12.7 detroit upgrades

Where o where did you guys find these numbers on cams and injectors to figure out which ones to get and not? Just picked up a 95 Pete 379 with the 12.7 and a 10speed drove home a 1,000 mile trip. Truck shifts great no fluid leaks but only makes 12lbs of boost gotta do some checks to see what’s up. Do different jakes equal better jakes? Anywhere I can look to see how to change cam and such very mechanicals inclined looking for more of the technical timing marks to line up torque and such ya know

 

Bobtail?

 

John, GREAT to hear from you, as always!

Thanks for all the info, I will try the additive!

I'm going to pu my truck today from my mech, he JUST put in 3.42 rears!!! What can you say, great minds think alike!

Will do on the turbo, and blue boots! I'll save my pennies and do that next. I dont think I have any issue with the manifold. I have heard some other 12.7 owners on TheTruckerReport suggest different injectors, a few who swear by a Bully Dog tuner as well. I've never owned a tuner, however as you know, I got a custom tune last year at The Diesel Dr and pretty happy with it. Not sure $2k for a display is worth it.

I'll let you know how the new rears go...pretty dang excited to get in it and drive. Had them freshen up the rears, truck had 1.5m on it, not sure rears were ever touched. New bearings, rebuilt power divider, etc. Only thing left original was the housing itself, and I'm guessing the axle.

 

Please pardon my long post...I am ONLY trying to be helpful, which is the purpose of this forum. I am not questioning your technical abilities or expertise in trucking. However, I must say, I am reading your questions, and, my guess is, this is your first truck??? Again, pardon me for assuming anything, and of course, we ALL know what it means to assume...makes an ### out of you and me!!! LOL!!!

First off, NICE truck! If I had my choice, an old Pete 379 would be right up there, and FOR SURE a 60 Series! Congrats on finding a true American classic and more so, one with a 12.7!!! Love it and make it your own! And, that motor will NOT let you down. But, like anything else, it is key to understand it.

Depending on what you paid for it, its current overall mechanical condition, and that you keep up with overall maintenance of it, it will likely NEVER be worth any less money than what you paid for it!!! Try saying THAT about a brand new truck from ANY manufacturer!!! All I buy is old iron. I have owned several different manufacturers trucks and motors...I have my favorites, the 12.7 is definitely at the top of my list.

Second, I want to point out, I am NOT a certified mechanic, however, I do have a technical background, and, for over 25 years have been a small fleet owner and now, a single truck owner operator, maintenance and having a solid understanding of the mechanicals of trucks has ALWAYS been very important to me.

So, regarding the crux of your situation....here we go!

WOW! 12 pounds is all the Pete can produce? What RPM's are you running it at? Not sure what work you will be doing, what you plan to haul with it, but, you probably can't do much of any kind of weight until you get that worked out! At a minimum, you should be able to produce 20-25 lbs. Perhaps THAT is why the previous owner didn't want this truck anymore. OR, you have a faulty gauge.

There could be MANY reasons for the lack of "oomph" your 379 has.

You now need to go through the process of elimination to figure out what is causing this.

The obvious way to go about it is, looking at and replacing things that are the lowest cost...for example, pull out the air filter, see if it or the chamber itself is plugged.

Next, replace fuel filters...you probably want to do a PM on it anyway so that you start out with fresh oil and filters BEFORE you put it to work. When you dump the oil, get a jar with a sealed lid, take the sample to the nearest Detroit shop, likely your closest Freightliner dealership, have the oil sample tested for contaminants. One thing I personally like to do when I buy a used truck is to drop the oil pan, get a visual inspection of the lower end of the motor, bearings, crank, etc. It is CHEAP insurance on a motor with unknown maintenance records to replace the rods, main bearings and get a good up close look at the crank. Depending on shop rates at your mechanic, it shouldn't be more than $2,500...if you can do it yourself, way less. Me personally, while I got the oil pan down, since I live in an area that gets pretty extreme low temps, I like to add an "in pan" oil heater while I got the pan down. You can get one of those at Wolverine Heaters, they are somewhere on the west coast, I want to say Oregon. They also sell a nice lineup of external heaters, I put one outside each fuel tank near the pickups and a little 100W sleeve heater for the fuel filters. I NEVER have a problem starting up in the dead cold, and often times, don't even bother to use the block heater. If your oil and fuel are warm, your truck will start right up, run smooth with no knock and warm up fast. Anyway, I digress. Also, check the pan itself for any obvious issues. 12.7 are notorious for having oil pan issues. But, it is an easy fix to replace.

