Cold no start 1981 911SC -090 WUR

[acorad]

Hi all, me again.

It's been about a year and a couple thousand or so miles since I've had problems starting my 1981 SC. Those starting problems were resolved after replacing the Fuel Accumulator with a new unit after many, many, hours of learning about the CIS.

Thank you all for all your help back then!

I'm now having starting problems again, and am trying to relearn everything about CIS that I've forgotten since a year ago. lol

A few days ago the car cranked fine but would not start at all about 4-5 hours after easily starting and driving fine.

As I did many times a year or so ago I then tried to manually prime the system by removing the air filter, turning the key to on, and lifting the air meter arm. This time the injectors squealed as usual, but I did not get the small cloud of atomized fuel coming out of the airbox that I was used to.

I then left the car sitting and tried to start it again a few days later with the same result - crank but no start, and no small atomized fuel cloud when manually priming.

So today, at about 60F, I detached the WUR's electrical plug, hooked up my pressure gauge in-line to the WUR's fuel line to the Fuel Distributor, pulled the red Fuel Pump Relay, jumpered 30 to 87a, and turned the key to on.

The System Pressure read what I believe is very slightly high at 5.3 Bar, but the Control Pressure was very low at 0.5 Bar, rising to a maximum of 3.4 Bar about 2.5 minutes after reattaching the WUR's electric plug.

I don't have access to a car lift at the moment, so I did not check the fuel pump pressure, etc. But if I remember correctly cold start issues are often/mostly WUR issues?

Right?

Andy

[mysocal911]

Why not check for a spark first? It's always the easiest to do!

[acorad]

Originally Posted by mysocal911

Why not check for a spark first? It's always the easiest to do!

Thanks, yes, I forgot to mention. Inductive timing light shows spark.

Andy

[mysocal911]

Next, spray carb cleaner or starting fluid.

[acorad]

Originally Posted by mysocal911

Next, spray carb cleaner or starting fluid.

Yes, thanks for reminding me, I also tried that, no start with starting fluid. :-(

Andy

[acorad]

If it helps, it appears there was at least some fuel getting into the cylinders, as fuel was leaking onto the ground from the joint/flange under the engine in the passenger side exhaust. I've added that repair to my list.

Andy

[boyt911sc]

Originally Posted by acorad

Yes, thanks for reminding me, I also tried that, no start with starting fluid. :-(

Andy

Andy,

Check for sources of unmetered air going into the system. You have a massive air leak that causing NOT to ignite even the starting fluid. Do a smoke test to locate and identify the source/s. Adjust your CCP (cold control pressure) to 2 bar/ 29.0 psi @ 68° F (refer to your WUR Control Pressure Chart).

Tony

[acorad]

Originally Posted by boyt911sc

Andy,

Check for sources of unmetered air going into the system. You have a massive air leak that causing NOT to ignite even the starting fluid. Do a smoke test to locate and identify the source/s. Adjust your CCP (cold control pressure) to 2 bar/ 29.0 psi @ 68° F (refer to your WUR Control Pressure Chart).

Tony

Interesting, thanks Tony. Will do.

Andy

[boyt911sc]

Andy,

Have you checked the residual fuel pressure? Make sure you have a strong ignition signal and use an inductive timing light to confirm it. Keep us posted.

Tony

[PeteKz]

I have found that an inductive timing light will be triggered by a weak spark pulse too, so remove one plug and ground it against the engine to observe the spark. Other possibility, the engine is flooded, and it needs to clear the unburned fuel. When you remove the plug to observe the spark, look for signs of wetness.

Another thing: When starting cold, the cold start valve must operate to help it start, which means the thermo time switch must work correctly too. When you previously observed fine fuel mist in the airbox, that should have been from the CSV, not the injectors (which are down at the ends of the manifold runners). Make sure the CSV and TTS are working correctly. Even so, squirting starting fluid into the intake should have made it at least fire briefly. Thus, I think either you have a massive air leak, or it's flooded. If the rubber intake boot is original, it may be cracked just above the large hose clamps. I've seen that several times.

Does your airbox have a pop-off valve? If so, squirt the starting fluid in there.

[Schulisco]

If no fuel smell is detectable after an unsuccessful starting attempt, there may not be enough fuel to start the engine. If the thermo-time switch/cold start valve fails, the engine should still start—not immediately, but after several attempts.

Check the spark with a spare spark plug (it's a good idea to keep a spare in the glove compartment for quick checks on the go). A weak spark can be identified by its brightness and strength. The spark must be bright and strong. Remove a few spark plugs to check if they are wetted with fuel and if fuel is being supplied.

As mentioned earlier, use a smoke generator to check for unmetered air in the intake system. Spraying the engine with starting fluid is not sufficient to detect air leaks. Also, check both diaphragm valves on the right side of the engine (start valve and throttle valve). Damaged diaphragms also cause significant air leaks. The test instructions can be found here: https://joe-e-n-g-i-n-e-e-r.com/porsche-911-cis-subcomponents-and-testing/ (remove the dashes in "engineer"). The aluminum line behind the air filter housing, between the AAV, CIS hose, and cold start valve/air filter housing inlet, rubs against the engine and will be damaged over time. It is not visible without disassembly or testing with a smoke generator.

0.5 bar cold start pressure is far too low at 15.5 °C (60 °F). The cold start pressure should be around 2 bar (https://nineelevenheaven.wordpress.com/adjusting-the-warm-up-regulator/). Such a low cold start pressure leads to fuel flooding of the engine, which should result in a strong fuel smell when starting. You report that you don_'t small fuel - this is confusing. As said - check the injectors for spraing fuel. Also remove the airfilter and watch the sensor plate from below if it get's lifted slightly while cranking.

