docmirror

The 88 I'm working on has suffered from a 'no crank' issue and I'm just getting back to sorting it. Has a new batt, clean terminals, swapped starter, cleaned 14 pin contacts and still gives a 'clunk' noise in the start position. In the failing mode, I have about 7 volts at pin 1 of the 14 pin connector and it should be about 11 or better. About every 10th time I turn the ignition to off and then start it will catch and crank the engine. If I jump the solenoid pick direct to the starter lug on the starter it will crank easily.

Pretty much have it down to corrosion on the ign switch contacts or the plug that goes into the ign switch. Is the ign switch servicable? Can it come apart and be put back together to clean the internal contacts? I'm going to check and clean the plug that serves the switch asm first, but wondering if I need to get a new ign switch, or if I can clean and re-assemble.

Mrmerlin

have you replaced the starter relay yet/ first?
Relay usually is bad before the IG switch.

you can run the starter via the 14 pin connector. this cuts out the IG switch and relay and associated wiring


the pin furthest to the front and the closest to the fender will run the starter when its touched to the hot post.
NOTE make sure its in park or neutral if a 5 speed as the engine will crank,

to start the car leave it in the run at the key,
then touch the 14 pin to the hot post

dr bob

Doc, No open-to-service option, but for sure you can attack it with contact cleaner. Then some Deoxit preservative if still needed. BUT... by the time I've gone through the trouble of loosening the pod and pulling the switch, I don't leave things to chance. Even if I can get the switch to work, I'd rather put a new piece in and not worry about it for another twenty-five years.

I trust you've already replaced the starter relay at XIV if this is an automatic-gearbox car. For those playing along at home: The auto-gearbox cars have an interposing starter relay at CE position XIV, used to integrate the neutral safety switch function. The ignition switch 50 (starter) contacts connect to one side of the relay coil (86), while the other side (85) sees ground via the combo switch on the side of transmission at the selector lever. Apply voltage via the ignition switch, and the relay only closes if the selector sees neutral or park position. A voltage drop from the switch means a lot less, since the relay is carrying the actual starter solenoid current. For manual gearbox cars, a jumper is installed in the XIV relay socket between (86) and (87), carrying current from the ignition switch contacts directly to the starter circuit.

Edit: Stan types faster than I do...

SeanR

If I have a suspect switch I get under the pod, unplug the ignition switch and pull the connector down so I can put a test switch in it and give that a go with a screw driver. Quick and easy. If it's bad just get you a new one and forget about it for 30 years.

docmirror

Yes, has new starter relay, should have mentioned that. I removed pin 1 from the 14 pin block and when touched to the jump post the starter will crank well. I'll repl the ign asm.

The good news is when it cranks finally, it starts and idles nicely. I'm pretty close to getting it on the road. Just been waiting for cooler weather to tackle it. A few more minor systems and it'll be rolling. Next up is the PS groans. I've heard the PS pump can be rebuilt, I'll ask Rog about that when I order the ign switch.

thx guys.

dr bob

Doc --

Jumper 30 and 87 momentarily in the CE panel socket XIV, Starter should crank.

Your symptom "gives a clunk in the start position" tells me it's not the switch. There's nothing to "clunk" except the starter relay engaging, relay X disengaging. Relay X would click closed on switch to "run", then click open on start position. Is the "clunk" the X-bus relay sequencing in the panel, or is it the starter solenoid trying to engage? (solenoid clunk noise from under your feet)

Alan

Only very early manual cars are configured with the starter driven directly from the ignition switch - almost all 928 have a true starter relay - but only the Auto's have the transmission neutral interlock.

Later models do have a relay bridge installed - but it is in place of the reverse/back-up lamp relay - on a manual the back-up lamps are switched by the HD transmission switch directly - no relay needed

Alan

docmirror

Ya know, that's what I was thinking. The ign switch just picks relay XIV. Shouldn't be any current in that circuit except the pick for the relay. The first(old) relay would just chatter. This relay now doesn't chatter but clearly picks with an audible sound. I'm now thinking I have some corrosion between 87 of XIV and the starter solenoid, which goes through pin 1 of the 14 pin conn.

