"What i dont understand is that when i disconnect the WUR to FD line after 1 day there will be not even a single drop of fuel although residual pressure is within spec."


1981 us, 911sc. I recently checked pressures and removed the wur several times. After 1 day for my car too I don't remember any fuel coming out of the line after disconnecting the wur to the fd line at the wur side. I have removed it under these conditions several times. I don't think there is anything wrong with my car at startup. Maybe others have more info as it's my only 911/cis.

Edit: Now that I think about it, the first time I removed it there was a little fuel but I can't remember how long it sat, usually 12 hours later and no fuel really, if I shook the line of course some would come out, maybe not having any drip out is not a bad sign on the FD side? Does it mean that it is well sealed?

Phil

Control pressure is far too low. Don't think it will make a difference when the gauge being connected over night. The fuel pump refills the system quite quick unless there are no pressure leaks or a faulty fuel pressure accumulator. From the very beginning the CP must (depending on the ambient/engine temp) not lower than 1bar/10°C (14,5psi/50°F) and must then climb up to 2,9-3,2bar (engine warmed up) depending on the particlular engine and it's CIS equipment. The CP should arise the upper/warm pressure value in 2-4 minutes. Not longer and not shorter time.

Thomas

That's weird! Never seen before. I always had fuel there. Of course more with reisdual pressure and less. if the RP is already gone. That's would explain why it took that much time to get a control pressure being measured...!
Did you checked the fuel lines being correct connected? The middle output/input of the FD supplies the WUR. And the WUR is being connected to the fuel return lines. I don't expect that it qould make a difference if the WUR is in wrong direction, but who knows? Of the FD has a problem that it won't supply the WUR with enough fuel...

Here's a good fuel flow diagram: https://jimsbasementworkshop.com/CIS/pages/fuel_flow.html

Remember: I have a new original Bosch fuel pump with a new check valve mounted. The check valve is far more important than most people expect...it works very closely together with the fuel pressure accumulator.

Thomas

CIS troubleshooting..........
 

George,

Take a look at Ginger77 recent post about his fuel accumulator test. You might as well perform a similar test to verify the condition of your FA. If it tested OK, no harm done.

Tony

Good day Everyone!

We have narrowed the problem.

As Thomas said the control pressure builds up very slowly. I guess that while control pressure is trying to build up to push the plunger down (lean the mixture) a large amount of fuel is injected into the cylinders. See below video from morning cold start with gauge connected from last night (Phil's suggestion).

CHECK THE WHITE SMOKE after start indicating a very rich condition.

https://youtu.be/GPXHHIFnsUw

Also set the basic mixture last night. My adjustment was only 1/2 off. So i dont think this is a problem. Didn't make any impact.

Tony i will do the accumulator test although it is a brand new Bosch unit. Just to confirm.

Thanks

Good morning!

Very good progress!

The white smoke is not that much. it's quite common I suppose...depending on every car and ambient temperature. Don't forget - the K-Jetronic is not that precise as modern injection systems are.

The video shows a tiny little bit of surge due to the rich mixture, but as long the engine kept idling currently no issue, this is fine tuning afterwards... We have to find out why the pressure/the fuel at the WUR drains that much...if there's no leak where fuel is getting out of the engine, it must drain internally. As already mentioned either a bad check valve, fuel accumulator, injector, fuel distributor, fuel pressure regulator valve at FD.

I would also make a cross check: Let the fuel gauge connected. Next morning let the fuel pump run without cranking the engine until it fills up the lines and the CP at the WUR is showing at least more than 1bar CP. Be aware, that the WUR will be electricially heated at the same time when ignition is on. But as the pressure of it is still that low no problem until you let the ignition on not more than 30secs...
When control pressure is high enough then try to start then engine. I suppose it will fire up right away...

Good idea to test the fuel accumulator itself again. I posted yesterday methods to test it:
https://forums.pelicanparts.com/porsche-911-technical-forum/1119829-accumulator-pump-check-valve.html

One last thought: just in case if those tests above won't bring us further - I would open the testwise the fuel filler cap after running the engine and before starting it the next morning...just to assure that we're not facing a gas tank ventilation problem....

