YACTT (Yet Another CIS Troubleshooting Thread)...

[ossiblue]

Originally Posted by m1sandman

OK, I have just run the tests as described below, 80 degrees ambient temp, cold engine (with the results):

Cold Control Pressure (tester between FD and WUR, valve open):
72 psi

Warm Control Pressure (same as above, power to WUR):
30 sec - 74psi
60 sec - 74psi
90 sec - 74psi
120 sec - 74psi

System Pressure (tester between FD and WUR, valve CLOSED, TPR return line pinched close):
78psi

Steve

Looks like you have an obstruction in the return line. Your cold control is way too high and the warm controlled pressure is, effectively, unchanged from the cold. Your heating element may also be faulty as there is not change in pressure but that can be accounted for by a restricted return line. Your system pressure also appears to be too high, indicating the restriction may be in the main return line from all your devices--FD, wur, and throttle valve.

[m1sandman]

I actually just realized why there is no variance with the different time periods for the Warm Control Pressure -- my WUR only gets power from the alternator, so even with the key on, with no alternator spinning it gets no power.

Based on my research, there was a very small percentage of 74s that were wired this way, just about everything else is wired with a switched relay into the rear fuse panel.

[m1sandman]

Originally Posted by ossiblue

Looks like you have an obstruction in the return line. Your cold control is way too high and the warm controlled pressure is, effectively, unchanged from the cold. Your heating element may also be faulty as there is not change in pressure but that can be accounted for by a restricted return line. Your system pressure also appears to be too high, indicating the restriction may be in the main return line from all your devices--FD, wur, and throttle valve.

I'm thinking I'll go ahead and replace all the return lines... they were tested with low pressure air but there is no way of telling that way if the line is partially blocked. They all look old anyway. I'll do that and retest afterwards.

[ossiblue]

Originally Posted by m1sandman

I actually just realized why there is no variance with the different time periods for the Warm Control Pressure -- my WUR only gets power from the alternator, so even with the key on, with no alternator spinning it gets no power.

Based on my research, there was a very small percentage of 74s that were wired this way, just about everything else is wired with a switched relay into the rear fuse panel.

Okay, that explains some things. You can connect a hot lead to the wur to get it to warm up and affect the heating element.

[boyt911sc]

Originally Posted by m1sandman

OK, I have just run the tests as described below, 80 degrees ambient temp, cold engine (with the results):

Cold Control Pressure (tester between FD and WUR, valve open):
72 psi

Warm Control Pressure (same as above, power to WUR):
30 sec - 74psi
60 sec - 74psi
90 sec - 74psi
120 sec - 74psi

System Pressure (tester between FD and WUR, valve CLOSED, TPR return line pinched close):
78psi

Steve

Steve,

If you happened to read the post about the fuel pressure setting I posted today, I deleted it. For the simple reason that it would give your troubleshooting work a lot of distraction. So I deleted it because it would need a separate post to settle a few questions.

The control fuel pressure is reading too high due to FLOW restriction!!!!! The only way you could get the control pressure to equalize or come close to system fuel pressure is blockage or flow restriction somewhere in the system. It could be the WUR (before or after). You could pin point where this is happening by isolating section by section of the fuel return line system. There are several posts I already made in this forum about the subject.

The system fuel pressure is on the high side and this could be a false reading. At this point, you are not sure if you have a flow restriction that could affect the system pressure. What your data shows is the sign or presence of flow restriction in the system. The question is where. Test and confirm.

If I could remember correctly, there was another member (Schmicat) that I assisted to locate flow restriction recently. Either search his post or PM him. He will be a good guide for you. I tend to over simply things about CIS troubleshooting and forgetting not everyone are aware or had the experience about doing these simple tasks. But the simple fact is that CIS troubleshooting is really simple and fun.

Tony

[patkeefe]

Hi, did you say the car sat for two years? Did it have fuel in it? Have you checked the injectors to see if they work OK? Fuel does turn to an icky shellac-like substance after a period of time, and clogs everything, such as injectors, screens in the fuel head. You may have some issues in addition to control pressure.

