They run open loop without O2 sensor. I think it provides trim adjustment to mixture. I'm running an 84 without one.

i didnt say cat clogged but the metal tube that runs beside cat up into the eng compartment connected (rubber hose, was it replaced when vac lines replaced this is way down under in eng comp) to the damper it might be. clogged screen?.

the cat probably is gathering the pollution, cough cough - the air mixture to blow it out clearly?

if old or stock or .... the muffler/tail pipe drop the hanger and disconnect shake , carefully bang it. mine was parked up against dirt/weeds/critters embankment for yrs, i actually filled with water due to any of the baffles or honeycombs being caked together grease/dirt/debri water would degrease/break it apart and flow whatever will come out out. the force of emissions not being able to come out , will heat that box to cherry red and quickly. with no where to go its going to back up choke car off.

course your on track for other reasons for soot. if you can keep it running by staying on gas pedal to get passed cold (4mins ) to warm up the soot can clear. that might tell you if its cold or warm issue better.

throttle linkage? idle? The noid light for injector harness test, obv if fuel will keep coming in can keep it going. injectors,clicking . Youve had them cleaned , electrical prob if anything.

Watch for cranking all the time the alt doesnt like to keep starting up and sit idle, wants go for charging.

Short video of the problem
 

Ok so long time riding the motorcycle - very little time working on the porsche.

Turns out the timing was off a wee bit (Landseer)
-timing light and we're within spec
but we did the adjustments with the AFM electrical unplugged (might matter -probably doesn't)

Why unplugged ? It's the only way the car will continue to run (still)

Here's a vid

YouTube - g2m1

Crappy sound quality -but should convey. I show the AFM electrical connector unplugged (kinda hard to see it hanging above spider) starting and running then a quick shot with the electrical plugged fully back in - then a cockpit shot trying to start it....2x --if I unplug that connector she'll run no problem...
I have a used AFM with similar pin to pin specs that gives the same results.

I've got an 8 foot fence post aluminum taped to the exhaust out the side door of the garage but phhheeeeew those unburned hydrocarbons will just about kill ya

A few no start threads for us 28 yr old 9 two 8's --must be a test :rolleyes:

So it must be running only on the cold start injector with the AFM electrical connector plugged in -
For some reason, with the AFM out of the loop -bingo she runs.

It feels like something simple here - I haven't replaced the TZK or the Ljetronic or the green wire or the ignition -it doesn't seem like it would be any of those...

what is that AFM telling or rather not telling the rest of my car

Are your injectors firing.
Hook up a noid light and see.

Try the three wire jump of the AFM/ign relay again / verify position with 928 specialist diagram.
Possible all injectors are clogged.
Has this car ever run for you?

Wow was just looking at that twin turbo honest 550

Back to my little car -

Umm you mean when the AFM is plugged in ? Noid light when the AFM is plugged in?

Injectors must be firing whence unplugged-- so the green wire is telling TZK send spark which it is and gas is flowing but the air mixture isn't mixing in air so I get black sooty death --my plugs get fouled <--

I had help a few months back and we thought vacuum -- I think I found no leaks but me being a n0ob at this spider type engine might have something to do with it....

Supposing I had a gauge and running with AFM unplugged --where should I test ( front left plug butterfly? What pressure should I see??

You were right about the timing being off a tooth --- it's just so strange to me that I have to eliminate the AFM to keep her running

OK.

There is a temp/time switch that is designed to turn off the cold start injector so it doesn't flood out. Did you replace it. They go bad.


AFM needs to be plugged in. Leave it alone, its not your problem.

You can have no big air leaks. If you have a big air leak, cracked boot or something, it would not pull enough air through the AFM and it will never swing the barn door (springloaded) open to let in air. Checking vac during starting at one of the little vac lines won't test anything.

Try sticking a piece of heater hose into the AFM to hold the barn door open a little bit and try it.

Also, 3-wire jump the relay sometimes called AFM or Ignition, depending on the reference, jumpering 30 to 87 to 87 (sometimes one of them is denoted as 87a)

Confirm injectors firing with a noid light.

Do you have spark?

Did replace Temp II (after success w/ the kbort resistor trick) but not the temp/time ...

Did you watch my youtube vid? You can hear the barn door slamming--i've propped it open/ jumper'd everything jumperable 2 and 3 wire with 2 different AFMs plugged in....It was a running vehicle I foobar'd with an intake, fuel line, injector cleaning refresh (which it didn't really need)

It runs without the afm plugged in - meaning to me -I've got spark, fuel, time, compression -just some silly 'lctrical (no -on a 928;)) issue keeping the air mixture off--there are only so many wires to the AFM -one of them is my problem ----it's got to be, right? I bought the cd's but really need to print out sections (or find a set cheap :)

Or I've got a huge vacuum leak that only matters when the AFM is plugged in....
This is why I left it on jack stands for months (well motorcycles are fun too)

I have to research where the wiring goes and try to figure the tests to move forward.

