1989 C2 starting Problems

[sourcandy]

My father owns a 1989 911 C2. On his way back from work it just died on him and refused to start again. It gave him warnings on his way to work however, it shut down twice, but let him start it again and get to work. Anyway, had it towed home and began diagnosing it.

Went through one of the manuals we have checking things, at first thinking it was a bad rotor, so we bought new rotor, cap and coil. NO fix, read the manual again, trying to test the speed and reference sensors, but we can't get the ohm readings it specifies, So he replaced those. Still doesn't start and no spark. So we called an old friend who works at a porsche place in OHIO and he said to replace the DME relay under the seat. Ok simple 30 buck fix, replaced that last night still no spark.

So at this point my father is on the verge of selling his dream car because he is so frustrated with buying new parts with no progress.

I suspect there is still a problem with the speed and reference sensor not be adjust just right however, even after replacing them i couldn't get ohm readings out of 2 of the 3 terminals on them. Maybe i'm checking them wrong? Also I should mention when we replaced them, we put never seize on the sides of the housing for the sensor so they don't get stuck in there again.. could this be throughing the signal off? I would assume not as it's a magnetic pulse sensor. The ends of the sensors are clean .

So as it sits... 12 volts to coil, 10 while cranking, no spark, I can smell plenty of fuel. DME relay replaced, new OEM coilc, rotor and cap, speed and reference sensors. Magnacore wires, and the plugs are good as a i pulled a couple to verify they weren't carbon fouled. Any ideas as to where to check next? I'm guessing mabye the DME control unit?

Input is greatly appreciated, Thank you

-Ed

[krauthead]

Have you looked at the drive belt on the distributor?

[bazar01]

Check the ignition module.
If you have 12V to the coil positive terminal, it is not switching to create the spark.

[sourcandy]

my manual does not have any information as to how to check the ignition module or DME control unit. Could you post instructions as to what exactly I should test on it to verify function?

How exactly do I check the distributor drive belt? I thought it was shaft driven?

[krauthead]

If you keep replacing parts that you are not sure are bad you will become very frustrated. Learn to use the search function here and also look at Rennlist. They have a much more active 964 forum. There also comes a time when a professional mechanic can quickly diagnose your problem and save you money by only replacing the failed part. Maybe someone else here can suggest a different approach you can take for your problem.

[Don Plumley]

Originally posted by sourcandy
How exactly do I check the distributor drive belt? I thought it was shaft driven?

The 964 (and 993) have essentially two distributors that are connected by a toothed belt. As an aside, this is the belt that becomes brittle over time if the distributor vent kit is not installed. Which is a fancy term for a hose that delivers positive pressure to the distributor.

If the belt breaks, one distributor turns and delivers spark, so the engine should probably start anyway.

I once had a problem with my 87 (surge under load) that I started replacing parts and not fixing. It took an ignition analyzer to pin point a defective spark plug. So at some point, rather than the frustration of replacing parts, seeing an expert is called for.

Where are you located? Let's make sure you go to a qualified shop.

[Don Plumley]

It's pretty rare for a DME to just die. Are you sure you have the speed and reference sensors in right (not swapped)? How about the temp sensor?

Is there an aftermarket alarm on the car? These are notorious for goofy starting problems.

[sourcandy]

speed and reference sensor are electronically identical, and sorry for not using the search function, but the "Search" button didn't exactly jump out at me when i was trying to look for it so i dind't realize there was one.

As far as the "2" and "3" wires crossed i already checked this and swapped just to make sure no difference.

Sorry for thinking a technical forum could actually guide some one to a technical solution. No I will not take the car to a mechanic as every single mechanic the car has been taken to here in Houston has messed something up with it.

The only person who has worked on the car and left a good taste has been Dave White of Dave White Racing in Tampa.

I guess I'll just solve this the hard way.


Just curious... but isn't half the fun in owning the car... fixing it? What's the point in owning a vintage or classic 911 if you can't fix it?

[Don Plumley]

They are electrically identical, but if in the wrong position I don't believe they work right. But if you have swapped the wires you should okay.

