Poor running after wiring fire 250SE

[wcelliot]

Hi gang... long term lurker, but first time poster. I don't have a W113, but my 250SE W111 has a 280SL engine in it and the technical resources here surpass anything else I've found.

http://fnader.com/Mercedes.htm

About a year ago, I nearly had my W111 burn up. In the postmortum, we discovered that the grounding wire at the starter was missing and that the large engine ground at the firewall had corroded at the bolts and was making intermittent contact.

To make a long story short, while trying to start the car, the starter hung on (even after releasing the key) with the engine grounding itself through the temperature gauge wire... which got hot enough to saw through wiring behind the dash and cause a number of dead shorts which exploded into open flame before I could get the battery unhooked. Luckily I was at a store and we were able to get the fire out using a commercial size fire extinuigher (the small one I always carry didn't do anything...)

Anyway, other than melted wiring and all of the heater/defroster shrouds on the driver's side turned to liquid, I escaped with a broken windscreen and some scorched wood.

So we've been redoing the car for about a year... finally got it finished this week and started doing shakedown runs.

The car was running perfectly before the fire, always starting quickly, idling smoothly, and running strongly (4sp manual trans). Now it's difficult to start, runs weakly, and appears to be running on 4 or maybe 5 cylinders.

At idle pulling the wires of 5 and 6 don't seem to make much difference. The plug on #5 looks normal (as do 1-4), #6 appeared to be wet with fuel.

Given the type of failure that I had that caused the fire, do you think the running issues could be related to that? Or more related to sitting for a year?

I've not begun the step by step general process of checking the various injection systems... I figured I'd post the situation here first just in case it might be something usual related to the fire or the wiring meltdown... if anyone has any ideas, I'd love to hear them. I'm ready to start driving this baby again!

Thanks!
Bill

[glennard]

Hi, I've a '69 280SE 111 manual.  Previous owner had a fire also.  Where did you get a new wiring harness?   Could some of your fire cause be from wiring errors/installation/changes/etc in the 250-280 transition?  The start soleniod, stop solenoid, relays, CSV, CSS, etc are different for the two models.  Very interestin situation----------

[wcelliot]

Thanks for the note.

The 250 to 280 transition was done pre-fire and the car was running perfectly. Is the wiring was changed substantially at that point, it wasn't obvious (everything looking completely stock and with the same patina).

None of the engine compartment wiring nor even the fuse box wiring was damaged (other than the temp gauge); all of the damage was behind the dash.

We replaced the ignition switch, center gauge package and tachometer with NOS and the necessary parts of the harness with a combination of bits from used harnesses and some new wire where necessary. So it's absolutely possible that some of this may be flawed... but the wiring restoration being where it is we assumed that the car would either run or not (the necessary systems either getting power or not)... not that it would run poorly.

I'm thinking that the huge amount of current flowing through the temp gauge may have hurt the termo-time switch and the "W" side does test out to be always grounded. But even with this switch unhooked, the car runs the same way.

I'm confused what would make the #6 plug wet with fuel... the car does not seem to otherwise be running overly rich

Thanks again!
Bill

[glennard]

Temperature gauge wire?  Don't have a filled thermal temp gauge?(non electrical).    A/C was added by you?

[wcelliot]

I should have said "tube" rather than "wire", but yes, that's what heated up and cut through the wires behind the dash before it burnt itself in half. I watched it in process.... by the time I got the battery unhooked it was too late...

This was a German market car with no factory AC; I added the AC to it myself. Factory underdash unit for the appearance; all modern compressor, etc.

Bill

[waqas]

quote:Originally posted by wcelliot


The car was running perfectly before the fire, always starting quickly, idling smoothly, and running strongly (4sp manual trans). Now it's difficult to start, runs weakly, and appears to be running on 4 or maybe 5 cylinders.

At idle pulling the wires of 5 and 6 don't seem to make much difference. The plug on #5 looks normal (as do 1-4), #6 appeared to be wet with fuel.

If all cylinders are firing, then pulling any plug should create an audible difference. Are you getting spark on plugs 5 and 6?

Another possibility: if 6 is excessively rich, then some other cylinder may not be getting enough fuel. I suspect your fuel injection pump is doing funny things. If it sat for that long, it's possible that some of the plungers got jammed with old fuel. Does your injection pump rack move freely?

Nice looking car.. very similar to mine. I've got a '66 250se/c with 4-sp and sunroof in green 268 and cognac interior.  I really like your anthracite gray though...

[wcelliot]

Thanks for the note.

I actually pulled the plugs on 5 and 6, grounded them, then watched the spark as I turned it over. Nice fat spark on both.

(Running an Ignitor and Flamethrower coil. The car would barely run at all to begin with and I decided we likely fried the original Ignitor during our wiring testing. I reverted to points and the car ran much better... then went on to a replacement Ignitor. In both the latter cases the miss was evident. I also swapped out the Flamethrower for a Bosch Blue coil for testing... no difference.)

