Low voltage faults- '94 W124 E420 Running Rough!
 

I'm attempting to save another soldier. A salvage 94 E420, black with saddle interior.

I have almost no history on this car. Had some minor previous damage to right rear. Then a second accident where owner may have slightly glanced something on right front quarter panel. Looks too like she ran over a sidewalk. That said, with lots of cash it might be OK. Engine currently has 109k on it.

Problem: The engine runs rough.

I replaced plugs, all of which looked OK, maybe one was a touch dark (rich).
Tested Vacuum lines as best I could to the engine (I'm a total novice). All did fine.

Decided to scan codes and here is where it gets interesting. On the 38 port connector I was pulling codes. When I got to the pin 8, I heard a click. The light high pitched whine I had been hearing (I'm guessing near the MAF) stopped.

The car would not start after this. I've borrowed modules from another parts car I have and nothing helped. I've lost sleep over this trying to figure it out.
Today, I start pulling codes again. I skipped pin 8 and went through all the pins. Then I came back to pin 8. When I started pulling codes from it, I heard what can only be described as the MAF (or something near it) begin to reset and start the high pitch whine again.

The car started back to its former rough running state (sounds like it's missing on one cylinder). Before, it would not go past about 4200 rpm, which may indicate a blocked CAT, certainly inline with the accident running over something. I'm not that sure.

While I have lots of codes, most of them point to low voltage, i.e. "Voltage supply for LH-SFI control module interrupted" or "Poly V-Belt Slipping" from pin 8 (base module).

Connecting the tester to pin 13 seems to affect the pitch of the whine near the MAF, but no codes. I think this is a fuel signal pin.

Pin #19 is throwing codes relating to the vehicle speed signal missing, which as far as I know may relate to low or no voltage.

It appears to me that at least a part of the harness is new. It is a "Delphi" with an "F.D date of 31/08/2010." Hard to believe that was made in 1993.

I tested the voltage at the battery while idling, which showed 13.95 volts. I don't think it's the brushes on the alternator.

I could sure use some advice! It's one hell of a learning experience.

In addition...
 

I forgot the obvious. Although the car does have the older style fuses, I checked each one with a multimeter. I also checked each and every fuse I could find attached to a relay behind the main fuse panel under the cover.

Also, I tested each fuse attached to the base module. There are four 10 amp blade fuses. All of those checked out fine.

I can only assume the over-voltage protection relay is integrated into one of the modules on the m119 engine.

Another fail..and interesting find.
 

Today I was again pulling codes and went through several voltage tests. I tried to clear the codes on pin 8 and held my tester button down for ten seconds. The high pitched whine near the MAF stopped again. Now, again, the car won't start.

The interesting find here is pin 8 is only showing 11 volts. I'm studying wiring diagrams trying to figure out where the base module gets its voltage from.

Any suggestions are welcome!

I think the whine you hear is the ETA motor, but Lord knows why probing #8 is shutting it down.

+1. But it stops on its own after a bit. Can you clear the codes? If you can see which if any return. Checked the caps and rotors?

M119 cars tend to eat caps and rotors, so yes, you should check those as stated. Not sure how to easily check, but the cam actuators will affect performance if they are not working.

Rgds,
Chris W.

Sorry for the delay and I really appreciate the suggestions.

I did remove the rotors and cleaned them. They looked fairly new. I have also jumped the fuel pump relay, replaced the fuel pump relay with a spare and no difference.

The Base module looks newer than the other modules. I suspect the previous owner was dealing with a similar situation and probably paid dearly for the parts.

I did find that the vacuum tube from the EZL was weak as it went under the throttle body. It crumbled in my hands. I've replaced it temporarily. Guess it gets hot right there on the M119.

For certain, when I do get the whine of the throttle motor, I'm sure the engine will start. So far, however, no joy. I tried briefly tonight to see if the pin code reader would re-activate it. I have NO lights on any pin now. I checked the reader to make sure it was working on another car. It did.

However, connecting it to pin 13 does cause a click on the fuel pump relay, but that's it.
When I have time, I'll do a more thorough check of voltages again and check the fuel pump. I don't want to jump the gun, but I suspect one or more of the modules is bad. I just don't wanna go broke trying to figure out which one!

The whine is normal and is the ETA. I get this noise when pulling my codes. The cable for the ETA is made out of the same bad insulation as the engine wiring harness. If you disturb that cable it could cause intermittent problems. I'm not saying it's causing the problem here, but it's something to consider.

Re-reading this your symptoms are very similar to what I had when I blew one of the blade fuses in that module. They are cheap, may be worth it to replace them since to check them you need to remove them.

More testing
 

All the blade fuses in the Base Module have been replaced and were fine.

At Arthurs suggestion, I did some more checks at the fuel relay under the seat.
The pumps work fine when given voltage from the battery. Fuel pressure was up around 50.

The problem I found at the relay, which is supposed to be receiving 12 volts directly from the battery, is only receiving 2 volts. I think this is symptomatic of a larger issue, but I'm going to conduct a voltage drop test once I isolate the line going to the fuel pump relay from the battery post behind all the modules in the engine compartment.

Another interesting issue I came across. I was pulling fuse 9 and heard a tiny spark when I replaced it. I tested the voltage on the lower side with the fuse removed. 12.5 volts. Testing the pin on the upper side (with the fuse removed) was about 1.97 volts. Hmmm, I think that should be zero, but what do I know?

My 92 400E ran like crap when I got it. I replaced the caps, rotors, wires, and coils (some with known good ones to save $) and it made a huge difference. I was able to drive it daily. I also fixed the engine harness and put a new O2 sensor in and it runs even better. Still not perfect though-it runs rough until it warms up.

Did you ever fix the no lights on the pin outs? I have the same issue

PNP may be your best friend for modules and relays.

AFAIK the 38 pin is not tied to any module, so that would be of little use. Ive replaced the majority of relays

Just fix the upper wiring harness and keep on trucking.