[ossiblue]

Originally Posted by boyt911sc

But the simple fact is that CIS troubleshooting is really simple and fun.

Tony

Tony, I bet you're getting a lot of eye-rolling from behind the computer screens with that comment!

[m1sandman]

Originally Posted by patkeefe

Hi, did you say the car sat for two years? Did it have fuel in it? Have you checked the injectors to see if they work OK? Fuel does turn to an icky shellac-like substance after a period of time, and clogs everything, such as injectors, screens in the fuel head. You may have some issues in addition to control pressure.

Hi Pat,
Yes, it did sit for 2 years but the FD was broken loose with B12 by the PO before I got the car. I've cleaned the screen in the WUR and checked the other screens and they are clean -- the injectors are all flowing well (I've got one that is leaking and am planning on rebuilding or replacing but haven't gotten that far yet).

The car does run when you manipulate the flap in the airbox to give it fuel.

Tony and Larry, I'm going to start with replacing all the soft return lines and re-testing. If the Cold Control pressure is lower, I will run a 12v line to the WUR for the warm test as well. Probably will not be until tuesday night before I can get back over there to work on it, but I will update as I have information!

As always, thank you for all your help!
Steve

[m1sandman]

Originally Posted by boyt911sc

Steve,

If I could remember correctly, there was another member (Schumicat) that I assisted to locate flow restriction recently. Either search his post or PM him. He will be a good guide for you. I tend to over simply things about CIS troubleshooting and forgetting not everyone are aware or had the experience about doing these simple tasks. But the simple fact is that CIS troubleshooting is really simple and fun.

Tony

Hi Tony,
I just went back and reviewed the thread by Schumicat (I had read it during my research before I posted my original thread hence the thread title ). Am I correct in assuming the return line he is talking about in his final post here is the line that runs from the FD to the WUR? If so, that line is brand new as the original was leaking the first time i pressurized the system after I got it home.

Thanks!

[boyt911sc]

Originally Posted by ossiblue

Tony, I bet you're getting a lot of eye-rolling from behind the computer screens with that comment!

Larry and et all,

Just for fun let me know a CIS problem that is difficult to diagnose that a DIY'er like you or me could not analyze or test? There is probably a few that I do not know but a solution is available to us. I've been looking since I got involved in CIS troubleshooting for a particular problem that 'we' could not diagnose correctly. And I'm still searching and looking. Thanks.

Tony

[ossiblue]

Originally Posted by m1sandman

Hi Tony,
I just went back and reviewed the thread by Schumicat (I had read it during my research before I posted my original thread hence the thread title ). Am I correct in assuming the return line he is talking about in his final post here is the line that runs from the FD to the WUR? If so, that line is brand new as the original was leaking the first time i pressurized the system after I got it home.

Thanks!

Steve,

The return line begins at the FD, runs along the firewall where there is a T connection for the line from the wur. From there, it continues through the frame, under the rear seat, into the tunnel, and into the tank. Your 74 does not have a line from the fuel accumulator into the return, if it is stock. If your new line does not cover the entire length of the return circuit, you still may have a blockage at the T, from the wur to the T, or down stream from the T to the tank.

[boyt911sc]

Originally Posted by m1sandman

Hi Tony,
I just went back and reviewed the thread by Schumicat (I had read it during my research before I posted my original thread hence the thread title ). Am I correct in assuming the return line he is talking about in his final post here is the line that runs from the FD to the WUR? If so, that line is brand new as the original was leaking the first time i pressurized the system after I got it home.

Thanks!

Steve,

The fuel return line system for your car is well described by LJ. Include the fuel line return going inside the tunnel up to the gas tank. The blockage or restriction could be any where in the 'fuel return line'. So isolating section by section of the fuel return line system is necessary to locate or pinpoint which is the culprit.

Remember that the return line from FD to gas tank is comprised of several pieces of fuel lines joined together by connection or fitting like T-connection, compression fitting, etc.

