Adding a new original Volvo diesel filter worked, the described issues disappeared (immediately...but later I had to learn: they were gone only temporarily) and after the quick fix of adding a filter I was convinced that a clogged filter was the source of the problem.
Well, it wasn't.
After the new filter the car ran great on the test drive. I filled it with ATF, bled it just a bit and idled some time then ran the car on higher rpms for a short ride. Because I bled it it ran That okay.
Only a couple of miles....but already the feel of the car, acceleration and the sound of engine was so much better than it was with the previous (relatively/technically new) fuel filter. I was convinced.
I could though *still* feel something wasnt totally right and I thought something was dragging or holding car (or the engine?!?) back from being 100 happy. That was the case.
Later I learned that I thought of "big things" but not the simple ones!!....
When I added the new filter, I wanted to adjust the idle too (suddenly sounded a bit low for some reason) and thought of doing something around the throttle linkage too because the pedal play never really felt right these days.
The actual repair then got postponed and only many days later I had the real time to do adjustments. Luckily. And I found it.
When I took a closer look at the ip area on another day, trying to remove the throttle linkage that connects ip to the throttle spool, I spotted a fluid leak at injector #5 and nearby. It was diesel fuel. Not much but seeping and enough to "paint" the surroundings wet/shiny.
I immediately thought it had to be the black injector return line(s) being loose, deformed, damaged, etc. But they are literally new and the proper German type also, installed correctly and gently with care.
When I pulled the hose, it would not want to come off the injector, instead it just popped out of it, the nipple part still in the little hose and a now a "hole" in the injector
I said wow but I didnt lose my mind... This has happened before...my fault! When the injectors were put in, gtd new 170bar ones btw, i havent had the proper tool so i used a SnapOn 27mm that felt right but it wasnt the best. It bent and pushed in (down!) several of the injector nipples.
It touched and bent most of all injector nipples on almost all injectors.
I fixed the injectors soon after, left #5 untouched because that time that was a dry one.
Now, months later, I found that leak and did the same little project:
Removed the return hoses from the injector, chemically dried it, let it sit safely so dirt could't get in, touch up the nipple w extremely smooth sand paper and clean it all over again, dry it, then
JB Weld nipples back, by adding just a touch of glue and push it in then create a nice ridge at the bottom of the injector nipple so it holds and looks alright. Then wait a day, have it all covered/protected from *any dirt that might get in.
A day later, I reconnected the black injector return lines, using a new piece, of course, bled the system again at the filter (idk why) and up at the injector hard pipe on the top too.
Car is equipped with the in-tank fuel pump that the gasoline Volvos use in there. It helps the pump and it helps a lot (or some) when/if there is any air intrusion anywhere.
In the past, I often saw air in the transparent fuel line in the mornings...the line that connects ip and filter but i never paid much attention bc car always gets it through with a single touch of the key (before even starting).
Only later I explored that when/if return line on #5 is touched (car not running) , air between ip and filter reappears. So I sealed inj #5 and calling it a day.
The brick runs AWESOME, the turbo used to spool too early and way too high but no real acceleration happened and the car was unresponsive and rpms topped at 2700-3200 in 5th gear (m46)...(problem gone!!!), engine now sounds smoother, balanced, high speed low rpms are gone, i can rev it anytime and turbo responds and sounds totally differently, no leak at the injector. Super peppy and the linkage was adjusted too so the pedal play isnt that sick anymore. I would like a quarter of a turn on the pump now. Just to see what it does. Or I will check and readjust timing first (add 0.02 probably)
#5 had one nipple jbwelded earlier so it took this much time for me to spot the problem (i first thought i did all 12nipples back then... but only did 4injectors= 4x2, plus one of the 2 of injector#5...#6 didnt need them fixed.... i learned the hard way now lmao)
I really like how it runs. Back to life...amazing. Air in fuel limited everything and as we know it: the tiniest amounts count!
Get those ugly dry rotted return lines off asap, dont let air create running issues...trustme it sucks to drive a d24t and think that it is how it supposed to run
)))) "it is an old car...diesel...etc...it is warm/cold out" etc
lol..not true! Runs like a real champ now. Always ran good but now it runs great again. Plenty of power and a real joy to handle. Small adjustments are coming.
The thing is, they run so simple and are so oldshool and also they do tolerate several issues for such a long time (including worn rings for example, high oil consumption, etc, they even run ok with low compression, for years, misadjusted pumps, all sorts of leaks, extremely high miles etc) ...nice engines, really.
))