To DDEC or Not to DDEC, that is the question

[keithshotrodshop]

After much calling around and various reasearch, I have come up with a 6L71TA DDEC Coach motor for a reasonable price with computer and harness. Any thoughts on this? I have thought much about turboing my stock motor, but this motor is actually cheaper than even the rebuild kit for mine, so I'm thinking swap time. Any advantages/disadvantages to the DDEC? I'm fairly new to the world of big diesel engines.

[tekebird]

I vote against the DDEC....too many electrical complexities.......plus I think you will need an electronic trans if going to auto as well.

Your bus is simple....keep it that way and you will be happier...than spening alot of time and Money chasing down codes and minor faults that make your engine not run.

non DDEC..........fuel air and compression and it will go.

[Buffalo SpaceShip]

I vote that way, too. I've always had MUI engines, and they're brain-dead simple to diagnose. Having a DDEC might give you slightly better economy, possible cruise control, no fear of a "runaway", etc. But sometimes simplicity is best. Especially at oh-dark-thirty and you're miles from the nearest DD dealer.

Not to mention the harness, senders, and expertise req'd. to install a DDEC in an old coach just might make you swear off bussin'. And we don't want that. 

My $0.02,
Brian B.

[NJT5047]

I'm a DDEC enthusiast, but unless you are an automotive fuel injection guru (same skills for DDEC), I'd pass on the DDEC for what you are trying to accomplish. 
If you use the DDEC, you can have the auto trans deprogrammed.  DD will do this.  They won't turn up the HP.  But the HP should be suitable...probably in the 215 HP range?   
You would want to get the whole donor coach, or access, for  the bits and pieces (radiator)  to complete the swap.  A "T" may be difficult to cool on your coach unless you upgrade the radiator and fan. 
An MUI would be too easy to swap into your coach...they are all similar.  With the DDEC, you gotta run a harness to the front of the bus...and install an accelerator TPS...that's the reason the engine is cheap...no one wants a 6/71 DDEC due to the extra wiring.
Want to check it out good too...it's out of a transit and may have some low RPM and/or road speed llimits that the DDEC dealer will not deprogram.   1800 would make you a little slow I would guess?   
If you cold get the engine and trans (the donor is a LH transverse mounted V drive isn't it) the install would be simple, if the "V" is the same as your drive axle...someone will straighten this out, but I think there are two rear drives with different angles?   Hanging the auto trans would be cool as H$$&LL
DDECs don't cause many problems.   My thoughts are that an MUI would suffer more from wear and tear...but DDEC is complicated to sort out if you have problems, and if you're not attuned to DDEC  you got more than a few minutes with some bailing wire.   DDEC is first thing that gets the blame when one runs out of fuel.   
May I suggest that you call a DD dealer and see if they would be willing to reprogram your ECM for your manual.  If they will, the DDEC wold be cool...if they won't...skip it. 
One very nice thing about DDEC DDs is the TPS throttle...fly-by-wire.  No effort at all.  And, as I believe Brian stated, cruse control can be enabled (probably already is since the road speed limiter is a function of the cruise), so cruise is a freebie.   That extra turbo HP would be cool as ^%%$^&%^* too!!  The end result would be unique.   
Post some pix of your ride! 
JR

[TomC]

If you have just the engine with the computer, it will be almost impossible to make the engine work with the gauges, sensors, etc.  On the other hand, if you had a crashed vehicle that you could tow home and meticulousy transfer each item one at a time and make sure each works, then go for it.  Otherwise, stick with the mechanically controlled engine. Any of the 71 series Detroits are THEE most reliable engines EVER made!  We will never see the likes of this kind of trouble free engine again since all engines are electronically injected for smog reasons.  Rebuild your engine to factory specs and you'll have an engine that should be good for 300,000 miles.  How many miles do you think you'll put on your bus in your lifetime of travelling?  Most likely not even close to the 300,000 mile mark. The only real advantage to DDEC is perhaps 1 more mpg, which I doubt you'd ever recoup with the low miles we do.  Stay with the mechanical and you'll have many miles and years of happy camping.  Good Luck, TomC

[keithshotrodshop]

I appreciate all the info folks. As an idea, does anyone know if you can strip a DDEC motor of all the sensors and like and put the old stuff on, kinda like simply taking fuel injection manifold off a small block chevy and putting a carburated one on? Or is there much more to it?

I do plan to put several hundred thousand miles in my lifetime on my bus, being that I'm only 27, I figure I have a good 100+ years of bussing left And I do plan on doing it all in my 47 silversides. The wife and I were discussing this the other day, by the time we retire, our silversides will be 100 years old! Now that will be cool!

I'm all for saving my stock motor, but rebuild quotes are all coming in over $10,000. If I do everything myself, 3,000-5,000. That means that alot of shops are WAY overcharging for labor in my opinion. When I worked at a chevy dealer, major engine/trans overhauls rarely were more than 20% of the parts cost. These Detroit guys are trying to get 100%+ of the parts cost. That alone is almost enough to have a guy swear off Detroits.

With that said, does anyone know of a shop who will do good work for a fair price within 500 or so miles of Detroit, Michigan? If not, I guess I'll just have to rebuild it myself.

Also, I still believe that my engine is not as "tired" as alot think. I went outiside the other day, it was around 30 degrees out, sprayed a small shot of ether in the intake, and the bus fired right up. The only smoke was white, and I attribute that to the burning coolant. What are the chances I could just pull the head, see if that is cracked or an o-ring is blown, and just fix that problem before doing a major overhaul?

