Rich9928p

No vacuum hook-ups there. I suspect they are drain holes for water.

The Hall Effect sensor signal in the distributor provides a signal to the spark box via the shielded cable {distributor pin A} (AKA green wire) to input 7. The spark box provides the signal at output 16 to the spark coil and L-Jetronic connector pin 1 (RPM reference), the fuel pump relay and tachometer.

A bit confusing, but the actual spark box connector pin numbers are (8 wires):

1 = coil (white wire)
2 = Tachometer (black-purple wire) (common to tach, L-Jet and fuel pump relay)
3 = ground {circuit 31}
4 = ground {circuit 31}
5 = ground {circuit 31}
6 = signal ground {distributor pin B} (brown wire) ["green wire shield"]
7 = signal {distributor pin A} (green wire) ["green wire signal"]
8 = power {ignition circuit 15} (red wire)

Rich
'93 GTS Cover Girl
'87 S4
'79 5-speed rescue
'79 Euro 5-liter track beast

Rich

JobeJoe

Sorry Kiln_Red, I don't see how I missed this post. Most of the time I am checking this thread from my mobile phone, and between me and that goofy browser I missed this sheet. Totally my bad. The whole time I thought you were referring to Groups 24 & 25 in the WSM. A few of those tests needed the car to be running. I was confused. Anyhow, it was super simple to check these readings once I finally saw that sheet.

Temp Sensor: Term 5 + 13 - 2.49 ohms. In tolerance.
Idle Microswitch A: Term 2 +18 - 0.L. In tolerance.
Idle Mircoswitch A: Term 2 +18 - 0.L. In tolerance. Pedal slightly depressed.
Full Throttle Microswitch B: Term 3 + 18 - 0.L. In tolerance.
Full Throttle Microswitch B: Term 3 + 18 - 1.3 ohms. (depressed until 30 degrees open) This should be 0.L like the previous test.
Air flow sensor: Term 6 + 9: 282 ohms. In tolerance.
Air flow sensor: Term 6 + 8: 185 ohms. In tolerance.
Air flow sensor: Term 8 + 9: 103 ohms. In tolerance.
Air flow sensor: Term 6 + 7: 63 ohms. In tolerance.
Air flow sensor: Term 7 + 8: 167 ohms. In tolerance.
Air flow sensor/ temp sensor 1: Term 27 + 6 - 2.55 ohms. In tolerance.
Fuel Injectors 1 + 5: Term 10 + 15 - 2.6 ohms. Tolerance is 1-1.5 ohms.
Fuel Injectors 4 + 8: Term 10 + 14 - 1.4 ohms. In tolerance.
Fuel Injectors 3 + 7: Term 10 + 32 - 1.5 ohms. In tolerance.
Fuel Injectors 2 + 6: Term 10 + 33 - 1.5 ohms. In tolerance.
Ground (camshaft housing): Term 16 + ground - .1 ohm. Tolerance is 0.L.
Ground (camshaft housing): Term 17 + ground - .1 ohm. Tolerance is 0.L.
Ground (camshaft housing): Term 35 + ground - .1 ohm. Tolerance is 0.L.
Ground (camshaft housing): Term 5 + ground - .1 ohm. Tolerance is 0.L.

I am not sure what to make of the full throttle microswitch A 1.3 ohm reading, I have yet to really diagnose throttle issues on a 928.

And it appears that despite my best efforts, it looks like my cleaning up of the cam cover ground still shows .1 ohms.
The fuel injector 1+ 5 test, measured to high of resistance? Would that shut down all the injectors?

The voltage tests. When checking these to the nuts on the two ground points, I would measure fluctuating numbers, mostly super low, but when testing these terminals to the ground plate that the nut threads into, I got more steady voltages. Here are the only two points that stood out to me:

Term 4 to ground - starter activated - I measured 5-9 volts. Minimum is 8 volts.
Term 1 to ground - starter activated - (reading varies according to sheet) I got 4-5V, when the sheet reads 2.5V, but noted it varied. Probably not a huge concern right?

JobeJoe

That really helps, thank you! How does my harness look, does it pass your eye test?

Kiln_Red

What is the status of the car's running condition at the moment? Constant no-start? Occasional no-start? Starts and runs poorly?

Since we have established a lack of faith in the NOID light you rented, then try a different one. Have to know if the injectors are firing. Sometimes, if you have good ears or a makeshift stethoscope, you can hear them fire while a helper cranks it over.

I assume there are resistors built in to the spark box. Maybe the spark box is spent as 4-5V seems a bit much for the input to terminal 1 of the L-jet if 2.5V is ideal.

