1980 engine rebuilt and in but won’t run

[worn]

Thank you so very much folks. I go tomorrow armed with a fuel pressure gauge, a mirror and a goose neck camera. Don’t have a smoke machine but suspect an air leake because it backfires through the intakes. I noticed the possibility of plug switheroos too. I think I have it right, but am not sure. In the end I am ready to drop the motor out again and triple check.
But first I will use all of your suggestions. You guys rock.

[worn]

I was so convinced that I had a vacuum leak that I went over photographs, used mirrors and boroscopes. And didn't find anything. So, I hooked up the pressure gauge and this revealed-
System Pressure: 4.5 bar. A little on the low side but exactly what it was several years ago.
Control pressure: 4.5 bar. Not at all what it used to be.

So I removed the WUR and couldn't resist opening it. The innards are displayed below.


Any advice on how to proceed? I am thinking that the way high control pressure leaned the mixture very rapidly on startup, leading to the engine dying with intake backfires. Maybe if I had finished the rebuild sooner the WUR would have gotten more use and it would have stayed more limber. Valve appears to be stuck shut.

[boyt911sc]

Originally Posted by worn

I was so convinced that I had a vacuum leak that I went over photographs, used mirrors and boroscopes. And didn't find anything. So, I hooked up the pressure gauge and this revealed-
System Pressure: 4.5 bar. A little on the low side but exactly what it was several years ago.
Control pressure: 4.5 bar. Not at all what it used to be.

So I removed the WUR and couldn't resist opening it. The innards are displayed below.


Any advice on how to proceed? I am thinking that the way high control pressure leaned the mixture very rapidly on startup, leading to the engine dying with intake backfires. Maybe if I had finished the rebuild sooner the WUR would have gotten more use and it would have stayed more limber. Valve appears to be stuck shut.

Worn,

For the control fuel pressure to be equal to system pressure, there is flow restriction to the return line. The restriction could be caused by a clogged WUR or a blockage any where along the return line. This is a partial blockage. A fully blocked return line will register higher than the system like 90 psi. Hope you are not using a HF brand CIS pressure gauge kit.

Are you sure the valve was opened when you did the test? Keep as posted. Thanks.

Tony

[worn]

Thanks Tony,
I was aware of the idea that return is blocked. I think it is blocked in the WUR, but I will explore further on. Hard to pressurize the banjo bolt fitting to tank return though.
Yes, it is an HF brand gauge. A man has to know his limitations, and I double check those tools, and have a lot of them.
Made a special point of triple checking the valve orientation. I have good reason to think that I conducted the measurements correctly. A reassuring point is that system pressure was dead on the measurement I made several years ago, but control pressure had changed. Also, I tried to blow air through the WUR, and it was blocked.
My car is kept in a building out of town a half hour or so. Circumstances permitting I will read up more tonight and possibly dissecting the valve tomorrow. If that is a dumb idea, now would be a great time to tell me. Thanks!!

[boyt911sc]

Worn,

If you get a chance re-assemble the WUR less pin, sombrero, and springs. Take another shot for the cold control pressure and share your findings. Just run the FP to check the fuel pressure. One more thing, could you measure the heater resistance (Ohms) of the WUR at room temperature?



Keep us posted. Thanks.

Tony

[worn]

This is from memory, but I think it had a resistance of 26 ohms. Is your suggestion to doff my sombrero a test to see if the screen is plugged? I was worried about the plug being downstream of the unit, so as a naive worker, I blew into the inlet side until my cheeks puffed out. No flow. Then something seemed to pop and there was a little bit of flow. Unfortunately the 40 year old part was sitting unused for over a year while I got around to the engine.

[Walt Fricke]

Worn
I'd unbolt the electrical part so I could get at the four bolts which hold the diaphragm piece to the upper housing (left side in your photo). There are two passages leading to the diaphragm - one from the fuel distributor, and one to where the fuel bled off goes. One of these has a strainer in it - it looked like the steel slug which holds the fitting up top was machined so the hole didn't go all the way through. Then tiny holes were drilled through the disk shape in the bottom of the hole.

