924Board.org

[TheBib]

Car has 50K, original and owned since new, so has not been driven much nor messed with much, I have made sure fuel is good, premium, pump and lines all clean. Put on new plugs, wires, cap, rotor 2 yrs ago. Just finished with new fuel filter and injectors just because i wanted to eliminate the idling issues i was having. i think my idling issue was the fact that many years i went to adjust the idle with the throttle stop which was ok at the time, but eventually the car ran worse and worse. Now i believe i have fixed by adjusting the idle stop and the micro switches that i ignorantly messed with many years ago when i was stupider then i still am. Ok enough of the background. Now the car starts fine, idles maybe with a little stumble here and there. Wife started the car at work and the engine sort of stumbled, but then a rev or two and all was fine. I checked it at home and with my timing light tach it did the same thing. RPM at first was around 800, then as i watched it eventually climbed to around 930 or so (bouncing around a lot +/- 50). Spec sheet in engine compartment says timing 0 degrees and 750-800 rpm. That seems rediculosly low for both. I have it adjusted to about 2-3 degrees adv. and 950 rpm. The rpm bounces anywhere from 920 to 1020. Is that alot of variation? Am i asking too much from an old car? Is the timing light too sensitive? It also says when adjusting the timing and idle Disconnect the electical contacts to the digital idle adjustment and put together (what are these?) if these are the microswitches on the throttle who cares at idle they should be off anyway. I have vacuum hoses coming to replace mine, but doubt that any of mine have any significant leaks. So don't know where to go from hear or even if i should call it good enough and leave it alone because i am asking too much for a car that is almost 30 yrs old even though it only has 50k on it. Could it be that the fuel delivery just doesn't control perfectly? I have a fuel pressure guage, but really didn't know where to connect it and didn't want to creat issues if i was barking up the wrong tree.
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TheBib

[924aussie]

Year and type please

eg 1980, NA, Manual


Alan
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green 924 .. 1980 rego 924PSH
1998 Mopar Neon ... sick
2003 Challenger / Montery 4WD
1995 Hyundai Scoupe ... sold
1998 Nissan Silvia ... sons back from OS he has taken it
BIG BLOODY MOTORHOME 300zx Sold
1980 Fire truck Sold

[TheBib]

sorry thought i mentioned it, guess not. it is a 1982, 924. not a turbo, just plain jane stock. i can definatly work on cars as i have rebuilt many classics, chevelle, nova, firebird from the late 60's and early 70's but this is a whole different bird and i simply do not want to mess with something like fuel mixture, or replacing a WUR when i am just learning what and were all these parts are on my car. Thought i had a huge vacuum leak using my stethoscope on the y hose that goes from the intake near the cold start valve to the break booster and to the intake boot, but learned that wow it has a venturi there. Why air circulates around that way instead of through the throttle body, well I am obviously a carburator guy not a fuel injection guy, it will take some getting used to. i a sure these are great, but sensitive on the tuning.
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TheBib

[ideola]

The plugs for the idle stabilizer are on the little black box that is mounted to the LHS inner wheel well directly behind the headlight bucket. Disconnect the two leads and plug them together. I believe on the NA, you also have to disconnect and plug the vac retard/advance lines to the ignition distributor (but double check this as my memory fails on a regular basis). THEN you can adjust the mixture and the idle.

The technique I usually use is to raise the idle to about 1200 or so (temporarily), then I use the stumble-lean/stumble-rich method to find the proper mixture setting. On my NA, I typically adjust it just slightly to the lean side (i.e. about 1.8th of a turn counter clockwise) of the midrange between stumble-lean/stumble-rich. This seems to yield a pretty good balance of power and economy. Be sure to remove the 3mm hex key after adjusting the mixture, and then be sure to rev the motor to allow things to settle in. Repeat as necessary until you get a good steady idle (don't worry about the RPM just yet, just get it steady).

