CIS Pressure test results - help?

[Tom '74 911]

Hi -

My engine is a '77 2.7L CIS. I have been having a hot start issue that seems to be getting worse. I bought a CIS pressure tester gauge and hooked it up last night. Aside from this website of course, there is a great CIS Primer here:

CIS Primer for the Porsche 911

I followed the directions and ran some cold tests last night - and was hoping for some diagnostic help. I hooked up the gauge so that it replaced the fuel line that runs from the top of the fuel distributor to the WUR, with the valve on the WUR side of the "T".

1. My car has been sitting for a week or more, so it was "cold". I turned on the fuel pump and with the valve closed, measured system pressure = 5 BAR which seems to be w/in spec.?

2. With the fuel pump still running, I opened the valve and recorded the WUR cold engine control pressure = .55 BAR which seems w/in range to me looking at the graph in my spec. manual as it was about 45 deg. F? The electrical connection on the WUR was unplugged for this test (I don't know if this matters?)

3. I then plugged in the WUR electrical connection; The reading did not change = .55 BAR?

4. I then turned off the fuel pump to do a cold system pressure leakdown test. With the valve open, when I turned off the fuel pump, the pressure dropped to zero almost immediately. Is that OK? Or should the system with the WUR in the loop be able to maintain pressure when cold?

5. I then closed the valve and turned on the fuel pump to repressurize the system. Then I turned off the fuel pump to check the cold system pressure leakdown w/out the WUR in the loop. The pressure dropped more slowly and settled at about 1.5 BAR. I didn't stick around for 20-30 minutes, but it seemed stable - far more stable than when the WUR was in the loop and it dropped immediately to zero. This result seems to make me believe that the accumulator and fuel pump check valve are working fine?

Conclusions: First, all the tests I ran were on a cold engine. I hope to run the tests again hot tomorrow. Is my WUR acting as it should? The Bosch part # is: 0 438 140 033. I took it out to examine it and it didn't appear to have any adjustability to it. I was too afraid to completely disassemble it - I didn't have a gasket replacement and didn't want to open a can of worms I couldn't clean back up!

Aside from running the same tests hot, what else should/could I be doing?

Thanks for the help,
Tom

[ossiblue]

Tom,

I have the same wur on my engine, so maybe I can help. I'll respond to your points in order.

1. Within spec.

2. Without the spec chart in front of me, your cold pressure seems a bit low. If you don't have cold start issues, leave it alone.

3. The wur does not get power to the electrical connection unless the engine is running (actually, the alternator.) You would not get a change because the bimetallic spring is not heating up. You can connect a hot lead jumper to the wur and test for warm pressure.

4. You should not drop to zero. You will get a fairly rapid drop but it should slowly fall to around 1 bar and hold there. You may have a leak at the connections to the gauge, or a leak in the check valve of the fuel pump, or the fuel accumulator.

5. This test may also indicate a slow leak in your gauge set up. Typically when I run the test, the pressure holds at system pressure and very slowly drops. May also indicate a check valve failure.


Your wur is adjustable and relatively easy to assemble and disassemble. Try running warm tests and take readings, and then post. You said you were having warm start problems, and your leak down tests back that up if the check valve or fuel accumulator have a leak--both would show up the leak down test.

At this point, if your pressures during a warm test are in spec (and they probably are if you aren't having warm running issues), your problems are likely not with the wur. Residual pressure (or lack of it) is usually the reason hot start problems occur. Be sure all connections to the gauge are leak-free, and report back with your residual pressure results.

Hope this helps.

[Gunter]

Good stuff.

Hot-start issues are usually a check-valve at or in the pump leaking or a faulty accumulator.

If the pump is really old, suspect the check-valve.

Your pump may have an internal or external check-valve; don't know until you open the banjo connection.

If the control pressures check out, leave the WUR alone. Like stated, it's easily disassembled but make sure that the pin meets up with the center of the little diaphragm when re-assembling. A dab of grease will keep the pin straight and steady during the process.

[Tom '74 911]

L.J. & Gunter -

Thanks for the help. My fuel pump is only a few years old and I can not remember what kind of check valve it has. I will look though.

After the cold pressure tests I was suspecting the WUR, as the system pressure leakdown test seemed to hold pretty steady when the WUR was taken out of the loop by closing the valve on the gauge rig, but fell dramatically to zero when the WUR was part of the loop, with the valve open. I have since done some more reading and am now unsure if that is normal operation of the WUR or not. I only know enough to be confused at this point!

