'83 911sc was running again....but not for long

springerman55 · 10-10-2010, 05:08 PM

After posting yesterday that my SC was running again, I spoke too soon apparently. I installed new a Bosch fuel pump and the car fired up on the second try. While I was letting the engine warm up, I was underneath the car checking for fuel leaks while the car was up on jack stands (car was level). There were no fuel leaks. Once the engine reached operating temperature, I shut the engine off. It cranked right back up. I finished the job very late at night so I decided that first thing in the morning, I would re-install the stone shield, take the car off of the jack stands and then go for a test drive. I tried cranking the car this morning and it would not start. After several rounds of unsuccessful attempts to start, I could smell a strong fuel smell in the engine bay (no fuel leaks). I removed the air filter housing cover and air filter. With the ignition in the ON position, I raised the air flow sensor and the injectors whistled so they are getting fuel. In addition to replacing the fuel pump, I drained the fuel tank and replaced the drain plug fuel screen and also installed a new fuel pump relay (just for insurance). There are 3 1/2 gallons of fresh Chevron premium fuel in the tank right now (surely that is enough fuel). I am stumped. Any ideas out there?

ossiblue · 05:14 PM

Check for spark...my first reaction. However, I'm not familiar with SC's but am aware there are some sensors (flywheel?) that will prevent starting if they are faulty. Someone who knows these engines will chime in soon, I'm sure.

longhornchris04 · longhornchris04's Garage

Are you sure the injectors whistled and it wasn't just the fuel system starting to pressurize? I asked because I had a similar issue, and I had to hold the plate for about 2 sec. During that time it got 'heavy' and then the injectors fired. In my case the check valve had failed an I was starting from zero pressure. Same problem as you - crank crank crank but no catch. Fixed the check valve, pressurized the system once, and I was good to go.

Is the engine attempting to fire at all, or is it sputtering and choking?

Aside from spark, another option could be the cold start unit. Without that burst of fuel there may not be enough to catch, especially if the fuel accumulator has allowed the system to bleed down.

Good Luck.

psalt · 10-11-2010, 03:52 AM

It may have flooded the engine. The plugs never really warm up at idle, then you added more fuel with repeated cranking. My advice would be too pull a spark plug and see if it is black and wet. If so, clean and dry the plugs, check the gaps and try again.

ossiblue · 07:16 AM

Quote:

Originally Posted by springerman55

...first thing in the morning, a test drive. I tried cranking the car this morning and it would not start. After several rounds of unsuccessful attempts to start, I could smell a strong fuel smell in the engine bay (no fuel leaks). I removed the air filter housing cover and air filter. With the ignition in the ON position, I raised the air flow sensor and the injectors whistled so they are getting fuel... Any ideas out there?

As posted by psalt, you likely have flooded the engine but the question is, how did that happen? The strong fuel smell in the engine compartment suggests flooding (be careful of hydro-lock) which, in turn, suggests lack of spark. You may wish to take the advice of pulling a plug and seeing if it's wet, then replace it and do a simple test for spark. I still think that's your area of concern.

One thing to note on CIS cars is the cold start injector. If it is working properly, you should get an immediate firing, assuming you have spark. If the injector is leaking, you can easily flood the engine. If the injector is not injecting fuel, you will get no firing until the cylinder injectors provide fuel and since they all work at once and provide a larger quantity of fuel to each individual cylinder than does the cold start injector, you can possibly flood the engine. This is another possible area to check, but I'd wait until you've eliminated the possibility of no residual pressure (check with a fuel pressure gauge) or a no spark condition as they are easy to check.

springerman55 · 10-11-2010, 07:34 AM

In reference to longhornchris04's post, the engine just spins and spins and spins. No almost started or trying to run (i.e.-running rich). It just spins (like it did before I replaced the fuel pump). The injectors did not whistle per say when I lifted the air flow sensor plate but I can hear a buzzing noise (like the fuel lines were pressurizing).

psalt · 10-11-2010, 08:05 AM

As posted by psalt, you likely have flooded the engine but the question is, how did that happen?

LJ,

My experience is it really easy to flood a CIS engine with good pressure and repeated cranking. This became more and more obvious dealing with intermittent and failed starters over many years. The CSV sprays a lot of fuel anytime the key is in start when cold and the 8 second TTS is not really eight seconds on separate attempts at cranking. The variable amount and duration of CSV spraying complicates getting the ideal compromise for best cold start. An example of this is a car that fires too quickly and stalls because the main fueling system cannot supply a rich enough mixture for transition, but after several stalls, the extra CSV sprays will let it run perfectly. It is the transition period, and you need to spend quite a bit of time on it when setting up a programmable EFI system if you want OEM drivability in many different temps. There are way to compensate for this on CIS, but you only learn about them by trail and error after many years.