Good luck!

Thomas

Start Tests.........
 

George,

After our telephone conversation, I went to the garage to start the two (2) cars sitting in the garage for more than 2 months without being started.

• The ‘89 Carrera 3.2 on jack stands needs a new clutch saver........started after a slightly extended 1st. attempt.
• The ‘78 SC on the lift needs newly rebuilt brake calipers........started after the 2nd. attempt.

Twelve (12) hours later today, I repeated the tests:

• The ‘89 Carrera 3.2 started after a normal 1st. attempt and slightly shorter than yesterday.
• The ‘78 SC started immediately at 1st. attempt. Quicker than the Carrera 3.2.

I will investigate the fuel line in between the WUR and FD later today after 9 hours rest and keep you posted.

Tony

Thanks Guys.

Will wait for test results Tony.

Will also test my Accumulator by plugging the fuel return line going to the bottom port and start the fuel pump.

Fuel injectors spray patterns...........
 

George,

A cold motor depends on a CSV to start and this is one of the basic principles for CIS. The spray pattern of a CSV is always good even for very old ones. They hardly fail but the fuel injectors are different. You need an atomized mist-like V-shape spray patterns for the injectors. Test and confirm.

I have NOT replaced or fixed anything in my ‘78 CIS except for a broken “Pope boot” years ago due to cracks for a long long time. And it ran using a 5-year old stagnant gasoline. Do not use old gasoline. I did it just for experiment and not a good practice. A properly set-up CIS will run if you have fuel, ignition, and no significant air leak. Plus a fully charged battery.

Tony

Hi Tony

Injectors are new. Old ones were crap. Last night i removed one new injector from the intake to perform the basic mixture setting. Spray pattern was proper. V shaped umbrella with good atomization.

Gasoline is premium 100 octane only as this is a high compression engine. I put gasoline every week as this car is now my testbed. I drive it every day...

Tony, please don't get me wrong, but now I'm confused about your last posting, because I think it distracts from the important things we're facing now ...

I don't understand why you're now talking again about the CSV again...as George in the beginning of this discussion mentioned - with the CSV his engine won't start, without the CSV it would. So conclusion is pretty clear to me - the mixture is too rich to start the cold engine with the CSV. Nevertheless - the CSV is, as you wrote correctly, required for a proper start. But this also requires the rest of the system works also well. And this is the point - it is not.

With the CSV it gets even way more richer and this prevents the start of the engine. Now we're getting closer as George this morning figured out, that his control pressure doesn't really exists until he cranked the engine several times, clearly seen in the video.
This means totally clear that the FD enrichens the mixture far beyond because of lack of fuel in the hose. This is a inacceptable situation antd the root cause of the problem. With the upcoming control pressure above 1,3bar the mixture is getting lean enough that the engine will start finally - with the CSV connected. So he has to figure out why and where the control pressure and the fuel at this place is drawning away ...

The CSV in Georges car works as it should. But it's not the culprit.

Beside that - you're absolutely right about the spray pattern and so on...but this is IMHO currently not helpful in finding out, why Georges engine drawns the WUR hose from fuel as he figrured out. Do you have an idea where and why the fuel could going from there?

No offense. SmileWavy

Thomas

Continue on as planned, but did you guys notice:

The last video the test equipment fuel lines were primed from the night before, the control pressure came up twice as fast and it didn't start.

The video before this with the test equipment not primed : therefore air in the control line at startup, the control pressure was near zero for many seconds, and... it started.

Just one data point that puts uncertainty in any particular theory.


George, do you have a sensor plate switch? It might be a good idea if it's unplugged for now to make sure it's not playing games and reducing possibilities as it would shut off the fuel pump intermitantly even on startup if it was switching on an off for some reason, if I understand the wiring diagram correctly. It's very tough to get to, maybe someone else has a way of disconnecting it that's easy.

Phil

George,

93 octane fuel is more than sufficient specially now that you are troubleshooting. How consistent could you make the motor to start at FIRST attempt? If you test run the motor once a week, it should start and run all the time. If you could not achieve this GOAL, then you have some work to do and to solve this annoying problem.

