wopfe

Since i raised this question about getting my '79 euro manual to run better, i have followed the advice of @GregBBRD to start from scratch (getting the fuelpressures into factory specs and follow the manual from 928Classics.com with "basic CIS settings'..

I followed these steps:
- I closed the air/fuel mixture to very CCW.
- I hooked up the Gauges.
- I Jumpered the fuelpump
- I did the "fuelpressure tests" like described in the 928 classic manual (i got all pressures within the factory specs. System pressure, cold start pressure and warm warm-up pressure).
- I the opened the air/fuel mixture screw clockwise until the injectors squeak (that started from 14 turns with me, porsche928classic says between 11 and 15 so also ok i think) and turned it back of 1/8 turn as described within the 928 classic manual.
- I then replaced the oil and put in 8 new sparkplugs.
- The idle screw is 3 turns CCW open.

I hope people can tell me what they did next? I understand you take about 1/8th of a turn to not get to big changes but what is normal? Last time i was working around 21 turns clockwise, my feeling is that that is very rich then.
I tried to start it after the porsche 928classis procedure (so around 14 turns open) and it did for like 20 seconds it then died. I could not restart it after that so i started turning it 1/8 turns richer and tried to start it after each change. At about 17 i quit because i started to smell fuel.

Hope to get some good advice or experiences before i swamp the oil again with fuel I am looking for experience with tuning it further with the air/fuel mixture screw. Last benchmark for me was 21 turns to get it starting and idling. Could that be normal?

Again thanks in advance!

Arjan

GregBBRD

Remove all of the injectors and attach them to the fuel lines. Modify 8 water bottles, so that you can reliably have all 8 injectors spray into the bottles, without the bottle falling over (I cut them in about 1/2)

Jumper the fuel pump relay, so that it runs by itself...with the key off. Allow no sparks in or around the engine compartment while doing this. Do not do this on days with high static electricity. Do this outside of your garage. Have fire suppression equipment very handy...just in case someone wanders by, smoking a cigarette.

The injectors should not be dripping or spraying, with the fuel pump jumpered. If they are, "lean down" the mixture screw until they just stop spraying....plus about 1/8 of a turn.
Push down the sensor plate as far as it will travel for a few seconds (this will remove any air from disconnecting and removing the injectors.....there will be lots of fuel coming through the injectors (and lots of atomized fuel "wafting" around.) Any movement of the sensor plate down (push gently down on the sensor plate with your finger) should result in the injectors all spraying exactly the same....no dribbling, no spraying off to one side allowed. Adjust the "mixture screw until any slight movement causes the injectors to spray (not drip or spray weird.) Push down gently a few times, checking the patterns. Allow the sensor plate to come back to rest. Make sure no injectors spray, drip, or leak. Replace any injectors that have funky spray patterns or which drip or leak. Use the factory injectors, not the Mercedes parts...the Mercedes injectors are shorter and the spray pattern will hit the walls of the intake manifold, instead of spraying into the air pattern. (There's a reason Porsche built the injectors longer.)

Remove the fuel pump jumper and empty all of the containers. Clean up any fuel. Allow any "mist or vapors" to clear. Order/find an electrical connector to the warm up regulator. Make the wires long enough to reach the battery in the back of the car and figure out a way to attach these wires to your battery. Plug in the warm up regulator, hook up your fuel pump jumper, hook up the power and ground to the warm-up regulator. Monitor the injectors. The amount of volume that sprays out of the injectors when the sensor plate is barely pushed down should be reduced, as the warm up regulator "warms" up.

Re-assemble the vehicle. Don't change the fuel mixture screw, more than about 1/8th of a turn.

If the car still doesn't run correctly, there is something else wrong.

Petza914

As you suspected, you're going to be way too rich now. Need to go back to where the injectors squeaked and then you closed them down another 1/8 turn. It likely ran for 20 seconds using fuel introduced from the cold start injector at the front of the spider intake body.

After following Greg's advice below, if you can't get the behavior where it needs to be, the next likely culprit is the fuel distributor.

wopfe

@GregBBRD & @Petza914 Thanks for the follow up in the advice. I got the oil out again and the sparkplugs, going for 1 more run of trying getting the injectors to open like described in the 928classic manual. I realised i might have f*cked up because i turned the idle screw after i got the "open injector point CW minus 1/8 turn". If after that it doesn't work i will go for the injector check. That procedure was low on my list because they are all replaced 2 years ago. But it is the usual next step so i asked the family to start gathering small bottles Thanks Guys!