Running an engine at idle under no load, the spark plugs never burn off, shut it down, then soak them with fuel the next day and you may get no spark. Some Bosch plugs will never clear themselves after a good soaking and I alway keep a known good set to speed up troubleshooting. I can usually start a flooded engine by holding the throttle wide open and manipulating the starter, but it is risky and you will get a big blast of black smoke and maybe a big surprise. With a new fuel pump in the equation, I would be doing a few other tests as well.

ossiblue · 10-11-2010, 08:37 AM

Paul,

Great explanation, thanks. I always try to opt for the easiest, simplest fix first and what you've described certainly fits springerman55's flooding problem. With this information, hopefully he can "dry things out" and begin trouble shooting with a clean slate.

springerman55 · 10-12-2010, 05:11 AM

This is hard for me to believe but less than 12 hours after it was running (replaced the fuel pump), I do not have any spark. I pulled one spark plug wire from the distributor cap and inserted an extra lead with a good, working plug into the vacant terminal. Grounded the spark plug to the engine, spun the engine and no spark.

Back to the Bentley manual for more troubleshooting. Having a hard time remembering why I love this car so much right about now...

lindy 911 · lindy 911's Garage

On my '78 SC I've had issues with the switched power to the CDI being intermittent. I think it has something to do with the key switch so I provided a dedicated 12 volts to the CDI box to test; viola! At least this will let you know it's not the CDI box and you can move on to other things.

Lindy

psalt · 10-12-2010, 06:21 AM

This is hard for me to believe but less than 12 hours after it was running (replaced the fuel pump), I do not have any spark. I pulled one spark plug wire from the distributor cap and inserted an extra lead with a good, working plug into the vacant terminal. Grounded the spark plug to the engine, spun the engine and no spark. Back to the Bentley manual for more troubleshooting. Having a hard time remembering why I love this car so much right about now

Test the coil wire for spark, then the box for 12v, then the green wire, then the trigger. Can you hear the CDI whine ?

boyt911sc · boyt911sc's Garage

Quote:

Originally Posted by ossiblue

Check for spark...my first reaction. However, I'm not familiar with SC's but am aware there are some sensors (flywheel?) that will prevent starting if they are faulty. Someone who knows these engines will chime in soon, I'm sure.

Larry,

No flywheel sensors in SC's. The're flywheel sensors in the Motronic system (3.2 Carrera). On the other hand, I agree with your suggestions about ignition sparks and also Paul's suggestion of inspecting the spark plugs.

After verifying the presence of the ignition sparks, you'll need fuel and air to complete the combustion. Knowing the control and system fuel pressures in any fuel injection system is the first and foremost thing to confirm.

There is some problem I find using the AFS (air flow sensor) switch to test and activate the FP, a very good chance of dumping too much fuel in a cold engine!!!! For inspecting the fuel injector's spray pattern it is OK to use the AFS but you got to limit the run for a second or 2. Otherwise, you could easily flood the cold intake manifolds with excess fuel.

Since he was able to start the engine the previous day, something has changed that affected the ability to complete the internal engine combustion. I would suggest to check the following:
1). Battery fully charge.
2). Fuel pressures (control and system)
3). CDI (Ignition sparks)
4). WUR (cold control pressure)
5). Fuel accumulator ( residual pressure)
6). FD (system pressure)
7). Vacuum leak.
8). Others

Something has definitely changed to affect the starting of the motor.

Tony

springerman55 · 10-12-2010, 07:17 AM

The car has a Perma-Tune CDI unit that I replaced the original Bosch unit with about 9 years ago. I did not hear the CDI whine with the ignition key ON but that does not mean that 12V is getting to the CDI unit. I wonder if the Perma-Tune unit has a similar issue that my H-D motorcycle had. The bike would crank and crank and crank but never start. There was enough voltage to spin the starter but I found out that the ignition control unit would not fire if the voltage ever dropped below 9.75V. I measured across the battery terminals while cranking and sure enough, the voltage was below 9.75V. The battery in the 911 is being fully charged as we speak. Next up will be checking coil wire spark at the distributor cap, then check to see whether 12V is getting to the CDI unit or not...

boyt911sc · boyt911sc's Garage

Quote:

