1981 380sl resurrection

[fischp]

Hi all,

I've just started my first MB project, the restoration of a 1981 380sl that was left in a field for four years with the windows down...

Ok, I've done most of the obvious things I can think of, drained and cleaned the gas tank, replaced the fuel pump and filter, the pump was seized. Rebuilt all of the brake calipers and put new rotors and pad on. The car starts but does not idle smoothly, also sounds like it has the infamous 1500 rpm idle issue. I replaced the spark plugs after the car idled for about 20 minutes, mostly just to let it run and get the old gas out of everywhere. Each of the plugs was black and smelled of gas. I don't see any obvious vacuum leaks and have used liberal amounts of carb cleaner looking for leaks around the injectors and the vacuum lines. I'm sure there's a leak or two but not sure if that's what causing the rough idle.

Can someone please provide some guidance? I just got the MB CD and trying to get through it...

Thanks,

perry

[timm9]

Welcome fischp!

My first SL was an 82 380SL. While it was not new to MBZ's, this was my first SL. My 107 had been sitting for quite some time alothough it was inside and had the high idle. A member on this board was very kind and helped walk me thru the different components to check until I was up and running.

In hind sight, if I brought home another 107 (which is highly possible) I would start with taking the car to a shop that has a smoke machine. They will typically charge about $100.00 but you will leave there knowing exactly where and how many vacuum leaks you have. I would also order a new O2 sensor. It's cheap (under $25.00) and does play a role in the 81's duty cycle. I literally spent months trying to 'find' each leak on my own which was very hit and miss and a huge waste of time.

Don't bother with plugs, etc. until you know all the vacuum leaks have been found and corrected or you will ruin those like I did. I might suggest you search for my user name and review the post regarding my 82 380SL as mine had major cracks in the air chamber making it impossible to idle or adjust the duty cycle.

Good Luck and get her ready for Spring and the top down!

PS. You will find that your posts will receive more answers if you include the year, etc. of the car and your location in your profile...:-)

[fischp]

Thanks timm9, I'll see if I can find a shop with a smoke machine, as soon as I get wheels on my new baby. Actually, what I'd like to do before I do that is disconnect all of the vacuum lines that go external to the engine, so I've just got the motor and it's vacuum lines, no external plumbing. Seems like that would be much easier to debug. Where is the "main" vacuum outlet that feeds the non-motor lines? I'm guessing somewhere on the intake manifold. Sure would be nice if I had a nice anatomically correct picture of the engine and it's various devices labeled. Does that exist anywhere?

I'll go ahead and get a new O2 sensor as well, $25 seems like a bargain compared to what I'm used to paying.

Thanks!

[timm9]

Perry,

I might suggest that you do not disconnect all of the lines. This way at the smoke test you will only see the leaks. When I finally took the 82 in for the smoke test we 'connected' the smoke machines line to one of the lines going into the WUR (Warm Up Regulator front on engine near temp sensor) and the smoke did its thing. You do not start the car, only introduce the smoke into the system and then use something to 'mark' each leak so you can repair without losing track.

Pay particular attention to the line that runs 'under' the intake from passenger side to driver side as I found a leak there as well. There is also (If the same as mine) a main vacuum line at the immediate rear/center of the engine that is prone to leaks. It can be difficult to see but would not be surprised to see a leak there due to heat.

Lastly, you can purchase a service manual CD ($30.00?) for your car that has vacuum lines, electrical, diagrams, and procedures to work on the car. I would strongly encourage you to buy one as you will quickly discover that the dealers will not have anyone 'knowledgeable and experienced' with your car as they have all retired.

Tim

[fischp]

Tim,

Thank you again! My only issue right now is that I can't drive the car and it'll be a while before I put a plate on it. I'm going to google for a "home made" smoke machine and see what I can cobble together. It sounds like something handy to have in my garage anyway. Thanks for the suggestions on where to look, I'll definitely look there first.

Perry

[fischp]

Btw, I started looking at my engine in detail yesterday and found that one of the wires to the idle speed adjuster was broken. I'll fix that first...

[timm9]

Excellent!

I seriously looked into buying a smoke machine but they are close to $900.00. Some months later I found one on CL for $350.00 but it was gone immediately. At this point I have smoke tested 4 cars which would be close to half the cost...

Once you have addressed every vacuum leak you can work idle, etc.

[fischp]

Silly question, but will a vacuum leak make the car run extremely rich? I'm used to newer 90s vintage german cars (BMWs) with computers.

[timm9]

Perry,

Not a silly question at all! Vacuum will definitely make the car run rich. I had so much extra 'air' coming into the system that it was staining my garage floor and fouling the plugs.

