450slc engine trouble

[joeltracey]

Hi All,

This is my first post on the MBOA forum (I`m so excited!!).

I have a 1979 450slc which I am soon to begin restoration work on. The engine has suddenly stopped running and I need some advice on what might be the cause. This is awful timing as I was in the process of moving it it from it's current location (drive) to the workshop (just complete) when it died.

I have had it for some time (12 months) and it was running fine before this. It was a little rough but I simply put this down to the fact that the car hadn`t been driven in the 4 years before I got it.

I have checked the obvious things. The battery is fine and the spark plugs are firing nicely. The engine seemed to be getting fuel but I changed the fuel filter today in case there wasn`t enough flowing. This had no effect. The fuel pump is new too. Is it the injection system?

When I turn the ignition the car seems to start for the briefest of moments. If I release the ignition however, it dies.

Does anyone have any thoughts on what the problem might be?? Has this happened to anyone else?

I would really appeciate any advice. I know y'all won`t fail me! Thanks,

Joel

 

[Myros]

just how obvious?

I'd have a look at the fuses as well. Give them all a twiddle, or better still, renew with new ones. Use some electrical contact cleaner spray down there while you are at it. Old torpedo fuses just love to let you down.

 

[joeltracey]

Thanks for the advice M.

After much head scratching and trial and error I found the problem and fixed it.

In the end the fault was a busted ballist resistor. There are two, which are located on the right hand side of the engine bay (if you standing in front of the car). They are white and are bolted onto the inner wing. The ballist resistors are connected to the ignition coil.

The plastic casing of one of the the resistors had cracked and exposed the wire. This had then rusted to the point that it snapped. A quick clean up and reconnection got her going again. Does anyone know where you can buy replacement ballist resistors?

During my troubleshooting exercise I also tested the injectors and found a few to be poor. If anyone has advice on where I could get new ones or even a good way to clean the old ones I would really appreciate it.

Thanks,

Joel

 

[television]

Not easy testing injectors without a test rig. I would put some injector cleaner in the fuel tank, run it for say 200 miles then take them out and test for an even spray.

Re Ballast ressistor's It was common before we had electonic ignition system's to use a 8volt coil, with a ballast ressistor in serries to run on 12 volt. during starting, the starter motor would short circuit the ressistor putting the full 12 volt across the 8 volt coil, this gave a 30% higher spark on the plugs for easy starting. to work out the value, it will be around 6 ohm's.
One could be taken from any early 70's car, they are all the same, or you could fit a 12 volt high performance coil, in this case you leave the ressistor out.

Malcolm

 

[joeltracey]

Thanks Malcolm,

I will look into the 12 volt coil idea. Seems like a better solution than sourcing replacement ballast resistors. Less parts to fail really!

The car is not currently road worthy so it won`t be possible to run a tank of petrol through it with injector cleaner added as you suggested. Could you take them out and soak them in a cleaner solution instead?? Would a mixture of petrol and injector cleaner do??

Cheers,

Joel

 

[television]

Thanks Malcolm,

I will look into the 12 volt coil idea. Seems like a better solution than sourcing replacement ballast resistors. Less parts to fail really!

The car is not currently road worthy so it won`t be possible to run a tank of petrol through it with injector cleaner added as you suggested. Could you take them out and soak them in a cleaner solution instead?? Would a mixture of petrol and injector cleaner do??

Cheers,

Joel

Why not do that, when they are soaked and while still wet, if you could put them on an air line, to open them, and close again ,that would allow the area around the seat to be cleaned. I used to do that myself, some time ago.

Malcolm

 

[joeltracey]

I have an idea, be it a bit unorthodox! What about using a syringe (minus a needle of course) to force the cleaning fluid through the injector? Would it generate enough force to push the fluid through? We have 50ml syringes in work that might do the job. What do you think Malcolm?

Joel

 

[television]

Hello Joe. That would certainly make a good high presure wash, do it after the have been soaking, whilst that would not open the injectors it would clean them well. they can only be opened by compressed air.

Malcolm