Warm Start Issue

[PARTON1080]

82 911SC 3.0

Car runs fine cold. After it gets warm it won't restart, and a buzz coming from the vicinity of the CIS/airbox is audible from within the car/ within 10 ft of the car. Buzzing/humming noise comes on an off with the ignition switch.

Once engine is warm and buzzing starts, engine will turn over all day but won't fire.

Takes more than 30 minutes of inactivity to start again.

Car sat for a couple of years. Had someone else put a new fuel distributor on it. Ran awful at first. Would bog down when I gave it gas. Let it run idle for 5-10 min at a time for a week and it cleared up. Took it to the gas station and ran strong and smooth. Restarted, ran down the highway, girlfriend got in to drive it, killed the engine, and we discovered the warm start issue. Ordered a new coil and fuel filter. Doubt that will fix the buzz though.

Hopefully this is obvious to someone with more experience than me. Any suggestions?

[oneblueyedog]

Buzzing. The red relay in the trunk may be bad letting the fuel pump run on. Check if it goes away, switching it with a known good relay. It can be a black one as a stop gap.

Could be the CDI unit is bad. When you have the key on, the sound should be a high pitched whine.
The CDI box is not near the Fuel Distributor though.

Hope this helps.

[PARTON1080]

The buzz comes from the above the engine. Is the fuel pump on the bottom of the car towards the front? What is the CDI unit? Why yes, I am a noob.

[PARTON1080]

Should the sound be a high-pitched whine if it's working properly or improperly? Where is the CDI box? Thanks for the help.

[oneblueyedog]

Patron,

Here's a great site to go over. I've got to go to work but I'll check on this thread later.

http://members.rennlist.com/jimwms/CIS/CIShome.html

The CDI box is on the left side engine compartment. Usually an aluminium finned box with a 6 plug terminal at the bottom

[oneblueyedog]

High pitched whine is normal. It should be constant.

[Paulporsche]

Usually when the engine starts cold and runs fine but won't start when hot it is the fuel accumulator. It is located next to the fuel filter on the driver's side of the engine compartment. Another possibility is the fuel pump check valve, but more often it's the accumulator.

If the whine is coming from a silver, red or blue square box on the other side of the fuel filter, it is the CDI )ignition) box. The Bosch ones whine. The blue Permatune ones are pretty reliable but don't whine. The silver Permatune ones do tend to stop working when hot. They don't whine either, and neither do the MSD ones, which are red and are a good alternative.

If the whine is coming from right above the engine then it's probably the injectors.

You should use the search function and check this out further. This is a common problem.

You should also get Wayne's 101 Projects book and the Bentley manual. A CIS fuel pressure gauge available from JC Whitney will let you see if you have sufficient residual pressure, which you need for hot starts.

The gauge can test your fuel and control pressures, which are important for proper engine funsctioning.

You can also check the fuel accumulator by pulling the line from the bottom and seeing if fuel leaks out. If it does, it's bad. NOTE: EDIT TO CORRECT. THIS APPARENTLY IS NOT TRUE FOR 2 UP, 1 DOWN ACCUMULATORS. THANK YOU, TONY.

With CIS cars, always make sure all ignition components are operating correctly before checking fuel injection components.

If you haven't already, post a picture of your car. Good luck and let us know what happens.

[PARTON1080]

Thanks to both of you guys, I will start tracking all of these leads after work.

Is the check valve near the fuel pump?

[Paulporsche]

Yes. Both are located beneath the car, behind the fuel tank. Some years have the valve external to the pump and adjacent to it; some are a fixed part of the pump.

[PARTON1080]

Just remembered something; would the fact that using starter fluid yields no fire whatsoever eliminate the possibility of a fuel issue?

[Rodney Nelson]

I had an '82 SC with the same problem. It was a simple do it yourself fix of a check valve that attaches right to the fuel pump. Try this first, it is the cheapest and easiest way to go and most of the time with this issue on the SC this valve is the culprit.