That is why I'm suggesting you deal with vacuum leaks first. Otherwise you will not be able to properly diagnosis your issues.

If you car is the same as my 82 You have an analog 'brain' under the floor on the passenger side that receives signals from the different components, i.e. O2 sensor, engine temp, etc.. If you have vacuum leaks the 'brain' is told to add more fuel causing it to run rich. If the vacuum is poor/leaking you will never find the underlying issue...

[fischp]

Tim, thanks, yes I found the "brain" while redoing the passenger side floor board. I'm also lead to believe that the idle control "computer" is behind the glove box. I'll pull that this weekend, as the PO said that that was bad.

I'll also build a smoke machine this weekend. I Googled it and seems very easy to do, simply a clean metal paint can and two fittings, one for a low pressure compressed air input and then the output to the car. The smoke comes from a smoldering dirty rag. Very much a kludge, but will definitely make diagnosis much easier. I can't get over how much plumbing is in the car. Computers have definitely spoiled us...

Thanks again for your guidance!

perry

[timm9]

Perry,

That is correct. The idle control module is located behind the glove box. You will need to remove the glove box liner. If you look closely there are small round 'pins' holding the interior liner of the glove box that slide out from the surround and pull out. Most of them will come completely out which is not an issue. Look closely as I believe the fuel pump module is there as well. You will want to confirm part number before pulling. Once out you can carefully 'pry open' the module and closely inspect for 'breaks' in the solder. Some folks have been able to re-flow the solder and fix the module. I ended up sending it for an 'exchange' for a rebuild from Programa at a cost around $200.00. I would also suggext that you also pull the Over voltage Protection Module. If in the same location as mine, you will find it behind the fuse box on the outside kick panel of the passenger side. It takes 2 or 3 very small screwss to remove the kick panel to access the OVP. Pull the OVP and check the fuse that is inside. The OVP is cheap compared to the ICM.

[fischp]

Thank you once again! I'll start checking the various modules ASAP.

I also finished building my "kludgey" smoke machine. Where's the best place to plug my smoke output into? There are so many vacuum lines and I can't see a good place that is not somehow switched or managed. I was looking at the thick line going into the master cylinder, but I found out that it's steel and can't easily be removed. Is there a better place?

Thank you again!!!

P

[timm9]

Perry,

On mine we 'introduced' the smoke into the vacuum line coming off the Warm Up Regulator (WUR) at the front of the engine next to the hose/thermostat and engine temp sensor. There is also a place very close to the master cylinder that you can also access but I only used that location to check for vacuum leaks inside/under the dash. You will not be starting the car, only introducing the smoke.

[fischp]

My first smoke test didn't reveal any leaks, I need to go back and do it again, I used the WUR vacuum line, this time I'm planning to use the vacuum line that's coming off the back of the intake manifold. That line looks like it feeds a line that goes to the driver's side of the fire wall and splits into a bunch of lines. I'm pretty sure I have a leak, since my power locks work great while the car is running but don't after a few minutes when the engine is off...

After I ran my smoke test I decided to start the engine and let it run for a while. The motor was running at 1500 RPM for about two or three minutes and then I heard what sounded like the handle of a screw driver hitting the firewall on the passenger side. The tapping or klunk happened once, then once again after about 10 seconds, then again at irregular intervals. That happened several more times and the low and behold my engine idled at a solid 600 RPM. I looked at where I thought the sound was coming from and didn't see anything in the engine bay. Next I looked behind the glove box and saw about four or five what look like electrically operated vacuum switches. I'm not sure what these do, but my engine definitely was very happy at 600 RPM. I haven't heard the sound again, I'm back to 1500 RPM, but hoping that whatever this was it happens again and "sticks." Does anyone have a clue as to what could of possibly been tapping at the back of my firewall?

Thanks!

perry

[timm9]

Hi Perry,

If your locks are not functioning properly you do have a vacuum leak and that needs to be fixed before you can start chasing the idle issue. The vacuum line at the drivers side firewall routes into the interior of the car of for control of the pods for HVAC, etc. You may find 'smoke' coming from under the dash on your next test at that location.

With respect to the change in idle after the clunking noise I have no clue. Just out of curiosity, did you pull any of the plugs and check condition? It would be interesting to see what kind of shape they are in. if they are wet or fouled it would indicate that you have way too much fuel entering the system.

Unfortunately, you are at a standstill until the vacuum leaks are completely addressed. Once you have the leaks fixed I would start with the ICM behind the dash. Pull it and carefully pry open the case and inspect the board for breaks in the solder. There have been members that were able to 're-flow' the solder and fix the module.