930 died

[spoke]

Originally Posted by jlj

Got the car back after going thru everything, new over boost relay, rebuilt distributor , new green wire , checked all wiring , sensors , did valve adjust ....Car ran perfect on Wednesday for 150 kms and then hesitated and back fired. Didn’t die and cleared up . Today went for a drive , all good for about 20 kms, pulled hard no hesitating and then just backfired and shut down. Cranks over but will not fire or even try to fire .
I’m at a total loss as this makes no sense how it runs perfect and then just dies.
Any suggestions please ?

This sounds like the exact same problem I'm going through with my '86 930 although my tach was jumping like crazy when it first died. While idling the tach was jumping to redline and back before the engine died. I'm at the point where I'm looking at the CDI Permadoom unit and ready to purchase an MSD 6AL.

I'll be checking voltages, fuses, and relays this weekend.

[jlj]

Originally Posted by s5uewf

Check alternator and make sure you have enough spark to fire the engine with the plugs in the cylinders/under compression. Perhaps not enough voltage (could be bad or weak grounding too).

I have had backfiring in the past related to low voltage/not enough amps to fire the plugs under load...

Winner winner chicken dinner...the charging system was checked but turns out the alternator was intermittently failing . I put in a brand new battery and the car ran well but as the alternator couldn’t keep up as soon as the battery went down a bit all the symptoms came back. So alternator is being replaced with a nice new 150amp unit from classic retrofit.
It’s nice to have a solution finally. Thanks for everyone’s input

[jlj]

Originally Posted by spoke

This sounds like the exact same problem I'm going through with my '86 930 although my tach was jumping like crazy when it first died. While idling the tach was jumping to redline and back before the engine died. I'm at the point where I'm looking at the CDI Permadoom unit and ready to purchase an MSD 6AL.

I'll be checking voltages, fuses, and relays this weekend.

I would seriously consider the classic retrofit cdi instead

[s5uewf]

Hooray! Glad you solved it. I have one of those USB/voltage/temp LED cigarette lighter plug ins I grabbed from Amazon. I stick it in the dash and can watch my charging rate for peace of mind while also being able to charge my phone.

[puddy]

Originally Posted by s5uewf

Hooray! Glad you solved it. I have one of those USB/voltage/temp LED cigarette lighter plug ins I grabbed from Amazon. I stick it in the dash and can watch my charging rate for peace of mind while also being able to charge my phone.

I've got the same thing. Works awesome!

[spoke]

I'm checking the voltage at pins 31 and 15 at the CDI connector. First start today the engine fired right up, stumbled a bit, then idled at about 1500 RPM. I have the idle screw way out from the earlier loss of idle. Voltage was rock solid at 14.05V. Ran the engine for a couple of minutes and had no tach jumping.

Came out 1/2 hour later and started it up. Ran great but the voltage was now 11.8V. After 10-30 seconds, the voltage went to 14.05V but bounced around slightly 14.05-14.00 and the tach was jumping a very little bit like less than 100 RPM. Now I'm thinking the relay driving the CDI is suspect. On my schematic it's called Delayed Action Relay.

The bouncing voltage was measured with a voltmeter. I think I want to pull the DAR and inspect, as well as put my oscilloscope on these pins to see exactly what is happening.

[spoke]

I measured the voltage going into the CDI on pins 15 and 31/1. The traces are below.

The first trace is starting the engine; Key ON - 12V appears; Start - Voltage droops to 6-9V; Engine runs - Voltage goes to 14V with 2V spikes where the CDI fires.

Second trace is a close up of the 12V supply. The negative spikes are where the CDI is firing.

In the third trace the engine is starting to stumble then stall. The spikes disappears as the spark is not applied.

Next step is to monitor the inductive signal from the distributor. If the signal is consistent then definitely the CDI needs replaced.

[Rawknees'Turbo]

Spoke, sorry if I missed that you've already replaced this, but 99% of the time, a bouncing tach in one of these cars means that the alternator's voltage regulator is bad/going bad (irregular voltage . . . like you've noted above).

