Help me confirm my WUR diagnosis

[grillage]

Hi all,

The patient:

A 1977 2.7L engine.

Fuel distributor recently rebuilt at CIS Flowtech while I had the engine out doing a top end rebuild.

The symptom:

All has been running pretty darn well since the rebuild but the hard cold start I have had for a long time has remained. (Note that I fixed the warm start issue by replacing fuel pump and check valve, accumulator and then finally the tiny o-ring in the distributor that was the actual cause of losing residual pressure. I have not residual pressure issues

After getting everything back together I got a Gastester to try and dial in the proper air/fuel ratios and was able to dial it in just to spec. However, when I did this (by reducing fuel just a bit) the cold start issue became worse.

I checked all the pressures again yesterday and I have:
5.1 bar system pressure (right at spec)
2.0 BAR CCP at 28* C (hot day yesterday!) right at spec
But the warm control pressure only increased slightly. Up to 2.3 bar

So my theory currently is that since I’ve dialed in a WARM engine at 2.3 bar, and have adjusted fuel and air at that pressure, when I run cold at 2 bar I’m running super lean

So likely the Bi Metallic Strip has failed? Either way, likely time for a WUR rebuild right?

Edit: I should mention, I confirmed the correct function of the thermo time switch and the cold start valve

[grillage]

Video for reference https://youtu.be/7LNQbpGjDCM?si=lNPfIMuzCsRznQhC

[PeteKz]

Bump this back up.

Yes, the WUR has a problem. Best to get hold of Tony (boytSC) here on the Forum and send it to him for evaluation. You could try to open and adjust it yourself. Search for threads that describe how to do that.

[Schulisco]

According to the video it seems to be a miracle that the engine won't stall...the popping sound seems to be the popoff valve in the airbox?! Indicates to me that it's running uber rich.
Agree with Pete - the WUR must be in spec, your's seem to have an issue. Did you already crosschecked the WUR part no. against the parts catalogue if its wrong?

Check the WUR pressures against the factory specs of course and let it overhaul.

But IMO that's not the only issue. Your fuel pump starts rightaway when you switch on the ignition. I'm pretty sure that the '77 models also have the security switch at the sensor plate housing to switch of the fuel pump in case of a stalled engine to prevent engine fire. As your's starts with ignition on tells me that there's is likely sth wrong. Therefore you also have to work on that. Otherwise you'll never get a proper running engine, no matter how often you overhaul or replace CIS parts...
So check if the plug at the back side of the sensor plate housing is plugged in. I bet it isn't.

1. How many turns do you need to close the idle screw? (set it back after measuring this)
2. check sensor plate height
3. Make start of fuel pump only when lifting the sensor plate by sucked air from engine

2. & 3. are documented in the manuals.

Thomas

[Schulisco]

Originally Posted by Schulisco

2. & 3. are documented in the manuals.

2:


3:

[grillage]

Funny you mention the fuel pump always operating. When I got the car the the harness had been cut (or maybe even burned apart) where the plug for the air box was. It also had a plastic tube running through the AAV!

When I did the top end rebuild I also had a complete new wiring engine harness made and reconnected the airbox. I wonder if I have a different fuel pump relay that doesn’t look for that signal or something.

I have a second “033” regulator arriving today so I’ll see how that one behaves and report back

[PeteKz]

We have several simultaneous threads on much the same issue with WURs. Please read those too.

https://forums.pelicanparts.com/porsche-911-technical-forum/1166969-wur-return-line.html

https://forums.pelicanparts.com/porsche-911-technical-forum/1167170-cis-hard-cold-start-idle.html