JoeH

Dumb question, are your starter cables and wires tight?

This truck is a ***** to work on the engine. I really like my MR688.

https://macktrucks.vg-emedia.com/ProductDetail.aspx?ProductId=6147 Go to that link and click "View File" in the item description. It'll download the book for that engine. Page 401 starts the Valve Adjustment Procedure. Follow it to a T.

Don't know about other DM's but this one definitely has 2 cylinders cooking away inside the cab.

Frame depth taper is from about 13 or 14 inches just behind the cab down to about 11 inches for the rears.

Here's some DM pictures for you @mrsmackpaul

1980 DM686SX chugging away at a screaming 1700 RPMs blowing cement into our silo. Even in retirement we find tasks for our old trucks. Our sand/stone hauler loads our trailer for us then we unload it at our convenience. We go through anywhere from 1 to 4 loads per month depending on demand and season.

Interesting air filter pipes on the R model, I knew the rear cab corners were different on Iranian R's but hadn't noticed the different filter housing ductwork.

So the truck is finally running right. What started out as replacing the heads turned into finding 3 bad EUPs, 2 bad EUP rollers, and one bad injector nozzle. I haven't heard the truck running in person yet, but dealer shop foreman says they finally got it straightened out. When they replaced the heads it still had the miss, so they did a cylinder cutout test and found 2 weak EUPs. One was failing in the solenoid, the other the spring was broken into 5 pieces. I picked up 2 aftermarket reman Bosch EUPs from Metro Fuel Injection im Allentown, dropped those off and told the foreman to pull the rest of the EUPs to inspect. That's how they found the 3rd bad EUP and the 2 bad followers. One follower has a chip out of the top of the cup, the other follower the roller's axle slid and the roller cocked a little bit. They had to weld a long stud on the one follower as a handle to get it out. Back to Metro for another EUP and 2 followers. Got all that in, still had a miss on #3, they swapped EUPs, miss stayed on #3, so they wanted to replace that nozzle. New nozzle and it's running good now. I think we can all agree I got lucky the camshaft survived. For now. Now they're just chasing ABS codes it didn't have before the rollover. Hopefully they get it straightened out today.

IDK, I ran into this on a 2000 or 2003 e7.

Sorry for taking so long to respond. RD model windshields/firewalls leak water and ruin the VECU. EECU is waterproof, VECU is not.

The two hot wires threw me for a loop when we were getting a spare engine running in a parts truck we bought. It uses a switched ground to run the solenoid. So both sides will test hot, but the power can't travel til you supply a sufficient ground.

Measure inside of the CAC rubber boots, if it's same as my '95 RD then two 4 inch pvc pipe caps should fit in there, one on inlet, one on outlet. Mount a tire valve stem on one and pressurize it. Should hold up to 35psi with no leaks, but if there's a leak you'll hear it quick. Does this turbo have a waste gate? Your waste gate could be faulty, which would explain sudden black smoke and low boost.

On the contrary, she's their insurance policy. He's 100% not in control, and if he keels over it's pretty obvious she's not in control either. Whoever is pulling the strings will keep right on working.

You'd need to pressure test it, not just smoke test.

What chassis is this? Probably not an RD600, but the charge air coolers on RD's do tend to crack along the seams where the core mates to the tank. But this shouldn't yield the popping sound in your exhaust, just the low boost. My '95 RD688 went down to 21 psi max til I noticed it had cracked.

How are your oil seals on your turbo? Do you have oily soot in your exhaust or oil in your intake pipes?

I'm wondering if there's a fuel delivery/ignition issue? Loading up fuel in one cylinder from poor atomization in a failing nozzle, or there's a hot spot on one piston that occasionally causes an untimely detonation. Our 1979 endt676 had a slight miss when my dad bought it, wound up being a piece of silicone stuck in the piston cooling nozzle. But that was before I was born, so just anecdotal on my part... Just throwing out dumb ideas...

I know you're working on the Volvo engine, but at the end of the day they all do the same thing.

My 2003 ai350 had a loose EECU fuse. Check your fuse boxes and see if wiggling your EECU fuse helps out. Also check your battery voltages. The vmac iii EECU shuts off around 9.5 volts, so if your power drops notably while cranking then you could just have battery issues. It's possible your alternator died and batteries dropped down, but I assume that'd trigger a code....

Im 5'11" and the backs of my knees start to burn when I reach down halfway down my shins, lol. 15 years in R models has shortened the tendons and muscles on the backs of my legs! The +3 can was likely introduced at the same time Mack went from the steel dash to the plastic curved dash.

Cabs are the same on U and DM. However, the R/U/DM cab started out early as a "flat back" cab, then they updated the cab to a "+3 inch" back wall. They added 3 inches to the back wall to allow more seat room. Not sure how long the U model was I'm production, don't know which backwall our U had, i gave the cab off to someone on here some years ago.

Saw one in person today for the first time. Awful, lol.

The frame rails on my dm686sx are 3/8 inch thick, both inner and outer. So each side has 3/4 inch total frame thickness.

We cracked one frame rail vertically on our 79 R600 at the frame splay, and had a 1976 U600 parts truck. Cut each rail (broken and donor) behind the cab, welded them together and put a sister plate (which the truck already had bolted to it) and everything lined up perfect. Spring mounts, steering gear box, shock bracket, etc.