For example:
If you break the connection of the return line at the fitting before it enters the tunnel, you have isolated fuel line from that fitting to the gas tank. So if the pressure test shows no change in the pressure reading (before versus after), the blockage is in the line between this 'fitting' and the FD. Keep isolating the rest of the fuel return lines as needed. Keep as posted.

Tony

[m1sandman]

Does anyone know the size and lengths I would need if I was going to replace all the return lines?
Thanks!

[Jim Williams]

Originally Posted by boyt911sc

sandman,

...[snipped]

If you are getting a cold cold fuel pressure greater than the warm control pressure, there is flow restriction in the fuel return line/s. When the flow restriction is severe or totally blocked, the control fuel pressure would be greater than the system pressure.

2). For the system fuel pressure: You need to isolate the WUR and the TPR to get the pressure reading. Closing the valve to obtain the system pressure is correct for the later CIS engine without TPR.

Jim Sim's has a simple solution to this problem without using an adaptor (clever idea) by pinching close the return line from the TPR. The problem I find with this set-up even if it works is the inability to confirm or verify the fuel flow is completely stopped. A small leak is not that critical for this measurement.

Another method with I personally prefer is to remove the banjo fitting from the FD going to TPR. This would need an adapter and plugged the banjo just in case there is fuel blockage at the return line. With the valve closed, both the WUR and TPR (disconnected) are isolated. No guessing!!!!

Tony

Tony,

I'm assuming you meant that in the event of a severe or totally blocked return fuel line the control pressure would be greater than the specified system pressure. The complete blockage of all the return flow back to the tank would certainly result in the measured system pressure being higher than the specified system pressure. (The measured control pressure can never be higher that the measured system pressure.)

In 2). Closing the valve to obtain system pressure is correct for engines with OR without the TPR, provided that the gauge and valve are correctly connected.

As far as pinching the TPR's return line, my problem with this is that the plastic line could very likely be too old (given that it's the original line) to recover from being pinched tight enough to stop the flow (either cracking the plastic line, or creating a permanent partial blockage of the return flow). This seems like a risky alternative to taking the time to make the proper hookup of the pressure gauge.

FWIW, here's my contribution to explaining how to hook up the pressure gauge -

Where to disconnect the WUR/TCPR lines from the Fuel Distributor:


Where to reconnect the lines to the pressure gauge:


Overall view of the connected gauge set-up:

Black and White photos from the Porsche Workshop Manual.

I hope to get these posted in an upcoming revision to the CIS Primer, now still under construction, along with better info on the early ('73 - '74) CIS. Hope the photos help.

[boyt911sc]

Jim,

The procedure shown in WSM for measuring the control pressure for CIS with TPR is quite vague or unclear. The pictures you have attached show only one (1) pressure gauge while there are two (2) active fuel pressure regulators present.

Removing the banjo fitting and connecting it with the WUR in parallel connection would measure the total control fuel pressure produced by WUR & TPR as tandem effect. The TPR has 3 settings (cam settings) while the WUR has a variable setting. Unless you have two (2) gauges set, one in each branch (parallel) we could not tell the pressure contributed by the WUR from the TPR.

In short, an out of spec control pressure reading could be caused by WUR or TPR or both if you are using a single pressure gauge. Follow my logic? Unlike in the CIS without TPR, there is only one thing to consider which is the WUR.

While I have your attention, where does the banjo fitting connected in the picture you have attached? Upstream or downstream? I like to solicit some feedbacks from others about this set-up shown in the WSM photo and most specially from you. NOTE (edit)......saw the connection in the second picture. TD.

BTW, Jim Sims has mentioned pinching the return line from the TPR not the delivery line (hard plastic line) and with that, you could measure the system pressure. Any comment or suggestion is highly appreciated. Thanks.

