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Unique CIS/ K-jetronic problem, I think...
Hi everybody
Recently been restoring an SC cabrio. Regarding k-jetronic, all it was done was: - rebuilt WUR and fuel distributor at a specialist - new fuel pressure accumulator - new cold start valve - new fuel pump with new no return valve - new fuel filter - new injectors Tests: control pressure (warm and cold) within the parameters, system pressure also ok. The car starts roughly when hot after 20 minutes stoped. I have to hold the key at the start for about 4 seconds for the engine run. At first Fuel pressure seems to be lower than normal, but right after pressing the accelerator , everything sounds good. After that, the car runs perfectly. And the worst thing is that the car didn’t have this symptoms before restoration... |
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Sent you a PM |
Ok, there is already quorum(2 users with the same problem), to start a rescue! :confused: :)
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How is the frequency valve behaving? All that stuff (except perhaps the O2 sensor itself) hooked up? Power to the relay under the passenger seat? Tried checking the pulse width modulation with a dwell meter (or, better, a scope) at the test port back in the left rear of the engine compartment?
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What do mean by the CCP being spot on but the fuel pressure is low ?
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It is more simple than that. :) |
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>Tests: control pressure (warm and cold) within the parameters, system pressure also ok.
Cold control, system pressures are fuel pressures. > At first Fuel pressure seems to be lower than normal, What fuel pressure are you talking about as low ? |
Ah - I didn't notice the Madiera address.
Hot start issues are normally ascribed to a lack of residual pressure. Yes, you replaced the valve at/in the fuel pump, and the injectors, which are the likely sources of pressure bleeding off. You don't report the result of a timed residual pressure test. Did you do that, and it also was within spec? It might be worth checking the operation of the thermo time sensor, which controls the CSV. Hard to miswire that. " At first Fuel pressure seems to be lower than normal, but right after pressing the accelerator , everything sounds good. After that, the car runs perfectly." Are you saying that after the 4 seconds of cranking, and the engine starting, that it runs rough? A blip of the accelerator resolves that? How are you measuring fuel pressure on a running engine? Easy to read control pressure. But if you leave the test valve closed for system pressure the engine won't run well or long, as the control pressure will become the system pressure, which will make things very lean. Though a momentary read seems to work. This assumes the standard CIS testing hook up. |
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Yes, Maybe not very well explained, but my main issue is, after eliminating all the possible (in theory) causes, what can be causing the loss of residual pressure ? Residualtests were: 1,9 bar residual right after switch of, 1,7 most of the time (up to 10 min) and I lost when it lowered to zero but for sure it was before the 20 min.... Yes, when I start it after de 20 min. It take a long time to start and when it starts, it behaves like the system pressure is low (for 5 seconds)... then it regains pressure after a blip or two, and the car drives well. I am measuring the running pressure right before the fuel goes into de fuel distributor and the control pressure on the hose returning from the WUR to the fuel distributor. I have a very simple process only including a gauge and a T piece and a couple of adaptors. No test valve! Hope now is everything clear. Today I am starting with the clamping test... very little hope... |
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Control pressure hot: 3,1 bar “Low fuel pressure behavior” when starting after the 20 min. Residual pressure: right after switching of the car around 1,9. 2,0. 2,1 After 5 min, 1,7 After 20 min, zero. ( cannot specify when it goes to zero because I was not looking all the time) |
CIS troubleshooting........
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Alex, Your WCP is out of spec and identify the culprit for your residual fuel pressure loss. The three (3) most likely suspects are:
Keep us posted. Tony |
Alex - Since you replaced the fuel pump/check valve, and the fuel accumulator, it makes sense to put these lower on the suspect list, although new parts have been known to be defective (which really makes diagnosis hard).
So I'd look at the PPV Tony mentions. By the way - fuel flows from the FD to the WUR, and from the WUR back to the fuel tank. The WUR bleeds off pressure, lowering system pressure to control pressure. The PPV sets the system pressure, which is lower than the pressure generated by the fuel pump. The PPV. The PPV also diverts excess pressure back to the fuel tank. The PPV has at least one (tiny) O ring, and if it goes bad it can cause problems. And if it is bad, it would act very much like a bad anti-return valve on the fuel pump. If you are measuring fuel pressure before the fuel gets to the FD, you are measuring pump pressure, not system pressure. Most of us haven't measured pump pressure, as the Bosch testing system (and others like it, including home made, since it isn't complicated) measures system pressure by blocking the line to the WUR after where the gauge is Teed in. I bet you can figure out how to do that. You don't need to (and usually don't) have the car running to check system pressure, as it doesn't depend on what the WUR is doing. You just need to run the fuel pump. |
Many thanks for your help, both of you.