[Rodney Nelson]

Here is the pelican parts part number: 893-906-093-M14

[psalt]

Car runs fine cold. After it gets warm it won't restart, and a buzz coming from the vicinity of the CIS/airbox is audible from within the car/ within 10 ft of the car. Buzzing/humming noise comes on an off with the ignition switch.


Your car has CIS lambda. On the backside of the airbox there is a pulsed injector called the frequency valve that functions as a variable restrictor to control lower chamber pressure to alter the fuel mixture in response to the O2 sensor. It makes a faint buzz in operation. Your version of CIS needs this valve to be pulsing in range for the fuel curve to be anywhere close to correct. When you start the engine, it pulses at a fixed frequency until the engine warms up, then it dithers back and forth to keep the average AFR near stoich for the converter. I suggest you hook up a dwell meter to the test plug and check the duty cycle during open loop and closed loop. It may be malfuntioning when the temperature switch tells the control box to go closed loop.

[boyt911sc]

Originally Posted by Paulporsche

Usually when the engine starts cold and runs fine but won't start when hot it is the fuel accumulator. It is located next to the fuel filter on the driver's side of the engine compartment. Another possibility is the fuel pump check valve, but more often it's the accumulator.

If the whine is coming from a silver, red or blue square box on the other side of the fuel filter, it is the CDI )ignition) box. The Bosch ones whine. The blue Permatune ones are pretty reliable but don't whine. The silver Permatune ones do tend to stop working when hot. They don't whine either, and neither do the MSD ones, which are red and are a good alternative.

If the whine is coming from right above the engine then it's probably the injectors.

You should use the search function and check this out further. This is a common problem.

You should also get Wayne's 101 Projects book and the Bentley manual. A CIS fuel pressure gauge available from JC Whitney will let you see if you have sufficient residual pressure, which you need for hot starts.

The gauge can test your fuel and control pressures, which are important for proper engine funsctioning.

You can also check the fuel accumulator by pulling the line from the bottom and seeing if fuel leaks out. If it does, it's bad.

With CIS cars, always make sure all ignition components are operating correctly before checking fuel injection components.

If you haven't already, post a picture of your car. Good luck and let us know what happens.

Paul,

I'm not picking on you. As a matter of fact, you give good advises and been very helpful to others. Since this is a technical forum, inadvertently giving misinformation and it happens to everyone inlcuding myself should be corrected without malice. Even a good fuel accumulator will have fuel coming from the bottom chamber when you disconnect the drain line. Why? The bottom chamber is connected to the main fuel return line going to the tank. One way to test the fuel accumulator is to pressurized it. Either with air or fuel (gasoline).

Tony

[PARTON1080]

Originally Posted by psalt

Car runs fine cold. After it gets warm it won't restart, and a buzz coming from the vicinity of the CIS/airbox is audible from within the car/ within 10 ft of the car. Buzzing/humming noise comes on an off with the ignition switch.


Your car has CIS lambda. On the backside of the airbox there is a pulsed injector called the frequency valve that functions as a variable restrictor to control lower chamber pressure to alter the fuel mixture in response to the O2 sensor. It makes a faint buzz in operation. Your version of CIS needs this valve to be pulsing in range for the fuel curve to be anywhere close to correct. When you start the engine, it pulses at a fixed frequency until the engine warms up, then it dithers back and forth to keep the average AFR near stoich for the converter. I suggest you hook up a dwell meter to the test plug and check the duty cycle during open loop and closed loop. It may be malfuntioning when the temperature switch tells the control box to go closed loop.

I do not have a dwell meter. Is there a relay for this lambda that i can pull to force it to be inoperable? If I pull the relay and the car behaves in the same manner do I then know that either the relay or the system is faulty?

[Gunter]

Originally Posted by PARTON1080

Just remembered something; would the fact that using starter fluid yields no fire whatsoever eliminate the possibility of a fuel issue?

Forget using Starter fluid for these engines.
Get the Bentley SC Repair Manual, read, read and read some more so you'll understand the CIS.

