Another CIS car causing trouble

[ethlar]

I have been searching through all of the CIS threads looking for a answer for the past 4 months and am still stumped. My dad is perfectly content do just drive the car, the engineer/mechanic in me wants to know exactly how everything works so i know whats going wrong.

My dad and i have a 77 911s, fresh out of restoration 4 months ago. The restoration was a 15 year process because the shop is owned by a friend of ours and my dad made the mistake of saying "take your time." So long story short, after 15 years he/we finally have the car back. Its been taken apart, media blasted, repainted, engine completely rebuilt.

Dad's the original owner, engine and transmission are the ones that came on the car out of the factory. Everything has been mostly smooth sailing, though in the past 4 months the car has been towed back to our shop several times.

Since getting the car back 4 months ago it has been hard to start cold and after any period of time sitting longer than about 30 minutes. To get it started the engine has to crank and crank seeming like its having to draw fuel back into the lines. Once it catches it sounds like only one or two cylinders are getting fuel for a few seconds as the rest of the engine catches up. Once running its smooth and perfect.

Immediately after getting the car back there was a lack of power up to about 3000 rpms, and we discovered that a backfire had cracked the airbox. Airbox replaced and pop off valve installed, fuel system pressure checked to investigate the hard starting. WUR replaced since the control pressure was sitting at 10 bar instead of 3. Mechanic says all other pressures hold as they should hot and cold. To humor me, fuel filter replaced as well. Hard start issues persist...

Couple weeks later I'm driving to the local dealer to get extra keys (i know to order though this site now, dealer is pretty useless), right now we only have 2 and one of them is worn completely smooth (but still works in the ignition). So i want to make sure we have a copy made of the good key before it wears down. Pull into the parking lot and i smell raw gas, not just rich exhaust smell. Look under the car and it is pouring gas, high pressure fuel line ruptured just after the banjo fitting on the pump and was spraying everywhere, including on the brake disk. Fuel line replaced and the hard starting still persists.

At this point I'm totally out of ideas, I've read through all the CIS primers i can get my hands on, bought the books on the 911, and as a stop gap measure got a battery charger/tender to deal with the couple minutes of cranking to start before every outing. But i want to be able to get the car back to being able to crank and go.

The only thing I'm thinking of doing is adding a in line check valve to the fuel pump, but since the whole fuel system pressure checks fine it isnt really necessary, right?


yes the tail isnt original to the car, it was the one non original impulse my dad wanted on the car

[ossiblue]

First, a beautiful car. Congratulations to you and your father! Original owner too!

My first reaction to your post is to ask the mechanic to give you actual numbers on your pressure tests, and especially specific numbers and times on the residual pressure test. Your symptoms are typical loss of residual pressure types. Loss of residual pressure may be from a faulty fuel pump check valve, fuel distributor relief valve, or fuel accumulator, but rather than replace parts unnecessarily, you need to get the actual values on the residual pressure test. We cannot really help you without the data and a mechanics words that things are "normal" mean absolutely nothing.

I would suggest you have him perform another complete set of tests--system pressure, cold control pressure (including the ambient temp), warm control pressure, and residual pressure--since you had a new WUR installed. Ask him to record the data for all tests, including how long the system held pressure after shut down. Let us know what you find.

Edit: Adding a check valve to the fuel pump is a solution for residual pressure loss and we don't know for sure if that's happening, though it's highly suspected. Here's something you can do in the meantime. Next time you have a difficult start, don't try to crank it to life. Instead, remove the air filter, turn on the ignition, and gently lift the plunger inside the air intake. Hold it up for ~2-3 seconds or until you hear/feel the vibration of the injectors. Now, try and start the car. If it immediately fires up, you have a residual pressure loss issue.

[Peter Zimmermann]

"Since getting the car back 4 months ago it has been hard to start cold and after any period of time sitting longer than about 30 minutes. To get it started the engine has to crank and crank seeming like its having to draw fuel back into the lines. Once it catches it sounds like only one or two cylinders are getting fuel for a few seconds as the rest of the engine catches up. Once running its smooth and perfect."

30 minutes after being at full temp? Cold start after sitting overnight?

Who replaced the airbox, and was the CO% set to factory spec? Makes me think that a mistake might have been made hooking up the cold start injector, or possibly the sensor plate plate was damaged/bent during the big bang - or it wasn't checked and set/adjusted when the airbox was replaced. Both items are critical for proper cold starts.

That said, a check valve at the fuel pump is always a good idea, and a new fuel accumulator won't hurt. And there is a temp switch in the left side chain box cover; it should have a rubber boot over two wire connections. Those wires will be fragile, and are pretty easy to break during install if it's not done with kid gloves. Don't worry if the boot is gone, they will rot away and are often discarded. But the wires should handle a gentle tug. Post if the wires are clean & tight; the switches are bullet-proof so I'll have to get out the manual to check the test procedure - it's been a long time.

[RarlyL8]

WUR replaced since the control pressure was sitting at 10 bar instead of 3.