When mine showed CP=SP, uncovering and blowing brake cleaner through this screen solved things - at least as far as having a suitable difference between the two pressures was concerned.

It was hard to undo the four screws which hold the thick steel plate (with a hole in its center)which sandwiches the thin stainless diaphragm to the housing. They are slot heads! Eventually I got all four out, and replaced them with Allen heads from my local hardware store.

I'm not sure what Tony has in mind with pulling the sort of cup washer collar off. It is what the bimetallic electrical part presses down on when cold, so there is less pressure on the diaphragm, so lower CP and richer mixture. But Tony has these apart all the time, so he's got something in mind.

If you get the diaphragm part stuff off, you can blow in both directions. I'd use shop/compressor air and a rubber tipped air nozzle.



For pressure

[cmcfaul]

see if it will keep running if carb cleaner is sprayed into the air box. If yes then you know its a fuel issue. If no you know its electrical.


Chris
89 Carrera

[worn]

After taking the WUR all apart and cleaning it, I reassembled it and checked fuel pressures. Control pressure moved from way off to spot on for 21 degrees C. So, I took the plunge and managed to get the car running at about 1500 rpm for ten minutes. Trying to break things in. Should I change the oil now or run it another ten minutes or so?
Then my amateur exhaust hose bit the dust and I shut it down. Not sure I have the ignition timing quite right, but progress!
Thanks folks.

[gsxrken]

Congrats!
Peter Dawe recommended that I break in for 20 minutes and let cool down completely, change the oil filter, and then run the break in oil for another 500 miles (!) making sure to vary the rpms and not lug the engine.

[worn]

OK, it ran for ten minutes, I shut it down and now it won’t run. Starts but dies in about 4 seconds. I can sort of keep it going by opening the throttle but it isn’t stable.

The big surprise is that system pressure has dropped to a little more than 2.2 bar. The control pressure is very similar. Replaced fuel filter and gas flows freely through the filter and into a container when the fuel pump turns on. I am thinking about the fuel pressure regulator in the main fuel distributor valve. Any other possibilities? This is driving me crazy.
I have read and reread the Bosch book and cannot understand what else to check. Would prefer not to dive into the fuel distributor if there are other options.

[Walt Fricke]

This doesn't explain the way too low system pressure, but how is your pressure drop after shutoff? You know - see what the system pressure is, turn engine off, wait X minutes, see what it is now. There is a spec for that. If it falls too fast, you have hot/warm starting issues - the WUR and TTS think the engine is hot, and won't turn on the CSV or lower the CP.

But aside from that, as you guessed the system pressure is way too low. One pressure setting valve is (on some FDs) on the right. You can unscrew it and inspect. It is the one you can use shims (washers) to boost the pressure. It has an O ring or two. On some FDs it is toward the back? There is a small O ring down at the tip of this or one of these. It can go bad, and per the mechanic who told me this, drive you nuts trying to figure things out. It would lead to lower pressure. I'll see if I can find a diagram or picture of it.

But Tony could tell you in a Philadelphia minute.

Of course, the fuel pump could maybe be crapping out? My experience has been that they work until suddenly, and awkwardly, they don't. Maybe after a short period of making noise to complain, or maybe not. You'd have to rig up something to measure actual fuel pump pressure. As I recall, if it is pumping against what amounts to a closed system, it just recirculates without harming the pump. So the pump not being strong enough would be low on my list.

[Walt Fricke]

Here is a drawing of the push pressure regulating valve, and of that part of the system.





You can see where the two seals are

[worn]

Thanks Walt!

[mike635]

Might not be best to introduce more variables but thought I'd throw this out - I see that you're in Madison (assuming WI), I live in the area and have a spare, working WUR that was installed in my '81 SC for 10 yrs.