If priming the system on cold starts after sitting for hours or days helped to start the engine, check the check valve at the fuel pump. It works closely in conjunction with the fuel accumulator. If one of both fails the car may still start successful, but esp the check valve can also start leaking the pressure after shutting down the engine more quicker which slowly leads to more worse starting behaviour.

Thomas

[acorad]

Originally Posted by boyt911sc

Andy,

Have you checked the residual fuel pressure? Make sure you have a strong ignition signal and use an inductive timing light to confirm it. Keep us posted.

Tony

Hi Tony, I didn't check the residual fuel pressure. I can do that when I get back in town on Friday.

Andy

[acorad]

Originally Posted by PeteKz

When you remove the plug to observe the spark, look for signs of wetness.

Will do.

Make sure the CSV and TTS are working correctly. If the rubber intake boot is original, it may be cracked just above the large hose clamps.

Thanks, the TTS is basically brand-new, I will check those.

Does your airbox have a pop-off valve? If so, squirt the starting fluid in there.

Yes, and I'll try that.

Andy

[acorad]

Originally Posted by Schulisco

If no fuel smell is detectable after an unsuccessful starting attempt, there may not be enough fuel to start the engine. If the thermo-time switch/cold start valve fails, the engine should still start—not immediately, but after several attempts.

Thanks Thomas, I did smell fuel at the exhaust pipe after trying to start the car.

The TTS is very new, I replaced it only a couple thousand miles ago. I will check the CSV.

Check the spark with a spare spark plug (it's a good idea to keep a spare in the glove compartment for quick checks on the go). A weak spark can be identified by its brightness and strength. The spark must be bright and strong. Remove a few spark plugs to check if they are wetted with fuel and if fuel is being supplied.

I will check the spark strength.

As mentioned earlier, use a smoke generator to check for unmetered air in the intake system. Spraying the engine with starting fluid is not sufficient to detect air leaks. Also, check both diaphragm valves on the right side of the engine (start valve and throttle valve). Damaged diaphragms also cause significant air leaks. The test instructions can be found here: https://joe-e-n-g-i-n-e-e-r.com/porsche-911-cis-subcomponents-and-testing/ (remove the dashes in "engineer"). The aluminum line behind the air filter housing, between the AAV, CIS hose, and cold start valve/air filter housing inlet, rubs against the engine and will be damaged over time. It is not visible without disassembly or testing with a smoke generator.

I do have a smoke generator, and I'll use it when I get back on Friday.

0.5 bar cold start pressure is far too low at 15.5 °C (60 °F). The cold start pressure should be around 2 bar (https://nineelevenheaven.wordpress.com/adjusting-the-warm-up-regulator/). Such a low cold start pressure leads to fuel flooding of the engine, which should result in a strong fuel smell when starting. You report that you don_'t small fuel - this is confusing. As said - check the injectors for spraing fuel. Also remove the airfilter and watch the sensor plate from below if it get's lifted slightly while cranking.

Will do, and I do smell fuel - and fuel leaks from the flange connection on the passenger side exhaust under the engine - so flooding seems like a strong possibility.

If priming the system on cold starts after sitting for hours or days helped to start the engine, check the check valve at the fuel pump. It works closely in conjunction with the fuel accumulator. If one of both fails the car may still start successful, but esp the check valve can also start leaking the pressure after shutting down the engine more quicker which slowly leads to more worse starting behaviour.

Thomas

Thank you, I will check it.

Andy

[acorad]

Hi all,

I decided to start with a smoke machine to test for vacuum leaks. I do have some leaks. After a number of hours of with the smoke machine there is one leak that I just cannot figure out.

There is a sizeable leak coming from or near the #3 intake runner, but it is so hard to see back there I can't really identify exactly where it is coming from.

It seems to be coming from somewhere on or near the #3 runner somewhere that is not the fuel injector seal.

I can't really get a good look at it where it originates, but when I put my fingers on the shelf on the #3 runner that the fuel line support bracket is attached to, the direction of the smoke stream shoots in a somewhat different direction. But I haven't been able to actually block the leak with my fingers.

Also the leak seems to change when I move the brake booster hose around. I guess that could be either a leak in the hose itself, or the smoke stream is blowing against the hose so moving the hose could change the smoke that I'm seeing.

Is there anything in that area that could leak smoke besides the intake runner and the brake booster hose?

Also, what is the hose indicated below that the brake booster hose Ys into?

Andy

[PeteKz]

Andy, yes, there is a thermovalve under the #3 intake runner. It controls vacuum to the WUR during the first few seconds of warmup. Make sure the vacuum hoses are connected and routed properly. Sometimes those TVs come apart.

[acorad]

Thanks Pete, appreciate it! Also any idea what that hose is that I circled in the photo? I think the brake booster Ys into it.

Andy

[PeteKz]

Not sure about that hose setup. My car doesn't have it. It looks like part of the power brake system, but not sure why it runs over to the other side. Does it connect to the rubber intake boot? Let's see if Tony jumps in.

[acorad]

Thanks Pete, it connects to the throttle body below the intake boot.

It's hard for me to tell, but that line may be leaking near, or at, where it goes through it's support bracket that's attached to the #2 and #3 intake runners.

Sorry the photo isn't larger.

Andy

[Schulisco]

More reading about CIS on http://forums.pelicanparts.com/cis911primer.com/home.html especially this page dealing with vacuum lines(lower diagram for lambda. CIS from 1981 on)

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

Replace all suspect rubber hoses while you're there...