Hot-start issues:
Check valve on, or inside, the pump. External check-valve is cheap but, when replacing, extreme caution because the fuel in the tank wants to come out!

Read about it in the Bentley.
The pump is located in front under the deflector plate which has to be removed to get to the pump/check valve.
If the pump is pretty old, consider installing a new one to get peace of mind.
Your problem may just disappear with a new pump/ check valve.
Careful with the gas! An empty tank would be best but most people clamp the line to prevent too much of a leak.

Accumulator failing (Not very often)

When turning the ignition ON, the fuel pump should not be running.
If it does, the Airsensor Switch on the metering body is not working. (could be disconnected)

Get the Bentley, you'll love it!

[PARTON1080]

Originally Posted by boyt911sc

Paul,

I'm not picking on you. As a matter of fact, you give good advises and been very helpful to others. Since this is a technical forum, inadvertently giving misinformation and it happens to everyone inlcuding myself should be corrected without malice. Even a good fuel accumulator will have fuel coming from the bottom chamber when you disconnect the drain line. Why? The bottom chamber is connected to the main fuel return line going to the tank. One way to test the fuel accumulator is to pressurized it. Either with air or fuel (gasoline).

Tony

I don't understand how this accumulator is supposed to function. Here at work, a hydraulic accumulator serves as a reservoir should system pressure drop do to a pump lag, etc. These hydraulic accumulators have the hydraulic fluid exposed to the system via a port, and have pressurized gas on the opposite end of the cylinder. The two are separated by a movable wall, (like a piston). Because the gas is compressible it absorbs shocks in the system.

Because I am unaware of the manner in which these fuel accumulators function, I also am unsure of how to leak check them.

Right now I am behind the curve.

Thanks for the help thus far, everyone.

[oneblueyedog]

Your car has CIS lambda. On the backside of the airbox there is a pulsed injector called the frequency valve that functions as a variable restrictor to control lower chamber pressure to alter the fuel mixture in response to the O2 sensor. It makes a faint buzz in operation. Your version of CIS needs this valve to be pulsing in range for the fuel curve to be anywhere close to correct. When you start the engine, it pulses at a fixed frequency until the engine warms up, then it dithers back and forth to keep the average AFR near stoich for the converter. I suggest you hook up a dwell meter to the test plug and check the duty cycle during open loop and closed loop. It may be malfuntioning when the temperature switch tells the control box to go closed loop.

I think this may be a good route to explore. My car does not have Lambda so I overlooked this possibility.

Dwell meter? Does this equal an Ohmmeter?

[psalt]

You need to borrow a dwell meter, CIS lambda will tell you what is happening, no guessing involved. Much better than the typical, knee jerk "it's the WUR" internet advice.

If you are hearing a loud buzzing behind the airbox only when warm, the FV is the prime suspect. There is a small square relay under the passenger seat and you can disable the system by removing it. These engines can run somewhat OK without an O2 sensor, but they need the FV to be pulsing at default or the mixture will be lean all over the place and they run like crap.

[Gunter]

Originally Posted by PARTON1080

I don't understand how this accumulator is supposed to function. Here at work, a hydraulic accumulator serves as a reservoir should system pressure drop do to a pump lag, etc. These hydraulic accumulators have the hydraulic fluid exposed to the system via a port, and have pressurized gas on the opposite end of the cylinder. The two are separated by a movable wall, (like a piston). Because the gas is compressible it absorbs shocks in the system.

That's the way it works except instead of using pressurized gas, it uses a spring-loaded diaphragm meaning. Your accumalator has two lines on top and one on the bottom. The 2 lies on top are: One in from the pump and the other out to the filter. The bottom line is a return line to the tank in case there is an internal leak. And NO, this line should not have any fuel unless the diaphragm is leaking

Because I am unaware of the manner in which these fuel accumulators function, I also am unsure of how to leak check them.

If the accumulator doesn't have a major leak, concentrate on the pump/check valve.
Is the pump running with ignition ON?

Thanks for the help thus far, everyone.

Get the Bentley.