Hello all,

I had originally posted this in the tech section but later decided it probably makes more sense for it to be here and I didn't know how to move the original post so I apologize for the double post.

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

Justin.

If you dont have the 107 cd i would get one.
Looks as if you are on the right track.
Good luck and please keep us posted

Gunny

I have what probably is a "bootleg" of what appears to be the 116 factory manual which has helped greatly with the re-wiring efforts although some of the troubleshooting calls for specific Bosch test sets which I don't have access to. Hopefully between this literature and this board I can figure out how it's supposed to work. I am a lot more comfortable working on CIS injection on Bimmers and Volvos, this is a whole new can of worms!

This would be all so much simpler if you tripped on a tester for the D-jet in the driveway....

Check the trigger points for operation -- remove and clean them (must pull the distibutor, alas), since if they don't switch, the injectors won't operate.

If they are shot, get new ones -- the appear on eBay once in a while, and are still available new.

The Brain is probably stil OK, since some of the injectors are working. They operate in pairs, by the way.

You will also need to replace any rotten rubber hoses -- the one for the MAP sensor in particular, as a large vac leak will prevent running (too much fuel).

Don't test the injectors by pointing them up, they spray WAY too much fuel.

Replace all the ignition stuff -- new points, wires, cap, and rotor -- the insulation is surely shot by now.

The milage is probably 134,000 -- and the odometer is probably dead, easy fix. Try resetting the trip odometer -- if the odo goes up one mile each time you go past all zeros on the trip odometer, it needs the zinc driving gear locktited down.

If you get fuel spray out of some injectors, my bet is fixing the wiring correctly will get you running!

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Good explanation Justin. I'm glad you made it over here from the BB. The guys here are super and will point you in the right direction.

Warren Bain aka Token Ring Man

__________________
Regards

Warren

Currently 1965 220Sb, 2002 FORD Crown Vic Police Interceptor

Had 1965 220SEb, 1967 230S, 280SE 4.5, 300SE (W126), 420SEL

ENTER > = (HP RPN)

Not part of the in-crowd since 1952.

Justin, you're going to have to take the cam overs off as well to make sure there are no timing chain or chain guide issues. I am including a link from Mr. W126 that shows how to change the chain guides. He also has procedures on changing the chain on his web site. Once you do the guides, you might as well do the guides while you're in there.

http://www.pindelski.com/cars/W126/W126_chain_rails/W126_chain_rails.html

Regards.

wb

__________________
Regards

Warren

Currently 1965 220Sb, 2002 FORD Crown Vic Police Interceptor

Had 1965 220SEb, 1967 230S, 280SE 4.5, 300SE (W126), 420SEL

ENTER > = (HP RPN)

Not part of the in-crowd since 1952.

Well, lemme see if I can address these suggestions! :-)

1. I'm afraid if I tripped on one in the driveway I would probably break it and still be in the pickle I am!

2. I was going to put a meter on the connector from the impulse triggers last weekend and that is when we discovered we had broken a wire or one of them was already broke. Will take big a$$ soldering iron with me in two weeks, fix and test. I would have to guess that at least two of them are working...

3. If we find that some of the contacts aren't working I'll try to fix as I am a cheap ba$tard! Really have to pull the dist? Drat...

4. I hope you are right about the brain box. I had decided from the wiring diagram that they are supposed to fire in pairs and the ones that are firing are paired up from the computer. That's why I am hoping the Mr. Monkeywrench that miswired all the stuff didn't short something out and fry some drivers in the brain.

5. I've replaced about avery hose I can find under the hood but will look for more!

6. Hehe, they spray a lot when they're pointed sideways too!

7. Bro-in-law did that a few years (8-10? He can't remember exactly) ago before he parked it.

8. I hope so!

I am still trying to figure out the relationship between the impulse trigger points and the injectors. Does the trigger point actuation tell the computer when to start the squirt and then the brain decides how much to squirt based on sensor inputs? There appear to be 4 sets of these trigger points so I guess if my theory holds it would follow that if two were non-functional then I would have 4 injectors that don't get fire? If this is the case then I must have other problems than the one wire as depending on the wire this would either take out all four or just one... My head hurts, I need a beer.

So far this has been a humbling and educational experience and I appreciate all the help I can get!

Justin

Justin

Try this link

Bob


http://members.rennlist.com/pbanders/ecu.htm

Bob,

That is cool! Now I have an excuse to get the scope out of the back of the closet and try to remember how to use it! With the pin-outs and block diagram I should be able to verify exactly what is wrong if it's not the impulse trigger points.

