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I give up, this 924 has kicked my butt.

Hello,

I have a well taken care of 1987 924s, the car ran fine until recently when it started cutting off on me and would not start until I let it sit for more than 20 minutes. The car also had an overheating problem, the culprit was a bad fan motor, I replaced the fan with an aftermarket one. The overheating problem dissappeared and I drove the car around for a while until one day when it would no longer start. It would crank, but would not turn over. I can hear the fuel pump but there is no spark. I have replaced the coil, the spark plug wires, the dist cap and the rotor button and the car still won't start. I even removed the DME relay and substituted it with a jumper wire to see if it would start, no luck. I also did this to see if the relay was bad. I've bought the factory manuals and George Hussey's 924 tech tips and still cannot get this beautiful monster started.

I would appreciate any help u can give me on where to get started in fixing this problem and no it doesn't show any signs of having a blown head gasket.

Thank you.
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1980 Porsche 928
1987 Porsche 924s
Old 12-30-2005, 02:39 PM
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check your speed and reff sensors
http://www.clarks-garage.com/shop-manual/elect-19.htm
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SOLD 1984 944 NA, Fr Wilk PowerProm, rebuilt engine, blisten shocks front and rear, 220lb springs, adjustable 968 rear sway bar SOLD
Old 12-30-2005, 02:52 PM
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That would be my guess. Does your fuel milage gauge move when you are cranking? When my speed/ref sensor was going bad, and I was having an intermittant no-start problem, if the needle wouldn't move when cranking, my car wouldn't start.
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Old 12-30-2005, 04:46 PM
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Had the same problem with my 951. I hate sensors....they make no sense sometimes!!

Ref sensor is the culprit.....willing to bet on it.
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Old 12-30-2005, 06:36 PM
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Thanks for the prompt replies, my fuel gauge moves when I try to crank the car, but I will double check those sensors. I guess the cdrom factory manual I bought must be an old one because it does not have those pages you linked me too, it says they are under construction.

Thanks again, pls keep the suggestions coming, eventually thru elimination I should find the problem.
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Old 12-30-2005, 06:56 PM
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Do you think the DME computer could have anything to do with this? I keep having visions of some evil ghost in the machine lurking in the computer and telling it to give no spark.


Can the DME computer give a signal for no spark. From reading the manuals it seems like the DME is dependent on getting signals, could not getting a correct signal from some part of the engine cause the no start problem.
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Old 12-30-2005, 07:01 PM
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I read the shop manual about the speed and reference sensors and it stated a good sign the sensors were bad was if the tach doesn't move. This might indicate a sensor problem or a bad dme computer. The tach doesn't move when I try to crank the car. I looked at the sensors and noticed the wiring from the sensor plug connector doesn't look so good, it has split apart and is showing the wiring.

I don't know how to test the sensors, I've never used an oscilloscope or multimeter before, but hopefully this is the culprit.

Thanks, keep the info coming, it's really appreciated.
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Old 12-31-2005, 08:51 AM
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Basic electrical testing.

With the key on:

Battery voltage at the coil; ingintion switch.

Battery voltage at the injectors; ingintion switch turning on the first contacts in the DME relay.

Spark; take off the first spark plug wire, insert a spare plug, lay it on the intake maifold, crank the car checking for spark. Spark is generated by the reference sensor sending it's signal to the DME and the DME triggering (grounding) the coil.

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

In most cases the DME/fuel pump relay is kaput. You can bypass the relay one of two ways. Either make the bifracated jumper that replaces the relay or use a jumper from the battery to the coil and a jumper from aux fuse #2 to aux fuse #3.

The reference sensor could be at fault. Could have metalic grit build up, out of adjustment or cracked wiring.

As to over heating; you need to bleed the system using the vent at the top radiator hose connection to the block. Not doing so leaves an air pocket that will continue to cause problems. Also look to a slight leak in ALL of the coolent hoses.

