Engine/Transmission (1998.5 - 2002) Off-idle engine sound w/ DD2s

[AggieJustin]

Off-idle engine lope w/ DD2s

Since I've had my DD2s in, I've noticed that when taking off from stop without giving it any throttle that the engine gets a sort of loping ("rump, rump, rump") sound to it. It's not enough that you can notice the tach jumping up and down, but it's noticable in the engine sound. If you give it a little throttle, just a 100rpm or so, it will keep the smooth sound. You can really notice it when trying to ease a trailer backwards.



It does the same kind of thing if you're moving along slow in a lower gear (like idling through a field in 2nd gear). It wants to go back to making this up and down sound which affects how smoothly you're idling along. On level ground it's not bad, but if it starts climbing a little hill it starts this again.



I've always thought it was just the larger injectors causing the governor to be too touchy, overcompensating when the idle speed gets down. But since this is my first experience with a diesel taken beyond stock, I wanted to make sure this was normal. If not, what should I be checking out?



The combination of this and my OFe grabbing some makes it difficult to back out of a parking spot smoothly or take off smoothly from a stop. I figured this was just a side effect of having BOMBed diesel but I've never heard anyone else heard mention similar things. Just wanted to rule out any potential problmes.



Thanks... . sorry for the long post. Don't think it's possible for me to state a problem in a few words.



JM



Edit: Thanks to puffincoal for giving me the word I was looking for. It's a lope... not a rump, rump, rump sound. I could not think of the term for it.

 

[puffincoal]

i have noticed the same thing but only with a heavy trailer, became alot more noticable when i pit the south bend in nothing bad though, just a little lope when the rpm's drop just below idle

 

[DEZLPWR]

Mine does it... . Perfectly normal, perfectly healthy, in bombed 5 or 6 spd trucks... Don't you just love that womp, womp, womp sound? I sure do! Oo. In fact, I often try to make it do that when backing or starting off from a stop. hehehehe

 

[mgoncalves]

Mine does it also, it scared me at first but now I understand it's OK. I get some weird looks in parking lots from other diesel owners.







Matt

 

[Hohn]

Mine does it ever since I put in the DD2s also. At first I was worried, thinking I goofed the install. It's proven to be a non-issue.



Yeah, it's all in the governor I think, too. Because each firing of the injector dumps in so much more fuel than the ECM is used to seeing, it gets a little sensitive and overcompensates pretty easily.



You can avoid this by giving it a little pedal when you start off, instead of making the governor do the throttling.



Justin

 

[RustyJC]

It's normal. In effect, the governor circuit now has too much gain. When the A/C compressor kicks in, you let out the clutch at idle, etc. , the governor circuit will tell the VP-44 to give "X%" more fuel to bring the engine speed back up to setpoint. Well, with the bigger injectors, the VP-44 (being calibrated for the stock injectors) thinks it's sending "X%" to the injectors, but the injectors actually deliver "X+30%" (30% is picked off the top of my head and used for illustration only) to the engine. This means that the engine speeds up more and faster than normal, so when the governor senses that, it chops fuel until engine speed drops below setpoint, at which point it begins fueling again. It will go through this cycle about 3 times before the speed settles out, thus producing the "romp romp romp".



If you listen closely to the diesel "rattle" at idle, you can tell that it's more irregular than with stock injectors - sorta like what we used to call a 3/4 race cam. Same reason. Personally, I think it sounds kinda neat!



Rusty

 

[AggieJustin]

OK... I guess I'm just paranoid after all.



I can now enjoy my romp, romp, romp without worrying about it.



I does sound cool and it does make it unique compared to the other diesels in the crowd I run with. It's good to be different.





RustyJC-



How's that Con OFE working out for you? I really like mine, but I've been having trouble getting a smooth takeoff (in forward or reverse, which is what made me worried about the lope from the injectors). I've always figured it was just because this clutch held tighter than the old one, but I wanted to get feedback from someone who was similarly BOMBed.



JM

 

[RustyJC]

I just got the truck back yesterday - this has absolutely been the clutch installation from h*ll!!! The shop that did the installation sent the flywheel out to have it ground, installed the OFE, put everything back together and pitched me the keys. I noticed right off the bat that the truck now had a vibration through the floorboard and seat at engine frequency. Something definitely wasn't right!



After some discussion with Peter and the shop, they tore everything apart again and found that the flywheel face was . 040" out of parallel with the crankshaft mating face - the machinist (and I use the term loosely) had screwed up when he set the flywheel up to be ground, and the shop didn't dial indicate the flywheel face when the flywheel was reinstalled on the engine and before installing the OFE.



Fortunately, a real machinist was able to restore the flywheel's clutch face to parallel and then grind it, so everything's back together and running OK now, 8 days after I took the truck in. I'm glad I don't use the truck as a daily driver!



I only have about 60 miles on the OFE, and I notice that it chatters some when taking off from idle in 2nd (remember, I have the 4. 10's). It seems OK in 1st or reverse, and it also doesn't seem to chatter if I'll rev the engine to around 1000 RPM before engaging the clutch in 2nd. It's almost like the clutch disc material wants to see a greater speed differential between the disc and pressure plate/flywheel when the clutch engages.



I'm hoping the chatter improves with the 1000 mile break-in requried before we can tow our 5ver because there are situations (like taking off or backing uphill) towing our 5ver where I have to hold the rig with the brake while letting out on the clutch with the engine at idle. Unless I grow a 3rd foot, running the engine up to 1000 RPM before engaging the clutch ain't gonna happen. Other than the chatter, everything seems fine - pedal pressure is actually lighter than stock.



Rusty

 

[Mtngoat]

Mine did thew same thing, but only when I put it in gear right after starting it (in a big hurry). If I start it and wait for a second or two, it doesnt do it.



Robin

 

[AggieJustin]

On a related note about the clutch...



I was hauling hay a few days ago. While we were in the field, I stopped and dropped it down into 4-Low/2nd gear. I was sitting there holding in the clutch waiting to pull up to the next bale and it started to crawl forward. It definitely wasn't rolling on it's own since we were on level ground and almost completely loaded up.



So it seems like the clutch was starting to re-engage even though I was still holding the pedal down. Which pieces should I be checking here? Or are there other tests I can do without dropping the trans to isolate a problem? That's the first time that has ever happened. I have had a couple of experiences where I was easing on and off the clutch backing up to a trailer, where I couldn't get it back out of reverse until I shut down or released and pressed the clutch again. Once again... something I can't seem to recreate and only happens on occasion.



Other than that it always seems to shift fine. And I'm hesitant to just take it to the local shop to have it checked it without having at least some clue what the problem might be.



JM

 

[Hohn]

AJ:

If your truck is fine at first, then creeps after having the clutch in for a while, I would check the cylinders (master and slave) and your release fork adjustment (there is one, right?).



If the truck creeps immediately, I would say you aren't getting enough release period. Check your rod (as discussed above), throwout bearing, etc.



Justin

 

[AggieJustin]

Thanks Justin. That's the first time it's ever trying creeping on me. I've sat before with just the clutch held in and it didn't move, but all those times were in 2-High. Perhaps being in 4-Low made it easier to start moving, I'll have to test this out again tonight.



The other Justin.

 

[puffincoal]

AJ:

If your truck is fine at first, then creeps after having the clutch in for a while, I would check the cylinders (master and slave) and your release fork adjustment (there is one, right?).



correct me if i'm wrong but i'm pretty sure that we have internal slave cylinders. this is were the slave cylinder mounts on the input shaft and works like a little hydraulic cylinder and just pushes right on the clutch springs, this is a great idea until it blows out and u have to pull out the trans to replace it:{