Cold start for CIS is much easier than Warm start because the CSV is utilized. You are getting closer to solving this mystery. Keep us posted.

Tony

Phil,

you're correct. And this seems to be confusing. Honestly I also do not have a clear explanation for this. Only that, that the ambient temperatures and other conditions also play in the game. Even the CP comes far quicker up than in the second video.

Video #1: https://www.youtube.com/shorts/GIcySvwJhXo
Video #2: https://www.youtube.com/watch?v=GPXHHIFnsUw

BUT: I'm pretty sure, that the CP must be far quicker on the 1,5bar from the beginning when the engine is cranked while the fuel pump runs when putting the ignition key in position "start". That's on my SC the case. Anyway - trhe problem is the fuel pressure which is too low in the beginning and - as George earlier wrote - the hose for the control pressure was pretty empty with no fuel. That's weird and quite unusual:

Thomas

Hi Guys!

My opinion is that Thomas is right. Although i can't prove it i think that control pressure is raising very slow. Only when it gets to 1.2 bar (correct setting for current ambient temp) the engine will start, BUT it gets more complicated as i have already primed the system many times prior cold start without any success as part of my troubleshooting.

If you notice the engine WILL fire from the CSV function but wont start.

Please ignore the first video. The second is based on the correct conditions. Cold start in the morning, gauge installed the night before and system primed.

Tony if i insist cranking for about 10 sec the engine will start, RPM will fluctuate, fuel smell from the exhaust. As per my tests, this is the time where CSV is deactivated due to excessive cranking. This is the reason i started disconnecting the CSV during cold start and things improved.

"Checked RP. Will keep 1.3 bar for more than 1 hour."


George, you mentioned that you primed the system many times before the last starting video. Earlier you wrote what is above in quotes but the video shows no pressure. Shoulnd't the gauge show some pressure early in the start cycle from the just prior to start fuel pressure tests? Weird that it holds RP on earlier tests but for this start test it goes to zero, unless something is wrong or I don't understand something, which is very possible.

But, if the information you've collected is correct it seems to say that with a start condition and the csv activated the residual pressure drops to zero? That would mean a start with the csv not plugged in and after priming the system would show pressure if you took another similar start video? Does this make sense?

Phil

Hi Phil.

Apologies for my inability to explain thoroughly.

1. I did prime the system when i installed the gauge last night. Actually started the engine and let it run for about 5 minutes so to check if any leaks present from the gauge fittings. Overnight pressure will decay. Next morning will start from 0 bar. This way i simulate a normal cold start and observe the gauge. This is what you see in the last video.

2. Past weeks i was priming the fuel system by jumper the fuel relay prior cold start in order to check if my starting problem is related to residual pressure loss. Although the system was primed the engine wouldn't start easily unless CSV was deactivated. All residual tests have shown that residual pressure is holding.

Hope the above are clear now.

Since i set the basic mixture last night I am thinking to adjust the mixture allen screw to the lean side and see if it starts easier. If it does i will take it to the gas analyzer and check CO%

Thanks

George,
Thanks, makes sense.

You do have a sensor plate switch? That thing is not false triggering the fuel pump?

Zero control pressure, the plate moves much higher on startup opening the switch with authority but runs very rich. (first video)
Some control pressure, the plate moves less and partially trips the switch for some reason and it activates and deactivates the fuel pump briefly during startup without you knowing? (second video)

Phil

Have checked switch operation by slightly lifting the plate. It works every time.
Besides that i have disconnected the plug during past troubleshooting without any positive results.

Thanks

Guys,

during cranking the engine, the fuel pump is powered through terminal #50 (1). After the engine fired up and is running, the fuel pump relais is powered by terminal #15 in a self holding mechanism until the engine and terminal #15 is switched off (2):

https://i.imgur.com/pJnD0iX.png

The situation shown in the diagram is when the engine already runs with connection to terminal #87a. That's why the relay is shown as it is. The resting position is on the right to terminal #87.

So - even if the sensor plate not really good adjusted, with that circuit the powering of the fuel pump is assured at anytime.

