mattylan

1980 928 euro ..not run for 24 years .as previous post i have now cleaned out the interior /fuel lines off car etc... decision to be made now whether to invest in car or part out.....so wanted to see if engine runs. have rigged up a fuel supply ( all clean) turned the key and she roared into life, but as soon as you relase ignition key she stalls. don't want to keep ignition key on for fear od burning out starter. engine is intact except air box is off. definately getting fuel, perhaps with a few air bubbles.......of course now i want her to idle!!!!! any clues as to what might be causing her not to stay running?

My thanks as always in advance!!!

James Bailey

Sounds like it is starting on the cold start injector, the 9 th injector which is electric and not very concerned about fuel pressures. The CIS however is controlled by very exact fuel pressures.

You also can test to see if you directly power up the small + wire on the coil (may be marked #13) to keep spark going to the engine when you release the key ignition off the starter mode to confirm you still have spark. If it does run you KNOW the fuel system is working and it is an electrical issue.. Use a jumper wire from the jump post to the coil, alligator clips make it easy to remove. Also note that full 12 volts is too hot for the coil to run for very long.

mattylan

Thanks for your response James, appreciate you taking the time. It seems like one step forward, two steps back on this car, the instument panel looked mouldy from the outside, turns out the circuit board is really ropey and so far the speedo / odometer gubbins are rusted up solid. I couldn't even remove the needle from the dial as it had bound up on the pin!!

Mrmerlin

to remove the needle use a fork on a towel placed under the needle ,
use a soldering iron to first heat the needle base to soften the connection,
NOTE not too much heat, then fit the fork and gently pry up,
the needle should come free

Mrmerlin

..

WallyP

As James sorta says, start and die sounds like a faulty 0.4 Ohm ignition resistor, or a fault in the ignition power circuit.

If you have access to the Workshop Manuals, look at Page 97-53. Power for the ignition coil comes from the 15 bus on a black wire from Terminal O6, and runs to Terminal 15 on the Transistor Ignition Unit. From there, the power runs to the 0.4 Ohm resistor, then on a black/yellow wire to the 0.6 Ohm resistor, then on a black wire to Terminal 15 on the Ignition Coil.

During normal running, the power thus goes thru both resistors. There is a black/yellow wire that runs from Terminal 16 on the starter to the output end of the 0.4 Ohm resistor. This wire has battery voltage only while the starter is operating, so when the starter is operating, the coil is fed power from the starter, bypassing the 0.4 Ohm resistor.

This increases the voltage to the coil, helping to make up for lower voltage available at cranking. When you release the starter, the coil is fed power thru both the 0.4 Ohm and the 0.6 Ohm resistors, making the coil last longer. If the 0.4 Ohm resistor fails, you will get your symptoms.

James Bailey

Just trying to narrow down the problem to is it fuel or spark ? Might even be an ignition switch issue but the jumper to the coil is a good test

basic logical problem solving of eliminating the most possibilities with each step as you work toward the actual issue. Why check 20 things if one test can eliminate 10 as possibilities ?

I did not go into discussing the ballast resistors as they may not be part of the problem and while excellent information may just misdirect his efforts. If faulty there are suitable Mercedes units to replace the no longer made Porsche specific units

mattylan

Guys, thanks for your continued input, problem is I don't understand what you are saying!! Seriously though, still stripping down car to ascertain whether or not there is sufficient left in good enough condition to justify the spend or whether it will simply end up being a parts car!

Looking for a little stand alone project this weekend, I decided to remove the heater blower as it's clear there has been leakage down into the passenger footwell in the past, and going on past experience of this car, its mechanism will be stippled with rust. Well what a pain in the backside that was, not so much from the top as the fact that the bottom grill nuts were all rusted to bu*gery on the captive bolts, four of which run along the back behind the big wiring loom, that's stiff as a stiff thing to move, tucked away right behind the CE board. Also, having searched the web for reminders on how to remove , indications were that there was a fixing through the grill that would release the heater.
So, one snapped captive bolt later, all the bottom bolts were released. But would the heater come out, like hell it would. It twisted, it turned but it was clear something was holding it in from below. Back round into the passenger footwell to confirm all the bolts were free, yep, but still stuck. So one infantile rant later a lightbulb goes on. So imagine this at the Porsche factory 35 years ago : ~~

yes Hans, in order to remove the heater in future years we will make it so that the 6 foot three man has to lie in the passenger footwell on his back with the CE bracket digging into his neck, whilst attempting to hold open a resisting flap not 3 inches from his nose, hold a torch with his teeth AND insert a screwdriver to release the rusty screw that doesn't want to turn that's just a blurry thing because of his failing eyesight .......funny ja!!

Anyway rant over, having finally managed to wriggle the heater out, sure enough the fan was stiff as anything due to corrosion. I then took the chance to clean out the bulkhead, using compressed air to force all the debris from under the windscreen wiper mechanism.

This appeared :



made out of balsa wood, with prongs similar in size to a paper clip.....what the hell.... does anyone recognize this part...... is it a vital part of the mechanics of the car which will cause me to die horribly in a fireball, or have I a secret society living in a minature village in my bulkhead?

Bill Ball

That is part of the framitz valve that fits into the klackston manifold.





Seriously, it's not part of the car.

SeanR

I had this problem on an '82 last week that was driving me nuts. Only had .7v at the coil etc. I replaced the .4ohm resistor and when I turned the key on it started getting hot. Not just warm but 751 degrees measured with my trusty IR thermometer. Next step was to test the continuity to ground and to make a long story short, inside the starter, the two small leads were grounding out. This was causing the car to only run when the starter was engaged.

ramcram

yes, same here, '81S would die as soon as crank dropped. Took out the near new hi-torque mini starter and fitted a stock one and no problem since.