Author Topic: 280SE ignition questions - what have I got? and it won't start after it rains  (Read 152 times)

kalpol

  • Newbie
  • Posts: 2
  • W116 Enthusiast
  • Location: Texas
Hi folks, I am new to this forum but have been all over MB forums on the Internet for my various cars for years, and this is a problem I have never been able to solve.

I have a 79 280SE, European model with what appears to be the TSZ 8u "breakerless transistorized ignition". It has the diagnostic testing port, distributor transmitter, etc. First question, from my research this ignition system came only on 80 and later cars, so do I really have it on a 79 model? The TSZ4 diagram does not appear to have the 9-port diagnostic socket that I have. I am pretty sure it wasn't retrofitted (but anything is possible).

I've owned this car for something like 17 years and it has never liked to start after sitting in rain. Even with a cover, it would not start, or if it did start, it would run terribly, die under load, etc. Sometimes cylinders would suddenly catch and fire then stop. After drying out for a while it would start and run fine. If garaged it was never a problem, but after a steady rain, even with a waterproof cover, it had issues.

I started in on the TSZ8u diagnosis chart this morning and it immediately failed for the diagnostic socket jack 5 test - battery voltage is about 11 (haven't driven it for a while) and jack 5 is only 4-5. So problem 1 - the next step is to test voltage supply from ignition lock, which I am not yet sure how to do.

I went on to test 2, where voltage between jacks 4 and 5 should be zero, and it is not - 4 volts present there. Next step is to replace the switching unit!

Is there any way I can verify the switching unit is indeed bad?

Thanks folks, I look forward to helping out :)

revilla

  • Classic
  • **
  • Posts: 204
  • W116 Enthusiast
  • Location: Aix-en-Provence, France
Hi,

One possible root cause is humidity is one of the 3 relays in the lower left A pillar at ankle level right behind the parking break pedal behind the little plastic cover with few vents where the hood release handle is located. That happened to me once.  Humidity got trapped there corroding one of the relays.  There's also the pump relay in the fuse box worth checking.  These relays are all over your car so you can simply visually inspect them and swap them with another just to check.

The other probable  root cause is your Warm up regulator.  It might be out of tolerances.  The best to tackle that is to adjust your system pressure (sp), control pressure (cp) and static pressure.  If these pressures are out of spec it can give the symptoms you described.  But before touching the WUR, it's better to measure those pressures. 

One quick test you can do before touching your WUR is the following:

When your car is cold, remove the filter assy.  Locate the 5mm hole on top of your fuel distributor head assy.  Remove the screw.  Inside, but not visible, is a 3mm hex head screw that control the fuel mixture.  Insert a long  3mm allen key.  Mark very well its initial position.  Have someone start the engine.  Turn the allen key first clockwise (richer mixture) 1 turn.  Any changes?  Idle more stable?  No detonations? If worse go back to original position then turn the allen key counterclockwise (leaner mixture) same questions.  This test must be done quick (2 minutes max) while the engine temp is still cold.  You are trying to test if your WUR needs further adjustment.  But if you manage to find the sweet spot while cold and it remains stable at op temp BINGO, you don't need to touch your WUR.  If, on the other hand, the situation improves at cold temp but worse at op temp, you probably have to adjust the WUR, pressure regulator and fuel accumulator to adjust cp, sp and static (in that order).  This is more complex as the location of the WUR in our 280s is quite odd and uncomfortable next to the oil filter. There's a procedure I did to adjust the WUR removed with the engine running that saves the hassle of removing, adjusting, reassy, test, removing... which is a pain in the neck!  Before we go there check the 2 easier points above and let us know how it goes.

Welcome to the forum.


note: 4V-5V after the 2nd ballast resistor is in spec.  9V after the 1st one and 12V before that. 
Robert
W116 1977 280SEL & 1979 280SE

kalpol

  • Newbie
  • Posts: 2
  • W116 Enthusiast
  • Location: Texas
OK thanks, I will have a look. Of course after drying out for a few hours it started right up.

beagle2022

  • Classic
  • **
  • Posts: 220
  • 1979 280 sel
  • Location: Sydney Australia
I used to have a 1979 280sel with that ignition.  It is legit.
Sydney, Australia