To be sure, that it runs, you can remove the plug from the sensor plate housing (this is the security circuit to shut off the fuel pump in case of stalled engine at a car crash to prevent fire the whole car on the hot engine). With the plug removed the fuel pump will run from switching on the ignition.

Again - this is not our problem.

Oh, and a little annotation concerning the thermo time switch:
If I'm right then George already replaced it with a new one. Bosch brought some years ago a new fully electronic version of them. The old one were half mechanic half electric (not electronic!) with a bimetall strip inside being warmed up with a resistance. The new one are fully electronic and they should not fail any more. The difference between both is: The new ones always powers the CSV for a second on every start of the engine! The older ones did not, if either the engine or the bimetallic strip were hot enough. Then the contact is interrupted as long the temperature is high enough. We had such a discussion in a german forum years ago:
https://www-elfertreff-de.translate.goog/showpost.php?p=213944&postcount=7&_x_tr_sch=http&_ x_tr_sl=de&_x_tr_tl=en&_x_tr_hl=de&_x_tr_pto=wapp

Thomas

George,

I did the test you asked. Car ran yesterday afternoon, just now I cracked open the 14mm FD to WUR connector at the WUR (I did not crack open or remove any other fuel line), pulled the hose up and away from the WUR, shook it and still not one single drop. Just like I remember.
Garage temperature today is hotter than usual, overnight maybe 22, at time of test 28DegC.

Note:
1981 sc us.

Over 20000 km and only one or two double starts. The last time I was playing with the wur so it doesn't really count. If each trip is 50km, then 400 successful starts, and one double start. That's my car, what can I say.
Should add, temperature of starts where I run was -5C to 38C. Mostly between 20 and 30C. I don't start in winter or below -5C in the garage overnight.


Phil

Clarification........
 

Thomas,

I spoke to George yesterday for a while. During the conversation I emphasized that the culprit was not the CSV. For a cold start, you need a CSV. So focus on identifying the culprit that is causing a cold NO start.

It is something right in front of our noses but have not thought about it. That is the reason I ran the 2 motors in the garage specially the ‘78 SC. The last time it ran was 2 months ago.

And I am installing right now an SC motor that I purchased 2 years ago on my test stand for a start-up. Just to demonstrate how easy and simple to make an SC motor run. Hope to get this motor running before George’s (just kidding). I need a week to get everything set-up.

Tony

This was mentioned by someone earlier in this thread but not verified that i could find.
Was this part changed also?
http://forums.pelicanparts.com/porsche-911-technical-forum/1020014-csv-flange-911-110-264-00-alert.html

Correct CSV flange.......
 

Pete,

I asked George about this CSV flange during our telephone conversation yesterday and said it has the hole.



George,

Please confirm the CSV flange. Thanks.

Tony

I mentioned it ... see https://forums.pelicanparts.com/porsche-911-technical-forum/1119098-911-sc-cis-residual-pressure-4.html#post11702682

But same here - this cannot be the culprit because Georges car before current trouble began started without any issues from my understanding...so this can't be the cause for his trouble now.

We're looking for sth, which has going bad over time whithout changing anything on the vehicle. So at least one thing has gone bad. We see that the cold CP is far too low, raises far too slow. This enrichens the mixture over all frontiers that the car won't start with the CSV. Without the CSV it will start after longer cranking. Either the WUR is bad or more likely somwwething else, because the fuel hoses at the WUR are dry after the car sits over night or several hours. From my understanding and what I've seen on my car is - there's always some fuel. But George reports there's not even a drop. And that's weird froim my point of view. My concern is the dry fuel control pressure line between the WUR and the FD. We see in the 2nd video that it takes way too long to fill it up and building some pressure...
And if he got the car starts and runs, it runs fine George said, right?

Thomas

Thomas,
On my sc the line appears completely dry after sitting, but is it really? zero issues starting (over 20k km). You have fuel dripping out of the fd to wur connection the next day. Either I'm lucky, or it doesn't matter or there are conditions on shut down that we simply don't understand. My system is very... very original, no work was needed to recover any modifications to the engine or kjet, except for a new bosch fuel pump that comes with a check valve, I just changed it because it's cheap and I don't want to be stuck somewhere for such a simple replacment. 81sc, usa. Sorry, new injectors as well when the top end done two years ago, again cheap and just makes sense to replace.

