CIS rebuild next steps

[Topocalm]

After some extensive testing and research across this forum, factory manuals and other online sources I believe I am clear on the problem with my CIS but would appreciate your help in deciding on the best way forward.

My car is a 1973.5 2.4T that is mostly original. Due to low compression on two cylinders I ended up rebuilding the top end of the motor (turned out to be broken cylinder rings). I also replaced the airbox, all hoses and rubber joints and carefully cleaned the throttle body and mass air flow meter and replaced the injectors. All in the motor was 10 month apart.

I was able to start the car and do the first 20min run-in at 2k rpm however the car is hardly drivable as the engine does not take on load.

I first re-checked (actually more like triple checked) and established the mechanical baseline, which seems to check out:

• Leak down <5% on all cylinders
• The engine has the OEM camshafts installed (numbers match spec) and they are timed correctly
• Ignition timing (static) is correct
• New spark plugs, I double checked that they are correct replacements for the original Bosch (I now run NGK BPR7ES)
• New batteries with combined 900 Amps

The fuel system check-up is a bit more interesting. Please keep in mind this car ran extremely reliable for the 13 years I have driven it.

Visual check:

• The WUR is not the original that came with the car. It was replaced in 2003 with a WUR from a 2.7 (BOSCH 0 438 140 090), I believe it is for the 1975 model. I can see the replacement in the historic records that came with the car.
• The fuel distributor is not the original that came with the car, it is from an SC (Bosch 0 438 100 006).
• The control pressure regulator that is connected to the throttle valve had been disabled / disconnected sometime before I purchased the car.
• Apart from that this is obviously the first CIS car they ever built and is a lacking a lot of equipment that was added in later years.
• The air flow meter was cleaned by me, it mechanically seems very sound, the sensor plate is correctly positioned, moves freely. When pushing it manually up it feels like it should, I can feel the hydraulic pressure build when pushing up and no resistance during downward movement
• I installed new seals, as mentioned the box and all rubber parts are new.
• I should mention the fuel pump was replaced in 2015 and has less than 5k miles on it

Measurements

• Pump delivery rate (fuel return line) 250ml / 30 seconds (vs. the 850ml / 30 seconds factory spec). I read on this forum that this low rate is rather normal and at this level not a big concern (?). Also read here that delivery rate at 70 PSI is what counts, I did not measure that.
• System pressure (control pressure line between WUR and fuel distributor): 4 bar / 60 PSI.
• Cold control pressure: 4 bar / 60 PSI. => Since control pressure and system pressure are the same I disconnected the fuel return line from the WUR to measure the flow rate. It is close to zero, basically drops. I left it in the tube and over time I gathered some 30ml. The gas is significantly darker than it originally is. Bottom line: The WUR is shut always, no more regulating. It seems to be totally gummed up. I suspect I set it to the side after disassembly without blowing it out and the fuel inside glued it shut (? even though in its cold state it should be open...).
• Leak test: 1.3 bar after 10 min / 1.0 bar after 20min => Very close to spec
• Fuel delivery across injectors (injectors are new). I went for 70 ml. Result across injectors: 74/70/64/70/70/70ml

Take-aways and what needs to be decided:

• I need a rebuilt WUR. My first question is: Which WUR should I go for. I have 3 options:
  1) Revert everything to factory spec for my car (WUR, fuel distributor etc.).
  2) Switch to the WUR that exactly matches the fuel distributor on the car (I believe it is the "033"
  3) Have the current one rebuilt ("090").
  I would assume the WUR and fuel distributor need to "match" each other. I checked the control pressure diagrams for the 090 and 033 and they are very similar, there is a ton of overlap. Otherwise they both seem pretty similar, including that they have the vacuum port...
  => My take away is that I should go for the 033 unless it is significantly more economic to go for the 090. In that case I should get away with the 090 given the similar curves and the fact that it ran very well for a long time.
  
