1983 911 CIS Pressure Test Evaluation

[Damon88]

Car has been starting normal hot and cold and suddenly now it's hit or miss.. the odd cold start up crank and sometimes hot... checked all connections and seems fine. new engine with all new vacuum lines. Here is the results from the pressure test. Cold seems fine. Warm pressure is out of spec and residual pressure is out of spec. Not sure what to check for this. Any guidance would be amazing. Cheers Damon

1983 911 3.0
COLD test
WUR #090 unplugged ( brand new from Kjet)
Temp 14.8c = 1.9 bar open valve on pressure test (in spec)
Temp 14.8c = 4.7 bar closed valve on pressure test (in spec)

WARM test
WUR plugged in
3.5 min =3.0 bar (not in spec ?)
10 min =1.1 bar
20 min =0.3 bar


Between the Bentley manual and Jims workshop this seems out of spec.

[joe912/62]

My pressure numbers from a unit that was rebuilt by Tony here on this website are (82SC)
residual pressure:
1.6 after 5 min
1.5 after 10
1.4 after 15
1.3 after 30 min.

[joe912/62]

Test was done at 14 degrees Celsius here in Montreal

[berndtj]

Originally Posted by Damon88

Car has been starting normal hot and cold and suddenly now it's hit or miss.. the odd cold start up crank and sometimes hot... checked all connections and seems fine. new engine with all new vacuum lines. Here is the results from the pressure test. Cold seems fine. Warm pressure is out of spec and residual pressure is out of spec. Not sure what to check for this. Any guidance would be amazing. Cheers Damon

1983 911 3.0
COLD test
WUR #090 unplugged ( brand new from Kjet)
Temp 14.8c = 1.9 bar open valve on pressure test (in spec)
Temp 14.8c = 4.7 bar closed valve on pressure test (in spec)

WARM test
WUR plugged in
3.5 min =3.0 bar (not in spec ?)
10 min =1.1 bar
20 min =0.3 bar


Between the Bentley manual and Jims workshop this seems out of spec.

I'm a bit confused about your warm test. Was the car/fuel pump running the whole time, or are these residual pressure numbers (i.e. car/fuel pump is off and we are checking that the system stays pressurized)? I'm kind of assuming that this is residual pressure, since the numbers fall off over time. Yeah, it's out of spec, but not sure that it's the cause of your issues. FWIW, I recently had similar issues and it turned out to be a bad connection at the FP relay (had to open up the pins a bit). Here's my thread just for reference:

https://forums.pelicanparts.com/porsche-911-technical-forum/1136382-loss-power-fuel-cutting-out-l.html

[Schulisco]

The warm test results are odd.
These are the values for the 1981-1983 US SC models with lambda control. I suppose that the car in question is one of these models? Lambda control is working? Catalyst with oxygen sensor still mounted and proved working?



The warm pressure reading must be achieved within minutes, after the engine ran warm, depending on ambient temperature and load or covered track...

Thomas

[SkiVT]

I assume you are saying it took 3.5 min after plugging in the WUR electrical to get to warm control of 3.0 bar. This warm pressure is below the min spec of 3.4 on the spec sheet. You also have pressure leaking off too fast after shutting off the FP.

- You list the WUR as new from Kjet. If so, they should fix the pressure to be in spec.
- The pressure leak speed could be caused by three things as explained here:

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

[Schulisco]

Also make sure that the check valve at the fuel pump is in place and fully functional. Without that the fuel accumulator can't do it's job.

[Damon88]

Thanks to all for responding. Test was done first thing in the morning. The warm test was done for 3.5 min with WUR plugged in and fuel pump switched on at Fues panel With jumper. Bentley manual mentioned running for 3 min to get WUR warm. I then shut of FP and then it sit while watching the pressure drop for 10,20 minutes. its loosing pressure to fast from what I'm reading.I ordered a FP check valve but it Was a 12mm and mine is a 10mm older style maybe ? Fuel accumulator is new. Here is what I received for a FP check valve.The one of the left is what I have now. I have a new one coming. (picture is not actually mine but of another posters) I will check out both of the links provided. Thank you again for all your help !!

