Won't crank from ignition
 

Hello,

I am trying to diagnose an interesting condition in my newly acquired 1981 928 5 speed.

Here is the background:

Purchased as a non runner two weeks ago. I cleaned battery ground and rewired the 14 pin connector as it was hacked and falling apart.

Car won't crank with the ignition, I have tried two ignition switches. I do hear the starter solenoid "click" when key is used.

If a small jumper is placed between pin 14 and the hot post, car starts immediately (first crank) and runs great.

Tested for voltage at the BRIDGE for starter in the CE, test light glows fine (with key in start position)

Tested for voltage at yellow wire in ignition when in start position, light glows.

Grounds cleaned above CE as well.

Here is the odd kicker, every now and again, the car will crank and start with key usually happens immediately after car started and run with PIN 14 jump method.

Could this be related to the anti theft system or a neutral safety switch (its a 5 speed)? All my keys are the same length.

Stumped, looking for suggestions.

Thanks to all!

A test light draws a lot less current that the starter solenoid. If you jumper the test light in place, and try to crank from the key, I wonder if you'll see that light dim or go out. If you do, that's an indication you have a bad switch contact upstream somewhere.

Not sure whether '81's use a starter relay. If they do, I'd check that. Regardless, the ignition switch itself would be a likely culprit as well.

Thanks. No starter relay, its a manual so it has the bridge installed instead. I guess I should measure the volts at the switch, bridge and 14 and see how much the drop is. It seems to be that 14 is not getting a clean 12.5.

More info to add to OP:

Battery reads 11 volts across the posts
Ignition YELLOW lead reads 11 volts when attempting to start
Bridge on CE (XIV) reads 9 volts when attempting to start
Jump post up front reads 11 volts
PIN #14 on plug reads 6 volts when attempting to start.

Loosing a lot of voltage along the way. Didn't check starter connections yet........

When you use the key to start it push upward on the key as you turn it if the car starts like that then either the ignition switch itself is loose on the end of the pod arm or the switch is worn out inside.

I fought with this problem for months and accidentally found the radio 12V wire grounded at dash metal frame right below the ignition switch... It's not finished the fix yet due to the amont of ignition wire harness melted, from the dash to fuse box.

The strange is everything working fine on the car, including the radio but the starter.

Seams to be a engineering mistake, it's notorious that it has no enough space for all wires there and they touch the dash's metal frame sharp edge - imagine this for 33 years (my case)

Seems like your battery doesn't have enough voltage at 11VDC to overcome all the drop between the ignition switch and the starter. There is enough voltage to engage and spin the started when using the jumper direct from the hot post to the #14 pin. Charge the battery full and then try again. If the key still won't spin the starter start by cleaning all the grounds and checking the circuit path from the ignition switch through the CEL to the 14 pin connector.

Mike

I would try jump-starting from a known-good, fully-charged battery, using known-good, heavy-duty jumper cables hooked to the jump start terminal and one of the bolts holding the engine bay cross-brace. If the car starts well, the problem is the battery, the battery connections, or the ground strap.

Thanks! I did try this on both ignition switches (I had two used switches and swapped them out) no luck!

Wiring is pretty ugly right now, gauges and switches are out of the car, I am sure I have issues as well. Thanks!

I need to get the car up in the air a bit to clean terminals at starter and grounds on block as well, thanks!

Worked like a charm. I put a jumper battery on the front jump post and car fires right up with the key! My ground strap at battery is new and I have it absolutely clean at the body. My positive cable, possibly??

I am still going to finish doing all the grounds as well.

Thanks to all for the help! Any next steps that I may have missed are welcomed:cheers:

clean the hot wire at the starter as well as the trigger wires if there may be two of these.
Clean the alternator connectons.
Inspect the positive wire run from the battery it may be damaged or corroded

You may have other things going on, but 11 volts across the battery posts is a DEAD battery.

Yes sir, I charged it today and its back to 12v.

It should be in the high 12V, something like this.

State of Charge

-------------Sealed or Flooded Lead Acid-------Gel battery------AGM battery
100%-------12.70+-------------------------------12.85+----------12.80+
75%--------12.40----------------------------------12.65------------12.60
50%--------12.20----------------------------------12.35------------12.30
25%--------12.00----------------------------------12.00------------12.00
0%----------11.80----------------------------------11.80-----------11.80

What Bill said. Fresh charge is no guarantee. Has this batt been load tested? It can show 12V on a MM and have a weak/dead cell.

I had a similar problem with my GT.. Ended up that the front engine harness (14pin across front of engine to starter) was badly frayed where the harness passes through the block to the starter. I bet if you pull that harness and rebuild, your issues will go away.