I will make new pressure readings tomorrow to have more accurate information. By the way the PPV was not on my suspect list because the fuel distributor was the last thing to assemble, coming from a full rebuild at a Bosch specialist. Thanks for pointing the mistake on reading system pressure. I will proceed correctly. Just to add some information: I have been asking for some help to the Person who rebuilt the WUR and fuel distributor. He suggested to preform a “clamp test”. Camping the hose between the tank and fuel pump to verify if the check valve is doing its job. Second stage, camping on the return hose to the fuel tank. In both test, after 20 min. stop, the car reacted exactly the same, with the known symptoms. I am starting to be suspicious if the electric system is having any contribution to this issue... I have been checking the fuel pump voltage and when I start the car, it is 11,3 V. After the car is running it goes up to 12,4 Volts. Is this correçt? |
- Defective fuel pump check valve. Brand new!
- Defective fuel accumulator. Brand new! - Defective PPV (primary pressure valve) for the FD. Brand new! What a nightmare! This is taking me out of bed many times...:confused: |
Searching for fuel pressure loss culprit/s.........
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Alex, Avoid using the “clamping method” to locate your mysterious fuel pressure loss unless you are using a clear plastic hose or tube. Use a hose with shut-off valve so you could verify and confirm that there is no fuel leaking. The test procedure is very simple. Another thing you have overlooked was your fuel injectors including the CSV. Pull them out and have them pressure tested for drips or leaks. Lastly, are you certain that all the fuel lines are good and not leaking? This would be obvious and easy to detect but it happens. You have seen and witnessed the gradual fuel loss in your tests but you did not know how to interpret the test result. Could you post a picture of your test showing where and how you connected the pressure gauge? Maybe there is a communication break down. Pictures would help. Thanks. Tony |
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Thanks for your message. Injectors were new Twice because at first I suspected there was a system contamination and I thought one of the injectors could be stuck... Cold start valve was new when I assembled the new WUR... I will take some readings today and I will send you the data. First I have to find a new reading gauge kit but with that safety valve you have mentioned. |
have you ever checked your sensor plate adjustment???That has to be done with the fuel system completely empty- and cold
Ivan http://forums.pelicanparts.com/uploa...1612352497.jpg |
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That is a good one! But has been done... By the way... The fuel pump is activated by the micro switch at a certain point when the plate starts to move... I am thinking if there is a way to actuate the fuel pump earlier than it is now... (???). Is there a setup for this switch? |
Back to this topic... finally found some time to do the measurements on the system, following your recommendations:
- gauge connected between WUR and FD, tap (valve) assembled, gauge at the segment on the side of FD... - car not running, cold engine, wur plug disconnected, tap closed, pump running - pressure system 4.5 bar - open tap (valve), wur plug disconnected, engine cold and not running, fuel pump running, cold control pressure, 0,8 bar. Detail: right after this test, when I disconnected the pump, cold control pressure goes up to 1,6 bar. - connect wur plug, fuel pump running, car cold and not running, it starts at the up mentioned, 0,8 bar and starts raising, after around 1 minute, 1,2 bar, 2 min 1,9 Bar, 3 min. 2.2 bar. - started the car. Control pressure goes right up to 2.2 bar and after 1 min running (car stoped), 2,4 bar and after 2 min. 2,9 bar. - went for a ride. Long enough to reach the working temperature. Back to the workshop and new readings with the car still running. Hot control pressure (gauge on place, tap opened, car running, working temperature), 4,6 bar! - switched of the car, (gauge in place), residual pressure, down immediately to 2.2. bar and slowly falling... after 15 min. 1.6 Bar, 20 min. 1.2 - after 20 min. started the car. Problem persists. Hard to start, taking a bit more than normal. For the first 2-3 minutes engine runs rough. If I run it high revs, pressing the gas, it starts becoming better. Note, at this point when I start the car again after the 20 min. period, the control pressure goes up to 4,7 bar and stays there! - If I drive the car for a while, after 2-3 minutes driving normally the car becomes perfect! Once in a while, and I am not able to establish a pattern, the car doesn’t hold the idle. On a stop, the idle falls abruptly and the engine stops. If I keep on driving, the problem disappears... and it will show up again at some point... Hope some of you can take any conclusions from this data. I’ll appreciate! |
Check your WUR........
