Another no start issue no spark or fuel
 

85 911 3.2 Euro
I just drove it the day before. Ran great..now just cranks.
Tested
No spark ,put spark plug in the coil end and cranked it over nothing .
No fuel smell..fuel pump runs when jumped fuse 3/4.
Where to start? DME relay new last year.will this cause no spark and fuel if bad..ordering a new one.
If speed sensor and crank sensor are bad will this cause this issue.
Where should I start?

ICV humms with key on
12v to coil with key on

Hi Len,

Am kind of surprised you didn't get a reply - but yes, one of the potential causes of a no-start is is the Ref sensor is bad. The DME allows spark and fuel when you are starting. If the engine doesn't start (as verified by the Ref sensor reporting flywheel revs to the DME), the DME will not latch the DME relay power to the FP.

BMW makes the same type of Bosch sensors (available here) and they are usually a bit cheaper in cost and a tad longer in the pigtail. If the insulation is crumbling, that's a sign they're toast.

If you have the Bentley manual, there is a troubleshooting table there and posted here too, although let us know and someone will cough it up.

yup ,here is some reading for ya

Ivan
http://forums.pelicanparts.com/porsche-911-technical-forum/311570-3-2-sensor-question.html

I cranked the motor and the tach does not move or jump. does this mean anything ?

I will be ordering all new sensors and a new dme relay today from our host. is there anything else I should order ?

Might be worth checking the connections from the sensors (3 in a row left side). I had a similar issue and it was the connector. Pull out the safety guide and clean the connectors, resemble. Easy job, might be the fix. They work themselves apart over time and bad road conditions do not help either. I have mine tie wrapped.

^^^ That's good check for an '85 NO START given all else noted. I experienced same with my '85... a connection there working loose. Eventually the plastic casings dry... and crack apart. Connections to car are not made in this pic but junction location is shown.

http://forums.pelicanparts.com/uploa...1518734035.jpg

Put a jumper in the dme relay and fuel pump came on but did not start....damit....i ordered all new sensors and an extra relay.. we will see...
Keep the ideas coming..

do you have a Bentley shop manual? did you test the sensors? did you pull the connections mentioned before and clean, reseat them?

I believe the 3.2 crank sensors are a maintenance item after that many miles.

Good thing is they are cheap, relatively speaking, and can be found new.

When putting the new sensors back in do I need to put any lube or antiseize on them.

I can't recall using any - others may chime in - i reckon a little can't hurt.
If you can, just remove each of the sensors from their mounting bracket.
If they won't budge, hit them with some PB blaster.
Only remove the entire bracket if you have to work them on a bench, otherwise it will be a bit more work to set their gap wrt flywheel teeth. If you just remove the sensors alone, you won't need to be concerned about matching the gap.

I just replaced my sensors a month ago. Based on how stuck they were I smeared a little white lithium grease on the barrels before inserting into the bracket. For removal, agree with steely, avoid removing the bracket otherwise you have to worry about setting gap. I hit the old sensors with PB Blaster, twisted them out a bit and then more PB blaster. Used some pliers to twist the sensor back and forth while pulling out and eventually got them both out.

My sensors appeared to be original. Insulation breaking off with every touch.

These two sensors pass thru a grommet that belongs to the CHT. I replaced that too. I read a lot of horror stories of folks having difficultly getting the grommet reinserted but I got mine in in under a minute. I wiped dishwash liquid on the grommet and it popped right in.

It was a good day..the sensors came right out an I also made a socket to get the cylinder head temp switch out..ot was 14mm so I am guessing it was replaced at some point.. new sensors will be here Wednesday...fingers crossed

Glad to hear yours came out easily. My CHT was easy too. Hopefully you marked which plug went to the speed sensor and which to the ref sensor?

I asked this question on another thread but didn't see it answered -- Instead of proactively removing and replacing these sensors, couldn't one hook up a multimeter to the sensor plugs and monitor whether the sensors are, in fact, sending proper readings to the ECU? If they all are, sensors are fine. If one (or more) is not, they you've likely found your culprit. Assuming I'm on track here, what are the readings one should expect to see from each of these 3 sensors?

Hopefully the sensors were the cause of the no-start. If they aren't, the next step would be to try your DME in someone else's 3.2, to see if the problem is a cracked solder joint in the DME. (I would have done that before going after the sensors, based on personal experience.)

But, again, hopefully replacing the sensors will do the trick.

Not necessarily.

I had one of the sensors go goofy. It would work fine, then out of the blue go wonky and the engine would die. It would restart then die in a 100 feet. It was a heat related issue. Stone cold they were fine. Once hot one of them would just get stupid. I replaced them both. Problem solved.

Glen -- makes sense, but seems the OP's no start situation suggests that something's not working, period. My point here is that, rather than throw parts at the problem, the OP might/could start by checking measurements to rule out sources of the no-start situation. I.e. if the reference sensor is outputting the proper pulse at startup, it's likely not the cause of the no-start situation and replacing it would be unlikely to change the no-start situation.

You can measure the CHT out of circuit.
32F 4.4 – 6.8k
60-85F 1.4 – 3.6k
105F 1 – 1.3k
175F 250 - 390
212F 150 - 210
265F 90

The other 2 sensors can be read with a resistance check too (I don't have resistance values off-hand), but it's possible to get a good reading if they are intermittent. It is tricky to measure the in-circuit AC value (around 1-2 vpp), but you need the engine turning, and if they're disconnected or bad, the engine won't turn for you to get a reading - it is a minor catch-22 unless you have a breakout box and keep starting the engine.

The DME must see a good ref sensor signal in order for it to latch the fuel pump ON and enable the ignition.
In Len's case, he verified the FP relay worked to the FP, and he verified the DME worked by checking the ICV, so this is a good logical step if his sensors are original.