Other things to look for, have the Charged Air system tested for leaks. All CAC's leak, the question is, how MUCH and how fast does yours? Obvious leaks should be something you can hear or feel, but, it's worth getting a read on where your at today, write it down, and then have it tested periodically to see if the system is leaking worst later.

Another quick and easy fix you should do before you put it to work, especially if the maintenance is unknown on your Pete, have the valves adjusted. That will quite and smooth the motor out, give it a bit more power and better economy as well. That is something you should do every so often, I know some people who do it annually, others do it in between in-frame. I have mine looked at every 100K.

There are some other things to do too...there is PLENTY of stuff posted here on TTR web site, or, you can go to YouTube and search. Water pumps, etc is what comes to mind right away.

My guess is, your low boost comes from the program for that 12.7. Depending on where you run or live, The Diesel Doctor is in Effingham IL and in NC is the best (and cheapest) I have found for DD and Cummins programming. I am sure there are others around who can do it too somewhere on TTR forums I found one that would do it if you mailed them your ECM. Obviously, you can't operate without an ECM, and literally, it takes the Dr no more than 15 min to upload their custom program. I cannot recommend anyone else since I have no prior knowledge. The Dr's tune significantly improved performance on my 12.7 and others who have posted here. You can search out posts regarding the Good Dr on this web site (TTR). Assuming you don't have other issues, your 12.7 is likely set up with the lowest performing tune, which is a measly 1,450 Ft Lbs of torque at 435/435 HP (you can set it up with different HP while on cruise control vs not). My 12.7 was set that way too. It was a DOG up even the smallest of hills or steady grades, very slow off the line and wasn't getting the kind of MPG it should! I had them bump mine up to the maximum recommended which was 550 HP and 1,850 Ft Lbs of torque. What an amazing and FUN difference it makes, AND it improved my economy too!

When I saw the Dr last, I asked if there was anything else they recommended for a 12.7 that would improve performance, economy and keep me running...they suggested a Borg Warner turbo and hardened manifold. I am sorry I don't recall the manufacturer, but, I am sure if you talked to them, they will tell you the same. I haven't done either of those to mine yet, not sure if I will touch the manifold until it needs it, but, the turbo for sure is one of my next investments.

The injectors would be something I'd mess with maybe AFTER you have done all this other stuff. If you had a problem with injectors, you would know it based on the performance, rough running, fluctuations in power.

Not sure about your question on your Jake's performance, or what you mean. Is yours not working right?

To answer your question in general, yes, you can improve the Jake's performance by putting in a different one. For example, I have owned a number of old Mack's with Mack motors...they were notorious for having almost non-existent Jake's. Turning them on, you could hardly hear or feel them. Now, I never cared that much, didn't run those trucks in hilly areas, so, I never bothered messing with them, but, the problem could be something as simple as an adjustment or they just needed to be cleaned. However, I am NOT a mechanic...I don't even play one on TV, however, this MIGHT be part of the problem with your boost! I'd have it looked at.

 

John, just an update for you.

I ran over 1,100 mi once I got my truck back this week with the 3.42 rears...I cannot begin to describe the difference it made dropping the gear ratio down from 3.90!!! It is like a TOTALLY different truck!

I now run at about 1,465 RPM at 70 MPH, not hitting 13th gear until I am already going about 60-65 MPH (depending how much I need to push it)!

I can fly down a 2-lane IL state highway, with all it's little (and some big) hills, valleys and turns, at 60-65 MPH without effort, and the motor is QUIET!!! FINALLY!!!