I will do all the same tests with a hot engine and report back the results. Hopefully there will be conclusive evidence to a specific failure.

Is there a way to isolate the accumulator and the check valve so if one is bad, I can just replace it and not both?

Thanks again,
Tom

[ossiblue]

Run your system pressure test again--with the wur closed off by the valve--measuring pressure only from the fuel distributor. Honestly, I can't recall how long my system held the high pressure with the fuel pump off, but there was little noticeable drop, IIRCC. If you find a drop from your 5 bar down to 1.5 within a few minutes, that's likely the check valve since the accumulator isn't in the equation. (Again, assuming the gauge set is not leaking!)

If you have a 3 port accumulator (with a hose connected at the bottom), then there is an easy way to check. Disconnect the hose from the bottom port and plug it--it is a return hose to the tank if the accumulator leaks. Turn on the fuel pump and see if fuel is coming from the bottom port. If so, you've got a bad accumulator. Be careful, put something under the port to collect possible fuel, and have a fire extinguisher ready--and an assistant, if possible.

Note: When you first disconnect the line from the bottom port, a bit of fuel may come out--that's back flow from the return line from the wur and doesn't necessarily mean the accumulator is bad. There should be no fuel coming out when the system is pressurized, however.

Sorry, I don't know of an easy test if the accumulator is the two port kind.

[Tom '74 911]

L.J. -

Thanks for the help. I will give your suggestions a try tonight. When I turned off the fuel pump to test the system pressure with the valve closed, as you just mentioned, the pressure did drop from 5 BAR to about 1.5 BAR w/in a minute or so, then stayed there. How does this test eliminate the accumulator from the possible list of suspects?

I'm going to assume that my gauge is good as it's brand new, but you never know.

I do have a 3 port accumulator and will test it tonight too. Just so I'm clear - with the bottom port open and the fuel pump on, if any fuel leaks out the bottom port, the diaphragm is broken and it's no good? The bottom port is just a safety drain in case of failure?

I will also check my fuel pump tonight to see what the situation is with the check valve.

Thanks again for the help.

Tom

[ossiblue]

You're right, the accumulator is still in the loop in the system test--sorry.

You got it right, also, on the accumulator test. Just be sure you take safety precautions--there could be fuel under pressure coming from that port. You can even make things safer if your gauge set is connected--close off the valve to the wur so no fuel is flowing through it nor the return line that it shares with the accumulator (some set ups have the return from the accumulator connect at the return line to the tank, others connect to the return line from the wur). Then, run a "system pressure test" and see if there is fuel coming from the accumulator port. This way, you won't need to worry about the backflow from the return line that you removed from the accumulator if it's connected to the wur line (but I'd plug it anyway.)

Let us know what you find.

[Gunter]

Check-valves fail far more than accumulators.

If your pump has a failing internal check-valve, you can add an external one as long as the threads match. M12 x 1.5 mm is usual.

You might also check for a dirty tank to see if dirt is making the check-valve fail.

[Tom '74 911]

OK. I did the cold tests again and had enough time to do a real test for system pressure leakdown (cold). With the valve on the gauge closed to eliminate the WUR from the loop, the system pressure was back to zero after about 10-15 minutes. So, either the accumulator or fuel pump check valve is no good.

I also did the accumulator pressure test that ossiblue suggested, but forgot to plug the removed return line, which wasn't good! Fortunately my wife was quick at the key to turn it off. If I can figure out a way to plug the line correctly, I will try the test again. Aside from the initial draining that happened when I unscrewed the return connection at the bottom, no additional fuel leaked out.

The fuel pump I have has an internal check valve. Optimally, I'd like to isolate it and the accumulator to find the exact culprit instead of throwing parts and money at the problem, hoping it gets fixed. Is there any reason I couldn't isolate the fuel pump by connecting the gauge in-line with the outlet? Would it be bad for the pump to flow momentarily into a closed loop so I could pressurize it and see if the check valve holds the pressure?

Thanks,
Tom

[Tom '74 911]

Just a bit more info. . . My fuel pump not only has an internal check valve, but also an external one too. I just took it out and it looked operational to me in that the spring and ball seemed to be moving fine and freely.