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Alex, Your WUR is out of spec. Look at your CCP (cold control pressure) it was only 0.8 bar (11.6 psi.) and the WCP (warm control pressure) was 4.6 bar (67 psi.) and too high. The WCP was equal to your SP (system pressure). I thought you had a newly rebuilt WUR? The control pressures were out of spec. and causing your erratic running condition. BTW, what is the Bosch ID # of your WUR ? It should read something like 0-438-140-xyz. The last 3 digits would identify your specific WUR. Keep us posted. Tony |
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Yes my WUR was rebuilt on a specialist. # xxx.089 ROW That leaves me with a question.... If I set the cold control pressure, in this case, if I increase, wouldn’t the warm control pressure also increase? |
Can this also be related to the WUR voltage?
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Wur-089.........
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Alex, Why don’t you have the WUR recalibrated by the rebuilder? Tinkering the WUR yourself might cost you to forfeit the rebuilder’s warranty. The control pressure adjustment for the WCP affects both the WCP & CCP. But the adjustment for the CCP does not affect the WCP. So you make the WCP adjustment first and foremost. Followed by the CCP last. Just make sure you have a good and reliable pressure gauge kit. Keep us posted. Tony |
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Something very strange happened today, after Tony’s suggestions..
As indicated, I decided to work on the WCP. The gauge was still attached to the system after the readings from yesterday. I started the car and went out for a ride. After it reached the running temperature, headed back to the workshop. When I arrived, the gauge for WCP was indicating 3.0 bar... everything was left as it was from yesterday,.. Why in two different days, two different readings? |
Faulty gauge? Have you checked the screen in the wur connection. Almost seems like you have blockages that clear and then maybe clog/restrict again. Inconsistent behaviors always seem the most difficult to troubleshoot.
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Multiple gauges for comparative testing.......
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Once in a while, I test my gauges for relative pressure readings. I run them in series and record their individual pressure readings. Since I don’t have a calibration standard for the pressure gauge, I use the individual readings to compare one gauge to another. So far, the S&G tool gauges have been very consistent and reliable. The oldest gauge is more than 25 years old and the most recent acquisition is a year old. The variance from the average is less than 1 psi. and considered them OK. It is mandatory for fuel injection system troubleshooting work to have a good and reliable pressure gauge kit. Otherwise, you will have inconsistencies in your test results. http://forums.pelicanparts.com/uploa...1612985136.jpg Tony |
It is a new set (gauge, valves and fittings), I bought specifically for this issue, when I understood I was not measuring the correct way...
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Anyway, considering that now I am reading the correct values (0,8 bar) CCP and (3,0 bar), WCP, I need to increase this values.
Any suggestions about what can I do locally to increase these numbers? |
Some "resources" I have read but never had to try:
https://www.impactbumpers.com/forum/index.php?/topic/33747-911sc-bucking-at-1500-revs/page/4/ https://cis-jetronic.com/index.php?rt=product/category&path=65_66 http://forums.pelicanparts.com/porsche-911-technical-forum/1007529-erratic-wcp.html#post10178579 |
I will have a look!
Many thanks! |
Clarification........
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Walt, I was going over Alex’s posts and noticed your post above. There are several ways to measure the system pressure in CIS:
The conventional way to measure the system pressure is between the FD & WUR where you measure the control pressures (CCP & WCP including the residual pressure). However, the fuel pressure entering the fuel distributor is not the fuel pump pressure but rather the system pressure caused by the PPV (primary pressure valve). Below is the picture of my CIS bench tester measuring both the control and system pressure during calibration. The gauge at the left (control pressure) and gauge at the right (system pressure): http://forums.pelicanparts.com/uploa...1613271404.jpg Control pressure reading (enlarged picture): http://forums.pelicanparts.com/uploa...1613271467.jpg System pressure reading (enlarged picture): http://forums.pelicanparts.com/uploa...1613271523.jpg Next time you have an opportunity to do some fuel pressure tests, install the pressure before the fuel distributor and you will get the “system pressure”. Tony |
Tony - I am sure you are way ahead of me on hydrodynamics (as with much else). If a pump can produce X PSI, but where there is work to be done by the pressure there is a recirculating reducing valve, does this mean that the pressure measured at the outlet of the pump will be the same as just after the reducing valve. I tend to get confused using Ohm's law hydraulic analogies backward to try to understand hydraulics. Would the readings be different if the pressure reducing system were of the non-recirculating type?
