Hi folks, continuing the long slog to get a neglected old car back to usability. I had been making good progress but hit a bit of a snag recently and I'm not sure what to try next.

The car: 1982 300d, 120k on the odometer (no idea if it works). It sat for decades with I think WVO or biodiesel in the system and was pretty gummed up. It was running when I bought it but just barely, rough and it would not rev up past 1000rpm or so and could barely drag itself forward on a level surface. It did not smoke at all.

The symptoms now after lots of work (see below):
Engine starts well but will die immediately without throttle input, and won't idle without some throttle until its warm (around 80C by the dash). Even when warmed up if you rev it up and then release the throttle it will often die when it hits idle. It revs up fine once its warm, is a little laggy until then. Moderate blow-by (based on oil cap teakettles a little bit). A litlte smoke from the tailpipe, almost none once warm. Air filter assembly has a SERIOUS vibration when cold at idle -- I worry about my bracket. Engine sounds pretty good to my ear. Idles at around 700rpm per the tach, I have not checked it with a laser. The issues persist even if I idle the car for an hour so things like residual air in the fuel or bad glow plugs seem unlikely.

The major relevant engine stuff I've done so far and any notes:
- new fuel tank and screen (old ones completely gunked up and screen plugged, didn't even drip when i cut the line)
- tank vent line cleaned and checked
- new fuel cap gasket (they seem NLA now, i made one from 3mm viton sheet)
- new tank pads (they're NLA i made some from neoprene foam, see other thread)
- fuel sender rebuilt (seized, ground corroded away)
- steel intake and return lines cleaned out (they were clogged with black polymerized fuel)
- new rubber fuel lines under hood
- lift pump rebuilt (old one gummed up)
- new hand primer (old one leaking)
- fuel pressure regulator banjo rebuilt (old one disgusting, spring was too compressed to provide good pressure, couldn't manage to bleed the injector hard lines until this was done)
- new fuel filters (x2)
- diesel purge (x2 including letting system soak overnight with purge in the system)
- oil changed, oil filter changed (oil level was 3 inches above high on dipstick when I bought the car, not sure if overfilled or making oil -- oil was dark but did not look contaminated, not milky, and no visible metal fragments)
- air filter assembly rebuilt, new bracket, new mounts, new filter (old one had no rubber mounts left, was held down by baling wire)
- valves adjusted (all valves initially very very tight; looked nice under valve cover, camshaft lobes looked immaculate)
- timing checked = ~2 to 2.5 degrees (based on lining up marks on cam gear sproket spacer)
- new firewall throttle pivot ball, throttle linkages cleaned (old ball disintegrated)
- rack tension bolt backed off a little, it was almost fully tightened (i wanted to replace this but its NLA now)
- new battery (H8 AGM, old one stamped 2002)
- new fuel (with healthy dose of startron and marvel)

Engine stuff still to do or that I haven't touched at all yet:
- injector rebuild (I suspect they aren't great given the state of the rest of the fuel system; I have the equipment to rebuild)
- italian tuneup (brakes dont work yet so no road testing but I'm sure it would help, there has to be a lot of deposits to burn off)
- idle setting (idles at 700rpm roughly per dash tach)
- vacuum system (a lot of the rubber vaccum unions under the hood are cracked and suspect; the car does shut off normally with key and the locks do somewhat work)
- ALDA
- intake boost pressure banjo and air line (definitely clogged, I can see it plugged 8 inches up the line towards the firewall)
- plastic "clear" fuel lines (so dark I can't see through them but not obviously leaking. can't see to confirm no air leaks, i bought a couple sizes of tygon to replace the line with)
- crush washers on various fuel system banjos (the aluminum crush washer on main fuel filter bolt definitely leaks air bubbles when I prime the system, not sure if that means it sucks air also)
- throttle linkage adjustments (there isn't much play but I noticed the linkage to the inside of injector pump did not have a tightened lock nut on the upper end, suspicious, not sure what a long forgotten PO was up to...it does seem to have full range on pedal)
- injector pump drip timing
- compression test
- glow plugs (i bought replacements but hasn't been a priority)

As of now I'm mildly worried about air in the system, since I can't see through my "clear" lines and I know the fuel filter bolt does bubble a little air under pressure. I also suspect my injectors need replacement but not sure if that is causing my current idle/power issues. And I'm not sure if there is a vacuum issue that could be causing these signs, the vac system is complicated and highly suspect. I'd appreciate some advice about where to go from here. Thank you!

