mr.mindless

I'm new to the Cummins world, and to fully mechanical diesels. I just traded my '02 Jetta TDI 5sp for a '97 3500 DRW 4x4 CC LB 5sp.

The truck has just under 242,000 on it and as of Sunday has a brand new head on it. About 2 weeks ago severe oil contamination was found in the coolant, the head was pulled, cracks (4) were found in valve seats, and the head was replaced. Hone marks still visible on cylinder walls.

Along with the head it got upgraded exhaust springs, and a 4k GSK was also installed along with a bunch of fresh gaskets.

It supposedly has the pump "turned up a little bit" (from 2+ owners ago) and an upgraded clutch.

So far I've only driven the truck with about 9,000# on the hitch. This was through the mountains of PA on 147-180-15 to 86 and 390 in NY for those of you familiar with the area. Mostly interstate quality roads with 65mph limits and a decent number of grades in the 5% area. Nothing stupid steep since it tops out at all of 2600' but lots of up and down.

I've got a couple questions for those more familiar. I've seen these things discussed in a couple other threads and I'm sorry for the rehash but I haven't quite found what I'm looking for yet.

boost - cruising at 70, when it's at WOT climbing, the boost is very steady but not at a fixed number. Some hills it's at 24, some it's only at 21. It looks like a vacuum actuated waste gate so I'm confused why this would vary. It seems rock solid at whatever level it picks.

EGTs - post-turbo. no matter how hard I beat on it I could not get it over 800˚. It's got a mostly stock exhaust: 3" DP to 3" to a 4" muffler and stock 3" tail pipe. No cat. That seems really low to me. I was expecting slow creep up as I climbed especially on the longer grades but I never saw over 800˚.

shifter - I had it pop out of 5th 3 while coasting downhill with no load on the shifter. it was still in the gate but not engaged. I'm guessing there are some bushings in the tower that can be replaced to tighten up the shifter and keep it in gear better?

RPMs & power - with 4.10s and near-stock tires this thing is screaming, relatively speaking. In 5th, 2,000 is 57mph. I'm near 2500 cruising at 70. I don't have a good feel for my power band yet but I feel like I'm way above it at interstate speeds. It doesn't take much to bring me down to 65 from 72, but it takes a LOT to drag it below 60. I found that when I'm being slowed to 60, downshifting to 4th (and about 2700 RPM) gains me _nothing_. Absolutely zero change in anything other than RPMs. Boost stays the same, EGTs stay the same, speed trend doesn't change at all. If I'm slowly loosing ground that continues, if I'm slowly spinning back up that continues. This seems oddest of all to me unless it's really out of breath up near 3k. I spun it up to 3300-3400 in lower gears and it still pulls up there with the 4k GSK, though not as well as at say 2300.

I guess as it stands I need to learn to drive it, but some pointers on the power from those who know would be good. I'm not looking to throw a ton of money at this thing right now, I need to get a trailer of my own first. I have a test route worked out so I can compare different loads and different performance levels. I guess ideally I'd like to move the powerband up the rev range a bit. I was also throwing around the idea of borrowing 2 35s and throwing them on the back to see what a swap to taller gears would feel like. It would look extremely hokey but at least give me a reasonable idea of what ~3.54s would feel like, and let me know if it's power I'm lacking or if I'm just out of my power band. It needs new drive tires anyway so now would be the time to make a tire size change too.


Thanks for any insight.

bob95065

I have had my truck for two years so I am sure there are others that can answer your questions a little better.

A pyrometer probe installed after the turbo isn't as accurate as one installed before the turbo. It is safer because if anything were to happen to a probe installed pre-turbo and it broke the broken piece would go through the turbo and cause damage.

That being said you may want to check the forum for how to get a rough idea of what your pre-turbo temps are from readings of your post-turbo probe.

Driving these trucks is a little different than a gas vehicle. My experience has been that my truck is happiest at 2000 RPM. I have 1:3.55 gearing so I am going a little over 60 MPH at 2k. I generally set my cruise control at 60 MPH and get 21 MPG. I figure if I wanted to go fast I should have bought a gas truck or a sports car. I am sure there are others who disagree, but this is what I have experienced with a mostly stock truck.

The most annoying thing I experience with my truck is the wide gearing between 3rd and 4th, especially when hauling a heavy load. This is why they went to a 6 speed transmission later. It won't be as pronounced with 1:4.10 gears as it is with the 1:3.55 gearing. That is the only problem I have with the transmission.

I haven't heard of a 5 speed jumping out of 5th, however loosing 5th gear is a common problem. Search the board and you will learn all about it and ways to fix the problem.

The best thing you can do would be to start reading the two boards for your truck (powertrain and non-powertrain). That's what I did and I learned volumes. There is a lot of knowledge to benefit from here.

Bob

mr.mindless

the 5th gear nut on this truck has been taken care of, as has the KDP.

