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no spark at cranking 75' 450sl

14K views 10 replies 6 participants last post by  Canuck 
#1 ·
Hi, I'm a newbie. I have a 107 D-jet that was running when I put it in the barn last year. Had a long history of running fine for 1/2 hr. and then sputtering. If at highway speed would completely die. Tried fuel direct to intake with no response. Next morning starts right up, running smoothly. Sat at a mechanic's for a year and no resolution.

Anyway, back to the barn. I decided to completely clean the fuel system, including tank and replace all hoses. Tried starting with no response. Sprayed starter fluid, no response. Cleaned every electrical connection/ground and replaced all fuses. No luck.

Checked power to coil with key on. Hot on both sides, hot on both sides of both resistors and hot on both sides of terminals just below resistors. Cleaned distributor cap, rotor and points. Installed tester light in coil lead to distributor and manually twisted rotor back and forth over dist. lobe to make/break points and tester light responded accordingly. Put the cap back on and got initial spark when attempting key start, nothing while cranking and then a spark when turning off key. I'm beginning to focus on the ignition switch but thought I would ask for input before I start throwing parts at the project. I live in Nova Scotia, right on the water, so the cars see a lot of humidity.

I have ordered a Pertronix 1885 which Pertronix technical staff says is the right unit. I don't expect this to correct my problem. My thinking here is it buys peace of mind. I've got a bucket of plugs and points from change out over the years. I had a number of these cars at one point. Now it's just this one and a 72' 107 [and it's not starting either] I might point out that having a number of these didn't help much in the knowledge department so if you respond please assume that I need tutoring!

Thanks, Don
 
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#2 · (Edited)
Welcome from another Canadian D-Jet owner.

Does sound like an ignition problem. Suspect would be the coil and the "switchgear" (The module on or under drivers side inner fender.)

If you have another D-jet, perhaps try switching the coils. You could also switch the modules, but although functionally the same, wiring is (I think) slightly different.

Ignition switch is a possibility. When you crank car, additional 12v supply is provided from starter circuit and this bypasses the first resistor. But as soon as you stop cranking that 12V source disconnects. If the 12v from ignition switch is flaky or a ground is bad, that could be your problem. I would check grounds first.

The Pertronix can be used either as just a points replacement. Or, in conjunction with a new coil, it can replace the points and the switchgear. (Pertronix Flamethrower coil is probably best, existing one is not suitable)

This thread has some good information on a similar problem:
http://www.benzworld.org/forums/r-c...tion-control-amplifier-module-failure-no.html

Check your grounds. In particular, the one right under the coil and the one at passenger side back of engine under the air filter. Running a ground from the casing of the distributor to one of those points is a good idea, but really needed in case of Pertronix.

When you get Pertronix, ignore the instructions that come with it. The 1885 does not fit as easily into the 75 D-JET, but some here have solved that. This link has the information you will need ( Michncraig posted how he did it):
http://www.benzworld.org/forums/r-c...668-pertronix-install-without-switchgear.html

That should be enough to go on with :)

BTW - Which part of Nova Scotia? Beautiful part of the world.
 
#4 ·
I live in Weymouth, a small village between Digby and Yarmouth [the 2 ferry ports] I've been here for 7 years and still content! Do you ever visit this area?

I have checked the coil against 2 others and they have same values. Had an extra switchgear module I took from a running car, tried with no success. Spent good deal of time tracking down and cleaning grounds. I have avoided trading out from the 72' because it has the same problems. I've located a new ignition switch for $56.00, so maybe I'll buy one and install that when I do the new ignition.

I've reviewed the other sites you sent and the will be very helpful.
Thanks
 
#5 ·
Thanks for responding. Yes, the fuel pump cycles on when I turn the key. Think I should confirm that it is constant while being cranked? One thing very interesting is that I recall sometime back that the pump was running backwards and I changed leads to reverse. I think I had to drill the contact to fit the terminal stud. This was a few years ago and I need to reconfirm this, may be I'm just dreaming. Seems I recall being thurough in the process, actually watching the pump go from suction on the discharge to actual flow. I do know the system is pressurized and I have tried spraying starter fluid while cranking. Are the ignition switches considered a weak link?
 
#9 ·
Put the cap back on and got initial spark when attempting key start, nothing while cranking and then a spark when turning off key. I'm beginning to focus on the ignition switch but thought I would ask for input before I start throwing parts at the project.
I'm going to give pretty strong odds that your ignition switch is frotzed. The underlined bit in the section of your original post above says that you have contact at some times while you're working on it, and those times are related to the ignition switch.

The switch is a replacable part. You will need to take the steering wheel off and remove the instrument cluster to get to it, but that's not as difficult as it could be: The '75 still has the wheel held on with a large nut. look in the E.G. v107 sticky for instructions. You'll need a VERY short flat blade screwdriver and flexible hands for the job, but it's about a 2 banana job. It takes some patience, but you can do it from the drivers' seat.

If you want more detailed instructions, or if the ones in the sticky are confusing, just ask. We'll help.

Good luck,
Scott
 
#10 ·
Before pulling the wheel etc, perhaps it would be possible to hot wire the ignition. In other words, bypass the ignition switch.

The car actually does this itself when cranking so there should be no problem. (There is a wire than comes from the starter circuit that provides 12V to the ignition by bypassing the first resistor, only during cranking)

Perhaps you could just run a wire from battery +tive to the first resistor. especially if you have installed the Pertronix, I would put a switch in the wire and only turn it on when starting and running the car.

As others have said, if you have an original fuel pump, the terminals only go on one way. Maybe you do have the pump running backwards?
 
#11 ·
Thanks to all of you for your input. In digging thru my parts boxes I found an ignition switch from a 1975 116 series, installed it and that was the problem. I've ordered a new one just to play it safe. If I remember, that 116 was from Wisconsin and the key looked original.

The fuel pump is interesting. I have 3 spares so I checked the polarity on all to verify rotation. I reinstalled the pump as removed and before driving I will revisit this issue completely. It's been a while since my first investigation but I believe I was thorough, I know fuel was coming out the discharge when I reconnected the supply line. What you will find interesting is that when I reversed the leads a few years back the car was running. Simply put, the car runs regardless. I'm sure there is an effect somewhere in performance. Twice I have taken the car to a repair shop and who knows what occurred, or was it a factory event? I'll let you know what I find. Hope you receive this post, my first reply never showed up here.
 
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