87 300D. lots of little things. - PeachParts Mercedes-Benz Forum

techno550 · #1 06-17-2009, 12:37 AM

I just picked up an 87 300D. It needs some TLC. Was hoping to get some guidance on a few issues.

The tach does not work. Not sure where to start there.

The instrument cluster lights also do not work.

The AC also does not work. Blower fan and whatnot work fine. The PO installed a switch in the center console that appears to be wired into one of the pressure switches for the AC and then on to other things? either way, that switch turns on the AC compressor. I think I have located the correct wires to reattach, but a diagram and other troubleshooting info would make me feel a lot better.

The center and left vents are broken. I've looked at them briefly and haven't figured out how they come apart or are removed. I might try to figure that out at the local junkyard first.

The driver front and passenger rear windows do not function. Its not the fuse. (swapped fuses with the other pair and no change.) is there a relay or anything else I should check before I trace all the wires? I would suspect switch, but two bad switches on the same circuit seems like too much of a coincidence.

Cruise control does not work. Also don't know where to start on that.

I also have a few vac lines hanging free under the hood. Those may be related to a few of my issues.

Overall though I'm extremely happy with this thing. Can't wait to get it sorted. Did an oil change, new air filter, and new battery today. Hopefully I can maintain this pace with a little direction.

TIA

tbomachines · #2 06-17-2009, 12:51 AM

This is off of my experience with a w126, there are probably some differences between the years so these are only "ballpark" suggestions. Someone with more experience will chime in.

1. Tach could be related to fuses, check/replace them all and make sure there are no hairline cracks. It could also be the tach amp if they still used them in 1987. That's the little black plastic "garbage can" behind the driver side headlight.

2. Do the rest of your dash lights work, such as window switches, climate control, etc.? If no, then it could be the rheostat, which is known to go bad. You'd have to pull the cluster to get at it, but you'd have to do that anyway to get to the light bulbs if they are burned out. You can solder in a jumper wire to bypass the rheostat if you choose.

3/4 don't know

5. Check the switches, they are known to get gunked up over the years. If that doesn't work, take the door panel off and check for power at the window motor. If you have power and the switches function, take out the window motor and rebuild. All 4 of mine were seized up, all it took was a cleaning-out and re-lube and they all work well now.

6. Vac lines probably contributing to your cruise control issue, and possibly your A/C, depending which ones are missing. Pick up a factory shop manual if you don't have one, it will help you tremendously with vacuum. There are also vacuum diagrams available on this site (sticky at top of forum) that can help you troubleshoot your mess under the hood. Also, a mityvac tool will assist in tuning the vacuum system and tracking down leaks. Welcome to the forum!

babymog · #3 06-18-2009, 07:30 PM

Check the fuse on the OVP relay, it is a relay next to the ECU / behind the battery. If the fuse is good, the relay is probably bad, ... which will take out your tachometer, your cruise control, and your A/C.

Wodnek · #4 06-18-2009, 07:48 PM

It is not uncommon for the switches to go bad in multiples.

Remove the center console, one bolt under carpet in center console, then it hinges up and comes right off.

if the left rear window is working, then swap it into the other 2 that dont work. The right front switch is different then the other 3. This will either solve your problem, or eliminate the switches as the issue.

Wodnek · #5 06-18-2009, 07:50 PM

The vacuum line you see may be the one that goes to the egr system. Most 87 owners disconnect the egr.

JEBalles · #6 06-18-2009, 08:05 PM

In my 123, if you just fiddle around with the dimmer (go from hight to low with the knob) and eventually the lights come on. Do your dummy lights work? I think they're on the same circuit. The cruise in these cars tend to never work, so it might just be a lost cause. I just tore out all the cruise stuff on mine.

techno550 · #7 06-19-2009, 03:12 PM

Thanks a lot guys.

New fuses (and bulbs and whatnot) on the way. will swap all of that as soon as it arrives.

The dummy lights do work.

The EGR stuff is still attached. The "random" vac lines are on the driver side. I need to take an afternoon (with a good diagram) and check/replumb everything. I guess I should remove the EGR bits?

I think I have the AC stuff somewhat narrowed down and it kinda works now.

The tach I haven't looked at.

I have another thing that is either weird or completely normal... when I turn the key to the start position nothing happens for a bit. Can be a second. can be 30. It always starts immediately as soon as the starter spins it over... just a long inconsistent pause before that happens. Just want to make sure this a normal thing and not a "OMG, check X before it strands you!" kind of deal.

I also need to ask why there is an AFM on my mechanically injected diesel.

brandlj · #8 06-19-2009, 03:29 PM

AFM controls the EGR. Honest!!

techno550 · #9 06-19-2009, 05:26 PM

the window issue is not the switches. So on to the next layer of troubleshooting.

The fuse next to the electronic thingy behind the battery was blown. no change in the tach functionality though.

so the AFM is part of the control system for the EGR stuff. thats.... interesting. Done some reading on the EGR now, and will be removing that shortly. There was mention of the tach circuit going through that. Anything else to be aware of? I should probably try to get the tach working before I remove yet another thing that could break it.

I'm also looking for a fuse box diagram. I haven't found a list of what fuse does what. Just fuse numbers when going through each individual wiring diagram. Any such documentation that would list everything?

Thanks again.

Jeremy5848 · #10 06-19-2009, 05:39 PM

Not sure what AFM means . . . air flow meter??? It can be left alone; as long as it doesn't jam shut it won't affect airflow. The easiest way to defeat EGR is simply to block off either the input or the exit of the EGR valve. Forum members sell kits for EGR removal, too. You can remove all the vacuum stuff under the air filter as it controls the EGR and ARV valves. The EGR electronics must remain because the tach signal runs through it and because the electronic idle speed control comes from the EGR electronics.

Once EGR is defeated, you can pull the intake manifold (maybe as part of a glow plug replacement) and clean out all of the crud. With EGR defeated, it will then stay clean.

Jeremy

Wodnek · #11 06-19-2009, 06:32 PM

If you PM me your email, i would be happy to email you some close up pictures under the hood so you can look how the vacuum lines are supposed to go.

When you pull your fuse box cover, a white data sheet should be attached to the underside showing what each is for. If yours is missing, I can take a close up picture of that too.

On a Benz, usually cruise issues are the cruise amp. You can resolder the connections on it and that may fix it for a time.

Jeremy5848 · #12 06-19-2009, 11:43 PM

Somewhere on this forum is a set of pictures for almost all fuse cards including the '87 300D Turbo.