85 Carrera no start problem

911231 · 09-03-2010, 03:03 PM

I have been chasing down a no start on my 85 Carrera 3.2 for the past couple of weeks. It is a 65000 mile car and I am the second owner but it was owned by a friend since new and is stock. I have had it about a year and had been replacing wear items slowly. It has always started easily and run strong, no oil leaks no problems I had replaced the fuel pump and O2 sensor when doing an AC upgrade earlier this summer using Griffiths kit because I was in the area and had been driving it daily until about a month ago when one morning it simply wouldn't start. Pushed it around to the garage where it sat until last weekend. I searched and read all 3.2 no start threads and have now replaced speed and ref sensors,cht sensor, dme relay, and done all electrical checks recomended in threads by Loren et al.. I have sent ecu to Steve Wong which checked out fine (I did have him add one of his chips)
Diagnostics so far are
Voltage to ecm at 18 and 35 12.5v
Main grounds 5,16,17,19 intact
Fuel pump runs audibly when relay is bypassed
ignition coil 12.5 v with key in run
starter input 4 12.5 v
full throttle swith and idle switch functioning properly
idle speed control valve 33 34 44 ohms
crankshaft speed sensor 8 an 27 1037 kohm 3 vac when cranking
ref sensor 25 26 1046 k ohm .045vac when cranking
cht 1602
fuel injector control 14 and 15 to ground audible clicking in engine bay
Coil within spec by Bentley
rotor and cap new.
When grounding a n spare plug to intake I do not see a spark
After cranking I do not smell gas

BUT
in desperation today i sprayed starting fluid into air intake and it started right up and ran smoothly and revs easily. But turn it off and it won't restart until another puff of starting fluid.

I am at loss of where to check next. I am thinking AFM or ICV

I would welcome any and all input

Thanks Al

85 3.2 Carrera
72 S Targa in process of rebuild with 2.7 rs mfi
65 C coupe

911231 · 09-03-2010, 05:20 PM

as I have been thinking about this my understanding of the start sequence is that the dme relay recieves a signal from the starter solenoid to turn the fuel pump on when the engine cranks and then the dme provides a signal that the engine is running to keep the fuel pump on once it starts. Lack of gas smell after cranking indicates lack of signal from starter but ability to run after starting with ether means dme is sending signal that the engine is running. so the fault is the origination point for the signal from the starter whatever that is. does that make sense or is it just my cigar blowing smoke? Do I look for a wire to the starter. I have tried 2 different relays.
thanks Al

rusnak · 09-03-2010, 08:13 PM

What voltage are you getting at the icv, and on an injector connector?

ischmitz · ischmitz's Garage

The same yellow wire that energizes the starter soleniod when the key is turned to START also is going to the DME. It is on pin 4. Inside the DME is an OR stage. One input is the signal from the yellow wire and the other is from the CPU when it detects flywheel movement. The output drives the DME relay (2nd stage)

Try to measure the voltage at the fuse for the fuse pump in the trunk while someone else cranks. This should tell you if it is the fuel pump not coming on during cranking. If there is nothing, disconnect the DME and measure inside the DME connector on pin 4 while cranking. You should see +12V there during cranking.

Ingo

911231 · 09-04-2010, 03:54 AM

Thank you for the responses
12.4 V at fuel pump when relay is bypassed
11.4 V at fuel pump when cranking
12.4 V at pin 4 when cranking
12.4 V at icv
0 V at injector connector when cranking

After starting with ether
.1-.2 V at injection connector varying with throttle position

Thanks Al

mackskibum · 05:18 AM

Alarm module?

Look up alarm module bypass...

disarm factory alarm?

To get you started.

911231 · 09-04-2010, 05:48 AM

no factory alarm or aftermarket alarm that I can find or in the service records of which I have all

911231 · 09-04-2010, 06:11 AM

Additionally there is + V at the injector plug with the ignition turned on

mackskibum · 09-04-2010, 06:46 AM

I thought that the factory alarm was standard equipment, although I could be wrong. If it has one, the key switch for it is on the latch end of the driver's door, and the module will be behind the trim panel and vents in the luggage compartment. You seem to have checked everything else.

One additional question- will the engine run with the fuel pump circuit jumpered? You said the pump will run, but did not indicate if the engine will run.

911231 · 09-04-2010, 06:50 AM

In reading back over no start threads I see different numbers for speed and ref sensor cranking V. Post 64 in the stranded thread says 2 V ref and 2.5 Sine wave on the sensor. post 266 says 8 and 27 (speed) 2 VAC and 25 and 26 .1 VAC. My speed sensor is 3 VAC and Ref .045 measured on a Fluke 23. I don't have a scope. But as I understand things there will be no start, even with ether, if there is no initial signal from the ref sensor and after start the ref sensor is not used. This makes me think that even though the V is low on the ref sensor that it is functioning or there would not be starting under any circumstance. What do you think? I am going all connections again

911231 · 09-04-2010, 06:55 AM

No key on door jam and engine runs beautifully once started with ether which seems to indicate that the pump is functioning properly

911231 · 09-04-2010, 07:20 AM

ECM has been bench tested and road tested by Steve Wong and is ok

kidrock · 09-04-2010, 08:08 AM

Quote:

Originally Posted by 911231

No key on door jam and engine runs beautifully once started with ether which seems to indicate that the pump is functioning properly

Does the engine run after being injected with ether, then quit after a few seconds?

techweenie · techweenie's Garage

I had a mystery 'random no start' condition on my '85 Carrera with many varying casual diagnoses. Turned out to be the pass-through connector between the ignition switch and main wiring harness. Under the dash and forward of the ignition switch, there are three plugs that pass current through the sheetmetal panel. Unplug/replug them. May not be the problem, but it's the easiest thing to do, and you can eliminate the possibility.

911231 · 09-04-2010, 10:08 AM

Engine runs until I turn it off after starting with ether. Revs smoothly with hesitation or misses.
I will check the pass thru connectors

techweenie · techweenie's Garage

I had the same situation. Would start & run relatively reliably when cold, but would not re-start when warm. Completely counterintuitive, I know, but the pass-through plugs solved it.

911231 · 09-04-2010, 11:03 AM

checked pass thru plugs and still no start

911231 · 09-04-2010, 06:02 PM

Correction: after ether into intake engine runs until turned off WITHOUT hesitation or misses. Runs perfectly until key is turned off but will not start without ether because injectors are not opening while cranking only after start up with the ether.

ischmitz · ischmitz's Garage

Can you think of any preceeding event other than what you descibred (changed fuel pump)? I am wondering if there is any chance your check valve isn't holding fuel pressure. I don't know fure sure but believe it is part of the fuel pump.

I simply can not see an electric reason why the fuel injectors would not inject during cranking but work fine once the engine is helped by the ether. I assume you haven't done anything to the wiring and have a battery in reasonable condition.

ingo

jlex · jlex's Garage

Instead of priming it with ether, try priming it with fuel by jumpering the fuel pump and letting it run for a bit to send gas thru the system, then try starting. Ischmitz may have something there... pressure the system up first to see if that check valve on your new pump is kaput.