85 will not start

[911st]

Mabe someone can save me a lot of time with the search button.

My car always starts easily on first try.

Gas not been driven for a couple of weeks. We have had cool weather here and some rain but car is kept in.

Just went to start my car and it turned over very well but did not start. Battery seems strong.

Got down on all four and could detect some gas smell at the tail pipe.

Any thoughts?

Would there still be some gas smell at the tail pipe if the relay is out?

How can I check the relay?

All the fuses in the boot seem good.

????

[911st]

Also:

I have a half tank of gas.


Whan I turn on the key and touch the idle valve in the motor compartment, it is active. ----Dose this mean the DME relay is ok??

[lally911]

If its not the relay, then check the resistance for both the speed and reference sensors with your trusty multi-meter. When the speed sensor goes the motor will crank but will never fire. I think resistance should be 960 +/- 80 ohms but check Bentley's manual.

[scottb]

First place I'd look would be the DME relay. Conventional wisdom is that the question isn't if the DME relay will fail, only when. I replaced mine before it failed, and kept the old one in the glove box as a spare.

It couldn't hurt to replace the DME relay and see if that solves the problem. The worst that can happen is that you've replaced a part that would have failed eventually. The best that can happen is that it solves your problem quickly and relatively cheaply. If you do replace the relay and it solves the problem, you should consider buying a second one to keep in the glove box as a spare.

My $.02.

Let us know how it turns out! Good luck.

[ruf-porsche]

If you smell gas in the tail pipe, and the engine hasn't started you FLOODED the engine. remove the spark plugs, dry them out and try again.

[DRACO A5OG]

+1 on the Speed/Reference Sensor.

'84 buddy of mine just had the same issue, replaced reference sensor and bingo!

But before that swap the DME relay just incase, it is cheaper

[500_19B]

The gas smell sort of suggests the fuel pump is working, but nevertheless, a pooched fuel pump is possible. Happened on mine (also an '85) and was very sudden. Just would not start one day.

However, the DME or speed and reference sensors are very, very likely possibilities and easy to check first.

[ischmitz]

I recommend a search and some reading - this has been covered in great detail at least two times in the last couple of days here.

In summary, you need to do a systematic diagnosis rather than throwing parts at it - the standard answer of "change the DME relay" or "replace the sensors" doesn't make any sense without proper investigation. Most of that can be done easily without any special tools. A 3.2 DME is not very complicated. Here is a quick list of checks:

- check if you have power to the DME with the ignition to ON (ICV vibrates with the key to ON) if not it could be the DME relay or factory alarm if present

- verify that your fuel pump comes on during cranking (test light on the correct fuse), if not it could be a bad pump, fuse, or DME relay

- check if you have spark (old plug connected to one spark plug wire while an assistant cranks the engine), if not it could be a bad DME, or one of the sensors, check the sensor resistance to be close to 1000 Ohm.

- check whether you get fuel injector signals (LED test light while an assitant cranks). If not same as above.


If you get one but not the other it is either something downstream (coil, rotor, cap) or the DME but NOT the sensors

Finally, for more advanced checks you need a fuel pressure gauge, an oscilloscope. The engine should start even with cylinder head temp sensor being bad, O2 sensor being bad, AFM being bad but run badly. My guess from experience is that if you have fuel but no spark you either have a bad coil or a bad DME. Hope that helps,

Ingo

[911st]

You guys are great. I do not have time yet to work on it.

Can I test the sensors at the ECU connector under the seat. If so, anyone know which pins to test?

Will keep ya posted.

Thank you.

[ischmitz]

Yes you can. Disconnect the DME 35 pin connector and get a DVM.

For the reference sensor measure resistance between pins (25 - 26)
For the speed sensor measure resistance between pin (8 - 27)
Both need to measure around 1 kOhm

Next measure pin (25 - 5) and pin (8 - 5). Both need to be close to infinite. If you meaure anything less than 100k Ohm you have a short to GND.

Ingo

[911st]

Excellent!

Are the pins clearly marked or in what order to I count them?

THX.

[jlex]

One more (easy) thing to check: Is your battery fully powered up? These cars require a good electrical source to operate properly. The recent cold weather may have stressed a failing battery. Just for fun, hook up a set of jumper cables to another (running) auto & try cranking again...

regards

jlex.

[WERK I]

Is this a 911 or 930?

[jlex]

Posted by "scarcellar" on another no-start post that you may find useful:

"The Speed and Ref sensors are identical parts and if either fails you will not have coil primary drive pulses (no spark) or injector drive pulses (no fuel).