I'm doing a lot of reading already, but coming from a fully electronic 1.9l with a variable geometry turbo, I have a lot of catching up to do. I figured I'd throw my questions out there and see what I could be fed while I dig

Your 2k comment jives with my brief experience and furthers my assumption that I'm simply overgeared for cruising that fast.

bob95065

If I need to go somewhere fast I drive my car.

I hated driving on the highway when I first got the truck because it liked staying around 2k which meant 60 MPH. Now I don't mind it at all. In fact, I started driving my car at 60 MPH and get 2 to 3 MPGs more than before.

Tate

Check what plate is in your truck? If its stock, or something like a 10 plate, it pulls fuel out of the top end, which would explain why you don't accelerate any when you drop a gear.

infidel

950° post turbo is about the highest you want to see.
800° is fine.
Rule of thumb is post is 300° than pre but I've seen up to 500° difference at times. That's why post can get you in trouble if you are modified.
Personally I'd move the probe if your pyro reads high enough.

Just a tail or head wind will effect boost, doesn't take much change in grade for the readings to be different.

As you are finding 4:10s leave much to be desired unless you are towing heavy all the time.

mr.mindless

as I expected when getting this truck. This will be doing some daily driver duties but I bought it to pull, and 9k is about the lightest I'll be. I'm trailer shopping now, I'm hoping to test tow a 12k soon as I'm considering a setup that will be pushing 14k, and this is through east coast near-mountains....


I'll do a little digging and learning on the fuel plate, thanks.

BigErksG2

Add a boost elbow to get your boost up and as mentioned before, a fuel plate would help. I like the 100 profile personally. Bumping your timing to 16* would also help with top end power.

infidel

You'll learn a lot here> http://dieseldatabase.com/read.php?id=58

Many folks, me included, find the #10 best for towing.
Plates on ebay seem to be high quality and are many times cheaper than you'll find anywhere.

G1625S

welcome to the site, Mr.Mindless! Where abouts are you in the northeast? I'm near Binghamton and am always willing to lend a hand, etc. It doesn't sound like the 4k springs were installed. I just put mine in last week and even at stock timing, the tach just flew to 4 grand in the blink of an eye. Now at 16*, it's snappier yet.

mr.mindless

infidel, thanks for that link. Its 90% of the IP info I wanted in one place.

having now put some miles on unloaded I can assure you that the 4k kit is in there. It's like a 7,000 pound sportscar heading up an onramp, and it's still pulling at 3600 which is about the fastest I've let it spin. Are they okay to 4 grand? I have upgraded exhaust springs and stock intake.

I have no complaints at all (aside from seeming to need a thermostat, it's running COLD) as a light hauler. Pulling heavier, I need to at least move the plate if not grind or swap it, and see where my timing is and move it more towards the 15-16˚ area.

I'm also looking at tire options to bring my revs down a bit, it needs drive tires now so it's a good time. Cheaper and less permanent than throwing two sets of 3.73s in it.

I'm in Rochester NY.

mr.mindless

Ha. Or not.

tall skinny tires are tough to find. and a set of Rickson 19.5s and tires to bring me down about as much as going to 3.73s would set me back about $3500. That's a lot of gear sets, especially when I know how to do them myself. Hell, I think that would pay for a GearVendors OD wouldn't it? Yeah, it would..... They run about $3000.

So much for that idea. 4 new 235/85r16s just got much more appealing

G1625S

Wish I'd have know you were so close, I just had a meet and greet at my place a couple weeks ago. Might do one more in mid fall if I can get caught up on work. My buddy just put 19.5's from a bread van (came out of Syracuse, I think) on his 95 3500 with 5speed and 4.10's and is loving them. They're not real hard to find, if you look around. Think he gave 300 for them with decent tires. Little rattle can spray bomb and they look respectable. Either way, sounds like you need some more fuel for the heavy loads. Most I've ever grossed pulling around here was about 22k, but I've got 3.54's and 315-70-17's. Still pulled the load over the hills on 90 in Mass. My pump is fairly molested. Never use much more than 1/4 throttle to keep boost around 35psi

STate

Depending on how cold your temp gauge is reading, I never see mine touch 190* unloaded. and while loaded Ive never been past straight up at 190* These engines run a little cooler than gassers.

I know you have a dually, so I dont have any direct experience with tires. But I wonder if a 255/85-16 might be a good fit? They measure out at around 33 in tall and just over 10"wide. Maybe someone on here w/ a dually will chime in and say if they'll fit without needing a spacer.

mr.mindless

those certainly won't fit comfortably without a spacer on the stock wheels. I only have an inch between 235s. a 6" wheel is pretty narrow for a 255 that spends 97% of its time on-highway too.

by running cold, I'm talking thermostat stuck full open. just off the peg reading 140-145 going down the road, coming up to maybe 160 at stop lights and in town traffic under 20mph. windows up heat on full blast in 65˚ weather for 30 minutes and it's not hot in the cab. I'm pretty confident the gauge is correct and my tstat is not.