Trying to get 74 450SE running after long sleep! - LONG

Hello all,

Just found this board and have been searching the archives for my issue and couldn’t find it so I’ll present it to this esteemed group for comment.

I have recently acquired a 1974 Mercedes 450SE that has sat for the majority of the past twenty plus years and I’m having some difficulties getting it started. The problems appears to be fuel injection related and I don’t have much experience with the D-Jet system. I never thought I’d ever catch myself thinking that I wished a project had K-Jet!

In the beginning… The history of this car (if it can be believed) is that it was purchased new in Germany by a US Army officer who then brought it back to the states with him. This individual passed on sometime around 1980 and I think the ownership went to his son and the car just sat there for about 10-15 years. My brother-in-law then talked this guy out of it about 10 years ago and claims he had it running (albeit roughly) for a while but never drove it. During this time period he enlisted a mechanic from the local Mercedes dealer to assist (in his spare time) with replacing both fuel pressure regulators and rewiring the injector/top engine wiring. Some critter had made it’s home under the hood and apparently used the harness as a midnight snack! My wife bought it from him about a month ago as he finally decided he’d never have time to fart with it. That’s how I wound up with it! If the odometer is to be believed it has 34k miles but looking at the grease on the bottom of the differential housing leads me to believe the odo had quit working or it has been rolled back.

The present… When I first started jacking with it everything fuel system wise was dead so the first thing I did was remove the fuel pump, disassemble, clean, and stick it back together. During this operation I also changed the oil and filter, flushed brake system, replaced fuel filter, drained tank, and put in 5 gl gas w/bottle of injector cleaner. Previously, my bro-in-law had removed all of the fuel injectors and soaked them in solvent for a couple of weeks as they were frozen. After reinstalling the fuel pump we gave it crank and no start but I immediately knew we had fuel pressure as gas sprayed everywhere from all of the rotted fuel hoses under the hood!

I replaced all of the rubber line I could see and tried again. This time no shower but still no run, it did cough a few times, though, and that encouraged me. I then unbolted all of the injector retainers and propped them (and the fuel rail) up so I could watch them during cranking and only two injectors on each bank were squirting. Switching the injector wires from a working to non-working injector indicated the actual injector was working so I started looking at the wiring.

I started to verify that all of the injectors had a good ground via the brown wire and when I got on the l/h side found this “mechanic” had re-wired three of the injectors with grounds on both connections! I was immediately excited as I re-wired that side according to the Mercedes factory manual wiring diagram. Unfortunately things did not improve so I pulled the computer and checked continuity on the two wires that connect to the not firing injectors, wires checked good.

I then attempted to see if the impulse triggers were functioning in the distributor but a wire broke off on the connector block. Bro-in-law did not have a big enough soldering iron so that is where my troubleshooting ended last weekend. I don’t know if we broke the wire or if it had already been broken. Car is about 150 miles away…

Next trip (in two weeks) I’ll take heavier soldering equipment, repair wire and finish tracing continuity. At this point I have the feeling that my problem is either in the impulse triggers or the ECU is dead. Is it likely the ECU injector drivers would fry if they were, say, wired or shorted to ground?

If I haven’t lost your interest yet I congratulate/thank you for reading this far but I thought that some history along with what has been done/tried/screwed up before and since I started hacking on it would help! I am pretty sure that I have all of the injectors wired up correctly and will fix the wire from the impulse triggers in a couple of weeks. Is there anything I have overlooked?

Thanks in advance,

Justin Bowser

[Kebowers]

sounds lik eyou are right at the problem. It's either trigger contacts not working or the broken wire. The injectors are supposed to fire in sets of 4 if I remember right. It may run if all of them fire together (not sure if fuel pressure would be right), but it would not be correct and would probably be rough

Probably next weekend I'll make the trek south and work on it some more, if the weather's nice/not rotten! I took this weekend off to baby my scooter (BMW R100RT) and catch up on some other stuff.

This next trip south I will be equipped with some heavier duty soldering equipment and might take my o-scope so I can look at some computer inputs and outputs.

I'll keep y'all updated on my progress.

Thanks to all,

Justin