1984 3.2 will not start

[198491132]

Good Day all....4 hours later and still can not get started. Any advice would be appreciated...here is the situation:

Battery is fine, no spark to plugs. Tested 12 volts at coil with ignition on, replaced coil. Replaced DME relay under drivers seat. Replaced fuel pump relay in luggage compartment. Cleaned dist cap and rotor. Tested voltage of both reference and speed sensors - readings of those tests are 1025 ohms between pin 1 and pin 3 (Bentley manual says this is OK). Between pins 1 and 3 and 2 and 3 I get "OL" on the meter, I also believe this is OK.

Car ran great last time I had it out about three weeks ago. Been extremely hot and humid.....

98K miles with orginal DME unit.....

Any advise would be greatly appreciated, Thanks...Dave

[lally911]

So it turns over but never catches?

Are reference sensors plugged in the right connectors? I've gotten mine mixed up before so just checking.

Can you hear the fuel pump running?

Original plug wires? Check resistance of coil wire.

[198491132]

Thanks for the reply.....sensors are correct, I didnt touch them until it wouldn't start. Coil wire is measuring .2 ohms, should be good. No fuel pump noise, so I jumped fuse 6 with fuse 5 and manual started the pump. Still no spark. Yes, it turns over fine.

Dave

[ischmitz]

Sounds like you covered all the usual suspects. and I was going to say the that leaves the DME itself. They have a tendency to fail in the igntion circuit. But:

You also said the fuel pump doesn't run while you crank?? The fuel pump should come on during cranking only. It is not supposed to run when the ignition is turned to ON. Check if it comes on during cranking - if not you have either a wiring issue or the DME is damaged or there is no power to the DME.

Check if the DME is alive: Switch the ignition to ON but do not crank. Then touch the idle control valve on the intake. It's a silver cannister about the size of a cigarette box. It should vibrate with 80Hz and jerk about once every second. If this is not happening the DME isn't powered (or dead) and you have to look for the reason. Maybe an aftermarket alarm unit?

If you need help I can test your DME. See here: 3.2 DME tester - my newest project

Ingo

[Thrlls]

I had this same problem and it turned out to be my fuel pump. You may want to check that out.
I applied 12v to the pump and the pump would turn over, car would start, but then it would not start at the next start up.
Changed out fuel pump and haven't had a problem since.

[JG911]

Looks like it a thing for 1984 911's this month.

Mines playing upc aswell

911 Not Starting !!!

[198491132]

Additional test results:

Fuel pump turns on during "start" only. I also jumped fuse #6 with twelve volts, fuel pump runs....but did not start the engine.

Idle control valve does vibrate with key in the "on" position.

Additional general info - low fuel light was on - added 1 gal of fuel before all this testing (vapor lock issue?)

I found a loose plug wire.....almost too loose to be running the cylinder..(shorted out the DME?)

There is an ignition cut off switch. My tests show it cuts the 12 volts to the coil when active.

The only sure failed test, is there is no spark at the plug..I tested two seperate cables.

Thanks for your support, Dave

[JG911]

Originally Posted by 198491132

There is an ignition cut off switch. My tests show it cuts the 12 volts to the coil when active.

Thanks for your support, Dave

Is there a cut off switch if so where abouts is it

[Tim L]

I have been chasing a no start problem for about a year now. Sometimes the car just wouldn't start in the summer on hot and humid days. To make a long story short it turns out my main coil wire would spark to the negative coil lead when the conditions were just right. It only took me a year to figure out!

[198491132]

Changed out dist cap and rotor, tested with older coil I had in the garage, being careful about the leads. Still no spark.

Dave

[198491132]

How much difference is there in DME units by year? Will my 1984 work in a 1985? 1986?

Thanks, Dave

[ischmitz]

If you can make sure that you get fuel (smell at the exhaust pipe) then you have good sensors and the fault is either the DME ignition output stage or coil/rotors. If you do not get fuel then it is a speed/reference sensor issue.

Ingo

[198491132]

Ingo, thanks for the help. I have fuel smell at the exhaust. I changed the coil, used a stock one I had on the shelf. Also tested coil voltage at 12v, either side to ground.

I changed the dist cap and rotor, measure rotor resisitence at .2 ohms.

I have a friend that has either an 83 or 85....can I test my DME with that car?

Dave

[pozee]

Although you state you replaced it, you may want to test the coil again per the Bentley instructions.

[ischmitz]

Yes, for testing purposes you can use any 3.2 DME. Some will result in hunting idle but don't worry about that. If your friend's DME starts your car you have isolated it to the ignition output stage being the culprit in yours.

Ingo

[198491132]

.....do you know the proper readings for testing the coil? The Bentley manual appears to have table b incorrectly referenced. My table b shows speed sensor data, not coil data.

Thought I would check it again..grrrrr

Thanks, Dave

[pozee]

Here you go...

Resistance should be 0.4 to 0.6 ohms between terminals 1(-) & 15(+) and 650 to 790 ohms between 1(-) and 4(dist.wire term.)

[198491132]

I have two coils....neither new...

#1 reads 5.53 and .800 - this is the stock one (shelf)
#2 reads 6.58 and .800 - currently in the car....

Close enough ? or far enough to not produce any spark?

[pozee]

Close enough may not cut it. Do you have your meter set correctly and are you testing between the terminals as specified? If term 1 and 4 needs to be between 650 and 790 ohms, then 800 is not acceptable.

I'm sure the electrical guru's will chime in soon.

Unless you have a distributor cap or rotor problem, you seem to have tested all other possibilities and the coil may be the issue.

[198491132]

I believe so..... between 1/15 = .8 ohms..(this may be the issue?)
between 1/2 = 6.58K ohms