These 2 sensors often act up as they fail and result in intermittent starts and stalls.
Measure the resistance of both sensors they should read about 1000ohms +/- 20%. Mine read 900ohms on both.

The Cylinder Head Temp sensor even if shorted or opened you will still have spark and fuel.

First, at the Air Flow Meter test for 5 volts on the Blue/Green Stripe wire by pulling back the rubber boot at the harness. You must have 5v here with key in RUN car not running. This is very fast easy way to know the DME is alive and the DME Relay is engaged. Also with key in RUN engine not running you should feel the Idle Control Valve vibrate if you place your hand on it. It is located right in front of the Throttle Body.

The best way to test for spark and fuel is with a 12V LED test light, it MUST be an LED light as a standard bulb light will not work. Walmart sells one for about $5 in the Auto section.

Put the light across the '-' and '+' posts at the coil primary (not the hi-voltage wire!) leave coil connected and crank/start the car, the LED test light will flicker if you have coil pulses.

Then unplug and injector like cyl #1 and then put the test light across the 2 pins in the harness (leave harness disconnected from the injector) and once again crank/start and the LED will flicker.

Don't worry about connecting the test light backwards as it has 2 LEDS within it one RED one GREEN and green will light if connected one way and red if the other.

If you do not have coil or injector pulses you most likely have a bad ref or speed sensor"


regards,

jlex.

[Laneco]

We followed the advice given on this and the above referenced threads for a no-start 3.2

Found one of sensors read "open", but the other read 1k. Ordered the replacement sensor from our gracious host. It arrived today.

Steve put it in and the car fired first hit. Still have the CHT to install. We decided to upgrade it to the newer two-wire "while we were in there"...


THANK YOU for the advice!

angela

[ischmitz]

nice work - congratulations.

[jlex]

Good Deal.
Which sensor was it: reference or speed?
Also, where were you checking them at: the connector at the vertical holding plate in the engine compartment or at the DME?

regards,
jlex.

[scarceller]

911st,

If you smell fuel this means:
1) The DME Relay is fine
2) your DME is up and running
3) It also means Speed and Ref sensors are also OK.

Bottom line is you will NOT have any fuel at all if those 3 things are not working.

My guess is you may have a bad Cyl Head Temp sensor or poor fuel pressure/delivery or bad coil/spark.

Do these following tests:
1) First, clean your ground points real well, the ground strap at the battery and where it connects to the body. Then the strap at the front of the transmission. Then the ground at cyl #1 intake runner.
2) Test the AFM harness for 5volts with the key in 'RUN' engine off at the Blue/GreenStripe wire, simply pull back the rubber boot at the plug. If this has 5v the DME is alive and the relay is active.
3) With key in 'RUN' engine off the IdleControlValve should vibrate, you can feel it with your hand.
4) Put a LED test light across the coil '-' and '+' posts and while cranking the LED test light will flicker.
5) Unplug the cyl #1 injector harness and put the LED test light across the 2 pins in the injector harness, then crank the engine and the light will flicker.

If test 4 and 5 do not cause the light to flicker then you most likely have a bad speed or ref sensor, but if you have flicker then this means you have coil and injector pulses (which I bet you do because you smell fuel) bottom line is that a bad speed and/or ref sensor will result in NO coil or injector pulses.

Now, keep in mind that even if you have primary coil pulses you may not have hi-voltage at the coil. The coil could be bad or the cap and rotor are bad or wet inside.

Right now, from what you described I'm betting your DME and ref and speed sensors are good.

Then the cyl head temp sensor could cause flooding if it has broken and reads infinite resistance, when this happens the fuel mixture goes extremely rich. So test the resistance of the CHT sensor at room temp 68F it should read about 2500 ohms +/- 20% ballpark here.

[jlex]

[QUOTE=scarceller;4302978]911st,

If you smell fuel this means:
1) The DME Relay is fine
2) your DME is up and running
3) It also means Speed and Ref sensors are also OK.

He must not have smelled gas at the tailpipe since one of the sensors was bad... must have just been plain old stinky Porsche smell...

regards,

jlex.

[scarceller]

[QUOTE=jlex;4303123]

Originally Posted by scarceller

911st,

If you smell fuel this means:
1) The DME Relay is fine
2) your DME is up and running
3) It also means Speed and Ref sensors are also OK.

He must not have smelled gas at the tailpipe since one of the sensors was bad... must have just been plain old stinky Porsche smell...

regards,

jlex.

I'm confused now? 911st posted and started this thread, I have not seen him post that he has repaired the issue. What I did see is user Laneco (Angela) report they fixed a problem like this or is Angela also working on 911st problem, are they one in the same?