to see if it is better with a load on it, I think it was.

Redleg

I'm wondering if you couldn't crack the injectors one at a time while running. Each one should cause it to miss and shake when the seal is broken. Maybe you'll find one that dosen't make much of a change when you crack it open, that could be the culprit?

Monty

Im with Redleg on this one. You need to cutout each injector while running to see if one is faulty. While cutting out the injectors, listen for a change in engine noise, if a change is noted, then you know that injector is good. If no change is present, you need to look at that injector and or cylinder. You also need to check for air in the fuel.

vinny

Hey Scott,

Those are PDR POD's,correct?
According to the log book they're are only about a year old...

It did this like CRAZY on the way home pulling the dolley with a major load in the back...

Redleg,
The motor runs perfect at idle...runs fine once it gets past this idle/chugging thing. It's not like it's missing or lacking power (in fact it romps)....
The truck sits fine and runs smooth in park and with the brakes on...it also doesn't do this AT ALL in reverse...never.
And...most puzzling of all,it doesn't do it all once in a while.

I noticed today that if you roll the truck back and forth by hand while it's in park, the axle seems to rotate a little. All of the bolts looked tight...spring clamps,u-bolts...nothing was obviously loose.
Although...there did seem to be a major lack of pre-load on the ring and pinion...lots of slack.
I'm thinkin' probably the reason for that little clunk I hear in the drivetrain sometimes.

I'm going to have someone induce the chugging/shaking and walk along side the truck and see if anything looks obvious (that's the only thing I'll notice anyway )...

Thanks for the suggestions,and I'll keep looking...

Vinny

wannadiesel

The slack in the axle is likely a worn out cross pin, or toasted clutch packs if it has a limited slip diff. You can get all the parts to fix it from Rieder Racing.

I'm really puzzled by this one. The fact that it will only do it in Drive is really wierd. I'm thinking maybe something is wrong with the trans?

Redleg

If you're getting the clunk in the back, pull the cover off and see if the guide pin and lock pin in the carrier are getting worn out. Check the bores in the carrier the guide pin rides in too. Make sure they're not getting egg shaped.

vinny

Wanna,

It really feels like the motor.
When it's doing the chugging it feels like a cam in a hotrod...kind of a rump-rump-rump on the power strokes of the motor...
And then when it climbs in the RPM's it smooths out.

But it idles smooth with the brakes on...

Seems to do it worst when I hold the brakes and let it go really slow...like just creeping.
Plays heck in traffic sometimes...when it's doing it bad,I'll shift into neutral while rolling...

The trans is a full-on DTT trans with upgrades for big power and a 91% convertor...it seems to work just fine...I pulled my Caravan home from VT on a dolley behind it with no problems.

I've dusted several people with the truck and shifts-out fine under full fuel...OD shifts in nicely,and shifts out at a touch of the button.

It has about a hundred K on it...but Nuttymopar (who I bought the truck from) had it maintained by the nearest DTT installer on a very regular basis...trans fluid and filter changes,along with band adjustments every 20-30 K.

It also has a Magtec pan on it, a trans temp gauge which I've never seen over 150 or so, and the under the bed aux cooler.

The weirdest thing is...it varies so much...

Sometimes it's really bad...other times almost not at all...most times it's just a little annoying. If your careful,most times you can just let it roll-out (no fuel pedal) a little from a stop and it does it just a little or not at all.

I'll get somebody to drive it for me while I watch (but not from underneath ) and see what it does in the next couple days and let y'all know what I'm seein'...

Thanks a lot for the advise so far...

Vinny

chrisguthrie

I'm thinking the same thing as wannadiesel, maybe you could check your flexplate i'm wondering if it's getting ready to let go. If you shift into 1st and drive does it do it or does it only do it when you have the shifter in O/D.

Chris