diagnosing '78 240d engine failure - PeachParts Mercedes-Benz Forum

AZ240d · #1 10-07-2014, 10:06 PM

What Happened:

Prior to the engine failing while driving, the car was having trouble starting for the first time each day (I live in AZ, ambient temperature was not really an issue). Subsequent starts would be easy (while the engine was hot) and the car would start right up. Each day the car seemed to have a harder and harder time initially starting (would turn over for a good 60-90 sec before starting) until eventually the car would need to be turned over for so long the battery would drain and the car would need jumped. Then one day even jumping the car would not start it, and it was stuck at a friend's apartment complex. I replaced the braided fuel return lines, primer pump, and fuel filters and primed the fuel system and bled the hard lines leading to injectors. Still nothing, even when jumping the car. In an act of desperation to avoid towing the car I decided to use the old WD40 as starting fluid trick. Sprayed WD40 in the air intake (took off the air filter housing lid to bypass the air filter) while my friend turned the car over and it started right up. The car ran 10-15 min while I put things in the trunk / got ready to drive home. After a mile of driving at 45-50 mph I notice dark smoke coming from the exhaust, then out of nowhere the engine revs uncontrollably high as if i had shifted into first and slammed on the gas (the car has a 4 speed manual transmission). I immediately let off the accelerator and push in the clutch, the revving did not go down immediately but went down after about 5 seconds. Once the engine rpm's went down there were a couple banging sounds (may have been metal on metal, may not have been it's hard to say) and a bunch of smoke from under the hood. Prior to this there was also no rod knock when the engine ran. Also, after pushing the car to a parking lot I noticed the temperature gauge was very high as if the car had over heated. The next day I inspected the radiator and it was still full of coolant.

Now:

There does not appear to be any water / coolant in the oil nor oil in the coolant (so not a head gasket issue?). The oil was not completely dumped from the engine (as sometimes / usually happens with a thrown rod). There does appear to be a bunch of oil coming from the valve cover gasket on the rear / passenger side of the engine. The crankshaft does turn when attempting to start (car turns over so not a timing chain issue?). Engine will not start at all, just as before (sounds the same when turning over, no weird noises / metal on metal etc.).

Any ideas as to what may be the issue(s)? Any help would be greatly appreciated, not sure if this was catastrophic or not, and I haven't had time to take the engine apart yet.

spdrun · #2 10-07-2014, 10:09 PM

Some sort of injection pump damage (explaining the hard starting previously)? Or you could have had a failure that allowed the engine to suck oil in (rings?) -- read about diesel runaway.

bricktron · #3 10-08-2014, 12:57 AM

i would take off the valve cover and see if the chain, cam, and valves are still intact. it would also be instructive to check the oil filter for metal debris.

AZ240d · #4 10-08-2014, 01:27 AM

Thanks for the input, it's much appreciated. Just a heads up, I work 40-50 hours a week and am in college full time as well, so updates concerning what I find using any suggested advice with the engine dismantled will likely come this saturday / sunday (oct11th / 12th ) and subsequent weekends if necessary (depending on what damage is found). I'll definitely be sure and keep everyone reading / helping out posted. Thanks again.

t walgamuth · #5 10-08-2014, 07:25 AM

Yes to all of the above, though I cannot think of fuel injection pump failure causing the symptoms you describe. I'd also do a compression test if no other physical evidence of catastrophic engine failure is found.

moon161 · #6 10-08-2014, 12:02 PM

Differential diagnosis for runaway is bound throttle linkage, tho 240 usually doesn't smoke dark till wound out and starved for air.

uberwasser · #7 10-08-2014, 12:29 PM

Where in AZ are you? If you're nearby I can help put a second set of eyes on the situation.

cooljjay · #8 10-08-2014, 05:45 PM

Chances are you needed a valve adjustment. Another good possibility, is when you installed the new return line, it got hung up in a place that caused the linkages to bind...

nelbur · #9 10-08-2014, 06:00 PM

I think the runaway likely came from a quantity of WD 40 laying in a low spot in the intake, which got swept into the cylinders when the engine finally started. The developing starting problem could have come from low compression. Typically an engine with compression problems will start easily if it has recently run as the oil is still on the rings, helping compression, but will start hard after standing long enough for the rings to become dry. Typically the longer it stands the harder it will be to get it started. This is of course a long distance guess, and I don't know what happened to the engine when it ran away.

leathermang · #10 10-08-2014, 06:04 PM

At first I was afraid of that..
but he said he sprayed it in ' while his friend cranked it' .... so that is not really likely culprit .....