Really can't be the ign switch if it's picking the relay solidly. I really don't want to go in the back of the CE panel, but I might have to. I've cleaned up the 14 pin conn. It seems to be getting better on its own. Now it starts every 5-6 attempt with the key in start. The other thing I want to verify is the ground strap from the eng to the chassis on the right side rear of engine. I'm wondering if there isn't some resistance there, even though everything is tight.

docmirror

OK, I just tested again. The clank is definitely the solenoid not extending the bendix gear well. I'm betting this is a starter(already swapped once) or a ground issue at the batt, or the engine to chassis. It's a good loud clank, and clearly from the starter area. The contacts on the starter are cleaned and tight. New batt. I'm going to fight the grounds tomorrow morning. Will update what I find.

docmirror

Two - bad - starters. Actually, two bad starter solenoids with slightly different failure modes. The one that came on the car would just chatter the solenoid contacts, and never engage the bendix to crank the engine. The second (used borrowed) one just does the 'clunk' indicating that the solenoid is throwing a bit, but not enough to make the high current contact for the starter to spin. I'm going to disassemble the solenoid on one of them to see what's going on and if I can save it. If not, I'll order a new one.

Now I've got a car that will run, but can't start it reliably so I can't go anywhere until I get this sorted. I also have an issue with the injectors firing, as it died after a few seconds which I'll need to investigate once the starting is cleared up.

Progress. One step forward 1.5 steps back.

dr bob

Doc--

In your collection of things, you have one of those starter buttons with thick leads and big alligator clips. Connect that between the battery cable post on the solenoid and see if it reliably engages the starter motor. You had previously reported that a screwdriver doing that duty would cause cranking, so it goes to the relay or the wiring between the relay and the starter solenoid. Voltmeter at each of the available test/contact points is your friend here.

The battery is fully charged through all this...

docmirror

OK, I'll futz with it Monday. There's a chance I have an issue from the 14 pin conn to the starter solenoid. I'll ohm that out, and check for voltage drops along the way.

Hey_Allen

I'll second the suggestion to try it directly at the starter solenoid.

I had a MB 300SD that was erratic starting, and I eventually found that it was due to insufficient current supplied through the ignition switch circuit.
I'd already chased through the wiring harness, as well as replacing the starter early on, but never found the final cause for it. The car ended up with a small, fuse protected relay next to the body/engine harness connection point on the fender, supplying the current to trigger the solenoid.

This is not the "proper" way to fix the issue, but I did the bump-start button test and found that jumping the starter solenoid was enough to start the car every time, but the ignition switch wiring wasn't passing enough current to snap the larger solenoid fully into place, and make the high current contact reliably.


I'm glad to see this question come up, as I had assumed that there was a starter relay supplying power to the starter solenoid in the car I just picked up.
I'll have to think about possibly retrofitting a starter relay to my '78, to reduce the current load going through the ignition switch.

docmirror

I seem to have this sorted out. There's a high resistance right at the solenoid terminal on the starter. The wires from the 14 pin all look very good, and the connector looks good. I have batt voltage at the socket end of the 14 pin on pin 1 with key in start, so getting full voltage through the new relay. I'm cleaning off the terminal, and the wire end, and now it's cranking pretty well. Still get the occasional click, but working much better to crank.

On to a next issue. I had this car running on its own when driven in the garage for fix up. One of the jobs done was replace all the injectors with rebuilt, which means I've handled, and moved all the injection harness wires. Also replaced all the soft fuel delivery hoses underhood. Well, now it will only fire with carb cleaner spritz down the MAF. I have the fuel pump jumpered, and have flow at the front cross line when I crack the line so fuel to the rails. Thinking I may have a short in the inj harness somewhere, although if I recall, there are two separate feeds from the LH. Other possible is a faulted LH module. I have the GT LH module, and may swap that later today. Hard to test the inj harness with a 'noid light with only one person, but I'll do that too.

docmirror

Correction, I just tested again today, and now will not fire even with carb cleaner spritz. One step forward, one step back. Suspecting my EZK or LH has given up.