'79 911 SC - No start

[tarix]

This car was running fine and completely died while driving. The electrical system is fine and I can crank the engine until the cows come home.

Tested the fuel pump by lifting the air plate. I can hear it running and hear the injectors. Sounds strong.
Cleaned the distributor rotor and cap, then replaced them.
Checked for battery voltage at pin 15 of CDI plug. 12.4v
CDI Box whines when the ignition is on.
Checked for spark. It exists, but it looked yellow instead of blue. (Weak, but not strong enough to run at all?)
Performed coil tests. Got 0.6 between the two posts and 1.726 between the ground and center. (That second reading is with the meter set at 2K.)
Car has no alarm and no pop-off valve.

I do get a spark so if I'm going in the wrong direction I'm sure someone will let me know. Also, I typically get a brief detonation if it's the first crank of any given day.

-- Mike

[Paulporsche]

Tarix, If you search, you should find lots of info on troubleshooting starting problems.

I don't know what those readings you got are supposed to be, but this will bump your post and maybe someone who does will see it. Otherwise, maybe a search will give you those specs.

Also, have you checked or changed your plug wires? That spark color sounds weak, as you indicated.

Make sure your distributor has not loosened up and rotated.

Are you getting fuel to the engine. Do you have gas (Slingblade)? There is a way to test for fuel flow by lifting the sensor plate and seeing if you get a good spray from the injectors.

How old is your fuel filter?

Are you sure the fuel pump is working? Check relay and fuse. Check wiring and grounds for all components.

Is your popoff valve in place and closed? Is the rubber bellows over the mixture control sensor tight and in place? Do you have any air leaks?

Do you have an alarm system? Check that, if you do.

Try disconnecting your O2 sensor.

If you have a fuel pressure you can measure your fuel and control pressures.

Good luck. This should at least get you going. Let us know if you get the car going.

[GB83SC]

I would double check the fuel pump fuse. Remove the black cover at the rear on the left side of the motor bay and check the fuses there.
There is also a relay under the passenger seat make sure that there is power to it.


good luck.

[tarix]

The fuel pump is working. I can hear it run when I lift up the air plate.

I haven't checked the spark plug wires yet mostly because the engine was just rebuilt. It seems odd that spark plug wires would cause a perfectly working engine to go instantly dead. I would have expected some rough running as a symptom.

Haven't checked for any sort of air leaks yet and haven't installed the pop-off valve yet either. (I do have one ready to go once the engine is operating.)

No alarm system, I already removed both of them while the car was still running. I believe most car alarms disable either the ignition or the fuel pump and they are both working. No O2 sensor on a 79. (Another post mentioned the relay under the seat. My car is too old for the lamda equipment.)

I have not yet tested the fuel pressure because I don't have a gauge. I'm currently testing all the ignition components first since I have all the tools to do that.

[Early_S_Man]

Mike,

Does your car have a factory alarm system that may have malfunctioned? If so, read the following thread:

'82 SC Won't run

Is your coil a Bosch 0.221.121.001 OEM small, black coil? If so, your readings sound suspicious.

If it is a Bosch 'Blue' coil, that sounds OK.

Does your tach needle move off zero while cranking?

Here is a diagram that may help.

Is the green coax cable coming out of the distributor ... the short 'pigtail' about 8" long ... cracked or turned brown??? If so, it needs to be replaced ... less than $30 from Pelican.

Test the magnetic pickup coil by disconnecting the 6-pin connector from the CDI unit ... and check for a 600 Ohm reading across terminals #7 and #31d of the cable connector ... +/- 10% at room temperature. If you get an 'open' or short ... the green coax cable is suspect.

If you get a good 600 Ohm reading of the pickup coil ... test for a trigger signal while cranking ... by putting a multimeter set to measure low AC Volts across connector terminals #7 and #31d ... 1.0 - 3.0 Volts is a normal reading.

[Paulporsche]

Check your wiring to the Cold start valve (blue connector) and the green connector to the rollover switch between the mixture control unit and firewall.

Check vacuum lines for leaks.

Try richening your mixture a little.

[CarreraS2]

The one time my SC wouldn't start, it was corrosion in the green coax cable connection. It comes out of the distributor, about 6 inches out, there's a connection. Maybe disconnect and clean. It sits kind of under the cam oil line, is a little hard to see, so doesn't get any attention over the years.

[tarix]

Originally posted by Early_S_Man

Does your car have a factory alarm system that may have malfunctioned?

My car is too old to have a factory alarm. It had two previous alarms, but I've been driving this car about 6 months after removing them both.

Is your coil a Bosch 0.221.121.001 OEM small, black coil? If so, your readings sound suspicious.

It is that exact coil. I might be reading my DMM wrong though. What setting should I be using for the secondary test?

Does your tach needle move off zero while cranking?

Barely. It does twitch though.

Is the green coax cable coming out of the distributor ... the short 'pigtail' about 8" long ... cracked or turned brown???