So I guess my question in my post above still stands - is it possible to isolate the fuel accumulator and fuel pump check valve(s) from each other to test them individually?

Thanks,
Tom

[boyt911sc]

Originally Posted by Tom '74 911

Just a bit more info. . . My fuel pump not only has an internal check valve, but also an external one too. I just took it out and it looked operational to me in that the spring and ball seemed to be moving fine and freely.

So I guess my question in my post above still stands - is it possible to isolate the fuel accumulator and fuel pump check valve(s) from each other to test them individually?

Thanks,
Tom

Tom,

The answer to your question is YES!!!! To check your FP's check valve, you need to pressurize the line before the FA (fuel accumulator) in order to isolate the FA. Hook up the pressure gauge to the fitting that connects to FA with gauge valve closed. Run the FP using a suitable jumper with in-line fuse for 1 or 2 seconds and observe the pressure reading. The objective is to pressurize the line under test to have a fuel pressure close to the system pressure. A reading of (50 - 60 psi) on the gauge is good but if you obtained a higher number no greater than 75 psi is better. Over 75 psi is not desirable. Bleed the excess pressure and observe. Record the pressure reading on the gauge versus time (mins.). If the residual pressure does not drop to zero in 15 mins., the check valve is doing its job. Then you could proceed for the second test.

The second part of the test with FA included is basically the same as above. But this time, the pressure gauge is attached after the FA. The pressure versus time data should be the same as above (check valve test OK). Any significant drop in pressure versus time is due to a bad FA. A very simple test I like to perform to check the integrity of an FA is to remove the drain line of the FA. Place the end of the detached drain line in a small container and another container under the FA. Run the FP for 1 or 2 sec. (max). A bad FA will have fuel dripping below the bottom port.

Caution and safety must be observed when handling pressurized flammable liquid like gasoline. If you are not comfortable doing this test, please do not attempt to try this test. Keep us posted.

Tony

[Tom '74 911]

Tony -
Thanks for the great info. I need some more adapters to hook up the gauge in those places as they are all 12mm I think and the gauge and adapters that cam with it are 10mm and smaller. I could have my sizes wrong, but the end result is the same - it won't fit with what I've got on hand. I will order a few adapters and continue on with the tests to try to determine exactly what is wrong.

I did drive it around a bit today to try the tests hot. The system pressure at idle is about 2.9 BAR. When I shut it down, it was warm (but not hot) and it took about 20 min. to drop to zero. It seems like it should stay pressurized longer?

As I mentioned in a previous post, I did unhook the drain line from the bottom of the accumulator, then turned on the fuel pump for a quick few seconds. The negative was that I forgot to plug the removed line which sprayed fuel all over! The positive was that no additional fuel appeared to leak out of the fuel accumulator. As I also mentioned earlier, my fuel pump has an internal check valve as well as an additional external check valve. I took a look at the external valve and it seemed to operate OK. So if either the FA or (both) check valves are failing, they must be doing so only under high pressure.

I also thought my injectors could be leaking - bleeding off the pressure. I pulled them, placed them in some jars, and pressurized the system to 5 BAR and none of them dripped or otherwise seemed to be obviously bleeding off pressure.

I was hoping to find a smoking gun, but haven't so far. Hopefully, after getting some adapters and isolating the FP check valves and the FA, it will be obvious which part of the system is failing.

Thanks for all the help. I will report back with my findings if I find a solution.

Tom

[Gunter]

Tom,
It sounds like the accumulator is working alright and it is unlikely that both check-valves are failing together.

How do you know the pump has an internal check-valve?
Bosch or Pierburg?
What is the number on it?

[Tom '74 911]

Hi Gunter -

The fuel pump number is BOSCH 0 580 254 984 which is the same as 911-608-102-00 as far as I can tell. This is the correct pump for '77 to '79 CIS engines from the Pelican catalogue. I cross referenced the BOSCH number with some BOSCH fuel pump specifications I found which indicated that it has and internal check valve. It also has a long neck at the outlet end.

Thanks,
Tom

[enjefriy]

Tom,
had similar problem wit hot start as you.
Have u eliminated ignition as a possible source of this problem. Wat ignition sys are u using.
I was doing same thing as u, until I retested the ignition. My msd module would not produce spark when warm.
Jus a thought. Never know

[Tom '74 911]

Hi -
I just had a thought - in my car, the fuel pump turns on when the key is in the "run" position. This has made it easy to do the CIS pressure tests because I haven't had to jump any fuses or do any hot-wiring; I just turn the ignition key a few clicks to turn the pump on.