There was a (very) sightly audible difference when pulling them on a running engine, but virtually no change in idle rpm (and nothing like the effect seen when 1-4 were pulled)

I should also mention that the idle was so low that it kept wanting to die on me (sub500). I turned the air bleed (on this car near the firewall on a hose/tube at the rear of the intake manifold) one fll turn anti-clockwise... the idle jumped up to 750/800 rpm or so and was much much smoother. I think the higher idle was just masking the miss (which was much more obvious... especially at the exhaust... at the lower rpm)

Rack moves nice and smoothly and returns easily as I understand it's supposed to do...

Going to run a compression test either tonight or tomorrow just to rule out any potential issues there (though I wouldn't think sitting or the dash fire would effect that.)

Thanks again for the help! I've dealt with D- and K-Jet injection, but this is my first shot at mechanical...

Bill
ps... the car was originally Bronzit. The Mercedes-saavy shop that painted it fought me every step in trying to go to the DB172, in the end making me give them the order in writing that I understood they recommended against it. (And Mercedes never offered the Cognac interior with the grey).  Afterwards they said it was one of the most stunning W111 combos they'd ever seen! ;-)

[wcelliot]

While doing a close once-over (again) I notice that I have a red wire dangling unattached ut of the injection pump wiring harness. Does the cold start soleniod have two wires attached to it (as the bakelite ridge would seem to indicate)? It currently has a single black wire attached (from the same wiring harness).

We were not in this area repairing wiring, so I'm tending to think this was never hooked up (nor can i see it having any effect on the current running status) but I wanted to mention it just in case...

Thanks again!
Bill

[rwmastel]

quote:Originally posted by wcelliot

I've dealt with D- and K-Jet injection, but this is my first shot at mechanical...

Then perhaps you need to start with some of the "tour" threads?
http://index.php?topic=5003
http://index.php?topic=1712
http://index.php?topic=3659
http://index.php?topic=6277
http://index.php?topic=5486

[ja17]

Hello Bill,

Look for a vacuum leak the vacuum line going to the the automatic (if it is an automatic) and any other vacume source on the intake manifold. Install some fresh sparkplugs in those weak cylinders and take a compression check as mentioned just to rule other issues out.

Since only these two cylinders seem to be mal-functioning, replace the those spark plugs, make sure those two spark plug wires are not reversed, check for vacuum leaks, then move onto more complex fuel issues if needed. Keep us up to date.

You came to the right place for help!

[glennard]

Once again---after 40 years, after engine transplants, after shade tree fixes, after MB fixes, after -ad infinitum.   There are no two alike anymore.   Didn't the 250SE coupe FI pump only have one solenoid hung on the back.  The 280SL FI pump has two?  Gotta establish what you have first-auto/manual, CSV, CSS, what wires are actually hooked up, relays, ignition/distributor type, etc, etc.  First, get it idling at 800 rpm with absolute minimum fuel from FI pump(on stop) and then idle air squeezed back to idle at 750(50 rpm rich).   Now you can start figuring out what is what.  Bosch mechanical FI is arcane.  It is an esoteric trip!  Welcome.

[Shvegel]

If number 6 is soaked it sounds as if you might have wired the cold start injector on at all times instead of through the thermo time switch.

Break out a meter and see if you have power and ground at the cold start injector at all times when the engine is running. You should have power at all times but the ground should switch off after a few seconds.

[wcelliot]

Sorry for the delay in updating everyone, but the car has pretty much sat since my last post, other priorities keeping me from moving forward. I finally got to mess with it today.

First, I did a compresison test. Nice and even across the board. Very reassuring. While the plugs were out I tested each externally for a spark... all were nice and fat.

However, I was still concerned that I had an ignition problem... so I had picked up a set of Bosch W7DTC's (non-resistor W7DC's apparently no longer available... and it was suggested that with the resistor wires, the WR7DC's I was using might be limiting my spark.  Remember that rotor, cap, wires, and plugs had well under 1000 miles on them and all tested fine.

Well I installed the DTC's and started the car... it immediately settled down to a nice stable idle just like it used to... no miss at all. I let her warm up then took her for a drive. Nice smooth power at all rpms, no miss at all, runs even better than before. She smoked just a little at the beginning at higher rpms(likely burning oil/carbon out of the affected cylinders) but was nice and clean at the end of a few miles.

Thanks for all the help and guidance... it's just beyond me how a couple of plugs would just "go bad" while sitting yet test out perfectly. Guess it's a lesson to be learned that if you have a miss like feels and sounds like ignition, it's a relatively cheap test to swap out the plugs... and completely rule out ignition issues before messing with the fuel system... like they say in LBC circles, 90% of SU problems are Lucas in nature...

Thanks again!
Bill

[waqas]

Glad to hear you got to the bottom of it!  You can get the correct Bosch spark plugs directly from the Benz Dr. (Dan Caron); contact info here: http://index.php?topic=8819

[wcelliot]

quote:Originally posted by waqas

Glad to hear you got to the bottom of it!  You can get the correct Bosch spark plugs directly from the Benz Dr. (Dan Caron); contact info here: http://index.php?topic=8819

Thanks much!!
Bill