Originally Posted by springerman55

The car has a Perma-Tune CDI unit that I replaced the original Bosch unit with about 9 years ago. I did not hear the CDI whine with the ignition key ON but that does not mean that 12V is getting to the CDI unit. I wonder if the Perma-Tune unit has a similar issue that my H-D motorcycle had. The bike would crank and crank and crank but never start. There was enough voltage to spin the starter but I found out that the ignition control unit would not fire if the voltage ever dropped below 9.75V. I measured across the battery terminals while cranking and sure enough, the voltage was below 9.75V. The battery in the 911 is being fully charged as we speak. Next up will be checking coil wire spark at the distributor cap, then check to see whether 12V is getting to the CDI unit or not...

springerman,

The CDI unit (Permatune) you have is notorious for this kind of problem. One of the most prevalent problem encountered with Permatune CDI is heat soaked. Make a search and most of the problem for lack of ignition is the CDI failure!!!! A great number of these posts had CDI by Permatune.

Since you mentioned it, I'm not surprised at all. I personally prefer the Bosch CDI but many have also switched to MSD and happy with the installation.

On second thought, also check your ignition coil. But they rarely go bad and only by confirming they are working could you eliminate it as a possible culprit. Since it is very technical to analize or trouble shoot the electronics in the CDI unit, switching to a known working CDI is my recommended procedure for troubleshooting. Keep us posted.

Tony

springerman55 · 10-12-2010, 11:57 AM

Boyt911SC,

I remember when I replaced the original Bosch CD unit with the Perma-Tune unit. The price of the Bosch unit almost gave me full cardiac arrest! The Bosch units are still pricey. Pelican offers a Bosch unit rebuilt (by Bosch or Porsche...not sure) for $1,924.50 and another option is a Bosch unit rebuilt by an independent it seems for $367.50. If it winds up being the CDI unit, do you know if the MSD model in a "bolt in" like the Perma-Tune model or do you have to make lots of modifications to make it fit and/or work. I have an MSD ignition in my '66 Chevy II street machine (really like the system) but the control unit is rather large...

boyt911sc · boyt911sc's Garage

Quote:

Originally Posted by springerman55

Boyt911SC,

I remember when I replaced the original Bosch CD unit with the Perma-Tune unit. The price of the Bosch unit almost gave me full cardiac arrest! The Bosch units are still pricey. Pelican offers a Bosch unit rebuilt (by Bosch or Porsche...not sure) for $1,924.50 and another option is a Bosch unit rebuilt by an independent it seems for $367.50. If it winds up being the CDI unit, do you know if the MSD model in a "bolt in" like the Perma-Tune model or do you have to make lots of modifications to make it fit and/or work. I have an MSD ignition in my '66 Chevy II street machine (really like the system) but the control unit is rather large...

springerman,

I have no hands-on experience with MSD system but numerous people have claimed to be satisfied with it. There are several posts regarding the installation process in this forum. With the Bosch CDI, I've not encountered any problem regarding heat soak failure. But they do fail too in some other manner.

A good used Bosch CDI unit costs about $250. If you decide to buy a used CDI unit, just make sure that the seller gives you an assurance that it is a good working unit and subject to test. You could easily get another bad unit!!!!

I like to have a spare or two for some CIS components for my cars. As an example below:

But I don't suggest you get multiple spares, I use them for my tests and trouble shooting work. One unit is sufficient in your case. MSD or Bosch CDI is up to you. It is a choice!!!! But stay away from Permadoom........unless you can't find any replacement CDI.

Tony

lindy 911 · lindy 911's Garage

The MSD 6AL can be found for about $200 and will mount nicely in your car. It has been recommended that the unit be mounted under the drivers seat and the wiring run under the carpet and out the tunnel. One important warning is that if you use the MSD (I personally have one) make sure you do not run the trigger wires from the distributor in the same harness as the rest of the wiring for the unit. It WILL cause cross-firing and screw up your day! It's not hard to run them separately as there is lots of room. It makes a lot more juice to the plug than the stock Bosch unit so theoretically it works better.

I mounted mine under the rear shelf and mounted the coils where the old CDI box used to be. I will be moving it to under the front seat shortly.

Lindy

springerman55 · 10-12-2010, 09:35 PM

I doubled checked to listen for a whine at the CDI unit with the ignition key ON. No sound at all (not sure if the Permatune whines like the Bosch unit does). I measured 12V in the CDI harness for pin 15 with the ignition key ON so there is voltage supplied to the CDI unit. I was unable to test the distributor pulse generator in the unplugged harness while cranking the car. I do not have a very robust volt meter. It only goes to 400VAC max. and since the Bentley manual says to measure in VAC, it does not state how many VAC you should read other than you should read voltage. So in fears of smoking my volt meter, I am going to borrow a more robust volt meter and measure the distributor pulse generator. More updates coming...