1973 280 SE Running Problems Need Help!

[paris1880]

Hi all!

We'd like some help to diagnose a problem with our 73 280se 4.5. We got the car a few months ago and it ran ok when we first started it up but started missing on the test drive. Had loss of power and seems like its not always running on all 8, sometimes only 4 are firing. Replaced points/cond/rotor/cap/wires/plugs and changed nothing. I removed fuel filter and found nothing bad. All original near engine compartment. It will sit at idle rough/smooth/rough for ever. I have moved the wire looms and tapped on things but cannot locate problem and don't know what to try next. Any ideas?

Tom


all

[MunichTaxi]

Heat riser plate (inside manifold) broke loose: M130 engine

[230/8]

Even though I own one, I don't know much about the FI systems on these 117 V8s. And what I do know is just enough to get me in deep s***. But I do seem to recall that the FI fires four injectors at a time, i.e. one set of four and then the other set of four. If the engine is truly is dropping out four cylinders and only firing on four remaining, maybe the trigger points or some related FI circuit is cutting out half the injectors on you?

You might try a search on injectors, I'm sure I saw something related to this on this forum.

230/8

[Tomguy]

Indeed, it can be bad EFI trigger points, or a bad ground for the injector wiring. Check the mass of cables connected to the body/frame behind the battery - that's where the fuel injectors are grounded at. Make sure it's clean and rust-free. To check each individual injector, get a long handled screwdriver and hold the tip of it against the base of the injector, and listen through the handle. You should hear the sound of it firing (several times per second). If you don't hear each one, you've isolated your problem. Remember, injector sequence is:

1 + 5
4 + 8
6 + 3
7 + 2

If any of these "pairs" aren't firing, then you probably have dirty or bad EFI trigger points. I bet you have grease or something else crudding the points up - they're located inside the distributor and you need to remove the dizzy to access them. I highly suggest you do this and give them a good cleaning with PAPER or a soft CLOTH (NOT SANDPAPER EVER!). Make sure there's no lint on them on reassembly. And by the way, snip the wire going to the condenser. It causes more troubles than it's worth.

Munich: M117 V8's are EFI and don't have a heat riser plate