at wits end...

[Skytrooper]

I have poured over the "won't start" threads, Clarks Garage, and anything else I could find. I have tried innumberable fixes and nothing works.

My '83 944 just will not start most of the time. I have replaced the DME comp, virtually every relay and fuse, battery, speed and reference sensors, fuel pump and check valve, ignition coil, dist cap, rotor and wires....blah, blah....and the dang thing will still only start when it wants to. No rhyme or reason

I am out of options...has anybody had this kind of crazy experience ? When it does start it fires right up and runs great.

[Rasta Monsta]

What's missing when it doesn't fire? Is it getting appropriate fuel pressure at every start attempt?

[minho78]

Before you replaced everything try some simple tests. First buy a spark tester and see if you get Spark or check voltage at the coil. Then check for fuel pressure? I think it should be around 29 PSI at idle(check Clark's garage). That no start maybe related to a bad harness(when cranking shake the Speed and Reference sensor harness(bad connector). Another thing may be a bad ignition switch.

[Tishabet]

Originally Posted by Rasta Monsta

What's missing when it doesn't fire?

Exactly... you must have more info than this. When it does not fire up, are you getting spark? Are you getting fuel?

[Skytrooper]

Replacing was cheap...I used the parts on my 924S. New ignition as of November 2008.

Please remember....this is a very random intermittant problem. Sometimes the car fires right up....most times it doesn't. When it starts it run great.....hence the confusion and frustration.

[Skytrooper]

Originally Posted by Tishabet

Exactly... you must have more info than this. When it does not fire up, are you getting spark? Are you getting fuel?

Yes, I am getting spark, and fuel. I have done the fuel flow test (as outlined on Clarks Garage) several times. Spark is easy to see.

[Grandad#3]

Well I was going to suggest the ignition switch module forward of the key. Mine went bad on me and I like to never found the reason for no start. It was like the car had a mind of its own. It would seem to start when it felt like it and not at other times.

Let start a NO START checklist

--------------------------------------------------------------------------------

Let's see what we need to start our cars. I am trying this off the top of my head so please correct or chime in with your experiences so it may help someone else.

Air/fuel/spark/compression
start by making sure we have a battery that is in spec.
all fluids topped off
no obvious broken wires and all vaccum hoses intact on visual inspection.
OK we have 12v at the battery with adequated cranking voltage we get in and turn the key.
12v from battery to ignition switch
12v from pin 50 on switch to pin 4 on dme plug (start signal)
12v on pins 1 (ignition pulse to ign. coil) and 18 (to G5 dme relay power supply)
12v pin 30 at dme relay (fuel pump power supply)
12v to pin 86 at dme relay in the run position (primary coil voltage)
12v to coil + black wire to ground 12v to - (green wire) to ground
12v to one side of the injectors
All ground contacts are clean
Fuel pump will run if dme relay is jumpered 30/87/87b
Fuel pressure at the rail is 29psig +/- 3 (jumpered 36 psig)
20 minute leakdown not under 14.5 psig
Fuel flow rate is 28oz after 30 seconds
Ignition coil primary resistance across + and - is between .4 and .6 ohms
Secondary resistance is between 5000 and 7200 ohms
Ignition wires are good no cracks or splits including coil wire and seated
Plugs are properly gapped
Ignition rotor is seated correctly with the set screw
Timing belt is installed correctly
Firing order is correct
Reference sensors are gapped correctly with .8mm clearance off the flywheel
Reference and speed sensors resistance checks in spec pins 8 and 27 speed 600-1600 ohms and pins 8 and 23 >1m ohm
Reference and speed sensors voltage checks 2.5 and 2v on oscilliscope (good luck)
Reference and speed sensor wiring is not broken at connector to sensor or to dme
Ok Im tired anyone else want to add or be more specific?

John_AZ
Do a compresion test.
Reference sensor tach bounce when attempting to start the engine. The tach bounce is very slight-1/16 of an inch. Clean connections as mentioned above.
Injector "noid" light. Very basic tool but will tell you if the DME is sending a signal to the injector. An oscilloscope is the best.
Clean connections at major parts like AFM, ISV, throttle body.
__________________

Cheers,
Larry

[Outback Porsche]

Originally Posted by Skytrooper

...has anybody had this kind of crazy experience ? When it does start it fires right up and runs great.

