Double Yellow's Company Driver to Independent Thread

Bad news: the mechanic says I should do an inframe.

The background: After retrofitting an engine brake into my 2000 Detroit 12.7 (in April), I've had some intermittent wiring gremlins pop up. I also had fuel dilution return after two spotless samples (no idling on any of them).

Symptoms: Engine starts running a little rough, like it is partially down a cylinder, and the check engine light comes on. Anywhere from 15 seconds to 15 minutes later, the light goes off and the engine runs smoothly. Flash code was 61 -- injector response time too long.

The shop diagnosed a chaffed harness and an intermittently bad #5 injector and recommended replacing both. That sounded reasonable to me, but given their age (they were replaced ~750,000 miles ago) I asked to replace all 6 injectors as well as the cups (advice I've seen here and heard from KR's show).

The shop didn't really think replacing the cups was necessary and advised me that the head would have to come off to replace them. I did a quick google search and confirmed that the head does have to come off to replace 12.7 injector cups. Despite that fact, it seemed close to an internet consensus that you really should replace cups when you do injectors. So I gave the shop the go-ahead.

Once they got the head off, the shop called asking me to come down in the morning. That's never good, so I prodded them for more info and they basically said that they'd recommend I do an inframe. I will take a look myself, but I think I heard something about a "scorched" piston and liner.

Now I've rebuilt a few gasoline engines over the years and could spot some obvious melted parts, a gouge in a cylinder wall, worn smooth crosshatching, etc -- but is there anything else I should look for? I mean if I just see a bunch of carbon on one piston and the top part of a liner, wouldn't that be consistent with a bad injector?

The shop came recommended from someone I trust and the mechanics and staff seem honest (well, aside from billing ten cans of brake cleaner on a prior A/C expansion valve & dryer replacement, but the total bill was reasonable and the receptionist assured me that wasn't a typo -- that mechanic just really likes brake cleaner).

What gives me pause is the fact oil consumption is minimal (1 gallon over 15,000 miles), zero coolant loss, the oil samples don't seem to show crazy wear metals, and the fuel economy has never been better. It also runs pretty smoothly when the malfunction light goes off.





The sudden jump in fuel economy recently has been an uneasy surprise since it doesn't correspond with any modifications and the weather in May wasn't significantly warmer than April. I mean I expected it to be around 9, but lately it has been over 10 with some regularity. I even joked to friends and family that I hoped this wasn't like the rally hospice patients often experience shortly before death. Guess fate doesn't like tasteless jokes...

On the other hand, I've never been impressed with the compression braking of this engine (even after the jake brake was installed) and, as a 370/430 horsepower model, it isn't a powerhouse under acceleration either. Aside from test driving absolutely junk, I'd never really driven a 12.7 so I don't have a frame of reference aside from ISX, DD15, & Maxxforce (all stronger).

No, I've never dynoed it -- It ran well enough and was cheap enough that I could have done a rebuild right after buying and still felt OK about the purchase. It's just the better it ran and the cleaner the oil samples, the more convinced I was that it had 200,000+ miles of life left.


Questions:

What should I look for when inspecting the engine?

Is a 2nd inframe even advisable? I heard somewhere that you want to do an out of frame overhaul between inframes... According to the prior owner, the 1st inframe was done when a head gasket let go at ~700,000 miles and was a "while we're in there" type of thing more than a requirement.


I plan on having this truck at least through 2017, and possibly longer (if I decide to leave California).

Paging @Heavyd & @Pablo-UA

 

Thanks.

I should also add that the engine starts easily, even after sitting for longer periods (weeks), which I think would be counter indicative of a worn engine (especially when combined with a lack of oil consumption and/or smoke). Nor does the coolant temp climb except when heavy on the longest of grades (and even then it never exceeds 210 which is when the fan comes on).

 

The other uneasy thought: whether it is all my fault and the old guard is correct in saying 1200-1250rpm is too low of a cruising rpm (I cruise at ~1225 when power demand is less than 150hp).

Possible, but I don't think a harness would cause fuel dilution.

Then again, KR says a "level 2 flag" is still OK (Polaris says <4% is level 2, Detroit says discard oil above 2.5%)