I would be amazed if the fuel head diaphragm survived this. A dented diaphragm can manifest itself in many ways but typically erratic start/run and overly rich condition. Fuel pressures may not vary off spec as the individual cylinders are being affected. AFR will not match fuel pressure readings.

To test this pull the injectors and measure flow/time for each cylinder simultaneously.

[ethlar]

Thanks for the quick feedback.

Im back at school and about 5 hours away from the car, but i will have my dad take it back to our friend for pressure tests and get a report on the results

Airbox was replaced by our mechanic, they had the entire injection and intake systems apart for the diagnostics, so something being left off during reassembly is entirely possible.

CO% was set back to the factory spec after WUR replacement.

the 30 minutes is pretty consistent regardless of how warmed up the engine was, I have yet to see how the car handles cooler weather since it has been during a summer of 80-100 degree days.

I never would have even thought to check the fuel head diaphragm, i will past that on to the mechanic as well


Im absolutely in love with this car, i have memories of riding around in the clamshell seats as a kid, and now getting to drive it puts the biggest smile on my face.

[lonewolf]

Sounds like fuel pump check valve. that would be the first fix i would do and it's the cheapest.
that year pump location is on an angle and if the valve goes it's easy for fuel to flow back to tank.
Next would check ACC

[lonewolf]

The fuel line bursting may indicate a problem further upstream which may also be the car of hard starting. look for a common link

[Dfwflyr]

Originally Posted by Peter Zimmermann

"Since getting the car back 4 months ago it has been hard to start cold and after any period of time sitting longer than about 30 minutes. To get it started the engine has to crank and crank seeming like its having to draw fuel back into the lines. Once it catches it sounds like only one or two cylinders are getting fuel for a few seconds as the rest of the engine catches up. Once running its smooth and perfect."

30 minutes after being at full temp? Cold start after sitting overnight?

Who replaced the airbox, and was the CO% set to factory spec? Makes me think that a mistake might have been made hooking up the cold start injector, or possibly the sensor plate plate was damaged/bent during the big bang - or it wasn't checked and set/adjusted when the airbox was replaced. Both items are critical for proper cold starts.

That said, a check valve at the fuel pump is always a good idea, and a new fuel accumulator won't hurt. And there is a temp switch in the left side chain box cover; it should have a rubber boot over two wire connections. Those wires will be fragile, and are pretty easy to break during install if it's not done with kid gloves. Don't worry if the boot is gone, they will rot away and are often discarded. But the wires should handle a gentle tug. Post if the wires are clean & tight; the switches are bullet-proof so I'll have to get out the manual to check the test procedure - it's been a long time.

You should test continuity on that thermal switch. Once warm the switch opens the circuit and breaks the connection to ground for the cold start valve. I'm not an expert but i would think to look at your AAR valve. If you take the vaccuum line off and use a mirror to look in the port you should see a small opening in the shape of a cresent moon. When hot the valve should be closed.

[prebordao]

Originally Posted by RarlyL8

I would be amazed if the fuel head diaphragm survived this.

Rarly, you mean the diaphragm in the FD, right ?

[E Sully]

This is interesting. "WUR replaced since the control pressure was sitting at 10 bar instead of 3."
Since system pressure is around 5 bar, how could this be? I don't think it is possible.
I would recommend leaving the fuel distributor alone. The only part I would say to check is the pressure regulating valve, which can be accessed by removing the cap nut. Splitting the fuel distributor halves can cause trouble when resealing. Make sure it is a problem before opening it up. An injector test can be done by removing the injectors from the intake runners and placing in individual containers to verify equal spray patterns and volume. There are a couple of threads on this test.
I would verify system, cold and warm control pressures again. Also make sure the Thermo time switch is working.

[boyt911sc]

Originally Posted by E Sully

This is interesting. "WUR replaced since the control pressure was sitting at 10 bar instead of 3."
Since system pressure is around 5 bar, how could this be? I don't think it is possible.
I would recommend leaving the fuel distributor alone. The only part I would say to check is the pressure regulating valve, which can be accessed by removing the cap nut. Splitting the fuel distributor halves can cause trouble when resealing. Make sure it is a problem before opening it up. An injector test can be done by removing the injectors from the intake runners and placing in individual containers to verify equal spray patterns and volume. There are a couple of threads on this test.
I would verify system, cold and warm control pressures again. Also make sure the Thermo time switch is working.

The first thing to determine is the fuel pressures including residual. The CIS FP's for 911 are not capable of producing such high pressure of 10 bar!!!! If it did, you got the wrong type of FP installed. At this point, I would say a mis- information. Keep us posted.

