560sl won't run, help! - PeachParts Mercedes-Benz Forum

lawrenceR · #1 10-18-2003, 11:59 AM

I've had a terrible time with my 86 560sl, first chasing a rough idle, mucking around with it, throwing parts at it, and now the bloody thing barely runs at all. Would appreciate any comments.

Started out addressing rough idle, so replaced plugs, wires, rotor-no help. O.K. then replaced injectors, sleeves, o rings, air distribution hoses, no help. Then replaced intake manifold gaskets, throttle body housing, thottle position switch, fuel distributor o ring, fuel filter, vacuum lines and vacuum connectors. Replaced over voltage protection relay. NOW IT IS WORSE. Swapped idle control unit with spare, no differnce. Swapped fuel distributor with spare, no difference. Pulled fuel pumps, seemed to run fine. Fuel pressure test was fine. Drained tank, had clean gas.

Test revealed that it was only running on 5 cylinders. Compression test OK. Now the vehicle will start up instantly, run not bad for the first few seconds, then start running really rough, on perhaps 4 or 5 cylinders. What's wierd is that if I connect the electrical connector to the side of the fuel distributor, I think a fuel flap sensor, the car won't run at all. With this part disconnected, the car will at least fire, but go through the above sequence.

Before I started mucking with it, the car would idle a bit rough but ran very clean and strong otherwise. Smog report showed excellent emmissions. Looks like past owner did the heads on the car.

When I did the intake manifolds, I was a little too carful with torquing the intake manifold studs down and it burned white and made lots of smoke. Then idled at 2000 rpm, but smoothly. Re torqued everything, still burned white for a while, but smoke went away except for a little bit still. I had a bit of a problem getting the throttle body housing-the rubber air duct- with the throttle body causing a big vacuum leak, but now that is on properly.

Where I'm at now is the car will fire instantly, with the connector removed from the fuel distributor, run on all cylinders for a few seconds, then run like crap.

Where do I go now? Please anybody, I want to drive the car into the lake...
Regards, Lawrence.
BTW, this was a "cheap" ebay car, CA with 117,000 mi.

RickM · #2 10-18-2003, 01:17 PM

Lawrence, Have you replaced the oxygen sensor? If it has one you can usually replace with a locally available "Generic" Bosch unit from Autozone or Pepgirls. If you have more time on your hands and don't need to get locally I'd suggest purchasing from our Host.

RickM · #3 10-18-2003, 01:25 PM

According to the Bosch site your car takes the Bosch OE Oxygen Sensor Part # 13926 or the Bosch Universal version with a part # of 15735. Good luck.

http://www.boschusa.com/AutoParts/

BobK · #4 10-19-2003, 08:10 PM

Sounds like a big air leak to me. Maybe the car runs for the first few seconds because of the cold start injector adding extra fuel, then when it shuts off, you are not drawing enough air to bring in the proper fuel. Try this: disconnect the electrical connector for the cold start injector and see if it still starts and runs for the first few seconds. If it doesn't want ot start and runs bad from the getgo, look for a leak.

lawrenceR · #5 10-20-2003, 11:14 AM

Thanks for the comments. Spent some more time with it. Disconnected the Oxygen sensor to see if there was a difference, their wasn't. Replaced the fuel distributor with the original (a spare was swapped) checked all air connections, everything looked fine.

Interior of air duct housing was wet with gas...

Will try unplugging the cold start valve and see what happens.

Now thinking that I have a spark problem. Coil? I'll try swapping that out.

Regards, Lawrence.

lawrenceR · #6 10-22-2003, 01:08 PM

Well, spent some more time on the red POS. Swapped out ignition control module, coil, dist cap no change. Put the timing light on all the spark plug leads; and there is spark. Now I'm pretty sure it isn't fuel and it isn't electrical, and it isn't mechanical.

What's left? Well, I still haven't got rid of the white smoke, which I thought was just some residual coolant left over from replacing the intake manifold gaskets and spilling some coolant. I think I'm wrong about that. I managed to look at the tail pipe while keeping the car running and there was more white smoke than I thought.

So now it looks like coolant in the combustion chambers, presumably leaking from the intake.

When I replaced the intake manifold gaskets I noticed that somebody before me used a lot of sealant around the gaskets. I know the heads have been done. New theory is that the heads were milled upsetting the fit between the intake manifold and the heads, causing the water passages not to line up and leak. F**K.

Now I guess I strip it all apart and use some sealant around the gaskets. I'm so not very happy. Anybody have any experience with this?

Regards, Lawrence.

maheath · #7 10-22-2003, 02:39 PM

On the compression test, did you crank the engine until the needle stopped raising? What are the values you recorded?

lawrenceR · #8 10-22-2003, 07:38 PM

I had the dealer do a diagnostic and they checked compression on the cylinders that weren't firing, and said they were fine. I haven't done a full compression test. I'm scared to. But maybe I have to grit my teeth and do it. I'm going to get some goop and try to seal the manifold. And **IF THERE'S A GOD** the car will run after that.
Regards, Lawrence.

Tom McMenamin · #9 10-24-2003, 11:32 PM

Do the compression and then do a leak down test.

The leak down is the greatest. Search this site for the results of what you get when you run this test. I can't think of a whole lot in will not uncover of items you are describing!

Give it a try!

Good Luck

lawrenceR · #10 11-24-2003, 08:00 PM

Well, finallly, the red POS, runs-and runs nicely. Thanks to everybody for your help. I put a bunch of goo around the intake manifold gaskets, and now they seal properly. There was also some sort of hangup in the mixture control that I can't really explain, but a bit of adjustment to that made the car fire right up. What a relief, I've been at that job for 3 months. I'm happy I didn't buy the new fuel distributor as the dealer diagnosed...

Now all I have to do is replace the cracked dashboard and the car is done. I'm sure this will be a nightmare too.

Cheers, Lawrence.