Another 'Intermittent Start' Problem
 

Hi All,

I'm a newbie to Porsche tinkering (and virgin post).

My problem is my 83 944 N/A will intermittently start. Once started it runs perfectly. Problem began at the beginning of the hot Ozzy summer (Oct07). After searching through the forum, I've run though the following (not in this order, I'm just typing as it comes into my head);

replaced the DME relay, checked the speed and timing ref signals with an o'scope (both within spec), checked the coil resistance. Jumped the fuel pump - it runs fine. Found that when the car doesn't start, that there is no spark (also no tacho bounce), cleaned up all the bad solder joints in the DME. Bench checked the condition of the Darlington transistor (in the DME) that drives the coil (it's O.K. - again, the car runs fine when it does start).

Recently found that I can make the car start by disconnecting the speed sensor (in the engine bay) and reconnecting it. Replaced the three pin connector on the engine wiring harness for both the speed and ref sensors (both sensors are 6 months old). Checked the continuity of the engine wiring harness back to the DME - it's O.K. Suspect a ground problem. Have cleaned the grounds down by the speed & ref sensors on the engine. Problem still exists, but still suspect a ground problem - Slowly going through and cleaning them all.

Any one else have seen this before, and have any other suggestions?

The problem may be the sensor itself. Specifically the magnet that screws into the clutch bellhousing. Try replacing the whole sensor. Expensive, but will probably fix the problem after everything you've tried.

Welcome to the forum....glad you are here.

For someone just starting to tinker, you've checked a lot of the right stuff.

Usually when the tach doesn't jump, it's the sensor. I'm wondering if the gap is barely in spec, but I really think the connector is the problem. Tighten the friction to make sure you have a solid connection there. Clean the connectors and coat them with dielectric grease. Did you check them with the oscilloscope when it was running or dead? Could still be the DME though.

'For someone just starting to tinker, you've checked a lot of the right stuff.'

Thanks to this forum and places like clarks garage, Bills 944 World, etc.


One thing I neglected to mention is that I swapped the speed and reference sensors - the problem didn't go away. It's unlikely that I've got two new bad sensors (not discounting anything though. After six months, I'm at my wits end).

Also, not totally discounting the DME. I did also neglect to mention that I tried starting the car with the DME open and hitting all the semiconductors with a blast of zero freeze. It didn't change anything either. Has anyone got a schematic for a ML1.1 DME, I could then properly bench check it.

I haven't yet verified the sensor gap - although the signal on the o'scope is strong at almost 3Vpp (running or dead there's no change) . Sort of indicates that it's O.K. I'm hopefully swapping out the oil separator this weekend (if the parts arrive). I'll verify the gap at the same time.

The last thing I did was to slightly bend the male pins 8 & 27 on the sensor cable, so that when they mated with the females, it would make a tighter connection. The car has been starting flawlessly for the past two days (I've had it working for two weeks before a failure - I'm not holding my breath yet). Time will tell.

I'd appreciate any more thought/ideas.

Cheers,
Jeff

G'day mate and welcome to the boards!

I believe your problem with starting had to do with the connectors for the engine harness, DME plug to the reference/speed sensors.
One of my restoration projects involved the same type of issues and it turned out to be the connections there.

I ordered some new connectors from Atlanta Auto, they do Porsche 944 parts really well.

Good luck with the car and happy driving.SmileWavy

Whoops! *********** is the proper name...you can Google them and see.

There just happens to be a Atlanta Auto, but that is NOT who I meant.
Sorry about that.

G'day all,

Thanks guys for the help so far.

Ed, I purchased my AMP connectors from EagleDay.com. Perhaps the connectors from *********** are a better quality? I'll see how long the current fix lasts - 3 days now and all is well (I shouldn't put the moz on it, should I).

Cheers,
Jeff

If it quits, then you can always put an ohm meter on both sides of the connector to make sure you have a strong connection there. Sure sounds like that is the problem but it's so hard to tell.

Do you know the part number of your DME?

DME is;

Bosch 0 261 200 016
Porsche 944 618 111 02

Thanks...let us know if it keeps failing..might have a spare DME to loan you but I'll have to check the numbers.

Yes! That is great.

AMP is ultimately the supplier of the best connectors in the electronics industry, IMHO, so you did good there.
I think/hope it solved the problem since three (days) out of three is very good statistically.

