73 450sl runs horrible - PeachParts Mercedes-Benz Forum

JBR · #1 03-14-2006, 07:33 AM

It seems as if every time I do something to the car it runs even worse.
New fuel lines, Injector cleaner, Some new vac lines,new cap,rotor,plug wires,new plugs fuel filter.
Things I have noticed.
Manifold pressure sensor, The wires were in reversed. I switched.
On the fire wall are 2 vac pods, with small vac lines top and bottom, also electrical wire on bottom. The one on the pass. side has an open port(no vac line to it?). Should I plug it? The one to the right of it has an open port on top with a small goose neck vac line. The vac storage container under the pass fended had a broken line which I fixed.
The car seems to run on only a few cylinders. It starts easy now that I found the small red wire on the + battery post was not allowing the fuel pump to run.
It runs like s**t when its cold and like s**t when its warmed up. Once it warms up it will idle so low that it will stall. When I drove the car home in Nov 05 it ran much better than it does now.
I have sprayed carb clenaer around the injectors and heard no difference.
Any ideas out there. Thanks

autozen · #2 03-14-2006, 11:32 AM

Set the engine on TDC, remove the distributer, and clean the trigger points in the base of the distributer. Also run the folded edge of a piece of white paper through the ignition points. The paper will have blue collored depsits where it went through the points. Check back after you've done that.
Good luck.

JBR · #3 03-14-2006, 11:59 AM

Thanks Autozen. I have read a couple items on cleaning the trigger points but never heard that it had to be on TDC. Also when I remove the dist. does the ignition points have to be removed? The reason I am asking is,if the ingition points are not moved then I should not have to redo the dwell.
Thanks again.

autozen · #4 03-14-2006, 12:10 PM

You do not have to remove the ignition points. The reason for TDC is to check where the rotor points and where the hold down bolt is positioned in the slot. With these two references, you can drop the dist back in the hole and tighten the hold down without fussing with timing or dwell.

JBR · #5 03-14-2006, 03:14 PM

I am not certian on how to find TDC. Also what cyl.to get and also where is #1 cyl. on a 4.5 . What if I put a mark on the dist. lip showing where the rotor should point, and put a mark on the dist and engine block showing where the dist. should align. Thanks

JBR · #6 03-15-2006, 06:37 AM

Thanks for your help Autozen. I borrowed a dwell meter for this weekend. My plan is as follows.
Remove dist. cap and rotor.
clean ignition points.
check gap,set to .016 if needed.
pull dist coil wire lay on block to ground it.
hook up dwell meter,green wire + side of coil,blk wire to ground.
have my son turn key to turn engine over.
read dwell,set to 30* if needed
put rotor,cap and coil wire back on.
check timing with light, set to 5* atdc with dist vac. line on,car at 800rpm.
If this does not fix the very rough running of the car (hot or cold) Then.
Remove the dist. and clean the trigger points.
If the trigger points are good, the dwell is good and the timing is good, and plug wires and plugs all good. I guess I can rule out ignition as being a problem. How does this sound.

autozen · #7 03-15-2006, 10:13 AM

Congrats. You did make a plan which is smarter than just diving in, however, you're plan won't work. You do not need to set both point gap and dwell, because they are the same thing. Also if you hook the dwell reading to the coil, you won't get a reading. If your system hasn't been modified, you need to connect to terminal 7 at the bottom of the left front fender. #1 is the first cyl on right bank. #7 is first cyl on left bank. TDC looks like O|T on the crank dampner. Unless you pull the dist, there isn't much point in doing anything other than runnung the folded edge of a white piece of paper through the points. You really should grab an M117 book off of ebay.

JBR · #8 03-15-2006, 10:43 AM

Now you are going to think I'am real stupid.
When you say left or right- Left is the drivers side and right is the pass. side.
So first what the heck is terminal # 7 at the bottom of drivers side fender?
Thank you for the #1 cyl location (front plug on pass. side.) I did not realize that the crank was marked for TDC, just line up the O/T with the pointed.
Thanks again

autozen · #9 03-15-2006, 11:45 AM

Correct. Always identify left and right from driver's seat. If someone hasn't REWIRED your ignition circuit, you should have an ignition module somewhere low on the left front fender. You can follow the green wire from the dist down to it. There should be a little brass terminal to clip to. On some SL models there is a little terminal block with 2 terminals on the fender. Follow the green wire.

Toddski · #10 05-09-2006, 02:21 AM

JBR, sounds like you and I have identical vehicles. Mine's a 1973 450SL with M117 engine on a 107-044 chassis. I'm curious how your problem worked out. I'm working through similar issues.

Tomguy · #11 05-09-2006, 02:58 AM

Toddski: You may be best off posting a new thread in the vintage forum explaining your symptoms. What exactly is the problem you're having?

JBR · #12 05-09-2006, 01:36 PM

Hey Toddski: Just do a search for my posts, you will see what my problems been.
I did get the car running great, it was a combination of plugs, and tune up parts. But the biggest and badest of all was vacuum leaks. It is in, getting a complete new face lift at the paint shop. Should be done this weekend, can't wait.