Petza914

The other thing is as you push in the mixture screw to compress the spring and engage the tip of that adjuster with the actual mixture screw, the pressure of pushing it down will actually depress the air metering plate and allow fuel to flow so you'll hear that. That means you have to make an adjustment, let up and listen, then press down to adjust again, let up and listen, etc until you hear the squeak after you've let up, then back it off the 1/8-1/4 of a turn until when you let up, you don't hear it anymore. You can't engage the adjustment assembly the whole time as the pressure you're exerting to do that will push the plate down and the setting won't be accurate or correct.

wopfe

@Petza914 thanks for this advice, i will take my time this time getting it right. Do i understand correctly that basically the ideal mixture should be far from the "point zero (opening of the injectors) so 2 full turns should be way to rich or way to lean?

Petza914

Once the injectors squeak and then you close the screw down another 1/4 turn or so until they don't, you should be very close to the correct setting and should not need to move very far away from that even when fine tuning, so yes, 2 turns away from that setting is too many. Other than running the motor then inspecting plugs, I'm not sure how you'd fine tune beyond this point without an AFR gauge that shows you your exact mixture settings under various driving conditions. Because of my supercharger, I have a wideband AFR gauge so could adjust mixture to get it right where I wanted it under boost (12), under normal driving(13-13.5), and under very light throttle or coasting (14-14.5). I also installed a Knocklink that helped me to dial in my timing so I could detect too much timing advance in combination with the current mixture setting (red light flashes on dash) so that I'm not getting detonation or preignition under boost. I upgraded to a newer distributor that has both vacuum advance and retard ports and have an intake pressure line connected to the advance side of the distributor (opposite of it's intended design) so under boost, that pressure to the distributor actually retards the ignition timing - this helps to protect the motor but also lets the timing advance a few degrees at atmospheric pressure and below for better runnability and pick-up.

wopfe

So i finished the procedure today and replaced the oil and the sparksplugs again. I had the injectors open at 14 turns CW exactly, closed them down about 1/4. Just started her up shortly (it started direct as you can see at the youtube movie), i had to help a little with the throttle to keep i running, and it dies when i don't. Happy that it starts again and in base it felt quite good actually. Now i let it rest and i am first going to check oil level again before trying to start it again. I think my next steps is to make it a tiny bit more rich so it might idle without help. What do you think?

Petza914

The car seemed to run better the longer it ran. If that's the case, DON'T use the mixture screw to compnsate for the rough cold start as there are 3 other pieces in the system for that and you'll just mess up the correct mixture setting you've just achieved.

If when fully warmed up the idle is good, that means the idle screw position is also good. If its a little low even when fully warmed up, adjust the idle screw at the front of the throttle body to smooth that out and see if that helps with the cold start issue.

Next is the cold start injector at the front of the spider body. The plug on that should show 12v when the starter is cranking and it will only get triggered if the thermo switch in the water bridge closes the ground side of the circuit when that temp switxh says the car is cold. This keeps that injector from adding fuel when the car is warm. So on the next cold start, you need to check for 12v at the plug on the cold start injector while someone else turns the key - it only gets voltage when the starter is turning.

Next is the Auxiliary Air Valve. This is the metal piece to the left of the WUR where a larger hose then connects next to the cold start injector. That plug should have 12v whenever the key is not off. The inside of the AAV has plate inside that is open when the motor is cold and as the 12v from the wiring is applied to it slowly closes down by sliding the plate inside until the plate fully closes the aperture. You can test the AAV by removing it and putting it in the freezer, then look though it to see if it's open. If so, then apply 12v to the plug contacts and see if it slowly starts closing until fully closed - this takes minutes, not seconds.

Last is the Warm Up Regulator or WUR that adjusts fuel pressure in the system. The plug on the WUR should also have 12v whenever the key is not in the off position.

First thing to determine is whether the car runs right when all the way warmed up. If it does, we focus on the cold start assist components, if not, we do us on other things like idle screw, timing, or other stuff to get those right and then see how those changes now effect the cold start.