I don't know what I am getting for MPG but, I wanted to share this with you.

FYI - when I picked UP the truck, I didn't have my GPS on, which I generally don't operate under "personal conveyance" miles.

I got out on I-55 quickly, and was disappointed where the RPM's were based on what the speedometer was showing me...but, then I quickly recalled that it was always slightly slower than what we were REALLY going...however, no more than a few miles an hour at 70. This showed I was doing about 58 MPH at 1,500 RPM...BUT...I was keeping up with the 4-wheelers...so, I turned on the GPS...and, guess what, I was doing 72 MPH!!!

That means, my odometer is off too...CRAP! It never really dawned on me before.

I wanted to fuel up anyway so I could start a new trip on the odometer, so, I set the trip odometer on my GPS as well and checked both regularly! My dash is now off by a whopping 14.5%!!!

My guess is, before the rear end change, I was probably off around 5-6%, which means, when I THOUGHT I was getting 5.5 MPG, I was probably getting closer to 6, which, while a 12.7 is capable of more, maybe it's just the way I drove it....or, the 3.90 rears running at 70 MPH!

I haven't filled it back up yet....

The interesting part though, before, I could NEVER run more than 850-950 miles on full tanks. I know this because I, not once, but TWICE ran it out of fuel!!! I know...first time I was pissed at the fuel gauge and likely bad depth on the pickups, the second time, well, I was just mad at myself!!!

I will run a few tanks of fuel before I report back...this week I was pretty lightly loaded, but, more "stop and go than interstate driving making a couple trips from Oregon IL to Ft. Wayne and back. I have a load of polystyrene foam right now that goes up to Madison Monday, then back to my usual. The gauges connected to my airbags telling me how much I weigh barely moved! I really don't like driving around so light, especially in the wind and rain last night! Oh well.

Talk to you later!!!

 

@'07 KW w/53' Conestoga You will lose a little pull power on bigger hills, but over all I think you'll be really happy with the 3.42 rears. I've got a friend who runs to WI everyday in a day cab and I've been telling him for years to get 3.42 or 3.36 rears. He currently runs 4.10.

On another note, I would skip getting the bulldog computer. You already have a tune, spending the money on the bulldog is not going to gain you anything.

There's as shop in Minooka down the street from the Pilot that sells new Borg Warner turbo's for under $700. With the Dr's tune and a BW you will notice the extra boost and power. Definitely install a boost & pyrometer if you don't have one.

Glad to hear your getting the truck setup the way you like it.

 

Hi John, thanks for the info...whats the name of the shop in Minooka? My mechanic is in Channahon, Precision Truck Repair...Mark is the owner, nice guy, caring about providing quality service, very smart and easy to talk to.

Yes, the pull power is different, but, I have a 13 speed...drop half a year, I can make most hills in IL, drop a full gear and I'm good. I do notice needing LL on big hill with heavy load.

I appreciate the heads up on the Bully Dog...that's a big expense.

Definitely have (and watch) the pyro and manifold boost pressure. The boost gauge only goes to 30 lbs, which I can peg pretty easily. Maybe I should swap that for a bigger gauge.

I'll let you know on the economy.

You friend should DEFINITELY lower the rear ratio..,the savings in fuel will pay for it plus less wear on his motor = extended life.

My truck has 1.540 MI, and I had no records for rear rebuild, so, my assumption was it being original. So, I figured it was time to rebuild it anyway.

Mechanic said good thing I did, power divider had a chunk out of it...just a matter of time before it gave up.

 

R & S Distributing, 101 Industrial Dr, Minooka, IL 60447

I would swap out the gauge for sure. I'm getting 33-34 lbs at 1450-1500 rpm, 35 lbs at 1550 -1600.

 

12.7, 171702, GK series, 5915 injectors, Rebel127 tune- I try to keep it at 40psi or less. Couple times I caught it at 48 psi.

 

I'm coming up to the time to replace injectors. (I've replaced 2 of them already)
Is there a noticeable difference between the 5915 and factory injectors?