I have a spare spark box if you would like to try it for diag purposes. I wouldn't want to sell it, so I would need it returned.

JobeJoe

The car, as of 2 days ago is not running. Will start then die. I found another vacuum line disconnected under the spider, plugged that back in, but have not attempted to run it yet. I will try to turn it over this afternoon when I'm home to see if it runs.

I was just thinking on those resistance readings, the sheet said to measure zero ohms at some pins, but I may have mistaken the 0.L for being zero, but isn't it actually out of limit, or out of range? If that'd the case, then maybe I have more issues than I thought.

I may take you up on that spark box soon. I could put a deposit if you're more comfortable with that. I'll definitely let you know soon.

ltoolio

Yep. Out of limit

JobeJoe

It may be my meter as well. I think I remember touching the leads together and getting out of limit there as well. I'll double check when I get home.

Edit: yeah touching the leads, got .1 ohms, so those circuits are open somehow. But I spent some time after work cleaning those up, both the idle and full throttle leads. I'll test the resistance again once my 5 year old quits using me as a jungle gym as ets to bed lol.

JobeJoe

I checked the noid light with a couple leads at the battery and it lit up brightly. I'm going to send my brain to James to try in his 80 shark. If confirmed good, I'll take you up the borrowing your spark box for what is hopefully one of the last pieces of the puzzle.

I had another thread going about melted wires behind the ce panel in the main harness. Most of them were related to the J plug which involves instrument lights. I replaced all of those wires except one, still looking for the other end of it (most likely the cluster and trim lights).

I did find a couple wires that had been shorted from being next to the J plug wires that fried. Fixed those, but I want to double check that I didn't miss anything.

I feel like I have to be getting close.

Landseer

I had an Ljet with a corroded wire to one of the two final stage amps inside the cover of the brain box near passenger footwell. Its about the only think inside that box that was serviceable and visible to a layman.

Car would intermittently loose signal to 4 injectors. (figuring that part out was the trick - noid wouldn't flash during a stumble start / conventional wisdom was you loose all injectors or none at all - had to check all of them and keep a chart) Would run great for a while, then stumble to the side of the road and die. Then would stumble now and then trying to restart, and be unstartable for a month. Then run great again.

Its been bulletproof, knock on wood, since simply dremel-cleaning that screw mounted wire inside the box. Weird because it was the only bit of corrosion in there. But it sure had an impact.

Frustrating part was car was in Virginia Beach (daughter had it) and we were out here in BFE Midwest. Took two trips to Virginia and back to get the car home to Elkhart.

JobeJoe

Were you able to repair it? Mine is on its way to a fellow renner to see if it will run his same MY. Coming down to that or the spark box or ignition switch. I'm lurking these pages for a good ignition switch rebuild, if there is one.

Landseer

Yes runs great now. I think I'll drive it to work this morning.

Roger has those ignition switches fairly cheap I think.

Yes, if you uncrimp and take apart, you see its just a circle of very heavy point-like contacts. Not sure what a bad one looks like, but I replaced one just because somebody recommended it, took it apart, and it was clearly like new inside. Not sure if they fail by burning up the points inside or by mechanical looseness.

Kudos for your troubleshooting methodology, great measurements.

I was poised to send the electronic boxes to Rich Andrade for evaluation and repair, but stumbled on the oddball corrosion. I'm actually making the assumption that the thing I fixed was a power lead involved with an amp that handled half of the injectors. Electronics are a bit of a mystery for me.

Kiln_Red

You've already verified that it isn't the IG switch in what you've provided from your diagnostics.

JobeJoe

I believe I ruled it out, I just have a sneaky feeling that something is amiss in the switch. Maybe I have been reading too many horror stories on other posts about the intermittent issues within a bad or failing switch.

Landseer

Two things to consider.

Electrical troubleshooting heavy power connections with ohm meter isn't definitive. Case in point, ground straps often ohm showing no resistance, yet have failed because they can't pass enough electrons during operation. A couple of our legendary troubleshooting guys on this board have been bit by these ground straps and didn't suspect them initially.

Secondly, there is a list of electrical sensors fuses and ground points that fail on these cars. Best practice is maintain and replace that stuff before troubleshooting.

All that said, wow you guys are creating an epic ljet thread here
Awesome.

James Bailey

OK big drum roll................and it is a bad brain !! my 1980 with his brain starts and dies, starts and dies. So the brain is bad.....now we KNOW !! Hopefully nothing else is messed up on his car.