My 85 has a limp home mode when the MAF is bad. Two fuel settings one for less than 2000 rpm and one for more than 2000rpm. Both very rich settings. With your AFM unplugged you may also be getting a limp home setting allowing the car to run at the very rich setting. If so test your AFM. Make sure the electrical signals are at spec. That may be your problem.

Thanks for the tips --though it hasn't been easy finding the testing info
group 24 is not complete for early l jet cars but I found something
from an ancient post on rl from PorKen that has complete info
'82 Running Rich / AFM connection runs rough - Help! - Rennlist Discussion Forums --same problem I'm having

here's the AFC wiring diagram

http://inntandem.com/p928/LJet_AFC/AFC_13.jpg

and the most important part!

TEST VALUES FOR THE A.F.C. Fuel injection system type 928!!

http://inntandem.com/p928/LJet_AFC/AFC_18.jpg


Though with temps in the 20's here kinda hard to get the garage ambient up to 68 :)

Anyone know which is terminal # 1 on the jetronic multi pin plug?

Here it is !! Thanks to a Rich9928p on rennlist!

http://inntandem.com/p928/35%20Pin%2...20rennlist.jpg

1/1/11

L-Jet connector pin out detail
jetronic pin out / connector detail
computer plug schematic

All that information and much more is in the CD set sold by rog.

Yes in fact the Test Values for AFC injection are on page 18 -
disk1\fuel injection systems\928 Air Flow Controlled Fuel Injection.pdf

Not so sure on the 35 pin out pic though as the ones I've found from the Cd's reference 87 MY pages 52 and 53 of

disk1\fuel injection systems\Electronic Ignition and Injection System.pdf

Regardless it's good to see pics on a forum.

**** After some re reading, I shoved a length of heater hose down the AFM's gullet, keeping it open and viola once again you were right on Landseer
It will keep running, though the mixture is off -not as sooty but it'll stay running

One thing I noticed is that my CAT and intermediate muffler were starting to get red after running for around 10 minutes - I'm assuming it's all the soot from prior attempts.

Now I'm assuming a big vacuum leak - the funny thing is, the air box rubber mounts are kind of deformed and since the AFM is mounted to the air box, perhaps the AFM is not being seated fully into the U causing a pretty big vacuum leak.....( I do have a new o ring down there)

if the cats are glowing then you have extra fuel being put into the engine ,
and either not all the plugs are firing or a damper or FPR has a ruptured diaphram. Dont continue to run the car till you figure this out as the cats will start a fire that will consume the car

Good work.

On these cars usually a half dozen things are wrong at once. Many are interactive, so the logic of retrying something you've already tried before is masked.

They should never glow red.
You may need to run it a little bit to continue troubleshooting, but never that long for now.


Best to remove the lower air cleaner box from afm and run without during this stage (keep debris out, though). Virtually impossible to see anything with it in-place.

Reach inside where the AFM slips into the throttle body.
There needs to be a big O-ring fitted. ( Just reread, yours IS new, good)
If its edge (that touches the OD of the AFM) feels flat, then it is shot and MUST be replaced.
With a new O-ring, the AFM can be worked into the O-ring and will be held there in-place strongly enough to run without the air cleaner. It should stop a good bit of the bypass air thats screwing up your computer stocihiometric calcs. Still possible, based on your description, that the air leak (major) is right there. at the O-ring, but you've got more undersides of boots, central boot, and various crankcase vent hoses to check. Use a strong small flashlight. Move stuff looking for loose or cracked hoses.

The air cleaner mount rubbers get hard and skewed, so they often can't be used anymore to align AFM with throttle body especially if the O ring is old.

You'd might yourself another year of hell, or at least spare me and Merlin, if you'd start posting some pictures, BTW.

So, have you replaced the critical sensor called temp -time or more appropriately "thermal-time sensor"?

Totally different and no connection with "Temp II", BTW.

If thermal-time fails, and they commonly do after 20 years, it will keep barraging the intake with gas via injector #9.

Mr. Merlin points to fuel regs and dampers, also very possibly a problem, but quick inspection should determine if the diaphrams are leaking into the vac hoses.

Gotcha - very limited running; sniff testing dampners + fpr;
test 92860510100; more pics; -here's a pic of the afm when
I took it out back in Feb '10 (christ time flies)

note: orange silicon

http://inntandem.com/p928/airflowmeter.JPG

Uh oh. PO fix. This was a known issue.

but its tastefully done.
However it needs to come off . You should also consider replacing the 3 rubber standoffs that hold the lower plainium to the V.
If these standoffs are broken then the flap box will never properly seal,
this will require removal of the center spider section, the standoffs usually break off where they are vulcanized to the rubber

Right! And the two standoffs that the air cleaner bolts to.