bart1

I have had my 993 now for 7 pretty troublefree years. Had an issue last weekend that I am not sure the cause of yet and thought I would throw it out for ideas.

I was a couple hours from hom and suddenly the car started running very badly, sputtering and almost stalling under acceleration, no power, etc. I limped it along to a good stopping place and when I depressed the clutch, it died. I bumpstarted it since I was still not in a good place to pull over. Pulled over and it was idling smoothly as I looked around the engine compartment. No obvious issues seen, so I wiggled around some of the spark plug leads which all seemed to be okay. Drove home nervously, but it acted like normal the rest of the way.

A few notes:
- No similar issues in my ownership
- Plugs/caps/wires/et changed ~5k miles ago
- No driving issues or events immediately before this, was just driving in a residential area at 40-50 mph
- Filled up from 1/4 of a tank about 20 miles before this, used 93 octane Shell, as usual
- Check engine light did come on before it died, but went away after the bump start


Thoughts on root cause:
- Possibly was something in the fuel given the recent fill up
- Need to check distributor belt, but I guess this would not have fixed itself
- Double check all wires at the coils and distributors
- See if I can find out what threw the CE light (does the 993 have a self diagnostic function like my 968 did? Otherwise, I'm not sure if I have anybody local that can check it)
- MAF sensor or something?
- DME or another relay wouldn't cause this would it?

Any other thoughts on how to proceed?

Thanks,
Bart

Steve Weiner-Rennsport Systems

Don't forget the DME relay!!!!

BobbyT

Hi Bart,

Has the fuel filter been changed lately?

You might consider a good dose of Techron (from your Chevron dealer) to clean up any deposits in the fuel system.

You can read the codes on your 1995 without a code reader.

1. Turn on the ignition, but don't start the engine.
2. Depress the accelerator pedal fully for about 3 seconds.
3. The CEL will illuminate steady, and then begin to flash.
4. Ease off the accelerator pedal, and read the codes.

Each code consists of four digits, such as 1121. Each digit will be a number of flashes followed by a pause. Example: Flash pause flash flash flash flash flash = 1500, which means "no fault found". There may be multiple codes. You should have a single flash then a pause, then a single or a double flash. If the flash is double then the fault is intermittent (loose contact) otherwise the fault is constant. And then the following flashes;

11 Supply voltage
14 Engine temp sensor 2
15 Throttle potentiometer
18 Rpm signal
19 Speed signal <- Speedometer
21 Hot Film Mass Air flow sensor
22 Oxygen Sensor (Signal)
23 Oxygen regulation
24 Oxygen sensor
25 Intake Temperature Sensor
26 Ignition timing change
27 Opening winding of idle stabilizer
28 Closing winding of idle stabilizer
31 Knock sensor 1
32 Knock sensor 2
33 Control unit faulty
34 Hall signal
36 Idle CO potentiometer
41 Control unit faulty
42 Fuel pump relay (DME-relay)
43 Tank ventilation relay
44 Air Pump
45 Check Engine warning lamp
51 Injection valve cylinder 1
52 Injection valve cylinder 6
53 Injection valve cylinder 2
54 Injection valve cylinder 4
55 Injection valve cylinder 3
56 Injection valve cylinder 5
67 Ground and plug connections
69 Ground and plug connections


A MAF failure would look like;

FLASH pause FLASH pause FLASH FLASH pause FLASH

pp000830

Don't go too deep, one of your distributor caps might be loose. Check the distributor belt by starting the car on the secondary only. The take the caps off and flip them over if the carbon marks look consistent on each contact pin things are probably ok there.
Andy

bart1

Steve - mentioned that on my last bullet

Bobby - thanks for the procedure. Filter was changed 5k ago with those other maintenance items.

Pp - I didn't follow that. How do you mean start on secondary?

nine9six

Firstly, did you get a CEL light, and did you read the code(s) that threw the CEL? I ask because until you do, the misfire you describe is basically an assumption.

FWIW, after reading your description of the issue, my thoughts were the same as Steve W. comment on DME relay. Sounds like a possibly cracked solder joint in the DME relay which causes crappy running due to intermittent operation of the fuel pump.

I'd start my troubleshooting there. Do you have a spare DME as you should and if so, swap them out and see if that does not solve your problem.

You have a primary distributor cap and a secondary; pull the coil wire to the primary and see if the car starts with only the secondary connected. If it starts, the belt to the secondary is still intact. The car will run with only one set of plugs firing, albeit not at full power, but the point is to determine if the belt is broken or not.

Bobby T provided a very inclusive list of other possible culprits.

bart1

Thanks 996. I see what starting on the second one means now.

I do have a few DMEs, including the new spare i keep in the car. However, the car is running fine at the moment, so I don't know how I would be able to judge if it worked. I mentioned in the first post that I did get a CEL and It went away. I'll do the self test when I can.

IXLR8

Remove the DME relay and pop the cover off it. You want to find the cause otherwise you'll have doubts whether or not you'll make it home the next time.

Then under very good light, check the solder connections visually using a magnifying glass. They should all be smooth without any hairline cracks.

This is a failed relay that I got from a local 993er. Note the two solder joints along the top edge of the circuit board as well as the protruding pin with no solder half way down and to the left.

IXLR8

As for pulling coil wires, just make sure they do not short to ground.

nine9six

A cracked solder joint in the DME will cause intermittent running fine and then for no particular reason, exhibit the issues previously described in your OP. Do yourself a favor and change out the DME as Steve W. first suggested and see if that does not cure your issue. You can always run the diagnostics if not, but my money is on the aformentioned DME relay.

The proof would be that the issue does not resurface.

bart1

The proof that it didn't work could be that I was stranded at 11pm two hours from home

I'll change my dme, examine the old one and stay close to home for a few runs.

pp000830

Interesting, I had one fail and when I popped it open it was one of the solder joints to the plug pins that had broken loose.

I resoldered it and now I use the relay as a spare. I guess there are several solder joints that can fail in these things. Seeing that this relay was an active OE part under more than one part number for over 15 years one would have thought it would have been reengineered for reliability at some point. I guess not.

Andy :-)

pp000830

Maybe the DME had a brain fart and you will never see an issue again. My VW New Beetle has them occasionally where I have to disconnect the battery for a few moments and all returns to normal. I guess your issue falls under the old 12 step rule for owners of 993s, you know the line, “accept the things I should not fix, have courage to fix the things I must and have the wisdom to know the difference”

Steve Weiner-Rennsport Systems

Hi Bart,

The reason I mentioned was due to the number of brand new ones that either failed right out of the box, or soon afterward.

Now, I re-solder each and every one that I use or sell.

bart1

I see. Maybe I'll buy an extra from you.