CIS WUR issues … Maybe?

[Parr]

Hello again!

My 1980 911sc is giving me trouble. Initially, it was just running quite poorly (low power, seeming as if the mixture was off or something). I took it into a local shop to get some new rear shocks thrown on and asked them to check it out. They were able to test the fuel pump, and they found out it is producing 75 psi. All good there. They put the shocks on, replaced the fuel filter at my request and I went to pick it up this evening.

Earlier in the day, the shop owner started the car (it fired almost immediately) and he took it for a ride. After the ride, he parked it outside. It's roughly 22 degrees F out there here in michigan. When I went to pick up the car, it would not start. We pushed it inside and again tried to start it several times. We could smell fuel, and the engine would backfire, but the car would not run. We checked spark, and it is good. The owner believes the car will start after it has warmed up inside all night.

Can anyone point me in the right direction here? I don't have a proper setup to check control cold and warm pressure - not that it would do me any good without the car running. Is there something major I'm missing here? Perhaps I have a bad WUR? Should I just bit the bullet and order the CIS fuel pressure tester? probably yes, but is there anything else I should do?

[timmy2]

Pull the air filter and lift the air metering plate arm when the car is warm while you try to start it.
If it starts you may have a residual fuel pressure problem.

Get a set of gauges and learn how to test. CIS for dummies is a great thread.

[Parr]

I forgot to mention that I pulled the air filter and lifted the air metering plate slightly with the key in the on position. No change in the behavior. I'll have the shop try it again in the morning. If anyone reading this thread has a set of gauges I can borrow in the lansing michigan area, I'd be very grateful.

[ossiblue]

From your OP, it sounds as if the car may have been running lean before this no-start situation began and that lean condition might be due to vacuum/air leaks or out of spec control pressure, or both. Now that it's very cold, the lean mix is too much for the cold control pressure to overcome, especially if the cold control pressure is out of spec as well.

Next step, IMO, is testing--fuel pressures first then, if that doesn't remedy the problem, test for air leaks.

Just a question. In your last post, about lifting the metering plate, did you hear the fuel pump run and did you hear the injectors squeal?

BTW, your issue is almost identical to the one in this thread: Really hard to start Cold, though the solution appears to be found in an incorrectly installed pop off valve.

[boyt911sc]

Originally Posted by Parr

I forgot to mention that I pulled the air filter and lifted the air metering plate slightly with the key in the on position. No change in the behavior. I'll have the shop try it again in the morning. If anyone reading this thread has a set of gauges I can borrow in the lansing michigan area, I'd be very grateful.

Parr,

If your mechanic knows and understand how the CIS works, it would require 15 mins. of his time to determine your cold and warm control fuel pressures. Your FP should deliver more than 75 psi. A good FP could deliver close to 100 psi. Maybe the mechanic measured the system fuel pressure. Let your mechanic do his job and pay him. Take the car home and start learning how to maintain a CIS car.

Tony

[Parr]

We're trying to figuire things out as we go together. He tested the fuel pump at the pump and came up with 75 psi. if that's way too low, I need to have him replace it.

I guess I have to order the fuel pressure tester. I was hoping someone could steer me in the right direction with the info provided, but apparently there's not enough here.

[Parr]

also, I should mention that before I took the car in, when it was running, I removed the oil cap to do a quick/crude vacuum leak test. The idle reduced when I did this, leading me to believe the car does not currently suffer from a bad vacuum leak.

[boyt911sc]

Originally Posted by Parr

also, I should mention that before I took the car in, when it was running, I removed the oil cap to do a quick/crude vacuum leak test. The idle reduced when I did this, leading me to believe the car does not currently suffer from a bad vacuum leak.

Parr,

Ask your mechanic to test the WUR. You want to know the following information:
a). Fuel pressures (cold control, warm control, and system pressures).
b). What type of WUR is installed and heater resistance (ohms).
c). Does the mechanic know how to test run the FP with a disabled engine? If he says NO, you are out of luck. Find someone who knows about CIS. Keep us posted.

Tony

[boyt911sc]

Originally Posted by Parr

We're trying to figuire things out as we go together. He tested the fuel pump at the pump and came up with 75 psi. if that's way too low, I need to have him replace it.

I guess I have to order the fuel pressure tester. I was hoping someone could steer me in the right direction with the info provided, but apparently there's not enough here.

Parr,

How did he do it? Checking the FP at the pump requires removing the skip plate, etc. Testing the FP could be done conveniently else where. I'll give him (mechanic) the benefit of the doubt that he did it correctly. If so, you have a failing FP.

A convenient way to test the FP is to measure the delivery pressure before the FA (fuel accumulator). This is a ten-minute job. You don't need the engine running. As a matter of fact, you don't need an engine to test the FP, WUR, FA, FD, CSV, etc.. Keep us posted.

Tony

[T77911S]

good advise. maybe some miscommunication between you and the mech on how or where the pressure was tested. you dont need to know the pressure at the FP to get it started, just measure the system pressure and control pressures at the same place, between the FD and WUR. car does not have to run.

to start you HAVE to know cold control pressure and warm control pressure.
air leaks is another issue. the oil cap test is not a guaranty of no air leaks.

was the car outside and completey cold, as in he did not run it earlier, when it first started?
when you lifted the sensor plate did you immediately feel resistance or was it easy to move before you hit resistance? if there is free movement of the sensor plate with the key on (FP on) before you feel resistance then the plunger is stuck in the fuel head. that would make it flood and you would smell fuel.

[Parr]

I just got off the phone with bosch. They told me spec for my fuel pump is 75-80 psi. My mechanic tested the pump at the pump under the skid-plate, unfortunately for my wallet. So... I have a good fuel pump?