Once you have the mixture set, still leave the RPM a bit on the high side, then check the timing. On the NA, I find that the car is more responsive in the low end with a tiny bit of advance. Be aware that ignition timing changes WILL affect idle speed...but should be set while holding idle at about 2000 RPM. Once you have the ignition timing where you want it, THEN back the idle off to about 950-1000 RPM. I personally don't like going lower than that because when the fans kick in, the car may stumble a bit.

After all that, reconnect the adv/ret lines, and reconnect the idle stabilizer. This should help you get close.

Now, two other things that seem to affect idle surging. One is the Lambda system. You need to make sure your O2 sensor is fresh, is connected, and that your frequency valve is functioning correctly. If anything in the Lambda loop isn't working correctly, it seems like the idle will want to hunt a little. As I recall, the function of the microswitches is to interact with the Lambda circuit to impact full load enrichment, so it's during this part of the regimen that you should really pay attention to having them adjusted correctly, and making sure that the frequency valve is functioning correctly. I believe the Haynes supplement has a topic on testing the resistance of the frequency valve.

The other thing is that if you don't have clean grounds, every time the radiator fans kick in, the car idle may have a tendency to hunt as well. I've never been able to totally eliminate this, but cleaning up ALL of the ground points, and making sure you have good grounds on the engine itself will help. I usually install ground straps in the following locations:
- back of head to battery ground strap bolt (in the battery tray)
- back of block to coil mounting stud
- alternator to head
- alternator to block

Also make sure the battery ground strap is in good shape. There are several other ground points throughout the car that are helpful to look after, but typically shouldn't affect idle.
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erstwhile owner of just about every 924 variant ever made

[TheBib]

ok, understanding more and loven it, know where that mysterious box is. Did not know it was the idle stabilizer. Neat. on the sticker in the engine compartment they don't say to disconnect the vacuum advance, although if you have it at 2000rpm it may make sense. the part i am unclear on is the 3mm hex key. where am i adjusting the mixture. and on what and where is it. Understand I have never touched the fuel mixture since the car was new, is this something i should mess with? Why would it change such that it needs to be adjusted?

another question. the car has 50k is a 1982 and i never changed the O2 sensor. I thought that at idle the idle microswitch told the Lambda system that hey i am idling so don't control. ignore the o2 sensor be in open loop? the car doesn't exactly have great pickup, but doesn't bog to awful much.

Sorry to bug you guys but i am learning so much its scary. and I thought i knew cars, well not porsches thats for sure what a design.
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TheBib

[TheBib]

interesting at noon, took a look at the magic box and was going to ask you about how you said take the plug and connect them together. i was thinking i needed to use some jumper wire. What germans, there are two plugs to this control box and you take them both off one male and one female and plug them together.

Also on the fuel mixture adjustement. I looked and looked at my Kjetronic fuel thing many times and never saw any place to adjust, probably good because i would have messed with something i shouldn't have. but was reading another thread on this site. Is a little ball bearing covering this allen screw? I am guessing i just need to take a magnet to remove, then adjust away, then replace the ball bearing. if so either i cannot read very well, or no place in any manual probst or otherwise do they say a ball bearing is covering a screw you need to adjust.
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TheBib

[ideola]

Look at the image in this link:
http://www.pelicanparts.com/cgi-bin/smart/more_info.cgi?pn=911-110-934-00-OEM&catalog_description=Plug%2C%20911%20%281974-79%29

This is a diagram for the 911 fuel distributor, but it uses the same part to plug the access hole to the mixture adjustment screw. The hole to the adjustment screw is actually on the AFM unit, not the fuel distributor itself. It is between where the fuel distributor block sits, and where the rubber boot attaches to the AFM, as depicted in the illustration at the above link. FYI, you can't actually see the hex head that is used to adjust the mixture, it is down inside the AFM unit. The best tool to use to adjust it is a long-handled T-style allen key, but a standard L-shaped long allen key will work too.

If there is a ball bearing in that access hole, that is certainly not stock...maybe something a previous mechanic put there. If there is one there, hopefully it's not jammed down in there to the point that you can't get it out.

