Help interpreting confusing CIS pressure test results

[Showdown]

1977 911S with .033 WUR

Symptoms
Cold starts are really hard and irregular. Sometimes the car fires up instantly only to die. After a few tries cranking, starting and dying it will eventually start and idle rough for a minute or two until it settles in. I have to let it sit for a few more mins otherwise the first 5 mins of driving are rough.

I followed Tim's CIS for dummies instructions along with Jim's Basement Workshop as a guide. Had no trouble with the gauge install and tested the gauge against a very precise one I have at work and it's just about spot on accurate.

Results

System Pressure Test:
https://www.youtube.com/watch?v=2Cqcf2sHhSw

This one seems to be right on spec and the pressure is 4.8 bar, right between the 4.5-5.2 range for my car/WUR

Cold Control Pressure Test:
https://youtu.be/UVZ2KVBbo2s

Super confused on this one. It shows just like the other test and not like the ~1 bar it's supposed to.

Warm Control Pressure Test:
https://youtu.be/jcwLx0ui5Z0

Again, super confused about these results. Right back to 4.8 bar and almost no change as the WUR heats up. In addition loss of pressure is almost instant and not like it's supposed to

No signs of fuel leaks, no smell of fuel once the fuel pump is off.

The car was at my mechanic for some work and they claimed they fixed the starting issue but apparently not. Could they have tinkered with the WUR and thrown it out of spec?

I have a smoke machine and I'll perform that test next to check for unmetered air and vacuum leaks.

[boyt911sc]

Showdown,

Go back and review your videos. You were measuring the system pressures (valve closed) in all three (3) videos. Were you aware of that? And your SP was spot on. To measure your control pressures, the shut-off valve must be OPEN. Otherwise, you would get the system pressure readings.

Tony

[Showdown]

Thanks Tony,

Just tried again this time with the valve OPEN and same results...

https://youtu.be/rRTc0EtoEBY

[boyt911sc]

Originally Posted by Showdown

Thanks Tony,

Just tried again this time with the valve OPEN and same results...

https://youtu.be/rRTc0EtoEBY

Julian,

The WUR looks familiar. For the control pressure to equalize with the system pressure, a flow restriction is occurring at the WUR or after the WUR. If fuel is not flowing through the WUR while the FP is running, this scenario is similar with the shut-off valve CLOSED.

Test the outlet flow from the WUR (place some rags to catch the fuel coming out). All you need is a couple of seconds to test it. Do not exceed 2 sec. Keep us posted.

Tony

[Showdown]

Hi Tony,

Fuel flow freely from the FD with the gauges removed.

I checked the gauge and fittings for obstructions as well and found none; it flows freely.

[Showdown]

Photo of the inside of the WUR connection to the FD. Looks clean enough to me, but clearly I don't actually know that much so...

[boyt911sc]

Originally Posted by Showdown

Hi Tony,

Fuel flow freely from the FD with the gauges removed.

I checked the gauge and fittings for obstructions as well and found none; it flows freely.

Julian,

That is not the way to locate the restriction. The FD is NOT the problem. Your problem is the fuel flow through the WUR. So you have to determine if the restriction occurs at:

• Warm-up regulator
• Or after the WUR.

You need to test and confirm the location of the problem. Give me a call if you need some coaching. I PMed you my number.

Tony

[Paulporsche]

Showdown,

On some WURs there are more than one screen in the area you showed in your pic. You should open it up, pull the screen(s) inspect and clean if necessary.

[Showdown]

After a very generous phone call with Tony (seriously, how generous to walk a noob through something like this and explain the principals!) I disassembled the WUR, cleaned it thoroughly with acetone and compressed air and reassembled it.

I now get the following results:

Cold Control Pressure: 1.378 Bar

Warm Control Pressure: 2.75 Bar @ 23.8C (75F)

Time Delta from Cold to Warm Control Pressure: ~4min

Residual Pressure @ 5min: 0

Residual Pressure @ 10min: 0

Residual Pressure @ 30min: 0

Residual Pressure @ 60min: 0

Once I turn the key to OFF and turn the FP off the pressure drops to 0 within 30 seconds.


So what I can gather is that my WUR (stamped with a 722 and "DP" written on the underside) is within spec and was just really dirty... which is GREAT! What I can't figure is why there is no residual pressure...

Next step will be a smoke test.

Also, I'm now covered with gas... ha!

[boyt911sc]

Originally Posted by Showdown

So what I can gather is that my WUR (stamped with a 722 and "DP" written on the underside) is within spec and was just really dirty... which is GREAT! What I can't figure is why there is no residual pressure........

Julian,

Remember what I told you before? The WUR shown in your videos were very familiar to me. It has the RED paint markings I put on my rebuilt WUR’s. My record shows:

WUR-033 #722 DP...............was rebuilt in May 2015 for David Plantz.

Your residual fuel pressure loss could be due to:

• Defective FP check valve.
• Defective fuel accumulator.

Test first the fuel accumulator. It is the most common culprit for residual pressure loss. Keep us posted.

Tony

[Showdown]

What did I tell you Tony... the car was bought from a bad Porsche owner!! The plot thickens.

I’ll take a look at the check valve and accumulator.

[boyt911sc]

Originally Posted by Showdown

What did I tell you Tony... the car was bought from a bad Porsche owner!! The plot thickens.

I’ll take a look at the check valve and accumulator.

Julian,

I don’t think the previous owner was a bad Porsche owner. The PO , was not as good as the NO (new owner). You are motivated and interested to fix the problems you encountered along the way. You could make this car run before summer comes. You are doing well.

Tony

[KMoore68]

I also have a 77 911 S and would like to get my cold start issues cleared up. Can you tell me more about the pressure test you have, did you buy it recently, from where?

[gomezoneill]

Tony is the most helpful guy on this board and obviously organized.

[Showdown]

I bought the pressure test kit from Amazon because I wanted it fast and easy returns if it didn’t fit like so many seem to do.

CTA Tools 3420 K Jetronics C.I.S.... https://www.amazon.com/dp/B008FJXA3M?ref=ppx_pop_mob_ap_share

At first, like many reviewers I thought it wouldn’t fit but one must remove not only the fuel line at the WUR but also the adapter that marries the WUR and the fuel line. Then the brass fittings that come with the kit will fit.

And yes, Tony is a mensch and should be given some sort of Pelican award.