The car started after checking the fuel pump, replacing the fuel filter and sitting inside the warm shop for a while. After running it around town on a test drive, the car was put outside in the cold (around 12:30). It would not start when I tried to fire it up at 5:00.

The plunger seems to move pretty freely. There is some resistance when lifting it up, but its not difficult to move it at all.

[Parr]

I also, strangely, hear a slight whining sound in the engine bay when the ignition is on but the car is not running. I'm not sure if this is normal or not. It is not the heater blower. What else could it be?

[ossiblue]

Originally Posted by Parr

I also, strangely, hear a slight whining sound in the engine bay when the ignition is on but the car is not running. I'm not sure if this is normal or not. It is not the heater blower. What else could it be?

The whining you hear is probably from the CDI and, if so, that's normal.

Originally Posted by Parr

I just got off the phone with bosch. They told me spec for my fuel pump is 75-80 psi. My mechanic tested the pump at the pump under the skid-plate, unfortunately for my wallet. So... I have a good fuel pump?

The car started after checking the fuel pump, replacing the fuel filter and sitting inside the warm shop for a while. After running it around town on a test drive, the car was put outside in the cold (around 12:30). It would not start when I tried to fire it up at 5:00.

The plunger seems to move pretty freely. There is some resistance when lifting it up, but its not difficult to move it at all.

The information in this post (bold) still leads me to believe you have a fuel pressure problem coupled with a possible air leak. Marginal specs on cold control pressure and/or air leaks, can result in starting/running in mild ambient temps but when things turn very cold, failure results.

It's time to run fuel pressure tests, either by your mechanic or by yourself. Doing any other "problem solving" is a waste of your time, IMO, until you get the first and most likely suspect (fuel pressures) taken care of. One step at a time. When you get the results of your pressure tests, report back and things will be easier to diagnose.

[montauk]

Replace the relay O2 relay under the passenger seat. My car ran terribly when I got it and was difficult to start. I checked fuel pressures - all good. I checked and replaced with new the WUR, distributor cap, fuel filter, accumulator, wires, plugs, etc. Everything I did helped a little (at least I imagined it did). I popped in that relay based on advice I got from this board and the car started right up and ran perfectly. It's a $12.00 part from our host.

[Paulporsche]

Tony and LJ, and others, are giving you good advice here.

You have to get your mechanic to verify that all ignition components are functioning properly. then have him check the control pressures and keep track of the ambient temperature. You should then report back here and compare the CPs with this chart. You need tocheck which WUR you have.

Aside from vacuum leaks, it seems that one of the main reasons these engines fail to start is because the Warmup Regulator (WUR) goes out of spec, causing a too high cold CP, resulting in poor starting especially cold.

[boyt911sc]

Originally Posted by Parr

I just got off the phone with bosch. They told me spec for my fuel pump is 75-80 psi. My mechanic tested the pump at the pump under the skid-plate, unfortunately for my wallet. So... I have a good fuel pump?

The car started after checking the fuel pump, replacing the fuel filter and sitting inside the warm shop for a while. After running it around town on a test drive, the car was put outside in the cold (around 12:30). It would not start when I tried to fire it up at 5:00.

The plunger seems to move pretty freely. There is some resistance when lifting it up, but its not difficult to move it at all.

Parr,

If your mechanic is checking the FP by removing the skid plate under the car, it is obvious he is not a Porsche mechanic. If he is, he's not familiar with CIS engines. He maybe a good and trustworthy mechanic, but if he's not familiar with this work, it would be expensive on your part.

What's the ID number on your FP? Either you have the wrong FP or your FP is going bad!!! The delivery pressure of 75 - 80 psi. is too low to sustain a system pressure of 72 psi. (see spec.) that is needed by your engine. It might be able to start the engine when slightly warmed but would struggle when it is too cold.

Ignition is easy to check. The vacuum/air leak test is another story. Keep us posted.

Tony

[timmy2]

Parr,
Apparently your "mechanic" doesn't have a clue about a CIS fuel system and how to test it.
Checking system pressures and cold and warm pressures is a very simple procedure when done correctly.
It takes about an hour or so to do all the tests required depending on how much stuff is in the way to remove the line to the WUR and connect the gauge, hoses and fittings correctly.
Are you paying him to learn on the job?
Listen to Tony and Ossiblue and Paulporsche. They know what they are talking about.
The CIS test gauge set is around $130 from our host, what is that, about 1.5-2 hours of shop time these days?

Read this:

CIS Troubleshooting for Dummies

[T77911S]

what tony said above. you DONT check pressure at the pump. pressure is tested between the FD and WUR and that is where you should have 5bar. if he is getting 5bar AT the pump, there is a problem with the pump, BUT that would not keep it from starting under the conditions it does not start since it already starts and runs at other times..
the fuel pump itself should be able to provide much more than 5 bar, probably more like around 7 bar, tony would know for sure. there is a pressure regulator in the fuel head that drops the pressure down to 5bar.

probably not the O2 relay since it starts and runs. to make sure you can feel the fequency valve with the key on. it should be vibrating. it is possible the relay has a bad solder joint that opens up when it is really cold. if it vibrates when it will NOT start the relay is fine.

ossi is right. you HAVE to start with control pressures. its possible the pressure is not dropping enough.

you can get a set of gauges for around $100 or so, about an hour of your mech's time. you will also need an adapter that probably does not come with the gauges.
with the help here, you can fix this yourself.

[Parr]

I am picking up the fuel pressure gauges and running the tests tomorrow. I'll update you as I get more info.

[Charles Freeborn]

As much as I hate to admit it, the Harbor Freight FP gauge set is pretty good. Car does not have to be running to get basic readings. Definitely start there. Then go through the diagnostic steps already stated and start the process of elimination. It's a pretty logical system once you wrap your brain around it, but it does have a couple of Achilles heels.
-C