[Damon88]

[Walt Fricke]

Is this a '78 car with an '83 replacement engine?
The 2.7s had the 10mm banjo to connect the fuel pump to the fuel line to the engine. At some point the SCs switched to a 12mm banjo. Adapting can be a bit of a kludge, as for most swaps you end up keeping your old but working fine pump, and of course the 10mm swedged on banjo. So switching to a newer fuel pump when the old one gives out is a challenge.

Lots of conversions have run into this when switching to the 044 Bosch pump with the M12-1.5 thread from the M10-1.0 earlier setup. I can't remember what I did, but a search should turn up ideas for dealing with this. (Oh, found my discussion, but it doesn't say what I ended up doing. I installed a dash pushbutton to run the fuel pump some before starting, defeating the fuel pump safety feature - that may have been my fix. Later a shop with crimp tools replaced the 10mm banjo with a 12 Fuel Pump backflow valve type).

What problems are you having with starting and running your car? The residual fuel pressure stuff is important for restarting when the engine is hot - especially if really hot. Because an overnight cold engine has about 0 residual pressure. If the WUR's cold starting function is working, the car will start right up anyway.

Is residual pressure all you measured? That's usually the last measurement one makes: first cold control pressure, then maybe system pressure (shouldn't change cold or hot), then warm control pressure.

[Damon88]

Originally Posted by Walt Fricke

Is this a '78 car with an '83 replacement engine?
The 2.7s had the 10mm banjo to connect the fuel pump to the fuel line to the engine. At some point the SCs switched to a 12mm banjo. Adapting can be a bit of a kludge, as for most swaps you end up keeping your old but working fine pump, and of course the 10mm swedged on banjo. So switching to a newer fuel pump when the old one gives out is a challenge.

Lots of conversions have run into this when switching to the 044 Bosch pump with the M12-1.5 thread from the M10-1.0 earlier setup. I can't remember what I did, but a search should turn up ideas for dealing with this. (Oh, found my discussion, but it doesn't say what I ended up doing. I installed a dash pushbutton to run the fuel pump some before starting, defeating the fuel pump safety feature - that may have been my fix. Later a shop with crimp tools replaced the 10mm banjo with a 12 Fuel Pump backflow valve type).

What problems are you having with starting and running your car? The residual fuel pressure stuff is important for restarting when the engine is hot - especially if really hot. Because an overnight cold engine has about 0 residual pressure. If the WUR's cold starting function is working, the car will start right up anyway.

Is residual pressure all you measured? That's usually the last measurement one makes: first cold control pressure, then maybe system pressure (shouldn't change cold or hot), then warm control pressure.

Hi Walt, Yes it is. After reading your post, I went into garage and had a look at the fuel pump. Looks like it was replaced long ago.. Looks to be the older style you mentioned. I have found the correct part # and ordered a new 10mm FP check valve from our Host. I had Len build me new fuel lines when I rebuilt the car. So I will be sticking with the 10mm for now. Cold pressure was checked and all in spec. I did a smoke test with no leaks. I just found an old post from Tony that explains how to test the FA. If that checks out then I hope the FP check valve is the culprit of the warm residual pressure drop. If all else fails I will look at the fuel distributor O rings I guess. Thanks again for your help Walt.

[Damon88]

Just found this old post from 2008. I have this same set up. So maybe I don't have a FP check valve. I will now go test the Fuel accumulator even though it was new from last year..

When is a "check valve" not a check valve???

[Schulisco]

Without / with a defective or non working check valve the FA cannot do it's job either. The pressure will press the fuel through the fuel pump back in the tank...

[Damon88]

Originally Posted by Schulisco

Without / with a defective or non working check valve the FA cannot do it's job either. The pressure will press the fuel through the fuel pump back in the tank...

My fuel pump has the 10mm banjo fitting for 78/79... not sure if this is actually a check valve or just a fitting..

I did test my FA today and its working perfectly ..

[Walt Fricke]

There are two kinds of fuel pump check valves. One is in the neck of the fuel pump itself, below where the banjo bolt screws in. The other is in the banjo bolt itself (at least it is external to the pump casting). Can't recall which is which, but easy to check. I think the change one way to the other was when the bolt grew to 12mm thread from 10.. Both work/function the same.

[Damon88]

Just found a post where Tony mentioned a simple way to attach Fuel pressure gauge to top of FA to test pressure for the check valve. I will try this to confirm it is the check valve. Funny what you will find with the search function, very large coffee and hours of reading through old posts.. haha

Cheers and thank you for responding Walt.