Compared to everything else ignition related it looks brand new. Nice and bright green. Maybe this was replaced when the engine was rebuilt. (~1000 miles ago)

Test the magnetic pickup coil by disconnecting the 6-pin connector from the CDI unit ... and check for a 600 Ohm reading across terminals #7 and #31d of the cable connector ... +/- 10% at room temperature. If you get an 'open' or short ... the green coax cable is suspect.

Set at 200 my DMM reads .6 ... Does that help at all?

If you get a good 600 Ohm reading of the pickup coil ... test for a trigger signal while cranking ... by putting a multimeter set to measure low AC Volts across connector terminals #7 and #31d ... 1.0 - 3.0 Volts is a normal reading.

I'm not sure how to do this. I need to tap into them while the 6-pin connector is plugged in to the CDI right?

[tarix]

Originally posted by SoCal911SC
The one time my SC wouldn't start, it was corrosion in the green coax cable connection. It comes out of the distributor, about 6 inches out, there's a connection. Maybe disconnect and clean.

Interesting mine goes straight from the distributor into a wiring harness that leads back to the fuse box and CDI cable. It's also a lot longer than 6 inches, much closer to a foot.

[Early_S_Man]

The secondary winding resistance of the OEM Bosch coil should be from 650 Ohms to 790 Ohms.

No, to test the AC Voltage from the distributor you leave the CDI connector unplugged and connect meter to terminals #7 and #31d ... just like you did for the 600 Ohm test.

I suggest pulling the CDI unit and cleaning the six connector tertminals with Q-tips and 9% vinegar, followed by rinse with distilled water and 90% isopropyl alcohol. Same for harness connector, followed by a very slight re-crimping of the sides of the six Faston connectors ... just tighten the grip a bit, DON'T close the gap entirely!!! After normal ignition operation is restored ... dab a bit of Dow Corning #4, #111, or #112 silicone grease on the terminals to seal oul moisture and oxygen.

[tarix]

Originally posted by Early_S_Man

No, to test the AC Voltage from the distributor you leave the CDI connector unplugged and connect meter to terminals #7 and #31d ... just like you did for the 600 Ohm test.

I'm getting no reading. Perfectly zero while cranking. Wire 15 does show 12 volts when the ignition is on though.

[Bill Douglas]

The above sounds good advice.

If you still feel it may be fuel, unscrew the connector at the fuel filter and some should come out as it is under pressure if it's working right.

[Nitrometano]

I dont know if you turn the starter the engine rotates. If not, may be when you lifted the air plate, you hold it a few seconds and filled the cylinder with gasoline. If the engine dont rotate take out the spark plugs to get the gas comming out. DONT START THE ENGINE AND DONT CONNECT THE BATERY. THE ENGINE WILL GO ON FIRE. Wait until the next day when the gas evaporate.

[OldTee]

Check the pop off valve. Give it a good tug to make sure it is not leaking. Also check that the rubber intake hoses are properlly set. Mine stopped running three times within a short period of time. Once was a dead fuel pump. Next time was a coil that quit when it got warm. (not hot mind you warm, the damn car would run for a few minutes just fine, then quit dead.) The third time was the pop-off valve fell out.

Also, often they will not run after you have played with them for a while. What happens is fuel wets the spark plugs and you need to let it dry. You might try a little starting fluid. If you have spark it will run. Be careful with that stuff, use it as a last resort. Good luck.

[gerard vaglio]

If you don't have a pop off valve your engine didn't backfire by any chance did it?

If your engine is cranking easily but never starts you could have an air box issue. If there is a crack in the air box it will never start, ask me how I know.

[Paulporsche]

Have you checked the condition of your battery?

Have you tried jump starting the car?

[RazorRacer]

Sounds like a bad battery.

[tarix]

Originally posted by gerard vaglio
If you don't have a pop off valve your engine didn't backfire by any chance did it?

I believe it did after it died. Of course I'd need to fix whatever caused it to stop in the first place as well as the air box. I don't see tests in the Bentley manual
It probably did when it died. That would have been after-the-fact of course. I can't find any tests in the Bentley manual though.

To answer the myriad of battery questions. Battery is a brand new Optima that I actually installed post death. It has new battery terminals and a new negative wire. I'm getting the full voltage of the battery all the way to the back of the engine.

[steand]

What about checking that it's not the switch on the air sensor plate that cut off the Fuel pump. Simply disconnect the plug to the switch, it's placed on the back side on the air measuring unit. IT's a simple and free test, to eliminate that problem.

Also check the fuel pump relay. se if the contact point's is pitted inside the relay. Mine was, just celan with some fine wet sanding paper. FREE.

[OldTee]

Try the starting fluid. If it runs for a few seconds the electrical side is OK. If not concentrate on electrical stuff first.

To run you need fire (at the right time), fuel (not too much, not too little), compression, exhaust.