Kiln_Red

It wasn't my advisement to replace the green wire, although I second the advice. The next natural step down the diag rabbit hole for me would be to bridge the AFC relay, which requires two jumpers instead of one unlike a '53' relay. Replace the relay accordingly.

Wisconsin Joe

An old two stroke gas powered golf cart.

Really.

The carb was replaced (throwing parts), plug, fuel filter. Still doing it.
Cleaned the carb a few times. Some improvement, but not fixed.
My buddy wanted to replace the coil, but cobbling in one from a snowmobile (used alligator clip jumper wires to get it in for the test) showed no change.

It ended up being a whole lot of old, broken wires (conductor broken inside intact insulation). I found one, replaced it, and it seemed to fix it (again). But only for a while.
Found a couple more, where the wire was really green going up under the insulation and decided to replace all the control wiring (wiring between relays & switches and to/from coil, anything small gauge wire).
Worked for a while. Now it's doing a 'sorta warm' no start. It starts cold, and hot starts just fine. But if it runs, then sits for a bit (15 min or so), it will briefly fire but not stay running. It will do this once or twice and then just crank without firing. Spark is there when cranking, so I'm pretty sure the wiring is still ok.
May be the plug, may be a mixture issue.

May be just the fact that it's old.

Not a big deal. I was using it more as an example that throwing parts at a problem without doing proper diagnostics is generally not productive.

Landseer

We've seen distributor shaft roll pin fall out on an 83. Went dead as door nail. Epic diagnosis and repair. Happened at Frenzy 3 years ago. I know Mr. Merlin remembers that situation. Could it have happened again here?

I've also experienced cpu failure on L Jetronic. Same effect, you go from enjoying the hell out of life, cruisin proudly, to dead as door nail instantly. In my case, it was intermittent and we struggled with it shutting down dead, then after a couple months fiddling with it, start and run flawlessly. Went on for years. Don't let my esteemed colleagues here give you the impression, as they will, that the CPU is bulletproof and unlikely to fail. They fail. Swap in a known good one sooner rather than later in your diagnosis process if greenwire doesn't solve.

Landseer

A couple more possibilities:

If an injector wire pair shorts beneath the rubber boot it shorts all injectors. Can possibly be triggered with heat. You can use wire diagrams and pin out diagram for controller to trace them and test. Richard Andrade has posted test procedure before, I'll try to find it.

Controller and sensor grounds can corrode and take it down. They all ground at one of two points on pass side cam cover. Three dissimilar metals collide at those ground points, brass aluminum and steel. One of those points is buried under an emissions valve. You have to remove the valve to properly address it, but it's easier than it looks. I use dremel wire brush on these. This is worth doing routinely as preventive.

Just some ideas for you, keep us posted.

Wisconsin Joe

These are all good examples of why figuring out what it's doing (more accurately not doing) is important.

Bad distributor would give no spark, but would have injector pulse.

Bad injector wiring would give spark but no pulse.

Bad ECU would also give spark but no pulse (failure is not common, but it does happen).

mkhargrove

my apologies if this was suggested above....i am too lazy to read the thread.
if it was running then went instantly to running like crap, you could have a failure in mass airflow sensor. i know because i'm trying to sort mine out right now.

remove the air intake and unplug the maf (the wiring that connects to the airbox)

if it starts/runs (crappy, throttle response isn't right, very rough), then you know that the mass airflow sensor wasn't getting a signal to the injection brain or it was sending a bad signal. probably. i think.

Landseer

Our bad ecu progressed to where it killed both somehow. But very early on only killed some injectors, giving a stumble non start.

Bad distributor roll pin would spark on initial spin after being retimed and would kick over. I cant remember for sure the behavior, think it kept sparking, just at wrong time. Shaft was still driven, and would turn initially at different speed than reluctor I think causing spark at wrong time. Mr Merlin, Sean R, and Pete, all three professional 928 mechanics, plus a slew of us tinkerers, were entertained by this for a couple days. Fortunately when the pin dropped out it got caught by the magnet inside the distributor. Stan took it apart atop a hotel trash can, nearly in the dark, reassembled it and tapped pin home with a small landscaping rock.
Beer then flowed in earnest.

Sometimes the troubleshooting becomes very nuanced.

Thad Brej

Update on my '83:

Bought and installed a new "green wire" and the car still will not turn over.

Bought an inline spark tester and apparently, I am not getting spark at the plug.

Any suggestions about what to check to diagnose what appears to be a lack of spark?

Also, the fuel pump is still not running while cranking despite a new "green wire".
Is this because there is no spark signal for the green wire to detect in the distributor?

Thad

jpitman2

How can you test spark if it wont turn over? I think you mean wont start - if the starter motor cranks, its 'turning over'. Do you have the correct relay? If you push the barn door in the airflow meter, does the pump run?
jp 83 Euro S AT 57k

mkhargrove

turns over/cranks = starter turns engine
fires/runs = combustion
and of course there is starts/fires and dies (immediately)


this happened to me the other day and it was a bit of "pull your hair out" .....the "button" under the top of the distrubutor cap broke.....so no spark at plugs.

Mrmerlin

did you remove the distributor cap and see the rotor spinning while you crank the engine?

Someone else had a similar issue and it turned out that the timing belt had failed and thus the distributor wouldnt turn as the cams were not turning.

MK from your suggestion your car has a MAF unit ,
NOTE . the car we are troubleshooting is an earlier version and is not equipped with the MAF

Thad Brej

To clear up a misunderstanding, my engine is cranking but will not start/run.

This evening, I will crank the engine with the distributor cap off as recommended by Mrmerlin.
My deepest, darkest fear from the beginning was a slipped and then failed timing belt.

I will report back after this test is complete.

I told my son that we needed to stop randomly throwing money at replacement parts on hunches and be more methodical about the diagnosis.

If the distributor is turning properly:
Kiln_red suggested jumping the AFC relay. What does AFC stand for and what two sets of contacts need to be jumped to bypass the relay?
Mrmerlin suggested unplugging/cleaning/reconnecting the computer connector. I will look into this tonight also.
I have also read many related threads that all suggest cleaning ground connections. Can someone identify all of the critical grounds that I should clean?

Kiln_Red

There are two ballast resistors mounted in series on the driver's side inner fender. Clean the connections at both resistors and at the ignition coil. Verify resistance for both resistors. One should be 0.4 ohms and the other 0.6 ohms.

You should have no regrets about replacing the green wire. Also, since there were driveability issues prior to the failure, the TB should be fine.

Your engine is non-interference.

Jumpering the AFC relay is a moot point now that we know there is no spark.

j.kenzie@sbcglobal.net

Hi Thad,
A couple of relays and a green wire is far from throwing parts at a problem. I doubt the timing belt snapped, possible, but unlikely, although you can look at it through the circular openings where the intake tubes attach to the timing belt covers near the front of the engine. Did you replace the green wire yet? Sorry if I missed it. You will be pulling the distributor cap to replace the green wire, so you can crank engine to verify belt continuity as well.
Good luck,
Dave

Thad Brej

Although I haven't gotten over the hurdle yet, this new Porsche owner wants to thank everyone who has contributed their knowledge and experience.

Yes, the green wire has been replaced and I am glad that I did it.
After checking for distributor operation while cranking, I will look into the ballast resistors and the connections up to the coil.
Additionally, I will be checking the computer connector.

Thad