[spoke]

Originally Posted by Rawknees'Turbo

Spoke, sorry if I missed that you've already replaced this, but 99% of the time, a bouncing tach in one of these cars means that the alternator's voltage regulator is bad/going bad (irregular voltage . . . like you've noted above).

Thanks for the tip. Before I change the CDI I want to make sure the CDI is at fault. I think to get a better idea on the alternator performance I'd need to find a different place to measure its voltage. Measuring at the CDI introduces all the current drops of the CDI wiring, connectors, and relay.

One thing I noticed on the CDI battery voltage was intermittent negative pulses between the normal idle pulses. I couldn't capture these rogue pulses before the engine died.

[Jonny H]

Originally Posted by spoke

Thanks for the tip. Before I change the CDI I want to make sure the CDI is at fault. I think to get a better idea on the alternator performance I'd need to find a different place to measure its voltage. Measuring at the CDI introduces all the current drops of the CDI wiring, connectors, and relay.

One thing I noticed on the CDI battery voltage was intermittent negative pulses between the normal idle pulses. I couldn't capture these rogue pulses before the engine died.

You will always get a fair amount of noise on the 12V line, even measured at the battery.

A 'working' Bosch CDI will still fire down to around 7v (albeit with less energy) but below about 10v the tacho is wandering all over the place. Above 18v (failed alt or external regulator) the Bosch CDI is toast as there is no internal regulation but this takes out the power supply so no whine from box.

If it were me I would disconnect the CDI and look at the distributor signals across pins 7 and 31d at the 6 pin connector. On cranking, you should get a zero crossing 'jaggedy sine wave', maybe 10v pk-tp-pk. Post the trace if you can.

Having said that, on a Turbo the most common CDI fault is the signal input circuit failing. We get lots of boxes that still make the whiney noise but they do not fire at all or when the box heats up. Turbo is so cramped in there, hard for the heat to escape.

[spoke]

Originally Posted by Jonny H

If it were me I would disconnect the CDI and look at the distributor signals across pins 7 and 31d at the 6 pin connector. On cranking, you should get a zero crossing 'jaggedy sine wave', maybe 10v pk-tp-pk. Post the trace if you can.

Having said that, on a Turbo the most common CDI fault is the signal input circuit failing. We get lots of boxes that still make the whiney noise but they do not fire at all or when the box heats up. Turbo is so cramped in there, hard for the heat to escape.

I'm planning to do the pin 7 - pin 31/d tests today. I wasn't going to remove the CDI during the test but I'll give that a try.

[jlj]

Installed alternator from retrofit . Previous alternator was toast with rotor touching the stator so definitely one of the problems. Now car has no power to the CDI box but has power at the front of the car. Car cranks , has fuel ,no spark.
This car is so annoying. We are now assuming a wire is broken or frayed somewhere in the harness so will be running a new wire directly from the fuse box to the CDi. Has anyone done this?
What the **** else,could it be if this doesn’t work

[spoke]

Originally Posted by jlj

...no power to the CDI box but has power at the front of the car. Car cranks , has fuel ,no spark.
...We are now assuming a wire is broken or frayed somewhere in the harness so will be running a new wire directly from the fuse box to the CDi. Has anyone done this?
What the **** else,could it be if this doesn’t work

Wires don't normally fray or break in a harness unless there is significant stress or movement like between the chassis and a door. It would be best to find out why power is not getting to the CDI before running a new wire. It might be something simple.

Was there voltage at the CDI before the alternator swap?

Where did you measure the voltage at the CDI?

Are there relays or other connectors between the fuse panel and the CDI?

[spoke]

On my car, I found what was causing the stalling and tach jumping. The insulator for the wire from the inductive pickup on the distributor had broken at the connector and allowed the center conductor to touch the shield wire.

To test this I cut away some of the connector and separated the wire from the shield and used some JB Weld to hold it in place. Car ran fine all weekend. I've ordered a new wire from our host.

[Ken911]

Ah yes the green wire of death. I chased that one for about a year.

[jlj]

Found a frayed connedtion at the fuse box. Shop Cleaned that wire up before running a whole new one and the car fired up right away. Tiny hesitation at 5000 rpm is all that’s left to clear up now. Going to check timing and AFR