79 SC need help CIS/WUR

[hubosity]

1979 911SC stock except smog pump was removed. starts and idles fine warm or cold. fresh tuneup including valves adjusted. problem is irregular/weak acceleration and I can feel a slight bit of lumpiness when cruising at 75. drives "ok" but lacks it's previous pep. Decided to buy the pressure gauges and check the CIS (first time for me). Results:

cold control - 1.4 bar at 70F. a "bit" low (should be ~1.5-1.9)
system pressure - 4.3 bar. also a bit low (should be 4.5-5.2)
warm control pressure - 1.0 bar. WAY low (should be 2.7-3.1)

per bosch manual, i checked voltage on the WUR connector and read only 7.2V. I know this is wrong. should be 12-14V? I have no wiring diagram and don't know where to check. Anybody have this problem before? maybe corroded connection? Where does this wire come from? Also, is this likely to be the root problem or is the fact that overall pressure is a bit below minimum spec a big concern?

i am by no means knowledgeable on this topic and am looking forward to sage advice from this esteemed forum.

[Bob Kontak]

Pressures are rediculously low. You need to tackle this.

Find the Bosch number on the side of your WUR and post it.

What condition is your battery and charging system?

[Flat6pac]

Time to talk with Tony...
Bruce

[Dodge Man]

These guys know their stuff. The WUR is all about controlling fuel pressure vs. engine temp. Look for an on line copy of the little blue BOSCH CIS book. It is kind of like Cliff Notes for Bosch CIS. When my WUR went out, I sent my euro WUR to CIS Flow Tech for rebuild so I kept the proper part number on my WUR. Best of luck.

[fanaudical]

Pressures do look low. I wouldn't start changing things quite yet.

Please post the part numbers stamped on the WUR, fuel distributor, and air metering unit (this helps make sure everybody's looking at the right performance data).

I've found that when working on CIS it's always best to ensure that your ignition system is working as intended before doing anything else. Validate timing and advance are operating properly. It's often easy to mistake some common ignition issues for CIS trouble.

After validating ignition, look for vacuum leaks (hoses, air box, faulty EGR, idle air control, or decel valve if still installed). I usually do all this before pulling out my pressure gauges...

[boyt911sc]

Originally Posted by Flat6pac

Time to talk with Tony...
Bruce

Bruce,

Just got back from a 7-week vacation in AZ and AUS. Still suffering from jet lag and slowly recovering. Your protégée from Newark, DE called me on the phone while I was going through the Immigration/Custom in LA requesting for rebuild WUR & FD for his customer's late SC. The funny about this was that while I enjoyed the trip driving on the left of the road, seen beautiful and twisting country roads, played golf, etc. I missed CIS troubleshooting work while I was away from home.

Right now, I have for four (4) SC engines in garage excluding my '78 Targa. Two (2) are almost done, one (1) newly disassembled, and the last one just waiting on the sideline. CIS engines are very reliable, dependable, and easy to maintain but some people just don't have the patience to test or investigate things before tweaking the mixture setting. And this is the most common blunder CIS trouble shooters commit. I am back and have a few telephone messages about CIS troubleshooting assistance from fellow PP members I need to attend. Thanks.

Tony

[theiceman]

I have a 78sc , same set up as you exactly and the car runs flawlessly... well when its in the car.

I did a baseline CIs to play with my new gauges when I got them so I posted here my baseline results. Might give you something to compare to. do a search under my user name and " baseline CIS " and you might find something.

[jason2guy]

at some point, with CIS, the WUR is going to have to be adjusted. the thing is mechanical and the adjustment fades over time. to adjust it you need to wrap your mind around how it works and what it does, thats a must. warm CP gets set first with the heating element removed- that is done by moving the large circular fitting that the lines connect to, up or down in the housing. then cold CP is set by installing a screw and nut arrangment on the pin that the heating element mounts to

[RarlyL8]

Without 12V the bimetallic strip will never achieve spec height in the housing and the entire range will remain rich. Solve this before touching anything. If the electrics are worn out the unit needs to be rebuilt. We can do that for you. Check out our CIS Primer for some general information, Porche Enthusiasts Page

[Dr J]

^^^ this

or your warm control pressure will be very low. Dont know how it gets lower when warm than when cold though. You may want to double check your readings. I dont know how it can possibly run when the warm control pressure is so low. I have a 79sc as well and have done many experiments with control pressures on the wur.

[Bob Kontak]

Originally Posted by Dr J

Dont know how it gets lower when warm than when cold though.

That one raised my eyebrow as well.

[Dodge Man]

Please do not forget to carefully check the electrical plug to the WUR too. Is the low voltage really low voltage or a suspect/corroded connection? Just asking. Seen it before. Is it mechanical WUR failure or maybe a poor electrical connection is my question? Best of Luck.

[hubosity]

Thanks for all the good feedback.

I'll get the numbers off of the components over the weekend.

The charging system seems ok. The voltage everywhere else is 12.25V. The voltage at the WUR plug is definitely 7.2V. I traced it back to the next connector and still 7.2. The voltage at the fuel pump relay is 12.25, so i assume it is corrosion somewhere between the front and the back, but I don't know exactly where to look next as I am not so familiar with the harness.

I ran a jumper from the fuses in the back directly to the WUR and a quick check with the gauge showed warm control pressure more like 3.1 bar. Hopefully the WUR will be good to go once I locate the gremilin in the wires. I drove it like this to work this morning and the best I can say is that it seems "better", but still not "good".