As for why it would need adjusting, keep in mind, all of the CIS components are mechanical in nature, and subject to wear over time. The bi-metallic strips will "bed in" to each other, the fuel pressure regulator spring will wear over time, and many other variables in a mechanical system will require periodic adjustment. So not unusual that it would need tweaking even with low mileage.

The key to not screwing things up is to take careful note of where the position of the adjustment screw was when you started, and to take careful notes of the adjustments you make so that worst case scenario, you can put it back to the way it was. Another method you can use is to record the baseline (i.e. current) position of the mixture adjustment screw (while the car is NOT running) by screwing it clockwise all the way IN (not out!!!) and counting how many full turns you made until it stops. Don't lose count!!! Then back it back out counter-clockwise the same number of turns to get back to your baseline position. Having this number will allow you to always have a handy reference point to a "known good configuration" (even if that configuration is sub-optimal, you know it was running with the mixture adjusted at that location).

When I'm making adjustments, I use a T-handle allen key, and always start with the handle in the 12:00 position relative to where I'm standing (this is a little tricky to describe since the AFM & fuel dizzy are oriented differently on a 931 vs. an NA). On an NA, usually I would be standing in front of the car facing the windshield, so 12:00 would have the T handle pointing toward the windshield. Then from there, it's easy to ascertain a quarter turn, a half turn, a full turn, etc.

What I would do in your situation is bring the idle up to 1200 RPM as I described above. Then put the allen key in, and turn it COUNTERCLOCKWISE until the car starts to stumble. Usually, this will be about a quarter turn, or 90 degrees from where you started. If you have to turn more than a quarter turn CCW to get it to stumble, you are almost certainly running too rich. Once you know where the stumble-lean position is, turn the key back to 12:00 position. Then go clockwise to find the stumble-rich location. Rule of thumb is that roughly halfway between these points is the safe balance between rich and lean. More precise tuning from that will require a CO2 sniffer. I have one, and in my experience, my NA provides the best balance economy, CO2 reading, and power at about 1/8th of a turn to the lean side of this mid-point.
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erstwhile owner of just about every 924 variant ever made

[TheBib]

help and don't tell me i'm screwed. I have owned this car since new and no one has messed with it, but in the location you indicate should be a plug and then a set screw. well i have a nice shiney ball bearing. real hard and does not come out with a magnet nor trying to gently pry with an excato knife. the ball bearing is a little bigger then 1/8 inch.

tell me there is a way to get this thing out from underneath. poking it out from the bottom. I don't mind taking off the unit and keeping all the hoses on flipping it as best upside down, did that to clean the underneath lever arm.. maybe the arm comes off.

i am just at a loss
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TheBib

[TheBib]

My dad owned a Zeiss Camera. I broke the thing while using it when i was about 9. Built and engineered great, but complicated. Well I want to kick some Germans fanny right now. I did flip over the fuel unit and took a punch, was able to get around the arm and sure enough got the ball bearing out. and sure enough as you said the 3mm hex is now accessable. The ball bearing even looks like it has sort of an tan seal of some sort down below. Anyway this ball bearing will not be going back in to say the least. I will find some other manner to plug the hole. hell all it is is vacuum duct tape would work. no i am not that half you know what. What irritates me is that porsche just didn't want people messen around with these things i guess. cause the car had 130miles on it when i bought it new and no one has ever touched it so this is a factory job. thanks Porsche. My car i think was the tail end of the line just before the 944's. it is not a turbo but had the fin on the back so my guess it i am going to find out different things as i move through this endevor. thanks! you will see another post if something goes wrong. By the way I didn't know you were down in plymouth. i used to live in roseville and moved to midland 30 yrs ago. maybe if i ever trust this thing again and get it reliable enough, i will come see you in plymouth and have you really fix it.
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TheBib

[TheBib]

Ideola, i followed your directions and first tried to find out how many turns i could make on the adjustment screw, in until it stopped. However i believe it does not have a head so after 16 turns it began to get harder. later looking at the picture i believe it was simply pushing the air disk arm on the spring clip thing.

