Fuel Delivery Problem? Loss of power, oil pressure, and dead battery

[Benzboyx4]

Good afternoon all,

Please bear with me, this is a complicated issue I am trying to search for possible causes so I can help give some info to the mechanic that can help them diagnose and fix the problem.  I am also very much a novice when it comes to auto maintenance and repair, and I'm learning, but do not have enough experience to wrap my head around what the issue below could be.

1976 450SEL, 127K Miles.  I purchased the car a year ago.  It has always had a problem with cold starts, but once started and warmed up, runs fine.  Last May I was driving and when I hit the gas, nothing happened.  It was fine one minute, the next minute, I was getting no power to the engine.  I managed to limp off the road, had the car towed home, and after sitting for a few hours, it started up fine.  I took it to the mechanic close to home and had them look at it.  They put on a new fuel filter and checked the fuel pump.  The pump is only a few years old, based on the date stamp, but the mechanic cleaned out some rusty residue from it.  I haven't had any issues until last month when the same thing happened again.  I lost power to the engine again, noticed the oil pressure dropped.  I got off the road and shut the engine off.  When I tried to start it, the engine wouldn't turn over at all, like the battery was dead.  I had the car towed to the mechanic again.  They have been crazy busy and have not had a chance to look at the car yet and figure out the problem, and because of the cars age, I want to try and get some guidance because these days; they may not know where to begin either on a car this old.

Some have suggested it sounds like the car is in some kind of limp mode.  I have been told this car has no over voltage relay like my 1984 R107 does.  I would think it was a fuel delivery issue, anywhere between the tank and the engine, but I also thought it odd the car wouldn't even turn over like when you have a dead battery, which makes me wonder if the culprit is more of a relay/sensor issue somewhere in the fuel system.  Any insight or suggestions would be incredibly helpful.  Thank you!

[daantjie]

First of all we need to know if you have KJET or DJET fuel injection.  In the past we tried helping guys and halfway though the shenanigans we find out that they had either/or and we assumed they had or/either

Best to snap a pic of the engine bay for show and tell, then we go from there.

[raueda1]

To my knowledge these cars don't have anything like a limp mode.  Up until you said it won't crank I was thinking about garbage in the fuel tank clogging the in-tank filter.  The filter gets increasingly clogged towards the bottom.  When you're getting low on gas the tank fuel level drops to a point where you just can't get enough fuel.  Whenever work is done on that whole fuel delivery system in the back of the car, this filter should be changed.  Cleaning out the gas tank is also a good idea while you're at it.  Odds are high that this is the source of the rusty residue.  Regardless of everything else you should probably get this done.

As for hard cold start, I'm going to assume that you have K-jetronic (CIS).  If so, it points to the Warm Up Regulator (WUR).  There's tons of info here, just start searching to get up to speed. 

But none of this points to sudden oil pressure loss.  Did oil pressure drop abruptly on the road (i.e. at normal engine operating speed) or did the rpm's abruptly drop down to idle (hence lower oil pressure)?

[Benzboyx4]

Apologies.  It has K-Jet.  Attached are the few photos I have of the engine I took a while ago when I was working on the wretched servo unit; the car is currently at the mechanic so I can't snap one at the moment.  I have little history on the car with regard to maintenance.  The original owner took very good care of the car, and the second owner (the one I purchased it from) had the car repainted 16 years ago, so he owned it at least that long, probably more.  He always kept it covered in a garage (a really dingy one!) and told me he only drove it a few weeks each year, in good weather; the car has never really seen rain or snow.  However, I've watched enough "Mercedes Source" videos to know one of the worst things for old cars is for them to sit undriven with gas in the tank, etc.  I appreciate your interest and any insight you can give me.  Most mechanics these days are so used to hooking cars up to computers to diagnose them, I'm afraid they may be a little stumped so I'm trying to do my own homework to narrow down possibilities.  Thank you!

[Benzboyx4]

Thanks for the reply, Dave.  The drop in oil pressure, as you mentioned, was most likely due to the drop in RPM's as well, when the car started acting up.  I was kind of in a panic to get off the road and my eye just caught the oil pressure dropping.  I too am fearful it could have something to do with crud in the tank.  I had coincidentally just topped off the gas tank at the station a few minutes before the car started acting up.  I never let it get below 1/4 tank, just in case there is junk floating around in it.  Personally, I'm not experienced enough with car maintenance to tackle what would be involved with getting the gas tank emptied, removed, cleaned out and/or recoated, and then putting everything back together.  I'm dreading what kind of estimate I may be looking at for all of that LOL.  Bless its heart, the car has some other mechanical issues, nothing that can't be fixed, but as I am still learning myself, I am trying to leave the heavy lifting to a professional at this point, as I tackle less complicated things that I know I can handle as I learn about things.  I changed the spark plugs in my C Class this weekend and that was a huge step for me, but probably routine for a lot of guys out here.

[sc6.9]

Down on power (nearly stalling) and poor fuel economy equaled a blocked catalytic converter in my case. The poor engine behavior was rather sudden, as well. Putting on a new cat was an instant, positive and extremely noticable change in all around running quality and performance. I realize you have other problems, probably fuel system related as suggested above, but it might be worth it to ask your mechanic to check your cat for blockage. I would note that I had to insist THREE TIMES that my mechanic check the thing because he was positive it was something else, and he was annoyed and surprised to find that it was the problem.

