‘85 Carrera no start…help.

[Chsnsurf]

I drove the car for about 30-45 minutes the other day. Parked after in the garage and got a no start the next morning. Cranks, but doesn’t fire. Car acted totally normal the day previous. Tried a few more times to start it on different days and nothing. I have since replaced the DME Relay with a solid state one. Checked the fuel tank for blockage and found nothing. Jumped the fuel pump from the fuse box and DME and can hear it run, but don’t hear it come on when I turn the key. I have also replaced the spark plugs (it was time anyways). Could the cracked plug in the picture be causing the no start? Anywhere else i should be looking? Trying? Super frustrated.
Thanks
Chasen

[Chsnsurf]

Better picture maybe.

[Chsnsurf]

Update: I don’t have spark. I plugged a new spark plug into the spark wire and cranked the engine. No spark. Tried it on a second wire and again no spark. Where do I go from here?

[mysocal911]

Read here; 911 3.2 No-Start Troubleshooting

[Chsnsurf]

Thanks Dave. I’ll try those first steps from the link.

[ischmitz]

Confirm power to the DME with key in RUN (ICV needs to be vibrating). Check fuel pressure in the rails is present. Check for spark signals with a DVM across the primaries of the coil during cranking. If absent check FW sensors by unplugging DME and using a DVM or cheap oscilloscope on the pins in the 35-pin connector. Each sensor needs to show around 1kOhm. Then, crank and measure sensor voltages in AC mode. Speed sensor needs to read 2V - 3V AC and reference sensor needs to show some small voltage in AC mode while cranking.

If all that checks out it might be the DME itself. Ideally find a fellow 3.2 and swap the DME for a quick test. Either yours into the good car or the good DME into your car to see what happens.

For tools it makes sense to get a cheap pocket o-scope that will help tremendously for checking sensor outputs, spark pulses, fuel pulses and gets you pointed into the right direction quickly. They are under 35$.

For what it's worth I helped a friend yesterday to troubleshoot a 3.2 intermittent issue. He had gotten new FW sensors installed. Turned out the reference sensor failed open within a couple of weeks of being installed. Methodic troubleshooting is key.

[Chsnsurf]

Thanks Ischmitz. Part of the issue is also me. I’m learning all of this step by step. I’ve done basic car maintenance, but I really have no experience with electrical components/tools. Between what you have said and the link Dave posted I’ve got some learning to do.

[ischmitz]

There are many great resources here when you search for "no start" and DME and it'll be fun to get into this and learn how the 3.2 Motronic works. Fortunately, the system isn't all too complicated and doesn't require lots of special and expensive tools to diagnose. Follow the simple "it needs spark, fuel, and compression to run" idea.

Keep us posted on what you find and good luck

[darrin]

chsnsurf -- the cracked connector in your picture is the wire attached to your car's Speed Sensor -- a failed speed sensor and / or reference sensor would deprive the DME of the info it needs to allow the engine to start (as it wouldn't "think" the engine was cranking). The top connector is the Head temp sensor and the bottom one is the reference sensor.

[mysocal911]

Remember, basic engine troubleshooting begins with easy & simple tests - spark & fuel;

1. spark test - unplug the coil wire from the distributor & place it 10mm from the alternator housing
and observe while cranking
2. fuel test - spray carb cleaner or starter fluid into the air cleaner while cranking

Simple, less than a 5 minute effort! Next, follow the reference in post #4.

[Chsnsurf]

Ok so I tried with the noid light and coil plug by crankcase. No light and no spark. How do I go about the next steps? Any video tutorials? I have the Bentley manual, but some of it just isn’t clear to me. How do I know the placement for the multimeter pins on the DME plug or sensors?

[ischmitz]

Next smartest step is to get a cheap pocket oscilloscope for less than 30$ (eBay or Amazon) to test the flywheel sensors. You can get some limited information with a DVM (resistance and voltage in AC mode while cranking) but a definite test requires the o-scope.

Or if you want to throw parts at it you replace both sensors. BMW parts fit but be aware. Just a couple of weeks ago I helped a client and one of the new sensors was bad out of the box. So there is that. Diagnostics is still key.

Please don’t fall for “DME rebuilt” only to be told “I replaced an out-of-spec transistor but you have multiple faults”. The DME can go bad but there is 10:1 chance it’s one of the sensors before it’s the custom Bosch flywheel decoder IC inside the DME.

[ischmitz]

DME Wiring Diagram / Pin Out for 1986 ROW 3.2 (911.618.111.13)

See the pin diagram for the DME connector. Disconnect the DME and probe inside the 35-pin connector of the harness in OHM mode. Pin 25 - 26 is the reference sensor. And pin 8 -27 is the speed sensor. Both need to read around 900 - 1100 Ohm. Next, set the meter to AC voltage and measure the speed sensor while cranking. You need to see around 2-3 Volts AC. The reference sensor output is a lot smaller and the reading depends on the type of multimeter you have. It needs to show something but it can be as little at 0.2 Volts.

[Chsnsurf]

Ok. I’ll look into this info. Thanks. I connected the multimeter to the ignition coil like the Bentley said and have 12.6 volts when the key is turned.

[mysocal911]

Since you're using a voltmeter, check for 12V at the three edge/corner pins of the female DME connector with the ignition switch on.

[ischmitz]

You need to connect the positive lead to one of the screw terminals of the coil and the negative to a metal portion of the engine block and see 12V with ignition ON. Either terminal needs to show the same reading.

[Chsnsurf]

Ok. I checked the coil with the positive probe against the positive screw terminal and the negative probe against the metal bracket holding the coil. Ignition was on and 12v was shown.

[ischmitz]

That’s good. But you mentioned there are no ignition pulses and no fuel pulses. This requires you to check the flywheel sensors next.

[mysocal911]

Have you done the test in post #15, without it you're wasting your time?

[Chsnsurf]

Originally Posted by mysocal911

Have you done the test in post #15, without it you're wasting your time?

Working on it. Heading out to the garage here in a sec. Do I put the black (neg) probe in or the red (pos) probe in? Sorry. New to this.