To fanudical, I started with the ignition/vacuum stuff first but didn't go into details in the post. all the vac lines and o-rings have been replaced along with new plugs/cap/rotor. timing adjusted, valves adjusted. These symptoms preceded the tune-up and I was hoping they would be addressed with the tune-up, but alas...

Also, this is my first time to monkey with the CIS, so my technique may be flawed. appreciate all of your patience

[boyt911sc]

Hubosity,

Are you familiar how to test run the FP using the fuel pump relay terminals #87A & #30? Next time, measure the cold control fuel pressure versus time from start up to 5 minutes (max.). Record the control fuel pressures at 30 sec. or 1 min. intervals and stop after 5 mins. Please post your data including the WUR ID number (0-438-140-xxx). Last 3 digits are sufficient to identify your WUR. Thanks.

Tony

[hubosity]

OK, so I had a chance to hook the gauges up again today. I know at least a couple of you were scratching your heads regarding warm pressure lower than cold, etc, so I wanted to re-confirm the status.

Cold pressure: I tested 4 or 5 times and found that with ignition on (and jumper on #87A to #30), the pressure was very repeatable, but only measured 0.9 bar. What i found, though was when I shut off the ignition switch and went back to look at the gauge again, it jumped up to 1.6 every time. again, 0.9 with the pump on but 1.6 after shutting it off. I believe the number in my original post was taken after I had shut it off.

Warm control pressure: As mentioned previously, i have added a 12V jumper to the WUR. now it starts at the 0.9 bar cold pressure and slowly builds to 1.8 bar. So, the heating element seems to now be working to boost the pressure, but it still is too low.

System pressure: tested 5 times. very repeatable at 4.6 bar. So I guess this means the fuel pump is OK?

What can cause the control pressure to be too low? (cold and warm). From Jason2guy's post above, it seems that both are controlled by WUR. Are there any other possibilities or is it time to pull the WUR?

One other quirky data point. One time after testing warm control pressure, but while the pump was still running, I squeezed the bleed valve below the gauge. Of course, gas shot out, but the gauge immediately jumped from 1.8 up to 3.2 bar(which I think is about right). It stayed up there for a minute or 2 while i was watching and then it suddenly dropped back down to ~1.8 again.....weird.

Tony, sorry didn't see your post until just now. When I checked cold control pressure (with 87a and 30 jumpered), I didn't monitor for 5 minutes but I did watch it for at least 2 or 3 minutes. during that time it held steady at 0.9. It only increased when i connected 12V to the WUR. Should I try again and wait 5 minutes? When you say "start up"do you mean actually start the engine and watch for 5 minutes?

Also,I looked for numbers on the WUR, but couldn't see anything readily visible. Can you see them without removing the unit? the only numbers I could see were "083." cast into the top, but this may not be relevant.

Thanks again everyone. It is nice to have such an experienced group to reach out to.

[Ngrich99]

Hard to see # in the car, yours should end with 045. Mine was barely legible. I sprayed some brake clean on it and rubbed and I could barely make it out. Here is a reference pic for where then # should be, in this pic it's 069.

[boyt911sc]

Hubosity,

The cold and warm control fuel pressures are controlled by the WUR. The system fuel pressure is determined by the primary valve setting in your FD. If you monitor the control fuel pressure from cold to warm condition, you would be able to determine if the WUR is working or not. This was the reason I asked you to record the control pressure from a cold (initial) to warm control pressure. It might take 3 mins. to 5 mins. depending on the heater (resistance value) inside the WUR. No need to run the motor, just the fuel pump for this kind of investigation.

BTW, please check the number on your WUR. Like to confirm you have the correct WUR. Thanks.

Tony

[hubosity]

I went ahead and pulled the WUR. I confirmed it is 045. I may crack it open to see if anything obvious is amiss. Thanks all.

[hubosity]

Got some updates:

I took apart the WUR just for grins. immediately found evidence that the valve springs had not been seated properly (in the picture you can see the circular wear marks where the big spring was sitting). I have owned this car for ~30 years and have never serviced the WUR, so it must have been this way from factory (or at least a long time).


Aside from that there was a bit of corrosion. I removed the 4 screws and cleaned up the valve diaphragm(s), etc and put it back together. I know this made some fundamental changes to mixture,etc, as the car is hard to start and won't idle until it warms up a bit. New pressure numbers:

WUR # 0438140045
temp 60F (15.5C)
cold control 1.5 bar
warm control
0 min 1.5 bar
1 min 1.9 bar
2 min 2.2 bar
3 min 2.2 bar
4 min 2.2 bar
5 min 2.2 bar
warm control with engine started and idling 1000rpm 3.3 bar
system pressure 4.7 bar

According to the test sheet I have, these all look good EXCEPT for the warm control with only the fuel pump running. When I start the car, the pressure jumps up to the correct range listed for "with engine idle vacuum". Do I have a problem here? which adjustments are required to get the car to start and idle again?

Incidentally, the symptoms I was chasing initially are still present (inconsistent and uninspiring acceleration, irregular "hitch"or "miss" noticeable when cruising at 2500-3000rpm. I'm starting to suspect clogged injectors as I had trouble with a rusty fuel tank a while back. Also, I did notice particles on top of the mesh screen on the WUR input

[Targalid]

When was the fuel filter last changed? Can you easily blow air through it or is it restricted? If you had a rusty fuel tank maybe some residue is in your fuel filter.