rjtw

Hi all,
I'm debugging an intermittent no-start on my '83 928S. I have searched for and found many helpful hints here on Rennlist, esp. from Wally and Randy (including Randy's hotstart relay fix). I'm just starting to dig into it now, after cleaning all the ground points I can find under the hood.

One piece of information I can't seem to locate, should I need it: Does anyone know where the grounding point of terminal 85 is? Does it go out to the engine bay somewhere? If I have a bad ground on 85, I don't want to have to tear out the fuse board and track wires back there if I don't absolutely have to :-)

Thanks!!
Rick

Alan

It should be a direct ground - you can test it from the relay socket with a multimeter in connectivity tester mode (or ohmmeter). The physical connection should be "Rear of Wheel Arch Underneath Right Rear Trim Panel" - this is the direct location detail notes from the factory manual - There are intermediate connections in this circuit in the area forward & above the spare tire well (4 pin connector pins 1&2)

Alan

dr bob

The wiring diagrams fro '83 are less than stellar, The drawing shows a routing through two different connectors on the way to ground. Meanwhile, I expect that circuit to include the neutral safety switch on the automatic gearbox cars, as it does on the later (like my '89 car). The neutral safety switch is not included in the manual trans cars, and again referring to my later car, would be replaced by a jumper in the starter relay socket between relay terminal 86 (from 50 circuit at the ignition switch) and relay terminal 87 to the starter solenoid mounted on the starter motor.

Edit: Typing while Allan was typing. The routing through those connectors in the rear of the car as he describes would need to include the neutral safety switch.

Mrmerlin

its quite common for the ground point under the rear quarter liner in the right side of the hatch area to get corroded from leaking hatch seals, look for this first also check the spare tire well for ground points, I suggest to use deoxit spray on all electrical connections

rjtw

Thanks all for the quick feedback. The damn thing is starting just fine now. I did clean the engine to chassis ground strap just now, and also tested with an ohmmeter the resistance from pin 85 to ground -- it's 4.5 ohms (to a ground on the crossbar brace under the hood). For reference, the resistance just touching the wire to the door jamb hinge was 3 ohms, so 4.5 is a little high... but excessive? Not sure.

I also tested the voltage at the yellow wire at the starter, and it was 10.5 volts when cranking. I also tested the voltage at the main battery connection at the starter under cranking, also 10.5 volts, so the yellow wire connectivity seems to be fine.

Just for kicks I'm rigging a workaround so I can just jump from the jumper post directly to the yellow pin at the big connector next to the jumper post (with a wire) -- that should get me out of a jam should it fail to start when out and about.

I will dig around the back for that ground -- that's great info, and there may be a tiny leak back there somewhere.

Um, do I have to remove that rear quarter panel to access the ground?

THANKS!!
Rick

Mrmerlin

to get to the wires they will be on the floor of the hatch or the rear bulkhead depending on the year,


Its best to follow the brown wires as they go under the interior liner.

So to get to the wires , remove the RR floor hold down bracket, PB blaster it first.
then about 3 of the rear screws holding down the rear edges of the liner,
then gently move it just enough to get a wrench into the area, pushing it further will usually crack the hardboard

The Forgotten On

Happened to mine when I bought it. Be very careful as the quarter panels are relatively delicate.

rjtw

Just for reference, I did end up loosening the entire RR inner panel to get to that ground location. For future reference, here's how it came out on my '83: I removed the back seat, the three little screws in the back of the quarter panel, the two screws at the top forward corner (including the coat hangar), popped the three retainers on the C-pillar with a thin ruler and fingers, and the two sheet metal screws at the base of the panel over the gas tank area. I also removed the two screws holding in the plastic surround around the front seat belt upper support.

That left the secondary panel to be removed, which is immediately adjacent to the back seat. This is a small panel attached to the main quarter panel, but you have to remove it to gain access to yet another sheet metal holddown for the quarter panel hidden beneath the secondary panel. Remove the little screw at the upper back edge of the panel (it screws into one of the sheet metal holddown tabs for the quarter panel itself). The secondary panel attaches to the quarter panel by two upward-facing tabs... one roughly at the top middle of the secondary panel, and the second one at the front lower edge. On my car, the best way to get it out was to locate the upper tab, and push gently down on the secondary panel, causing the tab to slip out and disengage from the quarter panel. I then slid the back of the secondary panel backwards and up, while keeping the forward section as low as possible, which eventually will disengage the forward tab.

That left only two more screws... one on a third, forward-most sheet metal tab right in the middle of where the secondary panel was covering, and a second, small screw at the immediate forward lower end of the panel. This last one was the only difficult one -- it's really buried under the front side section of the back seat. Oh, and remove the door trim strip at the back.

After all that, it was relatively easy to gently rock and slide the quarter panel forward a few inches. That causes one final tab, approximately above the rear wheel on the broad upper horizontal section of the panel, to disengage. There is a tab sticking out from below the window, which engages a sheet metal slot bonded to the lower surface of the panel. Once that pops loose, you have plenty of room to swing out the back edge of the panel at least a foot and gain easy access to the big grounding bolt. There are also a couple of connectors back there, which I cleaned up as best I could and fit back together. I also cleaned up the two small connectors inside the spare tire area (I have no idea what they are for).

When all is said and done, I'm not sure I accomplished much... the grounding bolt area was totally pristine, not a trace of corrosion, and nice and tight, and the connectors were all in good shape. Still, it's nice to have that crossed of my list. Should the problem arise again, I will try the hot start technique on the yellow wire at the 14-pin connector. If that fails, I will know it's a bad wire from there to the starter or, more likely, a starter problem. If the hot start works, then it's either a relay or, more likely because I just swapped relays, an ignition switch issue or possibly ignition switch-to-relay wiring issue. That really narrows things down :-)

PS mine's a 5-speed.


Rick

Mrmerlin

Thanks for taking the time to update this thread

Alan

No neutral switch on a manual. On an '83 there is a real starter relay for Auto & Manual - the same for both - except for the coil ground config. On the earliest cars there was really only a starter DISABLE relay for the Auto cars - jumper for the Manuals - in both cases the ignition switch still switched the solenoid load...

Alan

Landseer

Those grounds for the panel mounted relays are at bulkhead/ firewall above the CE panel.
Its adviseable to remove, inspect, clean and re-fuse the CE panel.

Mrmerlin

and use Deoxit on all of the elex conections

Alan

No - not this one - its a potentially (for an Auto) switched ground and is remote.

I wasn't guessing.

Alan

Landseer

I was more reacting to the reticence Rick had about pulling the panel, which is a pretty easy thing to do and can solve a lot of problems. Its the first place I've been going when trying to resurrect one of these cars.

No, the starter relay 85 pin doesn't ground at the top of the panel at the bulkhead.
It passes through the transmission interlock switch that needs to be in either Park or Neutral, and a couple plug connections in the trunk area, terminating under the right rear quarter, just like you said. Fuel pump grounds there too, as do the taillights.

You rarely if ever guess on this stuff, I know that. Sorry, I skim read while immersed in something else, missed the fact you guys had already called it, including Dr Bob's workaround. Dumbness again on my part.

rjtw

As a final followup, the car has been starting just fine all summer long now. I'm sure that removing that right rear quarter panel and cleaning the connectors solved the problem. The ground point itself back there was pristine, and the only other thing I cleaned was the connectors -- thus I believe them to be the culprit. Prior to this fix, I'd have an intermittent problem that still had a high enough frequency of occurrence for me to say now that it is definitely gone.

Thanks again to all those who offered such valuable information so quickly, which led me directly to the fix.

Hopefully this can help someone someday!

Rick