Yep, I had this experience with my '83 - frustrating! http://forums.pelicanparts.com/porsche-924-944-968-technical-forum/398896-another-intermittent-start-problem.html

Agree with Larry, John_AZ gives good advice. Go through the list.

+1 for cleaning grounds, and check wire continuity.

Lindsay Racing have a good product in their replacement wiring harnesses if you need to replace them.

Cheers

[Skytrooper]

Damn car fired right up when I got home from work. Ran a few errands...all is good. The real test will be if it starts in the morning.

[rberry951]

These cars suffer from corrosion on the underside of the fuse panel, to the point it can eventually 'push' connections loose. Take it out, turn it upside down, if it's all corroded go over every single plug with a wire brushe, unplug them one at a time or you'll have a real mess on your hands. Oh, and try very hard not to break any brittle wires in the process. Experience has also taught me that as soon as you take it out and turn it upside down it's a good idea to take a picture of it. And keep it handy. Sometimes the wires pop off on their own...

Regards,
Russell

[Grandad#3]

Make sure you disconnect the battery before messing around with the fuse panel.

Cheers,
Larry

[Skytrooper]

Car fired right up and ran great going to work. We'll see at quitting time.

One thing I forgot to mention is that usually when it won't start, if I put the battery charger on ...it will. The battery is new and I have trickle charged it several times because of this strange behavior...not that it needed it, but for some reason just that little extra kick seems to help.

[exitwound]

You need air/spark/fuel to run. When it's not starting, check them independently of one another. I get intermittant spark due to high resistance in the female end of the speed sensor ONLY after it rains. I have to pop the hood, wiggle the sensor wire, and it starts right up. I diagnosed this by tearing apart the equation and saw that there was no spark (via a spark tester). It was intermittant though and took weeks of tests.

[AKCJ]

Great advice has already been given.

Two things I would do first.

1. Install a fuel pressure gauge on the front of the fuel rail. That way if it won't start you will know for sure if you have fuel pressure or not. If you do you can eliminate the fuel pump and the rest of the fuel system and the electrics required to make the pump run.

2. Get in the habit of checking the battery voltage before starting the car. Could be battery or charging system problem and it's possible that the battery isn't quite providing enough juice to start. You may be able to determine that if the battery voltage is 12.5 the car will start but if it's 12.3 the car will crank but not well enough to start. It's unlikely but you've already looked at some of the likely stuff.

Also clean the electrical connection to the AFM. I found mine was pretty bad. I wouldn't think this would cause the starting problem but it couldn't hurt.

Let us know when you find it.

[wild man]

The next time it doesn't start, try messing with the connector (jiggle, unplug, replug, etc.) where the fuel pump connects to the car's wiring harness.

[Skytrooper]

Well, I'm back..

Things went well for a couple of days, now it is back to its shenanigans. This time however the tach doesn't bounce....Grrr

[Outback Porsche]

This just sounds so familiar.

I'll bet that if you disconnect/reconnect your speed sensor, the car will again start.

Cheers,

[mr.944]

Next time your car doesn't start try opening and shutting your doors. If the car starts after doing this, check to make sure the door jam switches are not stuck in the door closed position. If they are stuck on one side or the other it could be messing with the alarm module. It will give the symptoms of a bad crank sensor and you'll have no spark and no fuel. Which this wont help you if your car doesn't have a factory alarm. I had an intermittent no start on my S2 for the first 3 years I owned it and I just happened to check this and the door jamb switch on the passenger side was stuck in the door closed position and was messing with the alarm. Also you can try the alarm bypassing procedure on clarkes-garage.com.

[Skytrooper]

No alarm on this one.

Nope, diconnecting and reconnecting speed sensor didn't do it.

Disconnected and reconnected all sensors...no dice

Put battery charger on and turned key...vrooom...it starts

Gol dang car !

[mattdavis11]

It's the power lead (DME, red) from the positive terminal on the battery. Cut the sheath back to see how much needs to be mended.