Crap! I couldn't get it to start this afternoon without doing the disconnect/reconnect thing.

On the brighter side, the parts arrived to swap out the Oil Separator - I know what I'll be doing in the morning......

I'll probably tinker with the sensor again and see what I can come up with next.

I'll let you all know how it goes.

Cheers,
Jeff

I have a similar problem with my 83 944... With mine I find that it will try to fire as the engine first turns over, but then will not even try to fire no matter how long you keep it cranking.. turn the ignition back to "off" and then try again and it does the same thing again.

A few times I got it started by litterally flicking it into the start position and then back to the ignition position quickly... often it will catch, fire and die, then eventually it slowly splutters into life and after a few seconds runs fine.

Got good compression, good leakdown, 2 new sensors, new ignition switch, plugs getting wet and it seems I am getting a spark only for the first split second of cranking the engine.

Have also tried a friends ECU, used a jumper leak to make sure the engine is earthed to chassis, changed the DME relay and tried all kinds of things.

Is this anything like your problem? anyone else seen anything like this??

His is a bit different in that his tach doesn't bounce indicating some type problem with the sensor. Yours sounds more like a ground problem.

harness wiggle
 

I have the same problem! except I just have to wiggle the sensor harness a bit and the spark comes back! It doesn't make any sense! I tightened the connector and put dielectric grease on it and it still does the same thing. It happens every couple of days. I feel your pain.

Sarbirus,

Your problem is a little different, as when my car stars it runs flawlessly.

To me it sounds like you have one of two possibilities;
1. No fuel pressure, or
2. A bad coil.

I gather you've also checked your rotor/distributor and plug leads? Plug leads should be no more than 10k ohms.

Jeff

UomoBello,

When I eventually find the problem, I'll let you (and everyone else) know.

Happy hunting.

Jeff

The tach not bouncing can be a bad connection at the + battery terminal, and or up into the shielding. When you are jiggling the connectors, might you be placing you hand on the wiring loom?

I encased those two connectors in aquarium sealer.

Saribus, it sounds like your ignition switch is toast. Does the radio power up when the key is inserted? If it's an 83 and it doesn't there is something wrong with the switch. $12 plastic part.

id try ign sw on both cases for $12 worst that can happen is you have a spare....

Good suggestions. Looking into the harness.

I checked my ign sw. It's functioning perfectly. It's a good suggestion though.

Sarbirus, the ign sw provides 12V to the coil in both the start & on positions. It may be that you have 12V in the start position, but not in the on position.

Jeff

cool. when you have the no start condition check the sensor signal at the dme plug, which will verify or rule out the harness cause thats what its looking like.
lindsay racing has a nice section on the dme plug sensor upgrade

Thinking about it, I am not sure if my rev counter does bounce when I try to start her up..

I tried a new ignition switch, no joy..

I've got a new fix action (I don't play with the speed sensor plug anymore).

If I spray the relay/fuse panel under the dash with zero freeze when I have the no start condition (no tach bounce), the tach will bounce and it'll start.

I think I have a dodgy connection around this area. Getting close to finding the fault....finally!

Cheers,
Jeff

My Son's car 83 944 always have that kind off problem sometime it could go weeks, with no problem starting. I have tried almost everything there is to check. speed sensor /ref. sensor cap rotor coil vacuum lines, even getting the DME rebuild. First I tough I got it fix, by replacing the speed sensor & ref. sensor connector from Radio Shack. The original connector crumble from age. It turn out to be the connector on top off the booster brake, there is two connector 2 & 9 wire connector. On the 9 wire connector I found the wire (red/yellow) has been soldier together and the housing is melted a little (burn mark on the plastic casing. It just started again last week the car will not start (maybe it knows I wanted to sell it). Since my Son have upgrade his Car to a 87 944S. But then again since He live at home, I most likely have to deal with all the repair on His car, beside my own 944's . Anyway take a good look at the connector (2/9 wire).
Good Luck

-----------------------------
Bud

87 930 black
86 951 black
87 944S white
86 944 N/A Guards Red totaled
83 944 N/A white Auto
83 944 N/A black

Thanks Bud,

I know the connectors your talking about. I've given them a clean.

Cheers,
Jeff

Don't know if it's the root of my problem, but it certainly can't be helping.

