911sc cold start issue

[Aurel]

My car does not start anymore. It used to have difficult cold starts, run on 4 or 5 cylinders, then warm up and run very well afterwards. It cranks well but will not even try to run.

It feels like no spark, but I checked for spark at the distributor and the spark is very strong.

I also get fuel at the injectors.

Now I checked my CIS fuel pressures and I found the following:

System pressure = 68 psi = 4.9 bar
Residual pressure = 40 psi = 2.75 bar
Cold operating pressure = 14 psi = 0.96 bar (WUR disconnected)
Warm operating pressure = 26 psi = 1.79 bar (WUR connected)
T = 80f = 26.6C

It seems like the cold operature pressure is way too low, meaning the car is too rich when cold. Even the warm operating pressure is too low.

Can anyone confirm that is my issue, and would leaning the CIS at the fuel distributor bring the pressures back in specs?

[PeteKz]

Do not mess with the CO mixture screw on air metering unit yet. It does not affect the pressures. Or did you already try changing it?

The SP is good.

How are you measuring residual pressure? RP should not be that high. When you shut off the engine, the pressure drops quickly to about 2 bar, which is held by the fuel accumulator (FA) for some time thereafter. The spec calls for the RP to be at least 1.1 bar after 20 minutes, but a correctly functioning CIS will hold it for much longer than that, typically hours.

Cold "Control" Pressure (CCP) is too low. Warm "Control" pressure (WCP) also is low. What is the number on your WUR? You need that to look up the specified pressure ranges. On a 1978 SC it should be 0438 140 045, and the WCP should be 2.7 to 3.1 without vacuum, and 0.5 bar higher with vacuum.

You also reported your CCP with "WUR disconnected" whereas, it should be connected, otherwise you will read system pressure. So something is odd in the way you tested the pressures.

Please describe how you tested the pressures and what gauge setup you used.

Some other troubleshooting I would try:
The cylinders may be flooded with fuel now. Pull a couple spark plugs to see if they are wet with fuel. Then, remove the fuel pump relay, or otherwise shut off the fuel pump, then crank the engine for about 10 seconds to make sure the cylinders are not flooded. It should try to fire as the excess gas is purged. If it does fire, then you can be pretty sure you flooded the engine. You can also be confident that the ignition is working. I would then squirt starting fluid into the intake and see if it fires on starting fluid.

Then plug in the FP relay and try starting it again.

The cold start valve (CSV) may be not working (hard to start when cold) or stuck on (causing flooding). But let's get those pressures correctly measured and sorted first.

[Flat6pac]

I’d check with Tony on here. He has tested warm up regulators, that is the weak spot of the CIS.
Bruce

Boyt911sc. Tony handle

[Aurel]

Pete,

My WUR is a 0438 140 145. CCP and WCP pressures at 25oC should be 1.7 and 2.1 bar.

I tested the system pressure by connecting the fuel pressure gauge between the WUR and the fuel distributor, with valve closed on WUR side for system pressure, then open for CCP. The residual pressure I reported was where the pressure dropped after the FP was turned off. I did not time the decay but the pressure dropped to zero after about 30 minutes. The WCP was measured after reconnecting the WUR and letting it warm up for about 180s.

I just disassembled the WUR , cleaned it, checked the warming element resistance which is a 26 ohms and read 27.4 ohms. I cleaned the filter mesh as well as I could and put everything back together.

I still have to reconnect the WUR that is on my bench, but if still no start I will look into the CSV.

I haven’t messed with the mixture yet…

[boyt911sc]

Aurel,

Check these:

• Residual Pressure Test (20 mins.)
• Do a smoke test. Verify the absence of significant air leak source.
• Set you control fuel pressures (WCP) correctly (42 psi. w/o vac and 52 psi. w/vac).

Your WUR should read like these: 0-438-140-045. I would bet the culprit to your problem is residual pressure loss. Test and verify.

Tony

[Aurel]

Originally Posted by boyt911sc

Aurel,

Check these:

• Residual Pressure Test (20 mins.)
• Do a smoke test. Verify the absence of significant air leak source.
• Set you control fuel pressures (WCP) correctly (42 psi. w/o vac and 52 psi. w/vac).

Your WUR should read like these: 0-438-140-045. I would bet the culprit to your problem is residual pressure loss. Test and verify.

Tony

Thank you for the advice, Tony. It is always nice to get the attention of the WUR guru!
I must have done something wrong when I reassembled the WUR, because now I have CSP the same as my system pressure, which means the WUR acts as a closed valve.

It must be the way I orientated the metal diaphragms. One has a little hole that I lined up with the hole that brings the gas in, but I then saw a YouTube video that lined the hole in the axis of the bimetallic plate, so I will try that.

I must admit I do not understand very well how those two plates work to control the gas pressure, but if I put everything back together the way it was without damaging anything it should be ok, right .