"steel intake and return lines cleaned out (they were clogged with black polymerized fuel)"

If the fuel return line was gunched up I would suspect the inside of the fuel injection pump is gunched up.

Also, on the emission sticker on the car it has the max idle speed. If I remember correctly it can go up to 850 rpms. And that is with a new engine. An older engine may take a bit more rpms.

Did you rebuild the Injectors?

You may not need this advice, but other people read these threads. Keep the 2 parts of the injector nozzle together as they are a mated set and also it is usually easier to set the opening pop pressure of the injectors if all of the parts for one injector are kept together.

The injector nozzle that came with the car have 2 small passages in them. Mine without WVO were entirely plugged and it effects the idle because the idle fuel is supposed to go through the tiny passages. See the attached picture.

In the last attached picture, you see the injector nozzle end with the tiny passage drilled down the center.

They did not have this type of nozzle when I worked in a fuel injection shop. But we had a set of different sizes of music wire and when I had a passage, I needed to clean Cabon out of I ground a hypodermic needle type tip on it and very carefully sort of drilled out the carbon. Note the wire needs to be smaller than the passage and it can get stuck and break off.

After that the parts went into an ultrasonic cleaner.

Attached Thumbnails

   

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84 300D, 82 Volvo 244Gl Diesel

The return line was clogged at the tank end rather than the engine end, I'd guess probably molassess-like sludge moving in via gravity while the car sat. That said, I'm sure the inside of the IP is not pretty, after all the inside of the fuel pressure regulator bolt was pretty gross and that is basically inside the IP But taking the IP apart isn't a very good option and a rebuild (if even possible to have done competently anymore) is probably considerably more than I paid for the car and thus a last resort. I will say I get fuel to all five injectors when I crack the hard lines so it is at least doing that much.

I have not rebuilt them yet, I am 100% sure they are gunked up given how dirty the fuel system was. They are on the list. Thank you for that advice, very helpful gotchas. I wasn't sure how likely injectors were to be the cause of this issue so I was hesitating. I have the pressure test setup from a certain mercedes resource in coastal washington and some new nozzles that are claimed to be rebadged Monarks from the same outfit. I figured by changing the fitting on the tester I might also rebuild injectors for my old truck and a couple old tractors that need them too.

There is no exact way right now to know what is causing the idle and dying issues.

Best of luck.

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84 300D, 82 Volvo 244Gl Diesel

Hello again gents (and ladies). I've made some progress on this vehicle, but it still idles rough especially for a while on first start. I've done a bunch of work since last update:

• put in a set of rebuilt injectors (eBay)
• replaced glow plugs, carbon removed from prechambers
• replaced the line on the 3 "clear" fuel lines running from the fuel filter housing
• cleaned, lubricated, adjusted all the throttle linkages per service manual
• adjusted idle to around 800
• new vacuum fittings everywhere in engine bay
• new viton injector return lines
• backed out rack adjustment bolt on IP all the way
• new stiffer spring in the overflow valve banjo on the IP
• tested with vacuum shutoff valve line disconnected (no change)

It runs a little better now, in that it takes less time before it will run without throttle input and once hot if you rev it up it won't stumble when it comes back down. I think more than half of the improvement was just raising the idle. But it is still running quite rough and is a bit slow to rev up. I've been running on 15% methanol (through a small temp tank in the engine bay) trying to slowly dissolve the WVO residue in my IP.

I bought a fuel pressure gauge and fitting to "T" into the line from the lift pump to the filter housing to sample pressure but haven't done it yet. I did rebuild the lift pump a few months ago however.

One new thing I have noticed is that there is a surprising amount of air in the return/overflow line from the IP. More than I would expect. I can't tell where this is coming from since there does not appear to be any air in the clear line from the lift pump to primary filter housing, nor in the line from the primary filter housing to the IP. There could be some residual air in the IP from the system being open but it has been idling a few hours and its still there (worse, actually). See video (you can also hear the engine in action):
https://youtu.be/B2v1oxyx_uI

I'd love some thoughts on what else to try and speculation on the origin of the air from the IP overflow/return line.

Oh, there's one more smaller hard plastic line that exits a banjo from the outboard side of the IP towards the back and runs forward in the engine bay somewhere under the PS pump. What does this serve? I didn't replace this line yet.