Petza914

Duplicate post.

wopfe

@Petza914 i am going to take this step by step so i hopefully don't screw it up this time. Today i checked the oil (could use a little extra as expected) and started the car again without changes. As you can see it starts instantly again, but it needs me using the throttle to keep it running after a few seconds. My idea was to let it warm up and then change the idle screw from 3 turns from fully closed to 3.5 from fully closed. After 3 minutes it dies because i am to late to keep it going by pressing the gasspedal. After that i turned the idle screw 0,5 turn more open and tried to start it again. It didn't so i stopped this session (see the movie and sound below, it was quite shaky today, you can her it bup bup bup like it sort of detonates to early or something. To react on your three other options:

- Cold start injector at the front of the spider body: i will check that asap.

- Auxiliary Air Valve. Tested and checked a few weeks ago. Also used the fridge Works correctly.

- Warm Up Regulator. Tested and checked a few weeks ago. Works correctly.

So what i see now its starting really good helped by the cold start systems. I failed to keep it running when warming up, my gut feeling is that it won't also when fully warm (i will try again tomorrow). So my next step could be opening the idle screw to 4 turns and i am also very curious how the timing is now. In an earlier iteration (weeks ago when i was working really rich, i adjusted to the correct timingusing a timing gun), wondering if i need to change that too now with the new setup. I think i need to check that also.

Input is welcome, taking baby steps not to screw it up Cheers!

Petza914

Seems like it starts up fine and also sounds good and smooth as your rev it and keep it running, so I don't think the timing is too far off. Fueling doesn't effect timing - timing is timing. If it's set right, it's set right. As you mention, I'd focus on the idle screw. Seems like if you could elevate the idle a bit, you'd be in good shape or at least it will make troubleshooting easier. Increase the idle by adjusting the large idle screw at the front - CCW increases the idle and CW decreases it. If your cold start injector, WUR, and AAV are working correctly, your idle at cold start should be around 1,200 - 1,500 RPM. Open it up so the car keeps running when you start it, then close it down to be in that range when cold started. After it warms up, you can set it more accurately to somewhere between 800-900 RPM, wherever it behaves best. Then on the next cold start see where the idle is once you had properly set the hot idle position. If it's in that 1,200-1,500 RPM range and it stays running and slowly falls as the car warms up, then you're good.

Then you can check the timing again. All vacuum advance/retard hoses removed, 3,000 RPM and you should be somewhere in the 28-31 degrees of advance range. Without knock sensors or real mixture information, setting it closer to 28 is safer so you don't have detonation / pre-ignition.

wopfe

Thanks again @Petza914 for bearing with me So today i turned the idle screw 1,5 full turns open or more rich. That is 4,5 open (manual says between 2-4 btw) After that i started the car. Again start instantly and felt like it idles a little higher. Did not want to let it stall so i kept pumping the accelerator softly and helping the engine to run about 1100 rpm, when i take my foot of the accelerator it felt ik wanted to stall. Tried to warm it up a little more but i quit after about 8 minute because it was clear it was nog going to idle. It stalled right after i got my foot of the accelerator. I tried to start it a minute later but it won't. First normal start, then with full WOT. Does not start. I then checked my sparkplugs: pitch black but dry (these are new):

So next try i think i wil open the idle screw another full turn to see if it idles. I understand letting the engine idle like this makes the sparkplugs get black, but at the other hand it has run for about 12 minutes total in 2 days. What else could it be? What i have read until now is: running too rich (i don't want to touch the air/fuel mixture but i am tempted , or too early combustion. Any other options?

Again, i have the fuel pressures correctly and the warm up systems ar refurbished and working correctly. I will try the "Cold start injector" next time btw, that could also be it (i don't suspect it but yes i will ...
Here another boring youtube film with the engine starting and running, i think the exhaust is smelly btw, not a fuel smell, it just smell like not burning fuel correctly i guess...

Cheers!

Petza914

Do all the plugs look the same or are some kind of normal looking and others very sooty like the one in your photo.

Some of this stuff is much easier to diagnose with a wideband O2 sensor.

Seems like it's too rich and neither the extra air from the AAV nor the increased idle screw adjustment is compensating for that. I wonder if it runs better if you take the hose off the outlet of the AAV that connects to the port with the cold start injector. That would give it a ton more air and might help with the diagnosis. If that improves it, then I think you need to lean the mixture screw setting maybe 1/8 turn and try it again.

wopfe

They are all the same (i hope that is good news ...I will try that next. That would be disconnecting the hose at this side right, makes sense...