Anyway i backed it out the 16 turns and used the method of connecting the idle leads together (removing the idle control module) and turning it CCW for lean stumble, than CW for rich stumble, went inbetween and then 1/8 turn lean.

runs fine when hot, starts fine, about 830 then increases to around 900, do not know why this is but i am not concerned about this.

cold start was fine until i rev'ed it, then it would die, stumble then slowly come back. to idle (sort of like a sine wave, up and down bigger at first than settling out over time)

if i mistakenly left the allen in the hole and rev'd the engine would that damage anything, i know you are thinking what an idiot. all i can say is oops,

also the air disk looks to be in the same place as it was before vertically so i do not think i bent that by cranking in the screw.

the arm moves freely, i know the warm up valve works how it should i had earlier taken it off and did the freezer test. I know all the injectors are good and the warm up injector works.

how much of a turn is significant on this allen screw?
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TheBib

[ideola]

Once you get things in range, adjustments to the mixture need to be very fine...as little as 1/16th or 1/8th of a turn WILL affect the mixture. As an example, I've been slowly dialing in my 941 (new motor) with the use of a wideband AFR gauge, and an 1/8th of a turn brought me from 11.4:1 at idle to 13.5:1 at idle. I still have some minor tweaking to go, but it's very difficult to get things precisely dialed in without a CO2 sniffer or wideband AFR. The method described is simply a rough tuning guide.

One thing to be aware of, you need to plug the port of the adjustment hole after each adjustment and then rev the engine. If the hole is unplugged, you'll be allowing unmetered air into the setup. So the procedure is: remove plug, make adjustment, replace plug, rev, allow to settle, adjust idle setting as necessary. Lather-Rinse-Repeat. Also, these adjustments need to be made AFTER the car is fully warmed up.

When you say the warm up injector works, have you tested it to make sure it's not leaking? Also, have you tested all four injectors to make sure none of them are leaking? I had an issue on the 941 where the #2 injector was leaking badly. It was not the injector. It was something wrong with the fuel distributor, one that was supposedly rebuilt. Took me awhile to find it because I didn't suspect the rebuilt distributor. You need to be extremely methodical and make sure that all injectors shut off when they should and spray as they should, as extra fuel leaking from an injector at idle will cause a rich mixture on only one cylinder and will make it impossible to get the mixture correct.
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erstwhile owner of just about every 924 variant ever made

[TheBib]

With the warm up injector, i unbolted it and cranked the car, i could not see it but when i looked at it it we definatly wet and looked that it did spray out. I didn't jumper it, and didn't have a helper at the time. i dried it off cranked some more and didn't see any more wetness. I didn't think i needed to perform a better test on this since I was really lost as far as what my problems were and quite honestly i didn't know what a lot of the parts were nor the issues. I actually unbolted it the same time i was checking the fuel injectors. I think i will try this again at lunch. Unbolt crank and it should spray for just a couple seconds i believe.

not postive on the injectors. they are all brand new. when i replaced last week, car ran the same as before. i do know on the ones i took out number 1 was not as nice as the rest, but the car ran the same after i replaced as before.

basically as far as i can tell my adjustment made things worse. And i am not positive i can get back to how it ran originally, even though i believe i can set the screw in the position it was. Maybe i have uncovered some other issue. I do know this is that you can definatly set the screw where the throttle response was way better then it was previously.

maybe what i need to do is simply keep tweaking the screw and see how it runs. Although obviously something changes from cold to warm because when i did my adjustements with car warm last night, this morning it had this surging to the point of stalling.
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TheBib

[ideola]

Maybe you should make the trip from Midland to Plymouth some weekend soon and we can look at it together...
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erstwhile owner of just about every 924 variant ever made

[TheBib]

regarding my other question, i couldn't have drastically busted or ruined something by leaving the tee handle allen while reving the engine, could I have?

or spinning the allen screw down too far and making it press the plate against the spring?
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TheBib

[TheBib]

Dan, Totally frustrated,

Would appreaciate a few minutes of your time if you would send me your phone number? And a time that I could call?
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TheBib