I am taking the weekend off from working on this monster to pay a little attention to my scooter (BMW R100RT) and catch up on some stuff! May make the trip next weekend to work on this problem and I'll let y'all know if I figure anything out.

Thanks a bunch,

Justin

Justin

Please keep us posted I have a 1975 that runs like a dog also.

Oh how i wish i had a scope

Good luck

Bob

Gy Sgt, some scopes can be bought failry inexpensivly. There are many older Techtronix or HP scopes available and you can even get software for your PC, and an external box I think, to plug into your PC to make it a digital VOM, scope or what have you.

__________________
Regards

Warren

Currently 1965 220Sb, 2002 FORD Crown Vic Police Interceptor

Had 1965 220SEb, 1967 230S, 280SE 4.5, 300SE (W126), 420SEL

ENTER > = (HP RPN)

Not part of the in-crowd since 1952.

Went down to work on the monster this weekend and was almost happy, for a while.

Found a wire broken on the connector from the impulse trigger points so soldered that back on and all of the injectors started firing, man I was pumped! Just had the injectors "laying" in their holes and cranked on it and it started - rpm immediately started to take off so we shut it down.

Clamped down all of the injectors and it started and sounded like it was only running on 4-5 cylinders so I started checking for spark. Several plugs not firing so checked plug wires and they were shot. Put on new plug wires and now it doesn't start any more!

Started checking firing order and everything on the cap was 180 degrees out so pulled distributor. Trigger point assy was only held in by one loose screw so scrounged a screw, tightened trigger point assy, re-stabbed distributor, moved plug wires to proper locations, still no start!!!

Drug my O-scope out of the car and looked at one injector signal, pulse width looked very narrow, 2-3 msec.

At this point I was looking for a fresh can of gas, a rag, and a box of matches so I decided it was time to quit as it was also dark.

Will go down in a couple more weeks with a fresh set of plugs and some waveform pictures to compare and have another stab at it. Told the wife this thing just took another step towards the bone yard. >:-|

Until next time...

Justin B.

Justin:

Did you verify both timing and condition of points? The ignition is transistorized, but the points can still burn, and will give erratic spark.

Also, veryfy that you do indeed have the distributor and spark plugs lined up -- the distributor can be put in at any position the gears line up, so it's easy to be one off, in which case no run.

Pulse width on the injectors may not be too far off -- the car starts on the start valve anyway.

Check the resistance on the MAP, too -- if it is out, you will need a new one.

I assume that you have verified fuel pressure and flow.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Peter,

Got bunches of fuel flow, have not hooked up a pressure gauge yet but the injectors squirt a nice fine consistent pattern.

Next time I go down I'll put in new plugs and pull the dist and clean the impulse trigger points and will check the points/gap as well.

If we dump some gas down the throttle body it trys to start so it seems to me to still be fuel related in some way. I'll also pull the cold start squirter out to see if it is actuating.

We did pull #1 plug and brought the piston up pretty close to TDC of compression stroke and dropped the distributor back in with the rotor pointing in the vicinity of the #1 plug wire so I would think it should at least be close enough to start. Please let me know if it is more critical than that.

Thanks,

Justin

Justin:

I thought I had mine right, too, but was actually one step off. The distributor turns quite a bit as the gears engage.

Probably best to set the engine to TDC on #1 (front cylinder on the passenger side, buy the way.....) and check that you are on the compression stroke -- you can see the cam lobes through the oil filler hole with the cap off. Make sure the rotor points to #1 wire, and that the point rubbing block is very close to on on top of the cam lobe, distrubutor installed.

Points are cheap, like $5.00, so it is silly not to replace them, just one screw. Gap is 0.3mm or very close (30 degrees dwell) -- make SURE you clean the feeler with solvent before you gap the points, oil will cause them to burn very quickly (this latter learned the hard way).

Check the two temp sensors and make sure they actually read resistance -- intake air (in teh air horn) should be 300 ohm at 68F, coolant sensor (intake crossover) should be 2500 ohm at 68F.

Duration will be short on the injectors -- they will deliver 200 cc of fuel in 30 sec continuously open.....

Having the injectors loose will cause the engine to run away -- the MAP is the only measure of airflow, so the control box will happily at fuel to match the pressure.

I suspect you have an ignition problem rather than a fuel problem, other than the dead fuel in the injectors themselves. No way to clean it out other than to run them.

You will love this car when you get it running, trust me!

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!