[daantjie]

What is the state of the ignition system?  Many a gremlin that shows up out of the blue can sometimes be attributed to a worn out coil or such.  Are you getting any kind of misfire symptoms when the car is running well, or perhaps once it starts acting up do you get hesitation and stumbling, as in not pulling strongly anymore?

Also check your voltage regulator, it screws into the back of the alternator.  They can also famously leave you stranded out of the blue.  Kent at mercedessource always harps on this, he has a few vids on youtube on this topic.

Another easily checked broad issue is vacuum leaks.  These cars are notorious for hiding a vacuum leak from a cracked plastic hardline or rubber connector.  Best check them all, it might not be the main reason but you have to ensure you have absolutely no place for vacuum to leak.

[Benzboyx4]

@ sc6.9 - I will mention the cat converter to the mechanic too.  Honestly, I have always felt like the car doesn't have the pickup it should.  I know it's a huge, heavy car, but it's slower to accelerate than what I think it should.  It barely almost immediately shifts from first to second, which I thought odd too.  Unfortunately, I don't know anyone else that has a 116, and I haven't driven any other than my own, so it's hard to know if some of the things I'm experiencing are typical, of specific to this car. 

@ Daniel - I don't think there are any misfires, and when the car is warmed up and running, it runs well.  Just a few days before it died on me, I had driven it in a 60 mile round trip to the office with no issue at all.  Then a few days later I take it on an errand down the street and end up walking home LOL.  It's frustrating because I bought the car as a light restoration project and to enjoy it by driving, and I can't drive it and feel confident it will get me from A to B.  Who knew there could be so many variables as to what causes a problem with a car?! 

[raueda1]

Thanks for the reply, Dave.  The drop in oil pressure, as you mentioned, was most likely due to the drop in RPM's as well, when the car started acting up.  I was kind of in a panic to get off the road and my eye just caught the oil pressure dropping.  I too am fearful it could have something to do with crud in the tank.  I had coincidentally just topped off the gas tank at the station a few minutes before the car started acting up.  I never let it get below 1/4 tank, just in case there is junk floating around in it.  Personally, I'm not experienced enough with car maintenance to tackle what would be involved with getting the gas tank emptied, removed, cleaned out and/or recoated, and then putting everything back together.  I'm dreading what kind of estimate I may be looking at for all of that LOL.  Bless its heart, the car has some other mechanical issues, nothing that can't be fixed, but as I am still learning myself, I am trying to leave the heavy lifting to a professional at this point, as I tackle less complicated things that I know I can handle as I learn about things.  I changed the spark plugs in my C Class this weekend and that was a huge step for me, but probably routine for a lot of guys out here.

Surprisingly this isn't nearly as bad as you might think after you get the car up on some stands.  You can siphon the gas out easily enough.  The fuel supply stuff underneath comes off in a pretty obvious manner.  A special socket is needed for the in-tank filter, available from Mercedes Source.  The tank itself is behind the front wall in the trunk and that comes off with just 6 screws.  It's one of those jobs that's a bit tedious but everything is pretty out in the open.  There are gas tank restorers out there.  You may well be able to get by just pressure washing it out and letting it dry in the sun.  I'm pretty sure there are more detailed posts here as well as a Mercedes Source video.  But one way or another, it's a job that ought to be done if it hasn't been.  I'd guess that the majority of people here have done it at one point or another.  Good luck with it!

[raueda1]

@ sc6.9 - I will mention the cat converter to the mechanic too.  Honestly, I have always felt like the car doesn't have the pickup it should.  I know it's a huge, heavy car, but it's slower to accelerate than what I think it should.  It barely almost immediately shifts from first to second, which I thought odd too.  Unfortunately, I don't know anyone else that has a 116, and I haven't driven any other than my own, so it's hard to know if some of the things I'm experiencing are typical, of specific to this car. 

@ Daniel - I don't think there are any misfires, and when the car is warmed up and running, it runs well.  Just a few days before it died on me, I had driven it in a 60 mile round trip to the office with no issue at all.  Then a few days later I take it on an errand down the street and end up walking home LOL.  It's frustrating because I bought the car as a light restoration project and to enjoy it by driving, and I can't drive it and feel confident it will get me from A to B.  Who knew there could be so many variables as to what causes a problem with a car?!

The issues are 2-fold I think.  First, they're just plain OLD.  And secondly, they're highly engineered and complex.  Finally, by the time we get them they've probably been sitting or ill-maintained. 

Anyway, with the fuel system everything interacts with everything else.  On top of that, the car may seem run, more-or-less, but with several things out of whack - maladjusted WUR, a slightly (but not totally) clogged filter someplace, a couple marginal fuel injectors, etc.  So it's often necessary to systematically go through it all.  At least you don't have the 6.9 suspension to worry about.   

[ptashek]

Aside from the strainer in the fuel tank, and the main fuel filter in the pump assembly there's also a small fine mesh filter on the main inlet pipe to the fuel distributor. Might be worth checking that one as well. This is what it looks like:



And this is where it lives:


Before you go chasing after fuel pressure, WUR, fuel distributor rebuilds etc. check all those filters in the path, blow out all fuel pipes with compressed air and once you're confident it's not a fuel delivery issue, go after the other stuff.

[rumb]

These old cars can have a quite a few gremlins unfortunately. Check the ground points for the engine.  As mentioned could be filter in bottom of gas tank. I would consider a new fuel pump. Your WUR can be tested by http://www.cisflowtech.com/