• Second question regarding the WUR: The current model (090) has a vacuum port that was simply left unconnected. I understand it is for leaning out the mixture under high RPM / low load conditions, my take-away is it is a feature that my early car never had, and by not connecting the vacuum port it simply remains unused = no issues.
  
• What do I do with the fuel distributor. My key question: The difference in fuel delivery on one cylinder of approx. -10% to the rest, is this an indicator to better have it serviced. My sense is that yes. In that case I should make sure the service provider has both parts WUR and fuel distributor tuned to match. Also, this part also sat for a year... def. a possibility that here too fuel gummed up.
  
• What about the mechanical control pressure regulator that has been disconnected in the past. At first I assumed the more modern WUR made the mechanical throttle actuated pressure regulator obsolete, but the 74 CIS still has it. In the PET it looks like starting 75 they where dropped? So - no issue not using this regulator when using my '75 WUR? (Again, car ran super well without it...).

Lastly, assuming that I will need to have the fuel distributor serviced and the WUR either replaced with a 033 or my 090 serviced as well - I gather Larry is the guy?

Thanks a lot for your help, this forum is a amazing and I appreciate the support.

[47silver]

https://cis911primer.com/pages/descr_basic.html

check this out first

[E Sully]

Seems as though there have been quite a few changes in you CIS.
Try this link, Workshop Manual .pdf
https://www.bing.com/ck/a?!&&p=2d59daf42e8ffd0bJmltdHM9MTY5NDQ3NjgwMCZpZ3VpZD0w MWY4OTEzMC0yZGI2LTYyN2UtMjQzNy04MmJhMmNhZjYzNTcmaW 5zaWQ9NTIwMQ&ptn=3&hsh=3&fclid=01f89130-2db6-627e-2437-82ba2caf6357&u=a1aHR0cHM6Ly9tZW1iZXJzLnJlbm5saXN0LmNvbS92aWxodW VyL0slMjBKZXRyb25pYyUyMFdvcmtzaG9wJTIwTWFudWFsLnBk Zg&ntb=1

[ahh911]

Topocalm,

090 return comes out in drips and is very dark, you think it's clogged.
Use brake cleaner or mineral spirits to break up the gunk.
There is a fine mesh in there that can be removed, search this out on forum.

090 does not have a vaccum line connection (control pressure is not vaccum adjustable), nipple is there to vent to intake.

You have a modified system that worked, start with the wur cleaning before changing more.
Of course you may want to ensure that full throttle enrichment is included by putting in the appropriate wur at a later date. Cleaning the existing wur costs no money and because it's so blocked you have nothing to lose by trying to clean it out first. (I'm surprised your car ran strong without full throttle enrichment?)

Phil

[PeteKz]

Phil is giving you good advice. I will add that a system pressure of 60psi is below the spec. Look it up, but it should be around 70 psi. Clean the WUR and reset the SP, then see how it runs. Don’t start changing parts until you get it back running the way it was. That will complicate your troubleshooting.

[porschedude996]

I’m bookmarking this…

[Jafo]

I’m also bookmarking this

[boyt911sc]

Topocalm,

You have a flawed understanding of your CIS components and your current set-up is a major obstacle for maintaining a consistent operation. First, FD-090 is not from a 2.7 CIS. But from ‘80~’83 SC CIS with lambda. WUR-033 is not from an SC but rather from a 2.7 motor ‘76~’77 CIS. You got them backward.

The removal of the TPR (throttle pressure regulator) disabled your 73.5 CIS’s capability to enrich the fuel mixture. Without the TPR, you will need a vacuum assisted WUR for enrichment. And using a WUR -090 would require you an ECU, OXS, and FV. You are making a simple problem more complicated.

A simple solution is to use a vacuum assisted WUR and a thermotime valve and manually operate the CSV for cold start. Or install back a TPR and convert to OEM configuration using the correct CIS parts not just any part. Unless you are a very experienced CIS technician, it would be a very difficult task to get your CIS to run well.

Tony