Tony

[ethlar]

Originally Posted by E Sully

This is interesting. "WUR replaced since the control pressure was sitting at 10 bar instead of 3."
Since system pressure is around 5 bar, how could this be? I don't think it is possible.
I would recommend leaving the fuel distributor alone. The only part I would say to check is the pressure regulating valve, which can be accessed by removing the cap nut. Splitting the fuel distributor halves can cause trouble when resealing. Make sure it is a problem before opening it up. An injector test can be done by removing the injectors from the intake runners and placing in individual containers to verify equal spray patterns and volume. There are a couple of threads on this test.
I would verify system, cold and warm control pressures again. Also make sure the Thermo time switch is working.

interesting, i have had no reason to question our mechanic, hes probably the only guy in our area who has any idea how to work on old air cooled engines, and being a friend we only pay for parts, labor is free

Originally Posted by boyt911sc

The first thing to determine is the fuel pressures including residual. The CIS FP's for 911 are not capable of producing such high pressure of 10 bar!!!! If it did, you got the wrong type of FP installed. At this point, I would say a mis- information. Keep us posted.

Tony

Im thinking maybe i need to get my hands on the fittings to do the pressure checks myself and take a trip home for a long weekend to spend some time working on the car.

[Jim Williams]

Just an observation - If the system pressure checks at the proper number - 5 bar or so - the control pressure can't be at 10 bar - physical impossibility. The control pressure maxes out at the system pressure. Maybe a decimal point was left out. 1.0 instead of 10?

[RarlyL8]

Actually the pressure can spike from 75 to 150psi, which will blow the lines and destroy the fuel distributor diaphragm.

How? Return line occlusion.

This may or may not have occured, but it is possible.
.

[Jim Williams]

Originally Posted by RarlyL8

Actually the pressure can spike from 75 to 150psi, which will blow the lines and destroy the fuel distributor diaphragm.

How? Return line occlusion.

This may or may not have occured, but it is possible.
.

Yes, I do recall past discussions where these events were believed to have happened. But I think you are talking about "spikes" - a momentary condition. If a return line is blocked, then I believe this would be reflected in the system pressure, in which case the system pressure would not be meeting the 5 bar spec during that time frame.

I just assumed the original poster (who wrote "the whole fuel system pressure checks fine") was referring to normal steady-state measurement conditions. I am having a hard time understanding how 10 bar control pressure can co-exist with a 5 bar system pressure, since both are set in the lower chambers of the fuel distributor.

Caveat to the above... Just when you think you have everything figured out, something new rears it's head. We are (or should be) always learning!

[marty911sc]

My -.1eInf cents worth.
i'm only posting to see if i have it
will high fuel pressure cause no start? would this flood out cylinders?
all this is fresh with me also. below is what i am doing now for my CIS
It was expalined to me it should try and fire to matter what in start.
if no start..
bump the sensor plate with igntition on listen for squeal of injectors.
if so, fuel is there (pressure still questionable)
then on to cold start injector and circuit.
since i tested this sensor plate fuel delivery once. My intermmitant no start has not repeated itself.
note:
wealth of misinfo

[ethlar]

I was quoting what our mechanic told me, hes originally from germany, english is his second language so maybe he meant system pressure not control?

Ive been hesitant to turn a wrench on the car myself, just because i would beat myself up if i ever broke anything. But at this point i want to get my hands on it and make sure I'm doing exactly whats supposed to be done. Plus its more fun to learn the car by doing the work rather than dropping it off and saying make it right.

That being said, im going to start by getting a fuel pressure testing kit, and running all of the system checks myself to figure out exactly what the car is doing. Im a engineering grad student at the moment though so time is precious and the car is sitting 5 hours away from me. I might not be able to get to it till thanksgiving.

I appreciate all the feedback and will test out all of the theories once i can get my hands dirty again and report back.

[Paulporsche]

When you do your pressure tests, make sure you record which WUR you have and the temperature @ which the test was done.

Here is a set of charts for various midyear WURs

As you can see, if you have the 033 WUR, a cold test @ 15C (59F) should yield a CCP of .8bar (12psi). The control pressure will rise as the engine warms up. After about 3 1/2 minutes or so it should top out @ about 2.3 bar (33psi). Your fuel system pressure should be constant @ about 5 bar (72psi).

[Peter Zimmermann]

I should add that you should hook up your gauge in the evening, bleed it down, and take your measurements the next morning. Have a good thermometer near your car!

Paul's charts (Canada numbers?), for the 033, are a bit different than the Porsche manual's numbers. For instance, 20C (68F) dictates a low of 1.8 bar, and a high of 2.2 bar (w/test vacuum of 520-546 mbar) as the acceptable range, compared to 1.2 to 1.7 (approx) bar on Paul's chart. This would indicate that USA cars are set to start with a leaner mixture. That said, system pressure has a small range from 4.5 bar (65psi) to 5.2 bar (75psi) as acceptable.

[Paulporsche]

Peter,

Those charts are from the blue Porsche CIS troubleshooting manual that came w/ the car as delivered to Atlanta in the fall of '76 so they are for US cars. Even though I live in Canada now and have a different engine, the car was originally sold to someone in Atlanta and had the 2.7L.

Which manual are you quoting from? Is it a Bosch publication?

I find it disturbing that the specs should vary so much...