I discovered today that my ingnition switch is intermittent.

Time for another parts order....

Finally got around to replacing the sensor harness with one from Lindsay Racing.

Now we, hurry up and wait!

Crap! Well, the harness is not the fault. The DME is next on the list. Bugger!

Well, I couldn't yet convince myself that it's the DME. Although, I came close to getting a refurbished one. The Aussie ones are not as common as the US or UK ones, although they would probably still work. But, they made Aussie DME's for a reason, don't know what that reason is...... Anyway, I not yet comfortable with the idea of parting with another $500. So today, I clanged the speed sensor, I got the Beamer 6 series one so often discussed (at half the price).

It worked a treat. The car started up no worries. Now we play the waiting game again......

My 83 used to do exactly the same thing. I used multiple nylon Ty-Raps to cinch up the sensor connectors very tight at the bracket until I replaced them with new connectors, AMP also. The Ty-Raps worked perfectly for 6 months though.

Clear silicon has been insulating those connectors for 12-13 years on my end. The bracket is no longer used.

I've been having an intermittent start issue with my 1987 924s for the past 2 years. I've replaced the DME relay, ignition coil, and DME computer, but the car still would only start when it wants to. Over the past month, I've noticed that whenever the car didn't want to start, it would always "pop start" with the clutch(this is why I've been parking it on inclines lately). I just now remembered a similar issue I had years ago with a Buick I had owned at the time. Even though it's starter whirled over fairly rapid, it was dragging just enough to deprive the ECM of vital current to ensure proper spark/fuel while starting. Despite turning over vigorously, I have noticed my Porsche starter lacks that new starter "zip", and has a characteristically deep, aged sound to it. I'm almost certain this is the cause of my issue! ;)

Yeah, my starter was also a little sluggish before I cleaned all my power and ground connections. My battery was only getting 12.9V from my alternator ATT. After all the cleaning, I now get 14.2V from my alternator and starting is strong.

The starter is scheduled for a overhaul anyway, the idiot PO has cross threaded the terminals on the starter. While they are being replaced I'll have the whole thing rebuilt.

So far she's been starting every time since the sensor change. Keeping my fingers crossed.

Cheers

Outback, is your car still having the problem after replacing the sensors? I have this exact problem and want to make sure that this fixed your problem before investing in a new pair.

Hi Razor,

The sensor only went in a couple of days ago (Sunday afternoon). It's too early to tell. My fault can disappear for a week, then return every day.

I replaced mine with the BMW 635i sensor (Bosch). The only difference is the tail on the sensor is longer. It's half the price of the genuine Bosch sensor.

Cheers

I noticed my car wont charge at an idle, I've replaced the rectifier in the alternator, but it still has this issue. Exactly what power and ground connections did you clean on your car? I've cleaned my battery terminals.

Clean;

Battery terminals and posts
Alternator terminals and posts
Starter motor terminals and posts
Chassis Grounds (engine bay and dash)
Engine grounds (bell housing)
Fuse terminals

I also cleaned the 9pin and 2pin connectors on the firewall, and the connectors/terminals for the AFM, TPS, AAV & both temp sensors.

The OPS also got a clean up while I was fault finding my OPG and the injectors connectors recently got a clean up when then new injectors went in yesterday.

Cheers

Five days now and all is well.

Giving it the ultimate test.......my 17 year old son has taken the car to school today.

I'm trying to bring my son's 84 944 back to life and have the same no start problems. The car has sat for 2 years, but when last run, had the intermittent no start that seemed to be related to the sensor connections. Thinking about the discussion on grounds, I remember that the radio would loose it's memory after about 10 minutes of sitting. I always suspected that it happened because of a bad ground somewhere, and now I'm wondering if that might be contributing to the no start problem.

Dave

Hi Dave,

It's possible that the grounds are an issue. It's worth cleaning them anyway. A lot of other things work better when you do (like your instruments tell the truth).

Cleaning the grounds didn't help my intermittent start problem but I'm glad I did it anyway.

I'm also glad I replaced the sensor harness with the Lindsay Racing harness. The original harness was hard and brittle and I kept breaking wires when manipulating it. The Lindsay harness is definitely a quality product and worth the $125.

And my boy didn't manage to break anything when he took the car to school yesterday. It's probably too early to call it yet, but I'm looking up.

Cheers