I'm always up for an improvement, cost is very low for most of these components, so if you can prove that there should be fuel dripping out of the line, then I can learn, or improve even further a very decent performing car. Just for your info, at 3500rpm, when the pedal is pressed to the floor, there is a shock of acceleration, so I assume my accumulator is acting properly. The acceleration doesn't let up either. This car has been driven it's entire life, so the fuel dist system has not sat. I've read that you've replaced several parts, probably more than me, either I am off factory, or you are. It would be great if someone else can verify or we can solve the discrepancy. Also, when the wur is cal'd right, it will start on first crank, warm/cold/hot so the basic intended functionality of the device is in order as well as all other elements required to keep the pressure up after shut down.

I guess what I'm saying is, don't look too much into the FD to wur line dripping after sitting for 12 to 24 hours as a very important piece of information until more data has come in from many others. I've provided my facts, you have a different result, if no other info comes in then this dripping or not dripping is questionable in the attempt to solve the issue, at this point. It's a very easy test to do, took me two minutes, if and when this is solved, if fuel comes out the next day for George, I will be very happy to benefit from this post, was not expecting anything in return, we'll see.

tschuss,

Phil

Just for Discussion....
 

We need a rich mixture for a cold start.

The empty fuel line between the WUR & FD is normal after several hours and won’t affect starting. Go check your engines and inspect the fuel line. It would be bone dry. Reconnect the fuel line and start the motor. The motor should run.



Test and verify. Confirm that your concern about empty fuel line is fact or myth. Not everything you hear or read in the Internet are facts. Let me repeat this again, the fuel line between the WUR & FD could be filled with fuel or bone dry and has no effect to the starting of a CIS motor.

This is a Technical Forum, feel free to discuss and disagree. This is how we learn from each others’ experience.

Tony

Good day Phil

Thank you for the test.

So no fuel from FD to WUR line after many hours engine stopped. Since your engine is always starting i consider your test valid.

So no problem there.

Hi Pete, Tony

If you have the wrong CSV flange (without hole) then engine's rpm will not increase during cold start as the extra air from AAV and AAR will not pass. This is not my case.

An easy way to tell if you have the correct CSV flange is to remove the corresponding hose from the intake boot , start the engine and put your finger on the hose open end. If there is vacuum present then the hole on the flange exists. I did this test also and believe me the vacuum is very strong...

@ Tony

""""Hope to get this motor running before George’s (just kidding). I need a week to get everything set-up.""""

Challenge accepted!!!

One week deadline

hahahaha!!!

Hi Guys

Yesterday i went to visit a friend.

Since i was there i hooked the car to his analyzer.

Results:

1. CO% idle after basic mixture setting: 5.5%
2. CO% idle after adjusting the allen screw : 1.58%
http://forums.pelicanparts.com/uploa...1654075290.jpg

3. CO% @3000 rpm: 0.69
http://forums.pelicanparts.com/uploa...1654075336.jpg

Note the HC readings also. These engines had incredibly low emissions for that time!
This is also a good indication that engine has no vacuum leaks.

Many posts ago your idle mixture data was in the 2 to 2.5% range. This new data started at 5.5% before being adjusted to 1.58%? Did you determine why this difference existed? Has the change impacted the problem?

Go back to the beginning.........
 

George,

Please help me understand where you are now regarding your car status.
Question #1:
After sitting overnight, how many attempts (start) before you could make the motor to start? When I do this test, I just reach for the ignition switch through the window and turned the ignition switch. I do not touch the gas pedal.

Share what ever observation you have noticed or anything of interest. Example: What are the control pressure readings versus time, etc. Give me numbers instead of using adjectives.

Question #2:
Could you re-start a warm motor after 30 mins? After an hour? etc.

I want to replicate your problem/s so knowing your conditions is critical to my next test. Thanks.