[tekebird]

as point of reference on your engines condition......

the 6-71 that I replaced and my DD guy said he was supprised it was still running due to the wear on the cyl walls.......started when below 40 and when below freezing with either.

when cold (air temp) most DD will blow white smoke until they warm up a bit.

keep in mind when getting price quotes from DD dealers....most of these guys working now have never worked on or seen a 2 stroke DD.

give hassinger diesel service in Middleburg PA a call and see what he gives you for a price.  I think my new crate motor, swapping of all the bolt on stuff and bringing to highway specs was less than 12k

[gg04]

I have only put about 60,000 miles on the 671ta ddec in my 04...did the swap myself just buy the ddec trouble shooting manual for how to wire and codes...transit motor will be set between 280 to 300 hp....and around 760 torque. or at least thats where all the ones I have had were set. If leaving the original manual trans no settings need changed,,,If going to an auto use the one for the engine .. The ddec motors are just as reliable as the mechanicals...Currently still running original style radiator with 190 thermostats...no overheating even in 110+ weather...DDEC II is not a really complicated system just a few sensors and wireing to keep up with..and the motor always has the correct fuel running down the road...If you want more HP or Torque  just change the main box to one programable...Easiest swap for a old 6 banger GMC.. gg04

[keithshotrodshop]

You wouldn't happen to have any pictures of your conversion would you?

[gg04]

All I had left are posted under bus pictures on this board just did it...Any questions just ask....gg04

[NJT5047]

The heads are different on DDEC engnes...no gov, no racks.   Turbo pistons are different...using parts of the DDEC and MUI probably won't go well.   Turbo engines may not start as easily in cold weather either....little lower compression.
FWIW, the guages on a DDEC II are analog, and if you keep your senders, you could very likely reinstall and use your existing guages.   If you have a mechanical tach, that will have to be replaced, but the oil pressure, water teimp, and charge (ammeter or voltmeter) will work with a DDEC system.  The DDEC has it's own sensors for the ECM...separate from the guages.   Other than a low water, hot water (surge tank), and throttle assembly,  I don't think a DDEC II has any other sensors or separate systems.   If the DDEC engine had an electronic fan control, that would be part of the engine...."should" be part of the engine.    Cruise is just a couple of switches.   On-Off switch isn't special.   
DDECs are 12V neg ground...be sure that your bus is neg ground...some GMs were pos ground. Alternator and starter will resolve the polarity problem.   
There will be some additional wiring to the trans ECM which you won't need...nor will you need the donor trans ECM.   
The ECM is going to "look" for a com link between the engine and transmision...if it cannot find such link, it's going to set a the CEL, indicating a stored fault code.  The trans programming would have to be disabled.   The engine may work fine with the code.  But you couldn't clear the code so the CEL would be lit all the time.   
Still, if I were doing this engine thing, I'd give major consderation to keeping the coach and MUI...however, as one that uses an LT4 powered Astro Van for a daily driver, simplicity has its limits! 
Wish you were nearby, I'd like to watch the "transition"!
JR

[keithshotrodshop]

I just recieved the pictures of the 6L71TA DDEC motor from the person I'm thinking about purchasing it from, and it is a tight little motor! I really like how it is set up, and I think it may be an ideal swap into my bus. With that said, I guess I should make myself clear that my bus project is also a hotrod project, and almost everything on it will get a modification of some sort.

My current tach doesn't work anyways, so I'll get a new one. I would like to get some vintage hotrod looking gauges (united speedometer?) to monitor the engine, so I'll just get some that I'll know will work with my engine. Being that this motor is also a silver series is a nice touch, and I've been told that these motors with DDEC can be tuned electronically in the range of 350 horses. I'd love that, and I think it would turn an auto just fine.

[RJ]

Keith -

Get the whole powertrain, better yet, get the whole bus, if you can, and you decide to go the DDEC route.

Then you can use the auto trans, as well as the bigger brakes off the transit.  Linda might like that, too. . .

4.10 rear end gears are available, for 75+ mph.

With all the other projects you've got, what's another one?

But you'd better hurry - Arcadia & Bussin' 2007 is only five weeks away!!

[NJT5047]

Reprogramming DDEC II units is done by DD only.  Unless you know someone very well, don't anticipate that they'll bump up the HP.  I doubt it's going to go anywhere near 350 HP in any event.   You may see 6/71T in this range in watercraft, but...that's special.  6/71T is going to be closer to 215 to 235 HP...I believe.  I'm gonna look it up and see.  A good 6V92 is considered bus-maxed at 350 HP.  Could you stuff a 6V92 in there? 
In order to reprogram, DD interfaces with the factory, at which time the ECM downloads it's serial number and application and that is typically what DD uses as parameteres.  They don't make any modifications that would add to the emission load. 
DDEC II must be reprogrammed by DD dealer...they are not "adjustable"....DDEC 1 has a replaceable EEPROM, which is unique to DDEC 1.
An altenator tach would work fine....automotive guages will also work....as long as you don't need matching turbo boost...you understand that part...
My point here is to be sure you make contact with a DD dealer and verify what is available, for reference, regarding reprogramming the ECMs on DDEC units.  The engine would do a decent job at factory settings....and that may be all you get.
Good luck, JR

[keithshotrodshop]

Russ, you might think I'm someone else? My wifes name is Katie, and this is my only real project right now. Any case, I've posted the thought of stuffing a 6V92t on other threads on this board, and it's pretty much been shot down. Not saying I won't do it, but I'm exploring all my options.