CIS pressure test, question

[npresley]

I have one on order. Upon further research, there may be a check valve indeed for my model, but as mentioned, one can be added. I suppose I am now in need of a WUR. Anybody got a good WUR for a '77?

[npresley]

I do not have a check valve on the car. I have the hollow connection with M12 thread on the pump side and M10 thread on the outlet side. What check valve will work? Most that I see are M12 thread on both sides. I would need to change the cap bolt and the banjo fitting. Might I actually have the banjo fitting with the check valve in it?

[bassfishman]

I had the same problem you have. It turned out to be the check valve on the fuel distributor. Your fp does have an internal check valve. I have a 76 basically the same as your 77.

[boyt911sc]

Originally Posted by npresley

I do not have a check valve on the car. I have the hollow connection with M12 thread on the pump side and M10 thread on the outlet side. What check valve will work? Most that I see are M12 thread on both sides. I would need to change the cap bolt and the banjo fitting. Might I actually have the banjo fitting with the check valve in it?

Nathan,

Check the number on the FP (Bosch) and post the part number. The Bosch product list will identify your FP if it has an integrated check valve or not. Keep us posted.

Tony

[npresley]

Can you post or send me a picture of the location? What check valve did you use?

[npresley]

This is the fuel pump #911.608.102.00.

[Vereeken]

Originally Posted by npresley

I have one on order. Upon further research, there may be a check valve indeed for my model, but as mentioned, one can be added. I suppose I am now in need of a WUR. Anybody got a good WUR for a '77?

Why an new WUR? It is expensive and you need to get past the check valve first. That is inexpensive. It lighth be that the pressures come within spec once the check valve is solved, no?

Michel

[Vereeken]

Here is the link to a thread that describes the internal check valve of the FD.
Might want to clean it out.

Residual fuel pressure loss.............

[npresley]

I checked behind the fuel distributor, just a thru adapter, no check valve.

[npresley]

This first picture shows the back of my FD. 2 hollow thru adapters, and one spring relief on the side.



This shows the spring relief. The O-ring looks fine.



The next picture shows the assembly at the nose of the pump. Another hollow thru bolt with a banjo type fitting and a cap nut.



This last picture shows the banjo type fitting.



I have seen a check valve - banjo fitting, but I don't see how it is replaced. The other check valves that fit into the nose of the FP have M12 x M12 threads. This banjo fitting has an ID for an M10 and the cap nut is an M10.

I'm not sure what to do now.

[Vereeken]

I have re-read your post.

In summary you have good fuel pressure, slightly to low cold control pressure for your outside temperatures and a pressure bleed with engine off that is way too fast.So reading that you have hot start issues and idle issue when hot the only elements that remain are in order of likelihood:

1. Fuel accumulator
2. What you call spring relief.
3. Check valve.
4. Fuel pump

Ofocurse there is always the ever present vacuum leak, but I assume you did that check long ago.

The failure mode of the Fuel accumulator can also be a tired spring. In that case it will also not hold residual pressure but would not leak fuel from the fuel return line. The tired spring will also not be able to dampen the pulsations from the fuel pump as it should.

I think you are now at the stage of replacing parts. I believe taht is the correct course of action after you have ruled out vacuum leaks and checked WUR pressures.

The Fuel Accumulator and relief valve are fairly cheap.

Michel

[porwolf]

Originally Posted by npresley

I have seen a check valve - banjo fitting, but I don't see how it is replaced. The other check valves that fit into the nose of the FP have M12 x M12 threads. This banjo fitting has an ID for an M10 and the cap nut is an M10.

I'm not sure what to do now.

The fuel pump check valve is built into the long neck of your fuel pump. Pumps with short necks have an external check valve. But they cannot be interchanged easily because the externeal check valves require a 12 MM banjo fitting. Your's is a 10 MM one.

[bassfishman]

You have a pressure tester so just clamp/block off each section of the fuel system and test for leakdown... Your Fuel pump does have an internal check valve. In addition to the accumulator I have seen WUR's leak down and small pinhole leaks in the plastic fuel hose.

[npresley]

I don't see any puddles or drips any where. I did a few more checks. Put everything back together and pulled the injectors. I got a WCP of about 2.4 bar and shut off the pump. The injectors did not leak a drop. I then re-pressurized and had my wife shut off the pump. I put a pair of needle nose vise grips on the pump outlet line. The pressure bled off at the same speed. Removed the pliers and started the car. I grabbed the air box and moved it around the best I could. There was no change in idle. If the WUR was leaking, where or how would I test it to see evidence? Would I remove a line , get a WCP, and then shut off everything? Other than removing the line from the bottom of the accumulator, how else would I test it?

[npresley]

I saw a mention of fuel pulsations. I hear the pump occasionally pulsate when checking pressures. The gauge will bounce slightly (maybe .05 - .1 bar). Does this help?

[timmy2]

Your wur would leak out the sides or out the side vacuum port. Personally I wouldn't suspect the WUR as it maintains the correct pressures when running. The internal spring would have to fail to allow that fast of a pressure bleed off. 2.4 bar to zero in under 30 seconds is a lot of fuel to move.

After all of this time, have you replaced the check valve if external, or pump and check valve if internal, and finally the fuel accumulator if the check valve does not fix it?
IE: have you replaced anything yet?
Even if a new part doesn't fix it, it's new and likely won't fail soon...

[timmy2]

On 8/10 12 top of page 3, you posted that when you removed the bottom fitting of the FA the fuel drained out.
There you go, your accumulator diaphram has failed.
The fuel is not supposed to drain out of the bottom. A few drips ok, drain out NO.
Your test afterwards, may not have given enough time to show the leak. Run it, let it cool, drop line, leaks = failed accumulator.

[Vereeken]

Originally Posted by npresley

I saw a mention of fuel pulsations. I hear the pump occasionally pulsate when checking pressures. The gauge will bounce slightly (maybe .05 - .1 bar). Does this help?

The Accumulator levels out any pulsations and reduces noise. I believe this is more proof that the accumulator is toast.

[npresley]

Finally got the accumulator replaced. The pressure bleed off is corrected. I'll have to drive it before I know if it took care of the rpms diving to 0 between shifts.

[timmy2]

CIS Primer for the Porsche 911
Deceleration valve may need adjustment if the rpm drop remains, also running too rich can cause the same symptom.
I'm glad the accumulator fixed the residual pressure problem.
Now you can set the car up to run right.
Good luck and keep us posted on your results.