If your stock fans have three blades you might want to find a set of the six blade fans. These have sealed bearings that do not rust and sieze up.
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Old 12-31-2005, 08:54 AM
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Ok,

I have taken the bolts out of the speed sensor and reference sensor, but the sensors won't come out, I've tried rocking them back and forth, but they won't budge. I put a metal bar on one of them and tried tapping gently with a mallet but they won't move, any suggestions on how to remove them would be greatly appreciated.
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Old 01-05-2006, 10:49 AM
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Have to remove the bracket and soak the sensors with PB Blaster. May also have to heat the bracket to get the sensors loose.

But before you go further check their resistance from the center pin to one of the side pins. From .6 to 1.6k ohms. The center to the other side is the shield and should be more than 1M ohms.

If the resistance checks out then you only need to remove the rear most sensor to check the clearance. Still may have to remove the bracket to loosen the sensor. Be darn careful or you will be buying a new sensor.
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Hugh - So Cal 83 944 Driver Person
NOT a 'real' Porsche -- Its Better!!!!
When was the last time you changed your timing and balance belts and/or cam chain and tensioner?
New Users please add your car's year and model to your signature line!
Never break more than you fix!
Old 01-05-2006, 11:39 AM
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Quote:
Originally posted by akinvan3
Ok,

I have taken the bolts out of the speed sensor and reference sensor, but the sensors won't come out, I've tried rocking them back and forth, but they won't budge. I put a metal bar on one of them and tried tapping gently with a mallet but they won't move, any suggestions on how to remove them would be greatly appreciated.
I feel your pain - I had the same problem a long time back with a speed sensor. Turned out mine wouldn't budge because the gap was poorly adjusted and the starter ring had clouted the sensor - deforming it and rendering removal impossible without taking the bracket off and pulling the sensor apart. If that's happened to you you should keep the old plastic sensor case - tap it for an 8 mm bolt and use it as an aid to adjust the gap (thread it in the same length as the sensor case). Much better than the haynes manual wheeze of gluing a washer on the bottom of a sensor when setting the retaining bracket.
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1983 944 Lux (manual) 2.5 litre 8 valve na and no pas

1991 944 (automatic) 2.7 litre 16 valve na and pas

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Old 01-05-2006, 03:13 PM
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Hello again,

Sorry for this, but I can't find any specifics in the manual on how to get the bracket out, I can only see one bolt and it doesn't look like it's holding the bracket.

Thanks in advance
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Old 01-05-2006, 04:49 PM
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Use a mirror. There are two bolts. To adjust the sensors you have to loosen both.
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When was the last time you changed your timing and balance belts and/or cam chain and tensioner?
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Old 01-05-2006, 04:56 PM
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To get mine out all I had to do was pull my bellhousing. Then I was able to use a hammer and remove the stuck sensor from the bracket. I couldn't pull the bracket with the sensor inside. I don't understand why the bracket needs to be adjustable in the first place.
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'86na, 5-spd, turbo front brakes, bad paint, poor turbo nose bolt-on, early sunroof switch set-up that doesn't work.

Malo periculosam, libertatem quam quietam servitutem.
Old 01-05-2006, 04:57 PM
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Quote:
Originally posted by akinvan3
Hello again,

Sorry for this, but I can't find any specifics in the manual on how to get the bracket out, I can only see one bolt and it doesn't look like it's holding the bracket.

Thanks in advance
There should be two M8 caphead screws holding the bracket - at 90 degrees to the sensors. Difficult to see AND get to. One is a pivot for the bracket whilst the other is a retainer to hold it in place. The latter runs in an arced slot so the bracket can be slightly rotated to set the gap between the starter ring and sensor. They can be quite tight.
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1983 944 Lux (manual) 2.5 litre 8 valve na and no pas

1991 944 (automatic) 2.7 litre 16 valve na and pas

"I have only five words for you: From my cold, dead hands."

Last edited by Dark Skies; 01-05-2006 at 05:12 PM..
Old 01-05-2006, 05:08 PM
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