Tony

[Jim Williams]

Tony,

There is only one pressure gauge. The point made in the WSM is that the proper procedure is to measure the joint effect of the two pressure regulators in tandem. I don't see that as vague or unclear. That is what the specs in the spec book and in the WSM represent. That is the whole point of my comments. You are second guessing how the test is supposed to be performed. I have additional information taken from some Porsche microfiche dated in the mid-70s that backs up what they say in the WSM, but is more detailed so there is no doubt about what was intended. There is additional info in the microfiche that shows what the pressure numbers should be measuring the TCPR alone. I don't know why they didn't include this info in the WSM, perhaps they though it might be confusing. (I plan on posting some of this microfiche info on my Primer update.)

I thought posting the pictures would indicate pretty plainly how the factory says to run the tests. I don't intend to try and justify why they stated to do the tests this way. The control pressure spec numbers are based on the (single) gauge being connected to the WUR and TCPR in tandem per the WSM.

I understand what Jim Sims said about pinching off the return line. The effect would be the same regardless of which side of the TCPR is closed off, however. Either way the fuel flow is stopped from it's return path back to the tank. I think you may be correct that most of the return lines are cloth braided soft rubber. My bad, perhaps, but the lines are still old.

[boyt911sc]

Jim,

Thanks for the explanation. I read the WSM several times and it never mentioned how to test the WUR or TPR using this set-up. My question is how do you differentiate if the culprit is the WUR or TPR using a single gauge? If the measured control pressure is off the chart as an example, using a single gauge does not tell you which is the culprit. There should be a specific test method for identifying the root cause of the problem. This is what I'm trying to find out and you are the best person to ask. Maybe there are documentation of the tests some where. I appreciate your feedback.

Tony

[manbridge 74]

Has a link to this thread been posted yet?

1974 911S CIS Problems/Questions

Answers a lot of questions CIS in 74s'.

[boyt911sc]

Originally Posted by manbridge 74

Has a link to this thread been posted yet?

1974 911S CIS Problems/Questions

Answers a lot of questions CIS in 74s'.

Jeff,

Thanks for bringing this up. It was explained in post #45.

Tony

[Jim Williams]

Originally Posted by boyt911sc

Jim,

Thanks for the explanation. I read the WSM several times and it never mentioned how to test the WUR or TPR using this set-up. My question is how do you differentiate if the culprit is the WUR or TPR using a single gauge? If the measured control pressure is off the chart as an example, using a single gauge does not tell you which is the culprit. There should be a specific test method for identifying the root cause of the problem. This is what I'm trying to find out and you are the best person to ask. Maybe there are documentation of the tests some where. I appreciate your feedback.

Tony

Tony,

I agree that the WSM doesn't address how to perform individual tests on the WUR and TCPR. I had the same question and after several years, realized the answer was not going to be found by re-reading the WSM. Or anything else I seemed to be able to lay my hands on.
My intent in posting the photos on this thread was to clear up what seemed to be murky water on how to connect the gauge (according to the Factory that built the CIS). Since the two regulators were apparently designed to work in tandem, the tandem outcome from the two regulators is the spec to test the pressures against. These are the numbers provided in the WSM and the little spec book. There are no separate numbers for each regulator. I think the WSM says something to the effect of "if you don't get these numbers, replace the TCPR". Not the kind of answer an inquiring mind wants to hear. So even if you find a way to measure the control pressures individually you don't know what are good numbers to check against.

Only recently did I come across some obscure Factory information (the microfiche I mentioned in a previous post) that addressed separate pressure readings for the TCPR. However, nothing in that document addressed how the typical shop (or for that matter, any shop) was perform the test. Here are the numbers:

Idle position: 2.9 Bar
Mid-throttle: 4.1 Bar
WO throttle: 2.8 Bar

No separate numbers were provided for the WUR alone.

To add further insight, here is what a friend and respected rebuilder of FDs and WURs recommends for those with a problem with the TCPR: Replace the dual regulator set-up with the vacuum operated WUR for the' 75 US models - 0438 140 129. The TCPR is not rebuildable.

To sum it up, the WSM is perfectly clear on how to run the test. What is not perfectly clear is why they didn't add separate tests for the WUR and TCPR. And what's further frustrating is that there is no one around now in the Porsche factory design group who can answer the question.