Candidly, we are all trying to help - you were the one that expressed frustration with the DIY swap everything out process - so we offered an approach to ameliorate your frustration.

For 964 and later 911's, the depth of resource on the board is 1/100 of what it is for earlier cars. That's just the nature of this forum. You will find a larger group on Rennlist with the newer cars. A 964 is hardly a vintage Porsche. If you were to stumble across some of the MFI knowledge on our board I think you would be stunned. So you are right, a big part of the fun of these cars is working on them yourself and using the resources here to help.

From my perspective, I'm an adventurous DIY. But a man's gotta know his limitations, and when I reach them, I reach out for an expert.

However, you might PM John Walker or Tyson Schmidt to draw attention to this thread.

Good Luck,

Don

[Don Plumley]

From the search button:

Mine does this too. I go thru this sequence. Turn the key on so the dash lights up, press the gas pedal to the floor and leave it pressed there for about 15 seconds then turn the key off and release the gas pedal. I then start the car. Works every time so far. I think it has something to do with the Wide open throttle switch or idle switch getting confused.

From RennlistIf your tach stays at 0 and doesn't bounce, its likely your speed sensor and not your reference sensor. The reference sensor wil only send a single pulse to the DME per every revolution of the flywheel - every time the flywheel goes back to TDC, the reference sensor sends a signal to the DME. The speed sensor sends a constant signal to the DME based on how fast the flywheel is spinning. If you've seen your flywheel, you've seen the multiple set screws positioned around the flywheel - these are the reference marks the speed sensor uses to output its signal to the DME.

A bad sensor is probably your problem as the DME must see at least 200 rpms before it will allow the coil to fire. If it is not reporting the correct data, the car won't run. The best way to test this is with an oscilloscope on pins 8 and 27 of your DME harness, but if you don't have an oscilloscope, a multimeter on the same pins will tell you the nominal impedance. It needs to be between 600 and 1600 ohms.
An o-scope is the better test as it will allow you to see the waveform. The best test is an oscilloscope capable of overlaying dual inputs onscreen. Put one input on pins 8 and 27, and the other on 25 and 26, then crank the motor. You should see a wave with peak to peak voltage of greater than 2.5 volts on input one and a regular single pulse of greater than 2V to correspond with TDC. If either are outside of their impedance tolerance or if either do not display the correct waveform they need to be replaced.

Replacing the sensors is pretty easy. If you remove the speed sensor take care to put the shim back in (if so equipped) as you can ruin an improperly gapped sensor pretty easily.

With a 964 you need a Bosch Hammer to read the OBDI codes - if you are going to do serious DIY on this generation 911, pony up the $1K and be master of your domain.

[Don Plumley]

More:

On the 964, on pins 47 and 48 of the DME plug, it should read 3V AC (not DC) when you crank the starter.

[sourcandy]

I'll guess I'll have to go make a post on Rennlist as it seems like you guys recomend them more for newer cars. Yes My oscilliscope will be arriving Friday however, I don't believe it's capable of dual overlay signals it's a basic 50mhz oscillscope i'm getting for free from a friend.

As mentioned before, I did not go through replacing parts trying to fix the problem. This was my fathers action, I'm simply trying to help him fix it before he does something he will regret such as selling it. I myself drive a 78 280z with custom fuel injection and an MS system so electronics is not unfamilar with me.

Thanx for the voltage check on the DME. I was thinking about it at work today, and i figure the relay is prolly there to prevent spikes and surges and what not to affect the DME so i figure the odds of the DME failing with the relay not faling are pretty slim. I'm still betting my money on the reference sensor/ speed sensors being too far away from the flywheel.

As far as an OBDI or OBDII code checker, I find these fail and give false codes more often than the correct one. I think it's better to self diagnose the problem, then you know exactly what works and what doesn't. I'll check the idle circuitry as well as this might be a lead. I did remember my father saying he wanted me to help him with the car as it was idling rough, aproximatly a couple weeks before it up and died.

Sorry for the strong words earlier, just wanted to be heard.

Thank you again.
-Ed