For testing I can see how measuring system pressure before the line to the WUR is convenient - on a running engine you won't shoot control pressure super high when you close the valve, and you don't need a valve for measuring there. |
Keep on testing and finally manage to set the pressures to spec.
Set warm pressure first and today before start, set the cold pressure slightly punching the pin. The values were accomplished. Went for a ride up to working temperature. Checked warm pressure when arrived : 3 bar, correct for this wur. Left it for half an hour, but still hard to start... when finally started, the warm control pressure was 3,8 bar! Is it supposed to change that much ?? in both situation the car was warm... ?????? |
Need some information.........
Alex,
When you did the fuel pressures testing, were you running the motor or just the fuel pump? I am not sure about your test procedures and if you could confirm which method you used, I might be able to explain some of the discrepancies you have observed. Keep us posted. Thanks. Tony |
Assuming measurements were made correctly, a warm starting control pressure higher than the last warm running control pressure makes no sense.
The cold control pressure is set by the warm up part of the WUR - the bimetal spring when cold presses down on the springs which press up against the diaphragm (which itself governs how much pressure is released). So the upward pressure is less, the control pressure lower, and the mixture richer. At a certain temperature, the bimetal part is high enough that it doesn't touch anything - it no longer has an effect. So physically it is not possible (at least without something really weird in how the WUR was assembled) to have the control pressure rise after you turn the engine off. When you turn a warm engine off, you may see a bit of an increase in system pressure. Tony explained this as the effect of the pressure accumulator, and it is short term as residual pressure gradually bleeds off as the engine cools. But system pressure isn't control pressure. Physically, the WUR is not complicated, and it is easily reassembled. 3.8 bar would make it hard to start. You have gotten suggestions that making sure the filter inside the WUR large metal cylinder is not clogged (which is one source of high control pressures) would be useful. In your case, though, the symptoms reported don't support the clogging hypothesis, as it should result in high cold CPs. Restrictions in the return line system from the WUR to the fuel tank would raise CPs, but why would this be thermally related? Some have blown air through the return system to see if there are restrictions. I don't recall those leading to isolating an issue, though. Located where you are, I can see that some diagnostic tricks are difficult. For instance, borrowing a WUR and a fuel distributor (the main controllers of these things) to swap in one by one, could help, but perhaps there are few of this model 911s on the island? The WUR swap is easy, the FD not so easy at all although possible. Where does control pressure come from? The FD has an area which is at system pressure, fed directly from the pressure regulating intake stuff connected to the fuel line and pump. A tiny hole in the stainless steel diaphragm which separates the two halves of the FD allow system pressure (but very little volume) to get through to the control pressure part of the upper FD, which in turn is connected to the WUR. This hole could, in theory, get blocked, or alternatively get eroded and larger. Not clear how either would cause your symptoms. The piston which air flow moves up (more fuel to the injectors) or down (less) has no rings or seals - it depends on close tolerances. The fuel the piston sends to the injectors is at system pressure. If it were to be worn, more pressure could leak up to the control system? These can stick from deposits, which can be cleaned off. They can't be replaced. People (Tony?) with experience with lots of FDs might know how often this piston/cylinder system gets worn or scratched - as well as whether this might cause your perplexing symptoms. Did you, by chance, measure the residual pressure and control pressure just before you did the warm start? |
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I suspect this is to help maintain pressure after engine shutoff to improve warm starts. Sorry for the interruption. http://forums.pelicanparts.com/uploa...1613599077.png |
No interruption at all. He has an '82 Euro SC. I don't know if those, which don't have the Lambda stuff, have the push up pressure relief valve, or the previous one.
This schematic shows the push valve system. http://forums.pelicanparts.com/uploa...1613605069.jpg I agree that the push valve would retain pressure in the whole system - the control pressure wouldn't flow past the O ring on the push valve, and the O ring on the other end of that valve would block off the return line to the fuel tank. Should help with hot starts, not make them harder. |
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