Tony

Yes. It was adjusted to 2.5%
If you read previous posts i reset the system to basic mixture setting.
http://forums.pelicanparts.com/uploa...1654082580.jpg


Yesterday i checked the CO% with the basic setting (5,5%) and adjusted to 1.58% afterwards.

Thanks

Hi Tony

I have provided numbers for all my tests. This is a technical forum and i respect that.
Have conducted all the tests proposed from all parties involved into this thread. Thanks everyone one more time for your assistance.

I need your help for a test.

1. Connect your pressure gauge
2. Prime the system. Start engine or pump
3. Let the engine relax for at least 12 hours.
4. Try to start without throttle, only key start (as you mentioned)
5. Compare gauge pressure raise with my video.
6. Does your control pressure take that much much time to build up?

Video link
https://www.youtube.com/watch?v=GPXHHIFnsUw

Thanks

Empty fuel line after several hours.......
 

Phil,

There is nothing wrong with the control fuel line. The fuel in the line would slowly seep out through the WUR after several hours. And would be filled up again in the next start-up. What is critical is to have the system pressure present immediately during start up. The control fuel pressure will come next after the system pressure.

To measure the system pressure in your CIS, you need the valve for the gauge closed and open for control pressure. This is the conventional way how the CIS pressure gauge is connected to your motor. You could leave the gauge installed and run the motor to measure the control pressure but NOT the system pressure. To overcome this problem, I installed 2 set of gauges. One for the control pressure and one for the system pressure.

So at any given time the motor is running, I could monitor both control and system pressures simultaneously. But this is not for everyone. Unless you have a curious mind.

Tony

@leonardo911sc

I suppose that you set up the CO on the warmed up engine. Because a valid CO value for those cars is nowhere listed, probably nobody can tell you a evan a approximation of a CO value on cold start, they vary greatly from one vehicle to another...
1,58% CO (on a warm engine) is pretty pefect, afaik the euro SC starting '81 with 204hp should run between 1-2% CO.

The topic of the discussion is "residual pressure" and yoiur cold start problems and that weird behaviour, that the car started without CSV far better. And you wrote that the WUR is in spec. But the video tells us another story. The CP should start above 1bar, better ~1,4bar. I already wrote that the CP raises from too low.

The supposition was that either the FA or sth else is leaking and therefore the pressure is that low - and as you wrote that the WUR is in spec.

Q: How did you verified the WUR that is in spec?
Q: Did you already checked the check valve & the FA?

Thomas

Hi Thomas!

I set the CO% with hot engine and as per spec you provided (1-2% CO). Thanks for that.

WUR pressure setting:

1. Engine stone cold
2. Check WUR temp with infrared temp gun
3. Jumper fuel pump relay and turn ignition key ON
4. Pump working
5. Set cold pressure as per diagram spec with WUR power supply disconnected and vacuum applied.
6. Install the plug and wait until rising pressure at gauge gets stable.
7. ALL within spec.
8. Pump and check valve are new
9. Accumulator is new
10. Residual pressure test is above spec

If you see the video the WUR will reach the 1.4 bar but takes long time. While cranking is below 1 bar. This is where i am focusing now. I will do some tests and let you know.

Thanks

Thomas, Tony,

I want to point out that the next start after I opened the FD to WUR line for the test asked by George, the car caught fire up as usual (csv & AAV* dominated), but then the rpm dipped to 400 for several seconds (Rich) then back up above 1000rpm. This was a unique start and I believe attributable to the opening to atmosphere of that line several hours earlier, requiring a re-build of pressure and a lower first 5 seconds of control pressure to evacuate the air introduced in the line. This tells me that even though the FD to WUR line looks empty, it's not filled with air, but I'd guess a vacuum, big difference in the meaning and understanding if that's the case.

Phil

That long time delay is our enemy...the WUR should reach those 1,4bar asap, even after several seconds when engine fired up.

Could you make 2 videos with the fuel pressure gauge connected to see how the pressure behaves after switching off the engine?
1. control pressure (not important if the engine is warm, but the WUR should have reached the warm cp)
2. system pressure

Thomas