It's not the correct WUR (p/n 0438 140 009) but worked perfectly. I replaced it when I tracked down a working correct WUR (0428 140 090) and installed it just to make the system right, didn't make a huge difference but I feel better knowing it's correct with the frequency valve/duty cycle set to spec.

I'd be happy to loan it to you if interested, just send me a PM

[boyt911sc]

Originally Posted by worn

OK, it ran for ten minutes, I shut it down and now it won’t run. Starts but dies in about 4 seconds. I can sort of keep it going by opening the throttle but it isn’t stable.

The big surprise is that system pressure has dropped to a little more than 2.2 bar. The control pressure is very similar. Replaced fuel filter and gas flows freely through the filter and into a container when the fuel pump turns on. I am thinking about the fuel pressure regulator in the main fuel distributor valve. Any other possibilities? This is driving me crazy.
I have read and reread the Bosch book and cannot understand what else to check. Would prefer not to dive into the fuel distributor if there are other options.

Worn,

If you are getting only 2.2 bar as system pressure you would be lucky to get the engine running. Installing a perfect WUR from your neighbor will not help you at all. What you need to do is find out why the system pressure dropped to 2.2 bar. There are two (2) likely culprits:

• The fuel pump is bad.
• The primary pressure valve is leaking.

If I were in your shoes, I would first check the condition of the FP. You could test it using volumetric flow rate measurement or a pressure test. If the FP is good, you have reduced the number of variables. Next, determine why a good FP could not produce sufficient system pressure. The primary pressure valve is located inside the FD (fuel distributor). Make sure you have a good pressure gauge.

Lastly, if you don’t want to do all these testings, send the WUR & FD to me and I will evaluate them for you for FREE. Your only expense is the postage to Philadelphia and back to you. And if you know someone willing to do test for you let them do it and I won’t be offended. It would take me about 3 mins. to evaluate the WUR & FD after I installed them on my CIS bench tester.

Tony

[worn]

Oh thanks Tony. Not sure that the free thing is legit though. But we can negotiate that!
Warren

[boyt911sc]

Originally Posted by worn

Oh thanks Tony. Not sure that the free thing is legit though. But we can negotiate that!
Warren

Warren,

I have been helping fellow PP members for a while now and it makes CIS troubleshooting easier if you know that the CIS parts you are using are good and working right. In your case, you have some questionable component/s that must be confirmed or evaluated.

It only takes a few mins. to test and evaluate if a particular CIS component is good or bad. It would saved you from aggravation and frustration. Test and confirm.

Tony

[Brian Cameron]

Originally Posted by worn

"If it does, and the pressures are reasonable, maybe the mixture screw is way out of whack? Hunting around on posts on CIS should lead you to some ways of setting the mixture screw to ballpark before you even try to start, I think I recall."

I will check that out.

When/if you get to that point, I believe this might be one of the posts referred to for ballpark setting CIS:

CIS Idle Speed and Mixture Setting Without an Analyzer

Tony is The Man so you’ll be ok with him in your corner.

[Dave Kost]

Engine Fails to Start

Here is a trouble shooting guide to test a no start. If you go thru these steps methodically, you will get to the issue.

Did you test the relay under the passenger seat is not blown? Can you confirm the Frequency valve is running? Your no start symptoms are classic FV not working. This should be the first thing you check on a 1980-83 CIS 911.

Sounds like you could have a fuel pump, blockage issue . Or interrupted voltage to the fuel pump.

Have you checked you have 11.5 volts at the fuel pump? Drawing no more that 8 amps.
Did you test fuel pump volume?
Did you reconnect and clean all grounds? Easy to miss reconnecting them. Maybe you are not getting proper voltage to the relays.

Last thing- Is the rubber peanut looking hat on top of the CIS box connected properly?

It's something stupid and I would check these things before sending or buying any new parts.