In normal starting, I usually turn the key until the pump turns on, wait a few seconds until I hear the tone change and the system pressurize, and then start the car. If my system pressure has a leakdown issue, wouldn't it be just be charged back up (pressurized) when I turn the key and let the pump run before starting the car?

So back to the original issue - my car has problems sometimes with starts after being parked hot. It really manifested itself at the track a few weeks ago when I would park it after a session, hot, and have difficulties starting it for my next session which was maybe an hour or so later. I would try my normal starting procedure by letting the pump run for a few seconds before engaging the starter. I could always start it in the end, but it sometimes took 5-10 min. of cranking, waiting, cranking, sitting, cranking etc... When it finally would catch, it would run very rough for 10-15 seconds before it would be responsive to accelerator input. Once the accelerator became responsive, it would clear up and run normally after revving up and down for another 10-15 seconds.

My fuel pump has been moved from it's original location in back, to the front crossmember. I had assumed that I had a system pressure or leakdown issue, but does this info change anything?

Thanks a lot,
Tom

[Tom '74 911]

Originally Posted by enjefriy

Tom,
had similar problem wit hot start as you.
Have u eliminated ignition as a possible source of this problem. Wat ignition sys are u using.
I was doing same thing as u, until I retested the ignition. My msd module would not produce spark when warm.
Jus a thought. Never know

Hi enjefriy -

I do indeed have an MSD ignition. That's very interesting info. Hmmmm. . . maybe its not a CIS/fuel problem at all.

Thanks for the suggestion - I will look into that (I'm not sure how, but. . . )

Thanks,
Tom

[Gunter]

BOSCH 0 580 254 984 checks out to have internal check-valve, 5 bar system pressure, etc.

I like that pump. Like you say, it's the right one.

Wonder why the external check-valve?

It could indeed be an issue with the MSD. Followed the long frustration experienced by enjefriy recently with this.

Personally, I like the Bosch CDI for reliability.

[ossiblue]

Tom,

Given the new information you posted about how you start your car (pump running), I agree with enjefriy, this may be an ignition issue--at least something to check out. The tests you performed so far on the fuel delivery are a bit inconclusive, and pressurizing the system before start should take care of that.

BTW, you stated it took 10-15 min of cranking to fire the engine during a hot start--be careful! Continued cranking without ignition pumps raw fuel into all cylinders and you run the risk of hydro-lock--though I suspect the times you posted included lots of sitting and waiting. Did you smell fuel during the no starts? The symptoms mentioned after the car finally catches does sound like a recovery from a flooded fuel situation. Lots of white smoke? Anything else you recall? Every little bit of information helps, no matter how irrelevant it may seem.

[Tom '74 911]

Originally Posted by ossiblue

BTW, you stated it took 10-15 min of cranking to fire the engine during a hot start--be careful! Continued cranking without ignition pumps raw fuel into all cylinders and you run the risk of hydro-lock--though I suspect the times you posted included lots of sitting and waiting. Did you smell fuel during the no starts? The symptoms mentioned after the car finally catches does sound like a recovery from a flooded fuel situation. Lots of white smoke? Anything else you recall? Every little bit of information helps, no matter how irrelevant it may seem.

ossiblue - Yes, I do not continuously crank the car for 10-15 minutes trying to get it started! That time frame includes 5-10 seconds of cranking, followed by a few minutes of sitting (while cursing quietly). I will try to pay more attention to fuel smells or other signs of flooding the next time it happens. Hydrolock is not something I'd like to experience.

Is there a good, easy quick way to check for spark during a failed hot start? Imagine yourself at the track or a highway rest stop, alone - what is the quickest and easiest way to check for spark?

I read through enjefriy's whole thread. It does sound suspiciously like my issue mirrors his and is an ignition problem and not an air/fuel problem. I do have a MSD 6AL ignition with a MSD Blaster coil. My issue only seems to pop up when the motor is REALLY hot. A quick run to town usually does not cause me problems. Driving on the highway for a long distance or driving sessions at the track seems to exacerbate the issue.

Thanks so much for the help,
Tom